1. Final Version Bob G. Beaman May 13-17, 2002 Micro-Arcsecond Imaging Mission, Pathfinder (MAXIM-PF) Electrical Power System (EPS)

2. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 2 EPS Summary  The Phase I Hubcraft is undeployed Single Hub spacecraft attached to the Six FreeFlyer spacecraft.  The EPS for the Hubcraft is a distributed EPS with 10 ah LiIon batteries in each Spacecraft. Three sun side FreeFlyer spacecraft solar arrays are enough power to provide the Hubcraft power requirement.  Batteries are provided for Launch loads and contingency.  Technology areas that should be available by 2015 are: Distributed EPS, 35% eff Quad Junction solar cells, EPS Autonomy and use of Structural Batteries.  Solar Array Temp was assumed at 105 deg C.  MAXIM Pathfinder to full MAXIM.  Solar array size increase by 1.4% from 5 to 7 years additional life.  Unused EPS margin may provide this.  With no S/A increase full operational requirements can accomplished except for 53 days during the 6 th year and 71 days during the 7 th year.  Use of 35% efficient solar cells would provide this and reduce solar array area.  Beginning Of Life (BOL) Solar Array power can accommodate up to 41.5 deg off pointing for the first year with decreasing angles as the solar array degrades.

3. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 3 EPS Conclusions  There are no Big EPS show stoppers.  Dual Cosine angles are used. First +/- 30 degrees comes from an instrument requirement. And +/- 15 degrees is needed the Phase II operation to avoided one FreeFlyer from shadowing the other when they are in the same plane with the sun.  The Phase I mission Hubcraft requires 3.72 M2 from 3 FreeFlyer Spacecrafts. Each FreeFlyer Spacecraft requires 1.25 M2 for the Phase II mission which is just slightly larger. The design goal was to keep the Phase I Hubcraft solar array size to be equal for less that the 3 FreeFlyer Phase II size.  Further analysis or additional development may increase the Phase I Hubcraft solar array size. If that happens, the sun lead FreeFlyer will need additional solar panels each adjacent side. Higher efficient (35%) solar cells can be used.

4. Final Version EPS Detail Charts Micro-Arcsecond Imaging Mission, Pathfinder (MAXIM-PF) MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center

5. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 5 Electrical Power System Driving Requirements & Assumptions  Launch:21 July 2015  Orbit:L2. No eclipses  Life:2 year Phase I 3 year Phase II  Battery:For Launch and contingency  Solar Array:Needed to provide Power for loads. Solar Array temp 105 deg C.

6. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 6 Electrical Power System Options Considered  Deployed Solar Array. A body mounted Solar Array size was achievable so solar array deployments were eliminated.  Phase I “sun lead” FreeFlyer adjacent side solar panels were not needed. The Phase II FreeFlyer solar Array size was large enough to be used as one third of the Phase I Hubcraft solar array.  Baseline a distributed EPS for the Phase I Hubcraft. The distributed EPS needs to be broken up for Phase II mission phase for individual FreeFlyer spacecraft and Hub spacecraft operation.

7. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 7 Electrical Power System Selected Configuration & Rationale  Use of 28% Tj GaAs solar cells. Provides enough power and will be a mainstay for 2015 launch. By 2015 35% QjGaAs cells may be available.  Use of LiIon battery. For launch loads and contingency in L2.  MAP type PSE, however must be modified to provide Distributed EPS functions. A Voltage regulated bus is recommended over a Battery Dominated Bus.

8. Final Version Detector Spacecraft Phase I & II EPS Baseline Micro-Arcsecond Imaging Mission, Pathfinder (MAXIM-PF) MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center

9. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 9 Detector Spacecraft Load Analysis

10. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 10 Detector Spacecraft EPS Curve

11. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 11 Detector Spacecraft Summary

12. Final Version HubCraft Phase I EPS Baseline Micro-Arcsecond Imaging Mission, Pathfinder (MAXIM-PF) MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center

13. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 13 Hubcraft Load Analysis

14. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 14 Hubcraft EPS Curve

15. Final Version Hub Spacecraft Phase II EPS Baseline Micro-Arcsecond Imaging Mission, Pathfinder (MAXIM-PF) MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center

16. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 16 Hub Spacecraft Load Analysis

17. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 17 Hub Spacecraft EPS Curve

18. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 18 Hub Spacecraft Summary

19. Final Version FreeFlyer Spacecraft Phase II EPS Baseline Micro-Arcsecond Imaging Mission, Pathfinder (MAXIM-PF) MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center

20. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 20 FreeFlyer Spacecraft Load Analysis

21. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 21 FreeFlyer Spacecraft EPS Curve

22. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 22 FreeFlyer Spacecraft Summary

23. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 23 EPS Technology Required  A distributed EPS system must be developed. Recommend the use of a voltage regulated system with distributed batteries and solar arrays.  By 2015 Quad junction gallium arsine (QjGaAs) solar cells at 35% efficiency would be available and can reduce mass but may increase cost and have life concerns.  Use of a Structural Battery would decrease mass. This technology should be available by 2015.

24. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 24 EPS 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.

25. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 25 Electrical Power System Additional Trades to Consider  Scrub the load analysis to reduce the solar array size and battery ampere- hour requirement.  Trade Battery Dominated Bus (BDB) vs Voltage Regulated Bus (VRB) for a distributed bus design.  Peaking analysis,  This EPS design has limited extra solar array due to full sun orbit and no battery recharge requirements.  Battery Life Test characteristics.  Cable harness inductive characteristics that will choke the peak current.  Use of a ultra capacitor near the peaking load device so harnessed do not see peak currents.  Look at propulsion orbit adjust maneuver and the power that is available.

26. Final Version MAXIM-PF, May 13-17, 2002 Goddard Space Flight Center Electrical Power System Page 26 Electrical Power System Issues and Concerns  None