Thank you for visiting the Deep Space 1 mission status information site, now
beginning its tenth month on the list of most popular sites on any
habitable planet in or near the plane of the Milky Way galaxy for
information on this technology validation mission. This message was
logged in at 4:00 pm Pacific Time on Sunday, July 25.
With its mission of testing high risk, important new technologies having
exceeded expectations, Deep Space 1 is now nearly ready to attempt a very
very challenging encounter with the asteroid formerly known as 1992 KD.
This asteroid was discovered 7 years ago by JPL astronomers Eleanor Helin
and Kenneth Lawrence as part of an extensive and productive effort to
locate and study asteroids. Faithful listeners know that a contest
organized by The Planetary Society and JPL was conducted to select a new
name for 1992 KD. As hard as it is to believe, a better name was found.
Kerry Babcock of Port Orange, Florida won with his terrific proposal to
name the asteroid Braille, after Louis Braille who invented the raised-dot
alphabet for blind readers. The Planetary Society will be issuing a press
release with more details about the newly selected name.
DS1 got some help from the operations team this past week. Previous logs have described the impressive performance of AutoNav in
determining its location and course. But because of shortcomings in the
camera, it is not quite accurate enough for the job of guiding DS1 to its
extraordinarily close encounter with Braille. So engineers borrowed the
navigation pictures AutoNav took and performed more analyses with them than
AutoNav is designed to do, so they were able to improve upon AutoNav's
results. (The work performed by humans in this case could have been done
easily by AutoNav if the necessary instructions had been on board.) For
the first time in nearly 5 months, an update to its location was
transmitted to DS1. AutoNav now combines that information with its own
navigation estimates as it progresses toward the asteroid.
To keep DS1 on course, AutoNav designed a course correction and executed it
on Friday. But it turned out that in order to point the ion engine in the
desired direction, the orientation of the spacecraft would have allowed the
Sun to point at the camera and the device that tracks stars, imaginatively
known as the star tracker. So the on-board system did what the operations
team refers to as "vectorizing the burn": it computed two different
orientations that were acceptable for ion engine firings that combined to
produce the desired effect. Then AutoNav turned the spacecraft, used the
ion propulsion system for 3 hours, and then turned DS1 again and fired it
again for another 3 hours before turning back to point the main antenna at
Earth. The course correction went well and changed the spacecraft speed by
about 2.5 miles/hour.
Very little is known about asteroid Braille. Even estimates of its size
are quite uncertain, but it is probably just a few kilometers in diameter
(perhaps a mile or so). This is the smallest solar system body ever
targeted for a spacecraft encounter. In fact, the asteroid is so small
that it has been difficult for astronomers to determine its exact location,
and it is still too far away for the spacecraft to see it. Beginning today
however, whenever AutoNav takes pictures of larger, more distant asteroids
for its navigational fixes, it also will try to find asteroid Braille. As
expected, the tiny asteroid did not show up in this morning's pictures,
even though it is only a little over 3 days before the spacecraft arrives.
One of the greatest uncertainties right now is where the asteroid really
is, and the sooner AutoNav can spot its target, the better job it can do
zeroing in on it. Braille apparently rotates very slowly, taking nearly 10
Earth days to complete one turn. Although DS1 was designed to test
technologies, it will attempt to make scientific measurements when it flies
past the asteroid. Black and white pictures may reveal Braille's size and
shape and show craters, hills, valleys, and other topography. Infrared
measurements may help scientists determine the minerals that make up the
surface. By searching for changes in the solar wind, the stream of charged
particles flowing from the Sun, in the vicinity of the asteroid, it may be
possible to determine if it has a magnetic field. Perhaps the solar wind
or sunlight even cause surface material to be slowly eroded from the
asteroid and flung into space, in which case the spacecraft may directly
measure the resulting free atoms.
To get close enough to make all these measurements, AutoNav will attempt to
bring DS1 closer to Braille than any spacecraft has ever come to a solar
system body without actually landing on it. Speeding by at 15.5 km/s, or
nearly 35,000 miles/hour, the spacecraft will pass by more than 50 times
faster than a commercial jet and more than twice as fast as the space
shuttle. But it will come a mere 15 kilometers from the center of the
asteroid, or less than 9 miles from the surface. This is a great challenge
to AutoNav and to the operations team, but if it works this high risk
encounter should be exciting indeed.
The small operations team has been continuing to refine the complex set of
instructions that will govern the spacecraft, including the ones that give
AutoNav the opportunity to design and execute more maneuvers to keep the
spacecraft on course, the commands to the new technology science
instruments to collect data, directions to the attitude control system on
how to turn the spacecraft as it nears the asteroid, and instructions on
how to transfer, manipulate, and store the large volume of data to be
collected. Completing this unusually complex choreography, in which all
the spacecraft systems including AutoNav need to work together, is the
focus of the team's work right now. A group of instructions is known as a
sequence, and each day, the sequences covering the final 6 hours before the
closest approach to Braille are run through the Deep Space 1 test facility
at JPL. This is a simulation of the spacecraft, created using some
hardware similar to what is on the real spacecraft and some computer
programs that emulate the behavior of other parts of the spacecraft. The
test facility is certainly not identical to the spacecraft, so a successful
test does not guarantee success on the spacecraft, but it has allowed many
of the bugs to be worked out.
The final sequences will be radioed to DS1 on Monday. In the meantime,
AutoNav will continue to check its course and, if necessary, make course
corrections as it closes in on the asteroid. DS1's closest approach to the
asteroid will occur at approximately 9:46 pm PDT on Wednesday, and it will
be several hours after that before it can begin reporting its results to
Earth. Returning all the data may require several days; this page
will be updated on Thursday or Friday with a report on the outcome of this
exciting adventure.
Deep Space 1 is still about 4.3 million kilometers, or 2.7 million miles,
from Braille. The spacecraft is now almost 25% farther away from Earth
than the Sun is and over 480 times as far as the moon. At this distance of
over 185 million kilometers, or more than 115 million miles, radio signals,
traveling at the universal limit of the speed of light, take almost 21
minutes to make the round trip.
Thanks again for logging in!
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