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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