>> The Next Step to More Power

Deep Space 1, although it validated the efficacy of ion propulsion, had traditional rigid solar panels.

The power subsystem on most spacecraft makes up a good part of the entire spacecraft mass. Existing state-of-the-art solar arrays are based on rigid composite honeycomb structures with complex mechanisms to synchronize their deployment. They tend to be heavy, take up a lot of space in their stowed configuration, and have low fundamental frequencies when deployed, complicating the design of attitude control systems. Recent advances in photovoltaic technology and lightweight structures can be applied to spacecraft solar arrays to greatly improve them, both decreasing their mass and increasing their power generation capability.

The highest power solar arrays in use on U. S. civilian spacecraft today are those used on the International Space Station. These ISS arrays produce 30.8 kW from each array and have a specific power of 32 W/kg. The largest solar array used on an interplanetary spacecraft is that used on the Dawn mission to two asteroids, Vesta and Ceres. The Dawn solar array provides 10.5 kW of power and has a specific power of 80 W/kg.

Lightweight solar array designs have been investigated that can produce two to three times the power per unit of mass as the solar arrays currently being used on spacecraft. These lightweight arrays are too flimsy and their deployment mechanisms too unusual for their in-space deployment in a zero gravity environment and their structural and electrical performance in space to be predicted with confidence. What is needed is an activity to validate empirically the analytical models used to predict the deployment, structural dynamics, and power generating performance of these ultra-lightweight arrays.

Space Technology 8 (ST8) will test a new type of solar array called the UltraFlex 175, which was conceived and is provided by ATK, Goleta, CA. This system merges the best features of advanced solar-array technologies and will yield a design capable of providing 7 kW of power with a specific power of 175 W/kg.

UltraFlex 175 fully deployed in the laboratory. Notice size comparison with legs of man standing behind it.

• The design of the array efficiently uses its structure to obtain the largest electrically active area while being sufficiently stiff to have a relatively high fundamental structural frequency.

• The innovative use of materials and power enhancement strategies maximize electrical output per unit mass.

• The technology emphasizes compact stowage in order to minimize stowed volume for pre-launch packaging.

However, a compactly folded lightweight structure introduces additional issues. What happens when it is deployed? What effect will the deployment have on the spacecraft? How well can the deployment forces be controlled? Hence, this experiment will also validate analytical models of deployment and how well and rapidly any induced vibration of the parts of the solar array can be damped. The successful deployment of this new, ultra-lightweight solar array will mitigate concerns over the handling of lightweight power generating structures and will be a major contribution to future applications of this technology.