In the meantime, you can register your opinion for what the bright spots are. Join more than 100 thousand others who have voted for an explanation for this enigma. Of course, Ceres will be the ultimate arbiter, and nature rarely depends upon public opinion, but the Dawn project will consider sending the results of the poll to Ceres, courtesy of our team member on permanent assignment there.

In addition to the bright spots, Dawn's views from its present altitude have included a wide range of other intriguing sights, as one would expect on a world of more than one million square miles (nearly 2.8 million square kilometers). There are myriad craters excavated by objects falling from space, inevitable scars from inhabiting the main asteroid belt for more than four billion years, even for the largest and most massive resident there.

The craters exhibit a wide range of appearances, not only in size but also in how sharp and fresh or how soft and aged they look. Some display a peak at the center. A crater can form from such a powerful punch that the hard ground practically melts and flows away from the impact site. Then the material rebounds, almost as if it sloshes back, while already cooling and then solidifying again. The central peak is like a snapshot, preserving a violent moment in the formation of the crater. By correlating the presence or absence of central peaks with the sizes of the craters, scientists can infer properties of Ceres' crust, such as how strong it is. Rather than a peak at the center, some craters contain large pits, depressions that may be a result of gasses escaping after the impact. (Craters elsewhere in the solar system, including on Vesta and Mars, also have pits.)

Dawn also has spied many long, straight or gently curved canyons. Geologists have yet to determine how they formed, and it is likely that several different mechanisms are responsible. For example, some might turn out to be the result of the crust of Ceres shrinking as the heat and other energy accumulated upon formation gradually radiated into space. When the behemoth slowly cooled, stresses could have fractured the rocky, icy ground. Others might have been produced as part of the devastation when a space rock crashed, rupturing the terrain.

Ceres shows other signs of an active past rather than that of a static chunk of inert material passing the eons with little notice. Some areas are less densely cratered than others, suggesting that there are geological processes that erase the craters. Indeed, some regions look as if something has flowed over them, as if perhaps there was mud or slush on the surface.

In addition to evidence of aging and renewal, some powerful internal forces have uplifted mountains. One particularly striking structure is a steep cone that juts three miles (five kilometers) high in an otherwise relatively smooth area, looking to an untrained (but transfixed) eye like a volcanic cone, a familiar sight on your home planet (or, at least, on mine). No other isolated, prominent protuberance has been spotted on Ceres.

It is too soon for scientists to understand the intriguing geology of this ancient world, but the prolific adventurer is providing them with the information they will use. The bounty from this second mapping phase includes more than 1,600 pictures covering essentially all of Ceres, well over five million spectra in visible and infrared wavelengths and hundreds of hours of gravity measurements.

The spacecraft has performed its ambitious assignments quite admirably. Only a few deviations from the very elaborate plans occurred. On June 15 and 27, during the fourth and eighth flights over the dayside, the computer in the combination visible and infrared mapping spectrometer (VIR) detected an unexpected condition, and it stopped collecting data. When the spacecraft's main computer recognized the situation, it instructed VIR to close its protective cover and then power down. The unit dutifully did so. Also on June 27, about three hours before VIR's interruption, the camera's computer experienced something similar.

Most of the time that Dawn points its sensors at Ceres, it simultaneously broadcasts through one of its auxiliary radio antennas, casting a very wide but faint signal in the general direction of Earth. (As Dawn progresses in its orbit, the direction to Earth changes, but the spacecraft is equipped with three of these auxiliary antennas, each pointing in a different direction, and mission controllers program it to switch antennas as needed.) The operations team observed what had occurred in each case and recognized there was no need to take immediate action. The instruments were safe and Dawn continued to carry out all of its other tasks.

When Dawn subsequently flew to the nightside of Ceres and pointed its main antenna to Earth, it transmitted much more detailed telemetry. As engineers and scientists continue their careful investigations, they recognize that in many ways, these events appear very similar to ones that have occurred at other times in the mission.

Four years ago, VIR's computer reset when Dawn was approaching Vesta, and the most likely cause was deemed to be a cosmic ray strike. That's life in deep space! It also reset twice in the survey orbit phase at Vesta. The camera reset three times in the first three months of the low altitude mapping orbit at Vesta.

Even with the glitches in this second mapping orbit, Dawn's outstanding accomplishments represent well more than was originally envisioned or written into the mission's scientific requirements for this phase of the mission. For those of you who have not been to Ceres or aren't going soon (and even those of you who want to plan a trip there of your own), you can see what Dawn sees by going to the image gallery.

Although Dawn already has revealed far, far more about Ceres in the last six months than had been seen in the preceding two centuries of telescopic studies, the explorer is not ready to rest on its laurels. It is now preparing to undertake another complex spiral descent, using its sophisticated ion propulsion system to maneuver to a circular orbit three times as close to the dwarf planet as it is now. It will take five weeks to perform the intricate choreography needed to reach the third mapping altitude, starting tomorrow night. You can keep track of the spaceship's flight as it propels itself to a new vantage point for observing Ceres by visiting the mission status page or following it on Twitter @NASA_Dawn.

As Dawn moves closer to Ceres, Earth will be moving closer as well. Earth and Ceres travel on independent orbits around the sun, the former completing one revolution per year (indeed, that's what defines a year) and the latter completing one revolution in 4.6 years (which is one Cerean year). (We have discussed before why Earth revolves faster in its solar orbit, but in brief it is because being closer to the sun, it needs to move faster to counterbalance the stronger gravitational pull.) Of course, now that Dawn is in a permanent gravitational embrace with Ceres, where Ceres goes, so goes Dawn. And they are now and forever more so close together that the distance between Earth and Ceres is essentially equivalent to the distance between Earth and Dawn.

On July 22, Earth and Dawn will be at their closest since June 2014. As Earth laps Ceres, they will be 1.94 AU (180 million miles, or 290 million kilometers) apart. Earth will race ahead on its tight orbit around the sun, and they will be more than twice as far apart early next year.

Although Dawn communicates regularly with Earth, it left that planet behind nearly eight years ago and will keep its focus now on its new residence. With two very successful mapping campaigns complete, its next priority is to work its way down through Ceres' gravitational field to an altitude of about 900 miles (less than 1,500 kilometers). With sharper views and new kinds of observations (including stereo photography), the treasure trove obtained by this intrepid extraterrestrial prospector will only be more valuable. Everyone who longs for new understandings and new perspectives on the cosmos will grow richer as Dawn continues to pioneer at a mysterious and distant dwarf planet.

Dawn is 2,700 miles (4,400 kilometers) from Ceres. It is also 2.01 AU (187 million miles, or 301 million kilometers) from Earth, or 785 times as far as the moon and 1.98 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 33 minutes to make the round trip.

Dr. Marc D. Rayman
10:00 p.m. PDT June 29, 2015

TAGS: DAWN, VESTA, CERES, DWARF PLANET, MISSION, SPACECRAFT, BRIGHT SPOTS

• 

  ABOUT THE AUTHOR

  Marc Rayman, Dawn Mission Director and Chief Engineer

  Marc Rayman is the director and chief engineer for NASA's Dawn mission, which was launched in 2007 on a mission to orbit the two most massive bodies in the main asteroid belt between Mars and Jupiter to characterize the conditions and processes that shaped our solar system.

We have discussed them here and there in recent months, and their luminous power continues to dazzle us. What appeared initially as one fuzzy spot proved to be two smaller spots and now many even smaller regions as the focus has become sharper. Why the ground there reflects so much sunlight remains elusive. Dawn's finer examinations with its suite of sophisticated instruments in the second, third and then final mapping orbits will provide scientists with data they need to unravel this marvelous mystery. For now, the enigmatic lights present an irresistible cosmic invitation to go closer and to scrutinize this strange and wonderful world, and we are eager to accept. After all, we explore to learn, to know the unknown, and the uniquely powerful scientific method will reveal the nature of the bright areas and what they can tell us about the composition and geology of this complex dwarf planet.

After having been viewed as little more than a smudge in telescopes for more than two centuries since its discovery, Ceres now is seen as a detailed, three-dimensional world. As promised, measurements from Dawn have revised the size to be about 599 miles (963 kilometers) across at the equator. Like Earth and other planets, Ceres is oblate, or slightly wider at the equator than from pole to pole. The polar diameter is 554 miles (891 kilometers). These dimensions are impressively close to what astronomers had determined from telescopic observations and confirm Ceres to be the colossus we have described.

Before Dawn, scientists had estimated Ceres' mass to be 1.04 billion billion tons (947 billion billion kilograms). Now it is measured to be 1.03 billion billion tons (939 billion billion kilograms), well within the previous margin of error. It is an impressive demonstration of the success of science that astronomers had been able to determine the heft of that point of light so accurately. Nevertheless, even this small change of less than one percent is important for planning the rest of Dawn’s mission as it orbits closer and closer, feeling the gravitational tug ever more strongly.

Let's put this change in context. Dawn has now refined the mass, making a proportionally small adjustment of about 0.01 billion billion tons (eight billion billion kilograms). Although no more than a tweak on the overall value, it is still significantly greater than the combined mass of all asteroids visited by all other spacecraft. Ceres is so immense, so massive that even if all those asteroids were added to it, the difference would hardly even have been noticeable. This serves as another reminder that the dwarf planet really is quite unlike the millions of small asteroids that constitute the main asteroid belt. This behemoth contains about 30 percent of all the mass in that entire vast region of space. Vesta, the protoplanet Dawn orbited and studied in 2011-2012, is the second most massive resident there, holding about 8 percent of the asteroid belt's mass. Dawn by itself is exploring around 40 percent of the asteroid belt's mass!

