SNAP Electrical Power System for SuperNova/Acceleration Probe

1. SuperNova / Acceleration Probe (SNAP) Electrical Power System Bob G. Beaman July 2, 2001

2. Electrical Power SystemOverview • Overview • Driving Requirements and Assumptions • Options considered • Selected Configuration and Rationale • Technologies Required • Requirements Verification • Mass, Power, and Cost Summary • Additional Trades to Consider • Risk Assessment • Issues and Concerns • Subsystem Summaries • Back Up Charts SNAP June 28, 2001Goddard Space Flight Center

3. Electrical Power System Overview, Supporting Data • Spacecraft Electrical Power System (EPS) consists of Solar Cells to collect/convert electrical energy, a Battery to store energy for launch, peak loads and eclipses. Electronics are used to regulate the solar array and charge the battery. • Solar Arrays • Solar arrays provide electrical power for the spacecraft during the sunlight and recharges the battery for electrical power during the eclipse. • Triple Junction GaAs solar cells are used. • Energy Storage • Provides electrical power during launch • Provides electrical power during eclipses • Provides peak electrical power during sunlight as needed • PSE (Power System Electronics) • Provides Solar Array power Regulation • Battery charge control • Power switching and distribution SNAP June 28, 2001Goddard Space Flight Center

4. Electrical Power System Driving Requirements & Assumptions • Launch: Dec 21 2008 • Orbit: 57 RE x 19 RE • Life: 2 Years Minimum 5 years Goal • Battery: Needed to provide Power during eclipse • Solar Array: Spacecraft rotation of +/-45 deg during orbit cycle. • Solar Array Temperature: 70 deg C SNAP June 28, 2001Goddard Space Flight Center

5. Electrical Power System Options Considered • Battery Mass. Many different battery masses were calculated based on changes in the load analysis. Many more traded can be done in this area. • Launch dated. Dec or June launches seam to be better than March or Sept. The March and Sept have eclipse cycles during the solar power min cycles. • Solar Array height vs coverage. Solar Array required is 2.39 M^2 at a substrate level and to keep the temperature to 70 deg C will require about 2.4 M^2 OSR’s (optical surface reflectors). On the curved surface and rotating 45 degrees this will require: SNAP June 28, 2001Goddard Space Flight Center

6. Electrical Power System Selected Configuration & Rationale • Solar Array. The Selected 7.8 M2 area will have about 3.9 M2 Triple Junction Gallium Arsinide (TJGaAs) solar cell area. TJGaAs is used to reduce solar array area and weight. • MAP type PSE. This PSE can be adapted easily for the study phase. • Battery. NiH2 IPV (individual Pressure Vessel) at 100 ah this is a EPT stock item SAR-10093. Note a EPT SAR-10063 may also work. The mass of either of these batteries is 81 kg and further search for NiH2 SPV’s (Single Pressure Vessel) and development of large ampere hour LiIon batteries could provide a mass savings. SNAP June 28, 2001Goddard Space Flight Center

7. Electrical Power System Technologies Required • Selected 3.9 M2 solar array area using Triple Junction Gallium Arsinide (TJGaAs) solar cells. This meets the Science 3 year requirement. • Impact on design. TJGaAs cells are available, however 28% efficiency is a small risk. • Alternatives: 26% efficient solar cells with increased solar array area. • Feedback to technology developer: Develop 28% efficient solar cells. • Battery will be 100 ah NiH2 IPV for the launch loads and eclipse season loads. • PSE will be a modification of the MAP PSE. SNAP June 28, 2001Goddard Space Flight Center

8. Electrical Power System Requirements Verification • Standard verification for PSE and Solar Array. A life test should be done on the battery design to ensure it will meet the cycle life requirement with normal eclipse seasons and instrument turn-on shallow discharges. SNAP June 28, 2001Goddard Space Flight Center

9. Electrical Power System Mass, Power, and Cost Summary SNAP June 28, 2001Goddard Space Flight Center

10. Electrical Power System Additional Trades to Consider • Battery large size (mass & ah) is driven by the long eclipse and eclipse load. • Look at LiIon life development data. The size of this battery is not presently being developed the capability of LiIon technology, however this should be reviewed in the future and may reduce the battery mass. • Scrub the load analysis to reduce the battery ampere-hour requirement. Scrubbing the launch power and eclipse power in the load analysis may reduce the battery ah and mass. • Continue to look at the Solar Array size vs Mission Life. • Continue to look at number of S/A quadrants vs height. SNAP June 28, 2001Goddard Space Flight Center

11. Electrical Power System Risk Assessment • Solar Cell Efficiency of 28% is a short term risk. • Solar panel production for 28% efficient cells is expected in the fall of 2001. This risk should be retired at that time. • This mission is not solar array limited and a fall back for this risk is to baseline 26% efficient solar cells. SNAP June 28, 2001Goddard Space Flight Center

12. Electrical Power System Issues and Concerns • Battery Mass: Baseline NiH2 IPV for reduced risk and to stretch the mass envelope. Need further work with reducing the load analysis and trading other battery technologies like the NiH2 SPV. Also should look at LiIon development for large ah cells. • Solar array trade for OSR, temperature and quadrants of coverage vs height, mass and cost. SNAP June 28, 2001Goddard Space Flight Center

13. Back Up Charts SNAP Electrical Power System June 28, 2001

14. Load Analysis SNAP June 28, 2001Goddard Space Flight Center

15. EPS Curve SNAP June 28, 2001Goddard Space Flight Center