Bob G. Beaman

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

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
EPS Detail Charts
Micro-Arcsecond Imaging Mission, Pathfinder
(MAXIM-PF)
MAXIM-PF, May 13-17, 2002Goddard Space Flight
Center
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
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
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
Detector Spacecraft Phase I II EPS Baseline
Micro-Arcsecond Imaging Mission, Pathfinder
(MAXIM-PF)
MAXIM-PF, May 13-17, 2002Goddard Space Flight
Center
9
Detector Spacecraft Load Analysis
10
Detector Spacecraft EPS Curve
11
Detector Spacecraft Summary
12
HubCraft Phase I EPS Baseline
Micro-Arcsecond Imaging Mission, Pathfinder
(MAXIM-PF)
MAXIM-PF, May 13-17, 2002Goddard Space Flight
Center
13
Hubcraft Load Analysis
14
Hubcraft EPS Curve
15
Hub Spacecraft Phase II EPS Baseline
Micro-Arcsecond Imaging Mission, Pathfinder
(MAXIM-PF)
MAXIM-PF, May 13-17, 2002Goddard Space Flight
Center
16
Hub Spacecraft Load Analysis
17
Hub Spacecraft EPS Curve
18
Hub Spacecraft Summary
19
FreeFlyer Spacecraft Phase II EPS Baseline
Micro-Arcsecond Imaging Mission, Pathfinder
(MAXIM-PF)
MAXIM-PF, May 13-17, 2002Goddard Space Flight
Center
20
FreeFlyer Spacecraft Load Analysis
21
FreeFlyer Spacecraft EPS Curve
22
FreeFlyer Spacecraft Summary
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
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
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
Electrical Power System Issues and Concerns

• None