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Atul
Electrical Power System
SuperNova / Acceleration Probe
(SNAP)
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Electrical Power SystemPage 2
SNAP June 28, 2001Goddard Space Flight Center
j Overview
j Supporting Data
j Driving Requirements & Assumptions
j Options considered
j Selected Configuration & Rationale
j Technologies Required
j Requirements Verification
j Mass, Power, and Cost Summary
j Additional Trades to Considerj Risk Assessment
j Issues and Concerns
j Back Up Charts
Electrical Power SystemOverview
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SNAP June 28, 2001Goddard Space Flight Center
Electrical Power SystemSupporting Data
j Spacecraft Electrical Power System (EPS) consists of Solar Cells tocollect/convert electrical energy, a Battery to store energy for launch, peakloads and eclipses. Electronics are used to regulate the solar array andcharge the battery.
j Solar Arraysy Solar arrays provide electrical power for the spacecraft during the
sunlight and recharges the battery for electrical power during theeclipse.
y Triple Junction GaAs solar cells are used.
j Energy Storagey Provides electrical power during launch
y Provides electrical power during eclipsesy Provides peak electrical power during sunlight as needed
j PSE (Power System Electronics)y Provides Solar Array power Regulationy Battery charge controly Power switching and distribution
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SNAP June 28, 2001Goddard Space Flight Center
Electrical Power SystemDriving Requirements & Assumptions
j Launch: Dec 21 2008
j Orbit: 57 RE x 19 RE
j Life: 2 Years Minimum5 years Goal
j Battery: Needed to provide Powerduring eclipse
j Solar Array: Spacecraft rotation of+/-45 deg during orbitcycle.
j Solar Array Temperature: 70 deg C
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SNAP June 28, 2001Goddard Space Flight Center
Electrical Power SystemOptions Considered
j Battery Mass. Many different battery masses were calculatedbased on changed in the load analysis. Many more traded can bedone in this area.
j Launch dated. Dec or June launches seam to be better than Marchor Sept. The March and Sept have eclipse cycles during the solarpower min cycles.
j Solar Array height vs coverage. Solar Array required is 2.39 M^2at a substrate level and to keep the temperature to 70 deg C will
require about 2.4 M^2 OSRs (optical surface reflectors).Heights Area
Two Quadrants 2.2 M 5.0 M^2
Four Quadrants 1.8 M 5.6 M^2
6 Quadrants 0.8 M 5.8 M^2
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SNAP June 28, 2001Goddard Space Flight Center
Electrical Power SystemSelected Configuration & Rationale
j Solar Array. Selected 2.47 M2 solar array area using TripleJunction Gallium Arsinide (TJGaAs) solar cells to reduce solararray area and weight.
j MAP type PSE. This PSE can be adapted easily for the
study phase.j 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 batteriesis 81 kg and further search for NiH2 SPVs (Single Pressure
Vessel) and development of large ampere hour LiIon batteriescould provide a mass savings.
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SNAP June 28, 2001Goddard Space Flight Center
Electrical Power SystemTechnologies Required
j Selected 2.47 M2 solar array area using Triple JunctionGallium Arsinide (TJGaAs) solar cells. This meets theScience 3 year requirement.y Impact on design. TJGaAs cells are available, however 28%
efficiency is a small risk.y Alternatives: 26% efficient solar cells with increased solar array
area.y Feedback to technology developer: Develop 28% efficient solar
cells.
j Battery will be 100 ah NiH2 IPV for the launch loads and
eclipse season loads.j PSE will be a modification of the MAP PSE.
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SNAP June 28, 2001Goddard Space Flight Center
Electrical Power SystemRequirements Verification
j Standard verification for PSE and Solar Array. A life testshould be done on the battery design to ensure it will meetthe cycle life requirement with normal eclipse seasons andinstrument turn-on shallow discharges.
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SNAP June 28, 2001Goddard Space Flight Center
Electrical Power SystemAdditional Trades to Consider
j Battery large size (mass & ah) is driven by the long eclipseand eclipse load.
j Look at LiIon life development data. The size of this batteryis not presently being developed the capability of LiIon
technology, however this should be reviewed in the future andmay reduce the battery mass.
j Scrub the load analysis to reduce the battery ampere-hourrequirement. Scrubbing the launch power and eclipse power inthe load analysis may reduce the battery ah and mass.
j Continue to look at the Solar Array size vs Mission Life.j Continue to look at number of S/A quadrants vs height.
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SNAP June 28, 2001Goddard Space Flight Center
Electrical Power SystemRisk Assessment
j Solar Cell Efficiency of 28% is a short term risk.y Solar panel production for 28% efficient cells is expected in the
fall of 2001. This risk should be retired at that time.y This mission is not solar array limited and a fall back for this
risk is to baseline 26% efficient solar cells.
