1. Competition Sensitive Gabe Karpati June 28, 2001 SuperNova / Acceleration Probe (SNAP) System Overview

2. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 2  Driving Requirements and Assumptions  Options  Selected Configuration and Rationale  Technologies Required  Mass and Power Summary  Requirements Verification  Additional Trades  Risk Assessment  Issues and Concerns Outline

3. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 3 Overview  Mission objective:  Determine the magnitude-redshift relationship for supernovae of type 1A over redshift range 0.3<Z<1.8  Determine the distribution of gravitational potentials along cosmologically significant lines of sight  Determine the magnitude-redshift relationship for other supernova types  Additional constraints, challenges, and measurements  Orbit w/ adequate thermal environment, good observing efficiency  Pointing stability and tracking / Observatory stiffness  Primary purpose of this study:  Establish/validate baseline mission configuration  Length of study:  4 days

4. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 4 Driving Requirements & Assumptions  Orbit:  Best candidates to date are 19 Re x 57 Re w/ lunar assist or 38 Re circular achieved w/ lunar assist  Launch year: 2008  Lifetime: 2 year required, 5 years goal  Quality level: Selective redundancy  End-of-life disposal: Not required for orbits > GEO  Instrument support:  Mass: 700 kg  Power: 135 W max, 85 W avg, 22W stdby  Average Instrument Data Rate: 40 Mbps continuous

5. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 5 Orbit Options  LEO orbits:  PROs: Simplify launch vehicle and propulsion requirements, easy RF comm  CONs: Enormous loss of observing efficiency, huge thermal problems for Payload, Bus, and Radiators  Disposal required  HEO orbits:  PROs: Easy observing, good thermal environment  CON: Radiation environment problems  SHEO orbits w/ lunar assist:  PROs: Easy observing, good thermal environment  CONs: Requires “exotic” launch vehicle, difficult downlink and ground station situation that limits inclinations, orbits. Difficult orbit calculations.  Sun-synchronous drift-away orbits:  PROs: Perfect observing w/o eclipses, best thermal environment  CONs: RF communication difficult, especially at EOL. Possible mass constraint.  Final orbit selection after detailed analyses. For some orbits, minor errors can easily propagate into fatal dispersion

6. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 6 Launch Vehicle Options  Delta 2920H-10L  Liftoff capability marginal but fairing is way too small  GSFC “actual” cost estimate is $67M to $72M  Maiden flight w/ SIRTF in 2002  Delta 3940-11  Liftoff capability adequate  GSFC “actual” cost estimate is $80M to $84M  Liftoff capability adequate, fairing volume tight but adequate  Atlas IIIB  Liftoff capability comfortable, fairing volume tight but adequate  Zenit 3SL w/ Block DM-SL restartable upper stage (Sea Launch)  Liftoff capability comfortable, fairing volume comfortable  For details see “SNAP_Launch_Vehicles.xls”

7. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 7 RSDO Bus Options  Ball Aerospace BCP 2000, Bus dry mass = 608 kg  Payload Power (OAV) (EOL) / Mass Limit: 730 W / 380 kg  Spectrum Astro - SA 200HP, Bus dry mass = 354 kg  Payload Power (OAV) (EOL) / Mass Limit: 650 W / 666 kg  Orbital StarBus, Bus dry mass = 566 kg  Payload Power (OAV) (EOL) / Mass Limit: 550 W / 200 kg  Lockheed Martin - LM 900, Bus dry mass = 492 kg  Payload Power (OAV) (EOL) / Mass Limit: 344 W / 470 kg  Orbital - Midstar, Bus dry mass = 580 kg  Payload Power (OAV) (EOL) / Mass Limit: 327 W / 780 kg  For details see “SNAP_ Candidate_RSDO_Busses.xls”  All above busses are designed for multi-year missions w/ redundant components.  Mission Unique spacecraft structure and several significant subsystem upgrades are required.

8. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 8 Other Options Considered  Earth Shield for Detector Radiator  Use in LEO to eliminate thermal coupling between Earth and Radiator  May have to be actuated similar to a solar array drive  Natural frequency must be > 1Hz (preferably >> 1Hz)  Rigid cylinder shape could be considered  PROs:  Would allow passive cooling of Radiator to 130K even at LEO  CONs:  Extra mechanism, increased risk  Complicates I&T  DISPOSITION:  Option dismissed, as LEO option was dropped due to several other problems

9. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 9 Other Options Considered  Slew rate vs. jitter  Select small reaction wheels for low jitter or “Heavy Duty” (higher jitter) reaction wheels for fast slew  DISPOSITION:  Analysis shows that the actual “driver” is solar wind, requiring bigger wheels  30 Nms/.05Nm wheels selected  Use isolation mount

10. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 10 Baseline Configuration & Rationale  3-axis stabilized, 4 Reaction wheels, IRUs, no torquer bar  Sun side w/ rigid body mounted solar arrays & anti-sun side w/ radiators  Standard Hydrazine propulsion system, 1 lbs.thrusters, ~150 kg total propellant required @ 100 m/s for apogee lowering, corrections and ACS.  74 Gbits SSR, storage only for spectroscopy data. (Avg. data rate ~52 Mbps; lossless compression plus overhead).  Continuous Ka band downlink @ 55 Mbps to 3 Northern Latitude ground stations (Berkeley, France, Japan).  3 gimbaled.7m Ka band HGAs; S-band omnis; S-Band T&C thru omni antennas

11. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 11 Preliminary Bus Subsystems Mass [kg] Bus Structure143.0 Payload Mount9.0 Antenna support30.0 ACS50.0 C&DH12.0 Power Electronics15.0 Battery81.2 Solar Arrays10.5 Thermal Hardware67.0 RF Communications53.0 Bus Harness8.0 Separation System, spacecraft side8.0 Bus Subsystems Total486.7

12. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 12 Preliminary SNAP Obesrvatory Mass [kg] Payload Total700 Bus Subsystems Total490 Propulsion Total (estimate)170 SNAP Observatory Total1360

13. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 13 Preliminary Cost Summary [$M]  Cost information  Details in spreadsheet  Subsystem cost estimates included  Other costs are rough estimates SNAP MISSION COST w/ Contingency SCIENCE SPACECRAFT BUS MISSION INTEGRATION OPERATIONS LAUNCH VEHICLE TOTAL (excl. data analysis)$307.8M

14. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 14 Requirements Verification  Standard functional and environmental verification per GEVS  Tight contamination control required  Main challenges are in Instrument verification  Ideally, observatory level thermal vacuum / thermal balance test is combined with and end-to-end image quality verification  May use double-pass test

15. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 15 Additional Trades to Consider  Revisit possibility of using LEO  Lower mission cost  More “realistic” launch / launch vehicle configuration  May eliminate propulsion  Simplifies RF Comm  Must assess disposal issues

16. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 16 Risk Assessment, Technologies  Risk on spacecraft bus is generally low, with well- understood technologies and readily available components.  Designed subsystem for a 3 year mission, solar array sized to 5 years  Higher risk on instrument, especially on the enormous CCD cluster  No significant technology development required for bus

17. SNAP, June 28, 2001 Goddard Space Flight Center System Overview Page 17  Mass, Power, and Cost information  “SNAP_Mass&Cost_Summary.xls”  Useful Web sites  Access to Space at http://accesstospace.gsfc.nasa.gov/ provides launch vehicle performance information and other useful design data.  Rapid Spacecraft Development Office at http://rsdo.gsfc.nasa.gov/ provides spacecraft bus studies and procurement services. Overview, Supporting Data