Upon concluding its first mapping orbit, Dawn powered on its remarkable ion propulsion system on May 9 to fly down to a lower altitude where it will gain a better view. We examined the nature of the spiral paths between mapping orbits last year (and at Vesta in 2011-2012).

In its first mapping orbit, Dawn was 8,400 miles (13,600 kilometers) high, revolving once in 15.2 days at a speed of 150 mph (240 kilometers per hour). By the time it completes this descent, the probe will be at an altitude of 2,700 miles (4,400 kilometers), orbiting Ceres every 3.1 days at 254 mph (408 kilometers per hour). (All of the mapping orbits were summarized in this table.) We have discussed that lower orbits require greater velocity to counterbalance the stronger gravitational hold.

Dawn's uniquely capable ion propulsion system, with its extraordinary combination of efficiency and gentleness, propels the ship to its new orbital destination in just under four weeks. The descent requires five revolutions, each one faster than the one before. The flight profile is complicated, and sometimes Dawn even dips below the final, planned altitude and then rises to greater heights as it flies on a path that is temporarily elliptical. The overall trend, of course, is downward. As Dawn heads for its targeted circular orbit, its maneuvering is also generally reducing the orbit period, the time required to make one complete revolution around Ceres. Indeed, if Dawn stopped thrusting now, its orbit period would be about 83 hours, or 3.5 days.

Dawn will complete ion-thrusting on June 3, but it will not be ready to begin its next science observations then. Rather, as in the other new mapping orbits, the first order of business will be for navigators to measure the new orbital parameters accurately. The flight team then will install in Dawn's main computer the details of the orbit it achieved so it will always know its location.

In addition, the intensive campaign of observations is planned to begin when the robotic explorer travels from the night side to the day side over the north pole. With the three-day orbit period, that will next occur on June 5. Controllers will take advantage of the intervening time to conduct other activities, including routine maintenance of the two reaction wheels that remain operable, although they are powered off most of the time. (Two of the four failed years ago. Dawn no longer relies on these devices to control its orientation, and it is remarkable that the mission can accomplish all of its original objectives without them. But if two do function in the final mapping orbit later this year, they will help extend the spacecraft's lifetime for bonus studies.)

We have already presented the ambitious plans for this second mapping orbit, sometimes known as "the second mapping orbit" and sometimes more succinctly and confusingly as "survey orbit." As with all four of Dawn's mapping orbits, it is designed to take the spacecraft over the poles, ensuring the best possible coverage. The ship will fly from the north pole to the south over the side of Ceres facing the sun, and then loop back to the north over the side hidden in the deep dark of night. On the day side, Dawn will aim its camera and spectrometers at the lit ground, filling its memory to capacity with the readings. On the night side, it will point its main antenna to distant Earth in order to radio its findings home. At Dawn's altitude, Ceres will appear twice as wide as the camera's view. (As illustrated in this table, it will look about the size of a soccer ball seen from a yard, or a meter, away.) But as the dwarf planet rotates on its axis and Dawn sails around in its more leisurely orbit, eventually all of the landscape will come within sight of the instruments.

Only one noteworthy change has been made in the intricate plans for survey orbit since May 2014's shocking exposé. With the observations starting on June 5, the subsequent complex orbital flight to the third mapping orbit (also known as HAMO) would have begun on June 27. As we have seen, the rapidly changing orbit in the spiral descents requires a great deal of effort by the small operations team on a rigid schedule. The capable men and women flying Dawn accomplished the maneuvers flawlessly at Vesta and are well prepared for the challenges at Ceres. The work is very demanding, however, and so, just as at Vesta, the team has built into the strategy the capability to make adjustments to align most of the tasks with a conventional work schedule. The technical plans (even including the exquisitely careful husbanding of hydrazine following the loss of the two reaction wheels) fully account for such human factors. It turns out that leaving survey orbit three days later shifts a significant amount of the following work off weekends, making it more comfortable for the team members. Three days is one complete revolution, and always extracting as much from the mission as possible, they have devised another full set of observations for an eighth orbit. As a result, survey orbit may be even more extensive and productive than originally anticipated.

What awaits Dawn in the next mapping phase? The views will be three times as sharp as in the previous orbit, and exciting new discoveries are sure to come. What answers will be revealed? And what new questions (besides this one) will arise? We will know soon, as we all share in the thrill of this grand adventure. To help you keep track of Dawn's progress as it powers its way down and then conducts further observations, your correspondent writes brief (hard to believe, isn't it?) mission status updates. And although in space no one can hear you tweet, terrestrial followers can get even more frequent updates with information he provides for Twitter @NASA_Dawn.

Dawn is 3,400 miles (5,500 kilometers) from Ceres. It is also 2.30 AU (214 million miles, or 345 million kilometers) from Earth, or 855 times as far as the moon and 2.27 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 38 minutes to make the round trip.

Dr. Marc D. Rayman
12:00 p.m. PDT May 28, 2015

TAGS: DAWN, CERES, VESTA, BRIGHT SPOTS, SPACECRAFT, MISSION

• 

  ABOUT THE AUTHOR

  Marc Rayman, Dawn Mission Director and Chief Engineer

  Marc Rayman is the director and chief engineer for NASA's Dawn mission, which was launched in 2007 on a mission to orbit the two most massive bodies in the main asteroid belt between Mars and Jupiter to characterize the conditions and processes that shaped our solar system.

We described last month, for example, adjusting the camera settings for upcoming pictures to ensure good exposures for the captivating bright spots, places that reflect significantly more sunlight than most of the dark ground. Scientists have also examined all the pictures for moons of Ceres (and many extra pictures were taken specifically for that purpose). And thanks to Dawn's pictures, everyone who longs for a perspective on the universe unavailable from our terrestrial home has been transported to a world one million times farther away than the International Space Station.

The final pictures before reaching RC3 certainly provide a unique perspective. (You can see Dawn's pictures of Ceres here.) On April 10 and April 14-15, Dawn peered down over the northern hemisphere and watched for two hours each time as Ceres turned on its axis, part of the unfamiliar cratered terrain bathed in sunlight, part in the deep dark of night. This afforded a very different view from what we are accustomed to in looking at other planets, as most depictions of planetary rotations are from nearer the equator to show more of the surface. (Indeed, Dawn acquired views like that in its February "rotation characterizations.") The latest animations of Ceres rotating beneath Dawn are powerful visual reminders that this capable interplanetary explorer really is soaring around in orbit about a distant, alien world. Following the complex flight high above the dark hemisphere, where there was nothing to see, the pictures also show us that the long night's journey into day has ended.

Gradually descending atop its blue-green beam of high velocity xenon ions, Dawn crossed over the terminator -- the boundary between the dark side and the lit side -- on April 15 almost directly over the north pole. On April 20, on final approach to RC3, it flew over the equator at an altitude of about 8,800 miles (14,000 kilometers).

The spacecraft completed its ion thrusting shortly after 1:00 a.m. PDT on April 23. What an accomplishment this was! From the time Dawn left its final mapping orbit at Vesta in July 2012, this is where it has been headed. The escape from Vesta's gravitational clutches in September 2012, the subsequent two and a half years of interplanetary travel and entering into orbit around Ceres on March 6, as genuinely exciting and important as it was, all really occurred as consequences of targeting this particular orbit.

In September 2014, the aftereffects of being struck by cosmic radiation compelled the operations team to rapidly develop a complex new approach trajectory because they still wanted to achieve this very orbit, where Dawn is now. And the eidetic reader will note that even when the innovative flight profile was presented five months ago (with many further details in subsequent months), we explained that it would conclude on April 23. And it did! Here we are! All the descriptions and figures plus a cool video elucidated a pretty neat idea, but it's also much more than an idea: it's real!! A probe from Earth is in a mapping orbit around a faraway dwarf planet.

When it had accomplished the needed ion thrusting, the veteran space traveler turned to point its main antenna to Earth so mission controllers could prepare it for the intensive mapping observations. The first task was to measure the orbital parameters so they could be transmitted to the spacecraft.

A few readers (you and I both know who you are) may have noted that in Dawn Journals during the last year, we have described the altitude of RC3 as 8,400 miles and 13,500 kilometers. Above, however, it is 13,600 kilometers. This is not a mistake. (It would be a mistake if the previous sentence were written, "Above, howevr, it is 13,600 kilometers.") This subtle difference belies several important issues about the orbits at Ceres. Let's take a further look.

As we explained when Dawn resided at Vesta, the orbital altitude we present is always an average (and rounded off, to avoid burdening readers with too many unhelpful digits). Vesta, Ceres, Earth and other planetary bodies are not perfect spheres, so even if the spacecraft traveled in a perfect circle, its altitude would change. They all are somewhat oblate, being wider across the equator than from pole to pole. In addition, they have more localized topography. Think of flying in a plane over your planet. If the pilot maintains a constant altitude above sea level, the distance above the ground changes because the elevation of the ground itself varies, coming closer to the aircraft on mountains and farther in valleys. In addition, as it turns out, orbits are not perfect circles but tend to be slightly elliptical, as if the plane flies slightly up and down occasionally, so the altitude changes even more.

