# Presentation: 219049

## Micro-Arcsecond Imaging Mission, Pathfinder (MAXIM-PF)

**May 13-17, 2002**

**Micro-Arcsecond Imaging Mission, Pathfinder (MAXIM-PF)**

**Electrical Power System (EPS)**

## 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 6th  year and 71 days during the 7th 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.**

## 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.**

## EPS Detail Charts

**Micro-Arcsecond Imaging Mission, Pathfinder (MAXIM-PF)**

**MAXIM-PF, May 13-17, 2002****Goddard Space Flight Center**

## 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.**

## 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.**

## 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.**

## Detector Spacecraft Phase I & II EPS Baseline

**Micro-Arcsecond Imaging Mission, Pathfinder (MAXIM-PF)**

**MAXIM-PF, May 13-17, 2002****Goddard Space Flight Center**

## Detector Spacecraft Load Analysis

## Detector Spacecraft EPS Curve

## Detector Spacecraft Summary

## HubCraft Phase I EPS Baseline

**Micro-Arcsecond Imaging Mission, Pathfinder (MAXIM-PF)**

**MAXIM-PF, May 13-17, 2002****Goddard Space Flight Center**

## Hubcraft Load Analysis

## Hubcraft EPS Curve

## Hub Spacecraft Phase II EPS Baseline

**Micro-Arcsecond Imaging Mission, Pathfinder (MAXIM-PF)**

**MAXIM-PF, May 13-17, 2002****Goddard Space Flight Center**

## Hub Spacecraft Load Analysis

## Hub Spacecraft EPS Curve

## Hub Spacecraft Summary

## FreeFlyer Spacecraft Phase II EPS Baseline

**Micro-Arcsecond Imaging Mission, Pathfinder (MAXIM-PF)**

**MAXIM-PF, May 13-17, 2002****Goddard Space Flight Center**

## FreeFlyer Spacecraft Load Analysis

## FreeFlyer Spacecraft EPS Curve

## FreeFlyer Spacecraft Summary

## 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.**

## 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.**

## 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.

## Electrical Power System  Issues and Concerns

**None**