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					                  Photovoltaic Panel Augmentation of Shuttle Power System

- Objectives
Develop advanced, photovoltaic panel enhanced power system for Shuttle utilizing Hybrid
Power Management (HPM) techniques. HPM is the integration of diverse power devices in an
optimal configuration. There is a rich heritage of photovoltaic cell applications for spacecraft,
including the International Space Station (ISS). The ISS photovoltaic array is 32,528 sq. ft. in
area, and provides 246 kilowatts of power. Photovoltaic arrays can withstand the harsh
environment of space, including vacuum, thermal, and the vibrations of launch aboard the Space
Shuttle. There are many options for photovoltaic cells. The conventional approach is to make
flat-plate arrays from individual crystalline cells with silicon as the conventional material while
gallium arsenide material provides some improvement in efficiency. Multiple junction cells
divide the solar spectrum and provide greater efficiency. Advanced multi-junction amorphous
cells manufactured on flexible substrates and other thin-film technologies provide somewhat
lower efficiency than other technologies, but substantially lower price, and may offer a good
solution for Shuttle power. The Shuttle Water Coolant Loop System (WCLS) provides thermal
conditioning of the crew cabin by collecting heat at the cabin-air-to-water-coolant-loop heat
exchanger and transfers heat to the water coolant loops. The WCLS also provides thermal
conditioning for the three avionics bays by an air-to-water heat exchanger in each avionics bay
which transfers heat to the water coolant loop. Strategic installation of photovoltaic panels can
reduce Shuttle heating and reduce the volume and mass of the WCLS, as well as improve
thermal performance. In addition, the combination of photovoltaic panels with an ultracapacitor
energy storage system (covered under a different proposal) results in a highly efficient power
system with excellent power characteristics. Overall, the key objectives of this effort are to
improve Shuttle safety, reliability, and performance, and to reduce the volume and mass of the
Shuttle power system.

- Envisioned outcome products
The Shuttle power system would be greatly improved through the incorporation of photovoltaic
panels, especially if integrated with an ultracapacitor based energy storage system. Photovoltaic
panels will generate significant electrical power, as well as provide shielding and cooling for the
Shuttle. Photovoltaic panels and ultracapacitors complement each other perfectly, providing
high power during surges. A photovoltaic power system incorporated into the Shuttle power
system substantially reduces main power source peak power levels. This reduces the volume and
mass of the Shuttle power system, as well as providing improved performance and reliability.

- Pros and Cons of implementation
Integrating photovoltaic panels into the Shuttle power system provides a significant
improvement in safety, reliability, and performance. Photovoltaic cells have an extremely long
shelf and cycle life and require no maintenance. Photovoltaic cells provide excellent low
temperature performance, and have minimal support requirements. Photovoltaic panels are an
ideal adjunct to an ultracapacitor energy storage system, providing high power during surges and
the ability to absorb high power during recharging. The peak power level of the main power
source is reduced, thus reducing power system mass and volume, and improving life.

- Level of effort estimate
Initially, the effort will primarily involve power system design, development, testing, and
analysis. This effort at GRC will require at least 5 FTEs in FY’03.