In their exquisitely detailed planning, the Dawn team has had to account for the unknown nature of Ceres itself, including its mass and hence the strength of its gravitational pull. Dawn is the only spacecraft to orbit large, massive planetary bodies that were not previously visited by flyby spacecraft. Mercury, Venus, the moon, Mars, Jupiter and Saturn all were studied by spacecraft that flew past them before subsequent missions were sent to orbit them. The first probes to each provided an initial measurement of the mass and other properties that were helpful for the arrival of the first orbiters. At Vesta and Ceres, Dawn has had to discover the essential characteristics as it spirals in closer and closer. For each phase, engineers make the best measurements they can and then use them to update the plans for the subsequent phases. As a result, however, plans are based on impressive but nevertheless imperfect knowledge of what will be encountered at lower altitudes. So even if the spacecraft executes an ion thrust flight profile perfectly, it might not wind up exactly where the plan had specified.

There are other reasons as well for small differences between the predicted and the actual orbit. One is minor variations in the thrust of the ion propulsion system, as we discussed here. Another is that every time the spacecraft fires one of its small rocket thrusters to rotate or to stabilize its orientation in the zero-gravity conditions of spaceflight, that also nudges the spacecraft, changing its orbit a little. (See here for a related example of the effect of the thrusters on the trajectory.)

The Dawn flight team has a deep understanding of all the sources of orbit discrepancies, and they always ensure that their intricate plans account for them. Even if the RC3 altitude ended up more than 300 miles (500 kilometers) higher or lower than the specified value, everything would still work just fine to yield the desired pictures and other data. In fact, the actual RC3 orbit is within 25 miles (40 kilometers), or less than one tenth what the plan was designed to accommodate, so the spacecraft achieved a virtual cosmic bullseye!

In the complex preparations on April 23, one file was not radioed to Dawn on time, so late that afternoon when the robot tried to use this file, it could not find it. It responded appropriately by running protective software, stopping its activities, entering "safe mode" and beaming a signal back to distant Earth to indicate it needed further instructions. After the request arrived in mission control at JPL, engineers quickly recognized what had occurred. That night they reconfigured the spacecraft out of safe mode and back to its normal operational configuration, and they finished off the supply of ice cream in the freezer just outside the mission control room. Although Dawn was not ready to begin its intensive observation campaign in the morning of April 24, it started later that same day and has continued to be very productive.

Dawn is a mission of exploration. And rather than be constrained by a fast flight by a target for a brief glimpse, Dawn has the capability to linger in orbit for a very long time at close range. The probe will spend more than a year conducting detailed investigations to reveal as much as possible about the nature of the first dwarf planet discovered, which we had seen only with telescopes since it was first glimpsed in 1801. The pictures Dawn has sent us so far are intriguing and entrancing, but they are only the introduction to this exotic world. They started transforming it from a smudge of light into a real, physical place and one that a sophisticated, intrepid spacecraft can even reach. Being in the first mapping orbit represents the opportunity now to begin developing a richly detailed, intimate portrait of a world most people never even knew existed. Now, finally, we are ready to start uncovering the secrets Ceres has held since the dawn of the solar system.

Dawn is 8,400 miles (13,600 kilometers) from Ceres. It is also 2.66 AU (247 million miles, or 398 million kilometers) from Earth, or 985 times as far as the moon and 2.64 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 44 minutes to make the round trip.

Dr. Marc D. Rayman
10:30 p.m. PDT April 29, 2015

P.S. Our expert outreach team has done a beautiful job modernizing the website, and blog comments are no longer included. I appreciate all the very kind feedback, expressions of enthusiasm, interesting questions and engaging discussions that the community of Dawnophiles has posted over the last year or so. Now I will devote the time I had been spending responding to comments to providing more frequent mission status updates as well as fun and interesting tidbits you can follow on Twitter @NASA_Dawn.

TAGS: DAWN, CERES, BRIGHT SPOT, SPACECRAFT, MISSION

• 

  ABOUT THE AUTHOR

  Marc Rayman, Dawn Mission Director and Chief Engineer

  Marc Rayman is the director and chief engineer for NASA's Dawn mission, which was launched in 2007 on a mission to orbit the two most massive bodies in the main asteroid belt between Mars and Jupiter to characterize the conditions and processes that shaped our solar system.

The dwarf planet is around 590 miles (950 kilometers) in diameter (like Earth and other planets, however, it is slightly wider at the equator than from pole to pole). At the spacecraft’s orbital altitude, it will appear to be the same size as a soccer ball seen from 10 feet (3 meters) away. Part of the basis upon which mission planners chose this distance for the first mapping campaign is that the visible disc of Ceres will just fit in the camera’s field of view. All the pictures taken at lower altitudes will cover a smaller area (but will be correspondingly more detailed). The photos from RC3 will be 3.4 times sharper than those in RC2.

There will be work to do before photography begins however. The first order of business after concluding ion thrusting will be for the flight team to perform a quick navigational update (this time, using only the radio signal) and transmit any refinements (if necessary) in Dawn’s orbital parameters, so it always has an accurate knowledge of where it is. (These will not be adjustments to the orbit but rather a precise mathematical description of the orbit it achieved.) Controllers will also reconfigure the spacecraft for its intensive observations, which will commence on April 24 as it passes over the south pole and to the night side again.

As at Vesta, even though half of each circular orbit will be over the night side of Ceres, the spacecraft itself will never enter the shadows. The operations team has carefully designed the orbits so that at Dawn’s altitude, it remains illuminated by the sun, even when the land below is not.

It may seem surprising (or even be surprising) that Dawn will conduct measurements when the ground directly beneath it is hidden in the deep darkness of night. To add to the surprise, these observations were not even envisioned when Dawn’s mission was designed, and it did not perform comparable measurements during its extensive exploration of Vesta in 2011-2012.

The measurements on the night side will serve several purposes. One of the many sophisticated techniques scientists use to elucidate the nature of planetary surfaces is to measure how much light they reflect at different angles. Over the course of the next year, Dawn will acquire tens of thousands of pictures from the day side of Ceres, when, in essence, the sun is behind the camera. When it is over the night side in RC3, carefully designed observations of the lit terrain (with the sun somewhat in front of the camera, although still at a safe angle) will significantly extend the range of angles.

In December, we described the fascinating discovery of an extremely diffuse veil of water vapor around Ceres. How the water makes its way from the dwarf planet high into space is not known. The Dawn team has devised a plan to investigate this further, even though the tiny amount of vapor was sighted long after the explorer left Earth equipped with sensors designed to study worlds without atmospheres.

It is worth emphasizing that the water vapor is exceedingly tenuous. Indeed, it is much less dense than Earth’s atmosphere at altitudes above the International Space Station, which orbits in what most people consider to be the vacuum of space. Our hero will not need to deploy its umbrella. Even comets, which are miniscule in comparison with Ceres, liberate significantly more water.

There may not even be any water vapor at all now because Ceres is farther from the sun than when the Herschel Space Observatory saw it, but if there is, detecting it will be very challenging. The best method to glimpse it is to look for its subtle effects on light passing through it. Although Dawn cannot gaze directly at the sun, it can look above the lit horizon from the night side, searching intently for faint signs of sunlight scattered by sparse water molecules (or perhaps dust lofted into space with them).

For three days in RC3 after passing over the south pole, the probe will take many pictures and visible and infrared spectra as it watches the slowly shrinking illuminated crescent and the space over it. When the spacecraft has flown to about 29 degrees south latitude over the night side, it will no longer be safe to aim its sensitive instruments in that direction, because they would be too close to the sun. With its memory full of data, Dawn will turn to point its main antenna toward distant Earth. It will take almost two days to radio its findings to NASA’s Deep Space Network. Meanwhile, the spacecraft will continue northward, gliding silently high over the dark surface.

On April 28, it will rotate again to aim its sensors at Ceres and the space above it, resuming measurements when it is about 21 degrees north of the equator and continuing almost to the north pole on May 1. By the time it turns once again to beam its data to Earth, it will have completed a wealth of measurements not even considered when the mission was being designed.

Loyal readers will recall that Dawn has lost two of its four reaction wheels, gyroscope-like devices it uses to turn and to stabilize itself. Although such a loss could be grave for some missions, the operations team overcame this very serious challenge. They now have detailed plans to accomplish all of the original Ceres objectives regardless of the condition of the reaction wheels, even the two that have not failed (yet). It is quite a testament to their creativity and resourcefulness that despite the tight constraints of flying the spacecraft differently, the team has been able to add bonus objectives to the mission.

Dawn will finish transmitting its data after its orbit takes it over the north pole and to the day side of Ceres again. For three periods during its gradual flight of more than a week over the illuminated landscape, it will take pictures (in visible and near-infrared wavelengths) and spectra. Each time, it will look down from space for a full Cerean day, watching for more than nine hours as the dwarf planet pirouettes, as if showing off to her new admirer. As the exotic features parade by, Dawn will faithfully record the sites.

It is important to set the camera exposures carefully. Most of the surface reflects nine percent of the sunlight. (For comparison, the moon reflects 12 percent on average, although as many Earthlings have noticed, there is some variation from place to place. Mars reflects 17 percent, and Vesta reflects 42 percent. Many photos seem to show that your correspondent’s forehead reflects about 100 percent.) But there are some small areas that are significantly more reflective, including the two most famous bright spots. Each spot occupies only one pixel (2.7 miles, or 4.3 kilometers across) in the best pictures so far. If each bright area on the ground is the size of a pixel, then they reflect around 40 percent of the light, providing the stark contrast with the much darker surroundings. When Dawn’s pictures show more detail, it could be that they will turn out to be even smaller and even more reflective than they have appeared so far. In RC3, each pixel will cover 0.8 miles (1.3 kilometers). To ensure the best photographic results, controllers are modifying the elaborate instructions for the camera to take pictures of the entire surface with a wider range of exposures than previously planned, providing high confidence that all dark and all bright areas will be revealed clearly.