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SNAP June 28, 2001Goddard Space Flight Center
Electrical Power SystemIssues and Concerns
j Battery Mass: Baseline NiH2 IPV for reduced risk and tostretch the mass envelope. Need further work with reducingthe load analysis and trading other battery technologies likethe NiH2 SPV. Also should look at LiIon development for
large ah cells.j Solar array trade for OSR, temperature and quadrants of
coverage vs height, mass and cost.
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Back Up Charts
SNAP Electrical Power SystemJune 28, 2001
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SNAP June 28, 2001Goddard Space Flight Center
Load Analysis
SnAP
5.0 Mission Life in Years
Nominal
Mode Day
Nominal
Mode Night
Safe Hold
EPSLoad Item Desc rip tion Avg . Pow er
Watts
Avg. Power
Watts
Power in
Watts
Peak
Power
Launch
Power
Requiremen
Total Power 522.4 267.0 430.6 957.8 321.4
Time Period Over Whic h
Averaging IsDone For EachCont ingency
Inst Globa l 20
Instrumentswith Continge ncy 102.0 12.0 84 162.0 20.4
Camera 20.0 0.0 15.0 70.000 4.0
Contingenc y 20 4.0 0.0 3.0 14.000 0.8
Telesc ope 65.0 10.0 55.0 65.000 13.0
Contingenc y 20 13.0 2.0 11.0 13.000 2.6Instrument #3 0.0 0.0 0.0 0 .000 0.0
Contingenc y 20 0.0 0.0 0.0 0.000 0.0
Instrument #4 0.0 0.0 0.0 0.000 0.0
Contingenc y 20 0.0 0.0 0.0 0.000 0.0
Instrument #5 0.0 0.0 0.0 0 .000 0.0
Contingenc y 20 0.0 0.0 0.0 0.000 0.0
Instrument #6 0.0 0.0 0.0 0 .000 0.0
Contingenc y 20 0.0 0.0 0.0 0.000 0.0
Spac ecraft Loadswith 420.4 255.0 346.6 795.8 301.0
Spcft Global 20
PSE Bob B. 7.2 4.0 7.2 10.8 7.2
Contingenc y 20 1.4 0.8 1.4 2.2 1.4
Elec tric a l - Ha rness Losses BGB Est 5.0 2.5 5.0 7.5 5.0
Contingenc y 20 1.0 0.5 1.0 1.5 1.0
C om m and & D a ta Hand li ng Te rr yS. 30.0 15.0 30.0 30.0 30.0
C ontingency 20 6.0 3.0 6.0 6.0 6.0
Da ta Record er Terry S. 103.0 0.0 20.6 154.5 20.6
C ontingency 20 20.6 0.0 4.1 30.9 4.1Sola r Array Drive Motor n/ a 0.0 0.0 0.0 0.0 0.0
Contingenc y 20 0.0 0.0 0.0 0.0 0.0
Sola r Array Drive Elec tronics n/ a 0.0 0.0 0.0 0.0 0.0
Contingenc y 20 0.0 0.0 0.0 0.0 0.0
Attitude Control Ap rille E. 89.1 77.0 88.0 193.4 110.0
Contingenc y 20 17.8 15.4 17.6 38.7 22.0
Com, K Band Transmeter Ron V. 61.0 20.0 61.0 64.0 61.0
Contingenc y 20 12.2 4.0 12.2 12.8 12.2
Com, SBand Transmeter Ron V. 9.0 8.0 9 .0 41.0 9.0
Contingenc y 20 1.8 1.6 1.8 8.2 1.8
Com, Rec iever Irene B. 8.0 8.0 8.0 12.0 8.0
C ontingency 20 1.6 1.6 1.6 2.4 1.6
Therma l Wes O. 38.0 78.0 60.0 150.0 0.0
C ontingency 20 7.6 15.6 12.0 30.0 0.0
Propulsion Estima te 0.0 0.0 0.0 0.0 0.0
C ontingency 20 0.0 0.0 0.0 0.0 0.0
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SNAP June 28, 2001Goddard Space Flight Center
EPS Curve
SnAP Mission Ove
5 Yr Life Wi
h Dep
oyab
ePane
;28% EffCe
s;
Average Load During Day=522 396W; Average Load During
Nigh
=267W
400
500
600
700
0 365 730 1095 1460 1825
Mission Time (Days)
Dayligh
Ave
ageSola
A
ayPowe
P
ovided
Dayligh
Ave
ageSola
A
ayPowe
Requi
ed