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

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.

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.

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

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.

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.

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 % 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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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.

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.

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