Dawn will observe Ceres as it flies from 45 degrees to 35 degrees north latitude on May 3-4. Of course, the camera’s view will extend well north and south of the point immediately below it. (Imagine looking at a globe. Even though you are directly over one point, you can see a larger area.) The territory it will inspect will include those intriguing bright spots. The explorer will report back to Earth on May 4-5. It will perform the same observations between 5 degrees north and 5 degrees south on May 5-6 and transmit those findings on May 6-7. To complete its first global map, it will make another full set of measurements for a Cerean day as it glides between 35 degrees and 45 degrees south on May 7.

By the time it has transmitted its final measurements on May 8, the bounty from RC3 may be more than 2,500 pictures and two million spectra. Mission controllers recognize that glitches are always possible, especially in such complex activities, and they take that into account in their plans. Even if some of the scheduled pictures or spectra are not acquired, RC3 should provide an excellent new perspective on the alien world, displaying details three times smaller than what we have discerned so far.

Dawn activated its gamma ray spectrometer and neutron spectrometer on March 12, but it will not detect radiation from Ceres at this high altitude. For now, it is measuring space radiation to provide context for later measurements. Perhaps it will sense some neutrons in the third mapping orbit this summer, but its primary work to determine the atomic constituents of the material within about a yard (meter) of the surface will be in the lowest altitude orbit at the end of the year.

Dawn will conduct its studies from three lower orbital altitudes after RC3, taking advantage of the tremendous maneuverability provided by ion propulsion to spiral from one to another. We presented previews last year of each phase, and as each approaches, we will give still more up-to-date details, but now that Dawn is in orbit, let’s summarize them here. Of course, with complicated operations in the forbidding depths of space, there are always possibilities for changes, especially in the schedule. The team has developed an intricate but robust and flexible plan to extract as many secrets from Ceres as possible, and they will take any changes in stride.

Each orbit is designed to provide a better view than the one before, and Dawn will map the orb thoroughly while at each altitude. The names for the orbits – rotation characterization 3 (RC3); survey; high altitude mapping orbit (HAMO); and low altitude mapping orbit (LAMO) – are based on ancient ideas, and the origins are (or should be) lost in the mists of time. Readers should avoid trying to infer anything at all meaningful in the designations. After some careful consideration, your correspondent chose to use the same names the Dawn team uses rather than create more helpful descriptors for the purposes of these blogs. That ensures consistency with other Dawn project communications. After all, what is important is not what the different orbits are called but rather what amazing new discoveries each one enables.

The robotic explorer will make many kinds of measurements with its suite of powerful instruments. As one indication of the improving view, this table includes the resolution of the photos, and the ever finer detail may be compared with the pictures during the approach phase. For another perspective, we extend the soccer ball analogy above to illustrate how large Ceres will appear to be from the spacecraft’s orbital vantage point.

As Dawn orbits Ceres, together they orbit the sun. Closer to the master of the solar system, Earth (with its own retinue, including the moon and many artificial satellites) travels faster in its heliocentric orbit because of the sun’s stronger gravitational pull at its location. In December, Earth was on the opposite side of the sun from Dawn, and now the planet’s higher speed is causing their separation to shrink. Earth will get closer and closer until July 22, when it will pass on the inside track, and the distance will increase again.

In the meantime, on April 12, Dawn will be equidistant from the sun and Earth. The spacecraft will be 2.89 AU or 269 million miles (433 million kilometers) from both. At the same time, Earth will be 1.00 AU or 93.2 million miles (150 million kilometers) from the sun.

It will be as if Dawn is at the tip of a giant celestial arrowhead, pointing the way to a remarkable solar system spectacle. The cosmos should take note! Right there, a sophisticated spaceship from Earth is gracefully descending on a blue-green beam of xenon ions. Finally, the dwarf planet beneath it, a remote remnant from the dawn of the solar system, is lonely no more. Almost 4.6 billion years after it formed, and 214 years after inquisitive creatures on a distant planet first caught sight of it, a mysterious world is still welcoming the new arrival. And as Dawn prepares to settle into its first close orbit, ready to discover secrets Ceres has kept for so long, everyone who shares in the thrill of this grand and noble adventure eagerly awaits its findings. Together, we look forward to the excitement of new knowledge, new insight and new fuel for our passionate drive to explore the universe.

Dawn is 35,000 miles (57,000 kilometers) from Ceres, or 15 percent of the average distance between Earth and the moon. It is also 3.04 AU (282 million miles, or 454 million kilometers) from Earth, or 1,120 times as far as the moon and 3.04 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 51 minutes to make the round trip.

Dr. Marc D. Rayman
6:00 p.m. PDT March 31, 2015

› Read more entries from Marc Rayman's Dawn Journal

TAGS: DAWN, CERES, VESTA, DWARF PLANET, SPACECRAFT, MISSION

• 

  ABOUT THE AUTHOR

  Marc Rayman, Dawn Mission Director and Chief Engineer

  Marc Rayman is the director and chief engineer for NASA's Dawn mission, which was launched in 2007 on a mission to orbit the two most massive bodies in the main asteroid belt between Mars and Jupiter to characterize the conditions and processes that shaped our solar system.

It may be surprising that prior to Dawn, no spacecraft had even attempted to orbit two distant targets. Who wouldn’t want to study two alien worlds in detail, rather than, as previous missions, either fly by one or more for brief encounters or orbit only one? A mission like Dawn’s is an obvious kind to undertake. It happens in science fiction often: go somewhere, do whatever you need to do there (e.g., beat someone up or make out with someone) and then boldly go somewhere else. However, science fact is not always as easy as science fiction. Such missions are far, far beyond the capability of conventional propulsion.

Deep Space 1 (DS1) blazed a new trail with its successful testing of ion propulsion, which provides 10 times the efficiency of standard propulsion, showing on an operational interplanetary mission that the advanced technology really does work as expected. (This writer was fortunate enough to work on DS1, and he even documented the mission in a series of increasingly wordy blogs. But he first heard of ion propulsion from the succinct Mr. Spock and subsequently followed its use by the less logical Darth Vader.)

Dawn’s ambitious expedition would be truly impossible without ion propulsion. (For a comparison of chemical and ion propulsion for entering orbit around Mars, an easier destination to reach than either Vesta or Ceres, visit this earlier log.) So far, our advanced spacecraft has changed its own velocity by 23,800 mph (38,400 kilometers per hour) since separating from its rocket, far in excess of what any other mission has achieved propulsively. (The previous record was held by DS1.)

Dawn is exceptionally frugal in its use of xenon propellant. In this phase of the mission, the engine expends only a quarter of a pound (120 grams) per day, or the equivalent of about 2.5 fluid ounces (75 milliliters) per day. So although the thrust is very efficient, it is also very gentle. If you hold a single sheet of paper in your hand, it will push on your hand harder than the ion engine pushes on the spacecraft at maximum thrust. At today’s throttle level, it would take the distant explorer almost 11 days to accelerate from zero to 60 mph (97 kilometers per hour). That may not evoke the concept of a drag racer. But in the zero-gravity, frictionless conditions of spaceflight, the effect of this whisper-like thrust can build up. Instead of thrusting for 11 days, if we thrust for a month, or a year, or as Dawn already has, for more than five years, we can achieve fantastically high velocity. Ion propulsion delivers acceleration with patience.

Most spacecraft coast most of the time, following their repetitive orbits like planets do. They may use the main engine for a few minutes or perhaps an hour or two throughout the entire mission. With ion propulsion, in contrast, the spacecraft may spend most of its time in powered flight. Dawn has flown for 69% of its time in space emitting a cool blue-green glow from one of its ion engines. (With three ion engines, Dawn outdoes the Star Wars TIE (twin ion engine) fighters.)

The robotic probe uses its gentle thrust to gradually reshape its path through space rather than simply following the natural course that a planet would. After it escaped from Vesta’s gravitational clutches, it slowly spiraled outward from the sun, climbing the solar system hill, making its heliocentric orbit more and more and more like Ceres’. By the time it was in the vicinity of the dwarf planet today, both were traveling around the sun at more than 38,600 mph (62,100 kilometers per hour). Their trajectories were nearly identical, however, so the difference in their speeds was only 100 mph (160 kilometers per hour), or less than 0.3 percent of the total. Flying like a crackerjack spaceship pilot, Dawn elegantly used the light touch of its ion engine to be at a position and velocity that it could ease gracefully into orbit. At a distance of 37,700 miles (60,600 kilometers), Ceres reached out and tenderly took the newcomer from Earth into its permanent gravitational embrace.

If you had been in space watching the event, you would have been cold, hungry and hypoxic. But it would not have looked much different from the 1,885 days of ion thrust that had preceded it. The spacecraft was perched atop its blue-green pillar of xenon ions, patiently changing its course, as it does for so much of quiet cruise. But now, at one moment it was flying too fast for Ceres’ gravity to hang on to it, and the next moment it had slowed just enough that it was in orbit. Had it stopped thrusting at that point, it would have continued looping around the dwarf planet. But it did not stop. Instead, it is working now to reshape its orbit around Ceres. As we saw in November, its orbital acrobatics first will take it up to an altitude of 47,000 miles (75,000 kilometers) on March 19 before it swoops down to 8,400 miles (13,500 kilometers) on April 23 to begin its intensive observations in the orbit designated RC3.

In fact, Dawn’s arrival today really is simply a consequence of the route it is taking to reach that lower orbit next month. Navigators did not aim for arriving today. Rather, they plotted a course that began at Vesta and goes to RC3 (with a new design along the way), and it happens that the conditions for capture into orbit occurred this morning. As promised last month, we present here a different view of the skillful maneuvering by this veteran space traveler.

If Dawn had stopped thrusting before Ceres could exert its gravitational control, it wouldn’t have flown very far away. The spacecraft had already made their paths around the sun very similar, and the ion propulsion system provides such exceptional flexibility to the mission that controllers could have guided it into orbit some other time. This was not a one-time, all-or-nothing event.

So the flight team was not tense. They had no need to observe it or make a spectacle out of it. Mission control remained quiet. The drama is not in whether the mission will succeed or fail, in whether a single glitch could cause a catastrophic loss, in whether even a tiny mistake could spell doom. Rather, the drama is in the opportunity to unveil the wonderful secrets of a fascinating relict from the dawn of the solar system more than 4.5 billion years ago, a celestial orb that has beckoned for more than two centuries, the first dwarf planet discovered.

Dawn usually flies with its radio transmitter turned off (devoting its electricity instead to the power-hungry ion engine), and so it entered orbit silently. As it happened, a routine telecommunications session was scheduled about an hour after attaining orbit, at 5:36 a.m. PST. (It’s only coincidence it was that soon. At Vesta, it was more than 25 hours between arrival and the next radio contact.) For primary communications, Dawn pauses thrusting to point its main antenna to Earth, but other times, as in this case, it is programmed to use one of its auxiliary antennas to transmit a weaker signal without stopping its engine, whispering just enough for engineers to verify that it remains healthy.

The Deep Space Network’s exquisitely sensitive 230-foot (70-meter) diameter antenna in Goldstone, Calif., picked up the faint signal from across the solar system on schedule and relayed it to Dawn mission control. One person was in the room (and yes, he was cleared to enter). He works with the antenna operator to ensure the communications session goes smoothly, and he is always ready to contact others on the flight team if any anomalies arise. In this case, none did, and it was a quiet morning as usual. The mission director checked in with him shortly after the data started to trickle in, and they had a friendly, casual conversation that included discussing some of the telemetry that indicated the spacecraft was still performing its routine ion thrusting. The determination that Dawn was in orbit was that simple. Confirming that it was following its flight plan was all that was needed to know it had entered orbit. This beautifully choreographed celestial dance is now a pas de deux.

As casual and tranquil as all that sounds, and as logical and systematic as the whole process is, the reality is that the mission director was excited. There was no visible hoopla, no audible fanfare, but the experience was powerful fuel for the passionate fires that burn within.

As soundlessly as a spacecraft gliding through the void, the realization emerges …

Dawn made it!!

It is in orbit around a distant world!!

Yes, it’s clear from the technical details, but it is more intensely reflected in the silent pounding of a heart that has spent a lifetime yearning to know the cosmos. Years and years of hard work devoted to this grand undertaking, constant hopes and dreams and fears of all possible futures, uncounted challenges (some initially appearing insurmountable) and a seeming infinitude of decisions along the way from early concepts through a real interplanetary spacecraft flying on an ion beam beyond the sun.

And then, a short, relaxed chat over a few bits of routine data that report the same conditions as usual on the distant robot. But today they mean something different.

They mean we did it!!

Everyone on the team will experience the news that comes in a congratulatory email in their own way, in the silence and privacy of their own thoughts. But it means the same to everyone.

We did it!!

And it’s not only the flight team. Humankind!! With our relentless curiosity, our insatiable hunger for knowledge, our noble spirit of adventure, we all share in the experience of reaching out from our humble home to the stars.

Together, we did it!!!

It was a good way to begin the day. It was Dawn at Ceres.

Let’s bring into perspective the cosmic landscape on which this remarkable adventure is now taking place. Imagine Earth reduced to the size of a soccer ball. On this scale, the International Space Station would orbit at an altitude of a bit more than one-quarter of an inch (seven millimeters). The moon would be a billiard ball almost 21 feet (6.4 meters) away. The sun, the conductor of the solar system orchestra, would be 79 feet (24 meters) across at a distance of 1.6 miles (2.6 kilometers). But even more remote, Dawn would be 5.3 miles (8.6 kilometers) away. (Just a few months ago, when the spacecraft was on the opposite side of the sun from Earth, it would have been more than six miles, or almost 10 kilometers, from the soccer ball.) Tremendously far now from its erstwhile home, it would be only a little over a yard (a meter) from its new residence. (By the end of this year, Dawn will be slightly closer to it than the space station is to Earth, a quarter of an inch, or six millimeters.) That distant world, Ceres, the largest object between Mars and Jupiter, would be five-eighths of an inch (1.6 centimeters) across, about the size of a grape. Of course a grape has a higher water content than Ceres, but we can be sure that exploring this intriguing world of rock and ice will be much sweeter!

As part of getting to know its new neighborhood, Dawn has been hunting for moons of Ceres. Telescopic studies had not revealed any, but if there were a moon smaller than about half a mile (one kilometer), it probably would not have been discovered. The spacecraft’s unique vantage point provides an opportunity to look for any that might have escaped detection. Many pictures have been taken specifically for this purpose, and scientists scrutinize them and all of the other photographs for any indication of moons. While the search will continue, so far, no picture has shown evidence of companions orbiting Ceres.

And yet we know that as of today, Ceres most certainly does have one. Its name is Dawn!

Dawn is 37,800 miles (60,800 kilometers) from Ceres, or 16 percent of the average distance between Earth and the moon. It is also 3.33 AU (310 million miles, or 498 million kilometers) from Earth, or 1,230 times as far as the moon and 3.36 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 55 minutes to make the round trip.

Dr. Marc D. Rayman
6:00 a.m. PST March 6, 2015

› Read more entries from Marc Rayman's Dawn Journal

TAGS: DAWN, CERES, VESTA, DWARF PLANET, ORBIT INSERTION, SPACECRAFT, MISSION

• 

  ABOUT THE AUTHOR

  Marc Rayman, Dawn Mission Director and Chief Engineer

  Marc Rayman is the director and chief engineer for NASA's Dawn mission, which was launched in 2007 on a mission to orbit the two most massive bodies in the main asteroid belt between Mars and Jupiter to characterize the conditions and processes that shaped our solar system.

"Slowly" is the key. Dawn is in the vicinity of Ceres and is not leaving. The adventurer has traveled more than 900 million miles (1.5 billion kilometers) since departing from Vesta in 2012, devoting most of the time to using its advanced ion propulsion system to reshape its orbit around the sun to match Ceres' orbit. Now that their paths are so similar, the spacecraft is receding from the massive behemoth at the leisurely pace of about 35 mph (55 kilometers per hour), even as they race around the sun together at 38,700 mph (62,300 kilometers per hour). The probe is expertly flying an intricate course that would be the envy of any hotshot spaceship pilot. To reach its first observational orbit -- a circular path from pole to pole and back at an altitude of 8,400 miles (13,500 kilometers) -- Dawn is now taking advantage not only of ion propulsion but also the gravity of Ceres.

On Feb. 23, the spacecraft was at its closest to Ceres yet, only 24,000 miles (less than 39,000 kilometers), or one-tenth of the separation between Earth and the moon. Momentum will carry it farther away for a while, so as it performs the complex cosmic choreography, Dawn will not come this close to its permanent partner again for six weeks. Well before then, it will be taken firmly and forever into Ceres' gentle gravitational hold.

The photographs Dawn takes during this approach phase serve several purposes. Besides fueling the fires of curiosity that burn within everyone who looks to the night sky in wonder or who longs to share in the discoveries of celestial secrets, the images are vital to engineers and scientists as they prepare for the next phase of exploration.

The primary purpose of the pictures is for "optical navigation" (OpNav), to ensure the ship accurately sails to its planned orbital port. Dawn is the first spacecraft to fly into orbit around a massive solar system world that had not previously been visited by a spacecraft. Just as when it reached its first deep-space target, the fascinating protoplanet Vesta, mission controllers have to discover the nature of the destination as they proceed. They bootstrap their way in, measuring many characteristics with increasing accuracy as they go, including its location, its mass and the direction of its rotation axis.

Let's consider this last parameter. Think of a spinning ball. (If the ball is large enough, you could call it a planet.) It turns around an axis, and the two ends of the axis are the north and south poles. The precise direction of the axis is important for our mission because in each of the four observation orbits (previews of which were presented in February, May, June and August), the spacecraft needs to fly over the poles. Polar orbits ensure that as Dawn loops around, and Ceres rotates beneath it every nine hours, the explorer eventually will have the opportunity to see the entire surface. Therefore, the team needs to establish the location of the rotation axis to navigate to the desired orbit.

We can imagine extending the rotation axis far outside the ball, even all the way to the stars. Current residents of Earth, for example, know that their planet's north pole happens to point very close to a star appropriately named Polaris (or the North Star), part of an asterism known as the Little Dipper in the constellation Ursa Minor (the Little Bear). The south pole, of course, points in exactly the opposite direction, to the constellation Octans (the Octant), but is not aligned with any salient star.

With their measurements of how Ceres rotates, the team is zeroing in on the orientation of its poles. We now know that residents of (and, for that mater, visitors to) the northern hemisphere there would see the pole pointing toward an unremarkable region of the sky in Draco (the Dragon). Those in the southern hemisphere would note the pole pointing toward a similarly unimpressive part of Volans (the Flying Fish). (How appropriate it is that that pole is directed toward a constellation with that name will be known only after scientists advance their understanding of the possibility of a subsurface ocean at Ceres.)

The orientation of Ceres'; axis proves convenient for Dawn's exploration. Earthlings are familiar with the consequences of their planet's axis being tilted by about 23 degrees. Seasons are caused by the annual motion of the sun between 23 degrees north latitude and 23 degrees south. A large area around each pole remains in the dark during winter. Vesta's axis is tipped 27 degrees, and when Dawn arrived, the high northern latitudes were not illuminated by the sun. The probe took advantage of its extraordinary maneuverability to fly to a special mapping orbit late in its residence there, after the sun had shifted north. That will not be necessary at Ceres. That world's axis is tipped at a much smaller angle, so throughout a Cerean year (lasting 4.6 Earth years), the sun stays between 4 degrees north latitude and 4 degrees south. Seasons are much less dramatic. Among Dawn's many objectives is to photograph Ceres. Because the sun is always near the equator, the illumination near the poles will change little. It is near the beginning of southern hemisphere winter on Ceres now, but the region around the south pole hidden in hibernal darkness is tiny. Except for possible shadowing by local variations in topography (as in deep craters), well over 99 percent of the dwarf planet's terrain will be exposed to sunlight each day.

Guiding Dawn from afar, the operations team incorporates the new information about Ceres into occasional updates to the flight plan, providing the spacecraft with new instructions on the exact direction and throttle level to use for the ion engine. As they do so, subtle aspects of the trajectory change. Last month we described the details of the plan for observing Ceres throughout the four-month approach phase and predicted that some of the numbers could change slightly. So, careful readers, for your convenience, here is the table from January, now with minor updates.

In addition to changes based on discoveries about the nature of Ceres, some changes are dictated by more mundane considerations (to the extent that there is anything mundane about flying a spacecraft in the vicinity of an alien world more than a thousand times farther from Earth than the moon). For example, to accommodate changes in the schedule for the use of the Deep Space Network, some of the imaging sessions shifted by a few hours, which can make small changes in the corresponding views of Ceres.

The only important difference between the table as presented in January and this month, however, is not to be found in the numbers. It is that OpNav 3, RC1 and RC2 are now in the past, each having been completed perfectly.

As always, if you prefer to save yourself the time and effort of the multi-billion-mile (multi-billion-kilometer) interplanetary journey to Ceres, you can simply go here to see the latest views from Dawn. (The Dawn project is eager to share pictures promptly with the public. The science team has the responsibility of analyzing and interpreting the images for scientific publication. The need for accuracy and scientific review of the data slows the interpretation and release of the pictures. But just as with all of the marvelous findings from Vesta, everything from Ceres will be available as soon as practicable.)

In November we delved into some of the details of Dawn's graceful approach to Ceres, and last month we considered how the trajectory affected the scene presented to Dawn's camera. Now that we have updated the table, we can enhance a figure from both months that showed the craft's path as it banks into orbit and maneuvers to its first observational orbit. (As a reminder, the diagram illustrates only two of the three dimensions of the ship's complicated route. Another diagram in November showed another perspective, and we will include a different view next month.)

We can zoom out to see where the earlier OpNavs were.

As the table and figures indicate, in OpNav 6, when Ceres and the sun are in the same general direction from Dawn's vantage point, only a small portion of the illuminated terrain will be visible. The left side of Ceres will be in daylight, and most of the hemisphere facing the spacecraft will be in the darkness of night. To get an idea of what the shape of the crescent will be, terrestrial readers can use the moon on March 16. It will be up much of the day, setting in the middle of the afternoon, and it will be comparable to the crescent Dawn will observe on April 10. (Of course, the exact shape will depend on your observing location and what time you look, but this serves as a rough preview.) Fortunately, our spacecraft does not have to contend with bad weather, but you might, so we have generously scheduled a backup opportunity for you. The moon will be new on March 20, and the crescent on March 23 will be similar to what it was on March 16. It will rise in the mid morning and be up until well after the sun sets.

Photographing Ceres as it arcs into orbit atop a blue-green beam of xenon ions, setting the stage for more than a year of detailed investigations with its suite of sophisticated sensors, Dawn is sailing into the history books. No spacecraft has reached a dwarf planet before. No spacecraft has orbited two extraterrestrial destinations before. This amazing mission is powered by the insatiable curiosity and extraordinary ingenuity of creatures on a planet far, far away. And it carries all of them along with it on an ambitious journey that grows only more exciting as it continues. Humankind is about to witness scenes never before seen and perhaps never even imagined. Dawn is taking all of us on a daring adventure to a remote and unknown part of the cosmos. Prepare to be awed.

Dawn is 24,600 miles (39,600 kilometers) from Ceres, or 10 percent of the average distance between Earth and the moon. It is also 3.42 AU (318 million miles, or 512 million kilometers) from Earth, or 1,330 times as far as the moon and 3.46 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 57 minutes to make the round trip.

Dr. Marc D. Rayman
7:00 a.m. PST February 25, 2015

› Read more entries from Marc Rayman's Dawn Journal

TAGS: DAWN, CERES, DWARF PLANET, SPACECRAFT, MISSION

• 

  ABOUT THE AUTHOR

  Marc Rayman, Dawn Mission Director and Chief Engineer

  Marc Rayman is the director and chief engineer for NASA's Dawn mission, which was launched in 2007 on a mission to orbit the two most massive bodies in the main asteroid belt between Mars and Jupiter to characterize the conditions and processes that shaped our solar system.

Mariner 3 was launched November 5, 1964, but the shroud did not fully eject from the spacecraft, the solar panels did not deploy, and the batteries ran out of power. The problem was fixed on Mariner 4, which began its successful journey to Mars on November 28, 1964.

Documentation found in the Archives does not identify the purpose of the sphere covering the magnetometer during this test.

TAGS: HISTORY, MARINER, MARS, VENUS, SOLAR SYSTEM, MISSION, SPACECRAFT, TECHNOLOGY

• 

  ABOUT THE AUTHOR

  Julie Cooper, Certified Archivist

  Julie Cooper is a certified archivist who identifies and processes collections for the JPL Archives, and helps researchers find information about the history of JPL.

In the original approach, Dawn would follow a simple spiral around Ceres, approaching from the general direction of the sun, looping over the south pole, going beyond to the night side, and coming back above the north pole before easing into the targeted orbit, known by the stirring name RC3, at an altitude of 8,400 miles (13,500 kilometers). Like a pilot landing a plane, flying this route required lining up on a particular course and speed well in advance. The ion thrusting this year had been setting Dawn up to get on that approach spiral early next year.

The change in its flight profile following the September encounter with a rogue cosmic ray meant the spiral path would be markedly different and would require significantly longer to complete. While the flight team certainly is patient -- after all, Earth’s robotic ambassador won’t reach Ceres until 213 years after its discovery and more than seven years after launch -- the brilliantly creative navigators devised an entirely new approach trajectory that would be shorter. Demonstrating the extraordinary flexibility of ion propulsion, the spacecraft now will take a completely different path but will wind up in exactly the same orbit.

The spacecraft will allow itself to be captured by Ceres on March 6, only about half a day later than the trajectory it was pursuing before the hiatus in thrust, but the geometry both before and after will be quite different. Instead of flying south of Ceres, Dawn is now targeted to trail a little behind it, letting the dwarf planet lead as they both orbit the sun, and then the spacecraft will begin to gently curve around it. (You can see this in the figure below.) Dawn will come to 24,000 miles (38,000 kilometers) and then will slowly arc away. But thanks to the remarkable design of the thrust profile, the ion engine and the gravitational pull from the behemoth of rock and ice will work together. At a distance of 41,000 miles (61,000 kilometers), Ceres will reach out and tenderly take hold of its new consort, and they will be together evermore. Dawn will be in orbit, and Ceres will forever be accompanied by this former resident of Earth.

If the spacecraft stopped thrusting just when Ceres captured it, it would continue looping around the massive body in a high, elliptical orbit, but its mission is to scrutinize the mysterious world. Our goal is not to be in just any arbitrary orbit but rather in the particular orbits that have been chosen to provide the best scientific return for the probe’s camera and other sensors. So it won’t stop but instead will continue maneuvering to RC3.

Ever graceful, Dawn will gently thrust to counter its orbital momentum, keeping it from swinging up to the highest altitude it would otherwise attain. On March 18, nearly two weeks after it is captured by Ceres’ gravity, Dawn will arc to the crest of its orbit. Like a ball thrown high that slows to a momentary stop before falling back, Dawn’s orbital ascent will end at an altitude of 47,000 miles (75,000 kilometers), and Ceres’ relentless pull (aided by the constant, gentle thrust) will win out. As it begins descending toward its gravitational master, it will continue working with Ceres. Rather than resist the fall, the spacecraft will thrust to accelerate itself, quickening the trip down to RC3.

There is more to the specification of the orbit than the altitude. One of the other attributes is the orientation of the orbit in space. (Imagine an orbit as a ring around Ceres, but that ring can be tipped and tilted in many ways.) To provide a view of the entire surface as Ceres rotates underneath it, Dawn needs to be in a polar orbit, flying over the north pole as it travels from the nightside to the dayside, moving south as it passes over the equator, sailing back to the unilluminated side when it reaches the south pole, and then heading north above terrain in the dark of night. To accomplish the earlier part of its new approach trajectory, however, Dawn will stay over lower latitudes, very high above the mysterious surface but not far from the equator. Therefore, as it races toward RC3, it will orient its ion engine not only to shorten the time to reach that orbital altitude but also to tip the plane of its orbit so that it encircles the poles (and tilts the plane to be at a particular orientation relative to the sun). Then, finally, as it gets closer still, it will turn to use that famously efficient glowing beam of xenon ions against Ceres’ gravity, acting as a brake rather than an accelerator. By April 23, this first act of a beautiful new celestial ballet will conclude. Dawn will be in the originally intended orbit around Ceres, ready for its next act: the intensive observations of RC3 we described in February.

Dawn’s route to orbit is no more complex and elegant than what any crackerjack spaceship pilot would execute. However, one of the key differences between what our ace will perform and what often happens in science fiction movies is that Dawn’s maneuvers will comply with the laws of physics. And if that’s not gratifying enough, perhaps the fact that it’s real makes it even more impressive. A spaceship sent from Earth more than seven years ago, propelled by electrically accelerated ions, having already maneuvered extensively in orbit around the giant protoplanet Vesta to reveal its myriad secrets, soon will bank and roll, arc and turn, ascend and descend, and swoop into its planned orbit.

As Earth, the sun, and the spacecraft come closer into alignment, radio signals that go back and forth must pass near the sun. The solar environment is fierce indeed, and it will interfere with those radio waves. While some signals will get through, communication will not be reliable. Therefore, controllers plan to send no messages to the spacecraft from Dec. 4 through Dec. 15; all instructions needed during that time will be stored onboard beforehand. Occasionally Deep Space Network antennas, pointing near the sun, will listen through the roaring noise for the faint whisper of the spacecraft, but the team will consider any communication to be a bonus.

Dawn is big for an interplanetary spacecraft (or for an otherworldly dragonfly, for that matter), with a wingspan of nearly 65 feet (19.7 meters). However, more than 3.8 times as far as the sun, 352 million miles (567 million kilometers) away, humankind lacks any technology even remotely capable of glimpsing it. But we can bring to bear something more powerful than our technology: our mind’s eye. From Dec. 8 to 11, if you block the sun’s blazing light with your thumb, you will also be covering Dawn’s location. There, in that direction, is our faraway emissary to new worlds. It has traveled three billion miles (4.8 billion kilometers) already on its extraordinary extraterrestrial expedition, and some of the most exciting miles are still ahead as it nears Ceres. You can see right where it is. It is now on the far side of the sun.

The sun!

This is the same sun that is more than 100 times the diameter of Earth and a third of a million times its mass. This is the same sun that has been the unchallenged master of our solar system for more than 4.5 billion years. This is the same sun that has shone down on Earth all that time and has been the ultimate source of so much of the heat, light and other energy upon which the planet’s residents have been so dependent. This is the same sun that has so influenced human expression in art, literature, mythology and religion for uncounted millennia. This is the same sun that has motivated scientific studies for centuries. This is the same sun that is our signpost in the Milky Way galaxy. And humans have a spacecraft on the far side of it. We may be humbled by our own insignificance in the universe, yet we still undertake the most valiant adventures in our attempts to comprehend its majesty.

Dawn is 780,000 miles (1.3 million kilometers) from Ceres, or 3.3 times the average distance between Earth and the moon. It is also 3.77 AU (350 million miles, or 564 million kilometers) from Earth, or 1,525 times as far as the moon and 3.82 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take one hour and three minutes to make the round trip.

› Read more entries from Marc Rayman's Dawn Journal

TAGS: DAWN, VESTA, CERES, DWARF PLANETS, SOLAR SYSTEM, MISSION, SPACECRAFT

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  ABOUT THE AUTHOR

  Marc Rayman, Dawn Mission Director and Chief Engineer

  Marc Rayman is the director and chief engineer for NASA's Dawn mission, which was launched in 2007 on a mission to orbit the two most massive bodies in the main asteroid belt between Mars and Jupiter to characterize the conditions and processes that shaped our solar system.

At the time the burst of radiation arrived, Dawn was thrusting as usual, emitting a blue-green beam of high velocity xenon ions from engine #1. Ten times as efficient as conventional chemical propulsion, ion propulsion truly enables this unique mission to orbit two extraterrestrial destinations. With its remarkably gentle thrust, it uses xenon propellant so frugally that it takes more than three and a half days to expend just one pound (0.45 kilograms), providing acceleration with patience.

Dawn's electronics were designed to be resistant to radiation. On this occasion, however, the particle managed to deposit its energy in such a way that it disrupted the behavior of a circuit. The control unit used that circuit to move valves in the elaborate system that transports xenon from the main tank at a pressure of 500 psi (34 times atmospheric pressure) to the ion engine, where it is regulated to around two millionths of a psi (ten million times lower than atmospheric pressure), yielding the parsimonious expenditure of propellant. The controller continued monitoring the xenon flow (along with myriad other parameters needed for the operation of the ion engine), but the valves were unable to move in response to its instructions. Thrusting continued normally for more than an hour as the xenon pressure in the engine decreased very gradually. (Everything with ion propulsion is gradual!) When it reached the minimum acceptable value, the controller executed an orderly termination of thrust and reported its status to the main spacecraft computer.

When the computer was informed that thrust had stopped, it invoked one of Dawn's safe modes. It halted other activities, reconfigured some of the subsystems and rotated to point the main antenna to Earth.

The events to that point were virtually identical to a radiation strike that occurred more than three years earlier. Subsequent events, however, unfolded differently.

In normal circumstances, the mission control team would be able to guide the spacecraft back to normal operations in a matter of hours, as they did in 2011. Indeed, the longest part of the entire process then was simply the time between when Dawn turned to Earth and when the next scheduled tracking session with NASA's worldwide Deep Space Network (DSN) began. Most of the time, Dawn operates on its own using instructions stored in its computer by mission controllers. The DSN is scheduled to communicate with it only at certain times.

Dawn performs a carefully choreographed 2.5-year pas de trois from Vesta to Ceres. Celestial navigators had long known that the trajectory was particularly sensitive to glitches that interfere with ion thrusting during part of 2014. To ensure a prompt response to any interruptions in thrust, therefore, the Dawn project collaborated with the DSN to devise a new method of checking in on the spacecraft more frequently (but for short periods) to verify its health. This strategy helped them detect the condition soon after it occurred.Dawn from Vesta to Ceres

When an antenna at the DSN complex near Madrid, Spain, received the explorer's radio signal that morning, it was apparent that Dawn was neither in exactly the configuration to be expected if it were thrusting nor if it had entered one of its safe modes. Although they did not establish until later in the day what was happening, it turns out that not one but two anomalies occurred on the distant spacecraft, likely both triggered by particles in the radiation burst. Dawn encountered difficulty controlling its attitude with its usual exquisite precision. (Engineers use "attitude" to refer to the orientation of the craft in the zero-gravity conditions of spaceflight. In this case, the spacecraft's orientation was not controlled with its usual precision, but the spacecraft's outlook was as positive and its demeanor as pleasant as ever.) Instead of maintaining a tight lock of its main antenna on faraway Earth, it was drifting very slightly. The rate was 10 times slower than the hour hand on a clock, but that was enough to affect the interplanetary communication. Ultimately one of the onboard systems designed to monitor the overall health and performance of all subsystems detected the attitude discrepancy and called for another, deeper safe mode.

In this safe mode, Dawn further reconfigured some of the subsystems and used a different part of the attitude control system to aim at the solar system's most salient landmark: the sun. It switched to one of its auxiliary antennas and transmitted a wide radio beam.

Meanwhile, the operations team began working with the DSN and other missions to arrange for more time to communicate with Dawn than had previously been scheduled. Projects often collaborate this way, making adjustments for each other in the spirit of shared interest in exploring the solar system with the limited number of DSN stations. Later in the day on Thursday, when an antenna near Goldstone, Calif., was made available to point at Dawn, it was stable in safe mode.

The team decided to aim for resuming thrusting on Monday, Sep. 15. They had already formulated a detailed four-week sequence of commands to transmit to the spacecraft then, so this would avoid the significant complexity of changing the timing, a process that in itself can be time-consuming. This plan would limit the duration of the missed thrust during this sensitive portion of the long flight from Vesta to Ceres. Time was precious.

While it was in safe mode, there were several major challenges in investigating why the spacecraft had not been able to point accurately. The weak radio signal from the auxiliary antenna allowed it to send only a trickle of data. Readers who have heard tales of life late in the 20th century can only imagine what it must have been like for our ancestors with their primitive connections to the Internet. Now imagine the Dawn team trying to diagnose a very subtle drift in attitude that had occurred on a spacecraft 3.2 AU (almost 300 million miles, or 480 million kilometers) from Earth with a connection about one thousand times slower than a dial-up modem from 20 years ago. In addition, radio signals (which all regular readers know travel at the universal limit of the speed of light) took 53 minutes to make the round trip. Therefore, every instruction transmitted from JPL required a long wait for a response. Combined with the intermittent DSN schedule, these conditions greatly limited the pace at which operations could proceed.

To improve the efficiency of the recovery, the DSN agreed to use its newest antenna, known as Deep Space Station 35 (DSS-35), near Canberra, Australia. DSS-35 was not quite ready yet for full-time operational use, and the DSN postponed some of the planned work on it to give Dawn some very valuable extra communications opportunities. It's impressive how all elements of NASA work together to make each project successful.DSN with cranes

Engineers hypothesized that the reconfigurations upon entering safe mode might have rectified the anomaly that prevented the spacecraft from maintaining its characteristic stability. While some people continued the previously planned work of finalizing preparations for Ceres, most of the rest of the operations team split into two shifts. That way, they could progress more quickly through the many steps necessary to command the spacecraft out of safe mode to point the main antenna to Earth again so they could download the large volume of detailed data it had stored on what had occurred. By the time they were ready late on Friday night, however, there was a clear indication that the spacecraft was not ready. Telemetry revealed that the part of the attitude control software that was not used when pointing at the sun in safe mode - but that would be engaged when pointing elsewhere - was still not operating correctly.

Experts at JPL, along with a colleague at Orbital Sciences Corporation in Dulles, VA, scrutinized what telemetry they could receive, performed tests with the spacecraft simulator, and conducted other investigations. The team devised possible explanations, and one by one they tested and eliminated them. Their intensive efforts were powered not only by their skill and their collective experience on Dawn and other missions but also by plenty of pizza and fancy cupcakes. (The cupcakes were delivered in a box lovingly decorated with a big heart, ostensibly by the young daughter of the team member who provided them, but this writer suspects it might have been the team member himself. Regardless, embedded in the action, your correspondent established that the cupcakes were not only a yummy dessert after a pizza lunch but also that they made a terrific dinner. What a versatile and delectable comestible!)

Despite having all the expertise and creativity that could be brought to bear, by Saturday afternoon nothing they had tried had proven effective, including restarting the part of the software that seemed to be implicated in the pointing misbehavior. Confronting such an unyielding situation was not typical for such an experienced flight team. Whenever Dawn had entered one of its safe modes in the preceding seven years of flight, they had usually established the cause within a very few hours and knew precisely how to return to normal operations quickly. This time was different.

The team had still more ideas for systematically trying to fix the uncooperative pointing, but with the clock ticking, the mission director/chief engineer, with a conviction that can only come from cupcakes, decided to pursue a more dramatic course. It would put the spacecraft into an even deeper safe mode, and hence would guarantee a longer time to restore it to its normal operational configuration, but it also seemed a more likely solution. It thus appeared to offer the best possibility of being ready to start thrusting on schedule on Monday, avoiding the difficulty of modifying the four-week sequence of commands and minimizing the period of lost thrust. The idea sounds simple: reboot the main computer.

Rebooting the computer on a ship in deep space is a little bigger deal than rebooting your laptop. Indeed, the last time controllers commanded Dawn to restart its computer was in April 2011, when they installed a new version of software. Such a procedure is very delicate and is not undertaken lightly, given that the computer controls all of the robot's functions in the unforgiving depths of space. Nevertheless, the team made all the preparations that afternoon and evening, and the computer rebooted as commanded two minutes after midnight.

Engineers immediately set about the intricate tasks of verifying that the probe correctly reloaded all of its complex software and was still healthy. It took another 12 hours of reconfiguring the spacecraft and watching the driblet of data before they could confirm around noon on Sunday that the attitude control software was back to its usual excellent performance. Whatever had afflicted it since the radiation burst was now cured. After a brief pause for the tired team members on shift in Dawn mission control to shout things like "Yes!" "Hurray!" and "Time for more cupcakes!" they continued with the complex commanding to point the main antenna to Earth, read out the diagnostic logs, and return each subsystem to its intended state. By Monday afternoon, they had confirmed that hundreds upon hundreds of measurements from the spacecraft were exactly what they needed to be. Dawn was ready to resume ion thrusting, heading for an exciting, extended exploration of the first dwarf planet discovered.

Throughout the contingency operations, even as some people on the team delved into diagnosing and recovering the spacecraft and others continued preparing for Ceres, still others investigated how the few days of unplanned coasting would affect the trajectory. For a mission using ion propulsion, thrusting at any time is affected by thrusting at all other times, in both the past and the future. The new thrust profiles (specifically, both the throttle level and the direction to point the ion engine every second) for the remainder of the cruise phase and the approach phase (concluding with entering the first observation orbit, known as RC3) would have to compensate for the coasting that occurred when thrusting had been scheduled. The flight plans are very complicated, and developing them requires experts who apply very sophisticated software and a touch of artistry. As soon as the interruption in thrust was detected on Thursday, the team began formulating new designs. Initially most of the work assumed thrusting would start on Monday. After the first few attempts to correct the attitude anomaly were unsuccessful, however, they began looking more carefully into later dates. Thanks to the tremendous flexibility of ion propulsion, there was never doubt about ultimately getting into orbit around Ceres, but the thrust profiles and the nature and timeline of the approach phase could change quite a bit.

Once controllers observed that the reboot had resolved the problem, they put the finishing touches on the Monday plan. The team combined the new thrust profile with the pre-existing four-week set of commands already scheduled to be radioed to the spacecraft during a DSN session on Monday. They had already made another change as well. When the radiation burst struck the probe, it had been using ion engine #1, ion engine controller #1, and power unit #1. Although they were confident that simply turning the controller off and then on again would clear the glitch, just as it had in 2011 (and as detailed analysis of the electrical circuitry had indicated), they had decided a few days earlier that there likely would not be time to verify it, so prudence dictated that near-term thrusting not rely on it. Therefore, following the same strategy used three years earlier, the new thrust profile was based on controller #2, which meant it needed to use ion engine #2 and power unit #2. (For those of you keeping score, engine #3 can work with either controller and either power unit, but the standard combination so far has been to use the #1 devices with engine #3.) Each engine, controller, and power unit has been used extensively in the mission, and the expedition now could be completed with only one of each component if need be.

By the time Dawn was once again perched atop its blue-green pillar of xenon ions on Monday, it had missed about 95 hours of thrusting. That has surprising and interesting consequences for the approach to Ceres early next year, and it provides a fascinating illustration of the creativity of trajectory designers and the powerful capability of ion propulsion. Given how long this log is already, however, we will present the details of the new approach phase next month and explain then how it differs from what we described last December. For those readers whose 2015 social calendars are already filling up, however, we summarize here some of the highlights.

Throughout this year, the flight team has made incremental improvements in the thrust plan, and gradually the Ceres arrival date has shifted earlier by several weeks from what had been anticipated a year ago. Today Dawn is on course for easing into Ceres' gravitational embrace on March 6. The principal effect of the missed thrust is to make the initial orbit larger, so the spaceship will need more time to gently adjust its orbit to RC3 at 8,400 miles (13,500 kilometers). It will reach that altitude on about April 22 which, as it turns out, differs by less than a week from the schedule last year.Hubble images of Ceres

During the approach phase, the spacecraft will interrupt thrusting occasionally to take pictures of Ceres against the background stars, principally to aid in navigating the ship to the uncharted shore ahead. Because arrival has advanced from what we presented 10 months ago, the schedule for imaging has advanced as well. The first "optical navigation" photos will be taken on about Jan. 13. (As we will see next month, Dawn will glimpse Ceres once even sooner than that, but not for navigation purposes.) The onboard camera, designed for mapping Vesta and Ceres from orbit, will show a fuzzy orb about 25 pixels across. Although the pictures will not yet display details quite as fine as those already discerned by Hubble Space Telescope, the different perspective will be intriguing and may contain surprises. The pictures from the second approach imaging session on Jan. 26 will be slightly better than Hubble's, and when the third set is acquired on Feb. 4, they should be about twice as good as what we have today. By the time of the second "rotation characterization" on about Feb. 20 (nearly a month earlier than was planned last year), the pictures will be seven times better than Hubble's.

While the primary purpose of the approach photos is to help guide Dawn to its orbital destination, the images (and visible and infrared spectra collected simultaneously) will serve other purposes. They will provide some early characterizations of the alien world so engineers and scientists can finalize sensor parameters to be used for the many RC3 observations. They will also be used to search for moons. And the pictures surely will thrill everyone along for the ride (including you, loyal reader), as a mysterious fuzzy patch of light, observed from afar for more than two centuries and once called a planet, then an asteroid and now a dwarf planet, finally comes into sharper focus. Wonderfully exciting though they will be, the views will tantalize us, whetting our appetites for more. They will draw us onward with their promises of still more discoveries ahead, as this bold adventure into the unknown begins to reveal the treasures we have so long sought.

Dawn is 1.2 million miles (1.9 million kilometers) from Ceres. It is also 3.65 AU (339 million miles, or 546 million kilometers) from Earth, or 1,475 times as far as the moon and 3.67 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take one hour and one minute to make the round trip.

Dr. Marc D. Rayman
5:00 p.m. PDT October 31, 2014

P.S. While Dawn thrusts tirelessly, your correspondent is taking the evening off for Halloween. No longer able to fit in his costume from last year (and that has nothing to do with how many cupcakes he has consumed), this year he is expanding his disguise. Expressing the playful spirit of the holiday, he will be made up as a combination of one part baryonic matter and four parts nonbaryonic cold dark matter. It's time for fun!

› Read more entries from Marc Rayman's Dawn Journal

TAGS: DAWN, CERES, VESTA, MISSION, SPACECRAFT, DWARF PLANETS

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  ABOUT THE AUTHOR

  Marc Rayman, Dawn Mission Director and Chief Engineer

  Marc Rayman is the director and chief engineer for NASA's Dawn mission, which was launched in 2007 on a mission to orbit the two most massive bodies in the main asteroid belt between Mars and Jupiter to characterize the conditions and processes that shaped our solar system.

After testing was completed, two spacecraft and a spare (the proof-test model) were partly disassembled, carefully packed and loaded on moving vans for a trip to the Air Force Eastern Test Range in Cape Kennedy, Florida. They were inspected, reassembled, and tested again before launch.

*To Mars: the Odyssey of Mariner IV, TM33-229, 1965.

This post was written for “Historical Photo of the Month,” a blog by Julie Cooper of JPL’s Library and Archives Group.

TAGS: HISTORY, MARS, MARINER, MISSION, SPACECRAFT, SOLAR SYSTEM,

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  ABOUT THE AUTHOR

  Julie Cooper, Certified Archivist

  Julie Cooper is a certified archivist who identifies and processes collections for the JPL Archives, and helps researchers find information about the history of JPL.