1. Frank Stocklin Ron Vento Leslie Ambrose June 28,2001 SUPERNOVA/ACCELERATION PROBE (SNAP) Data Systems

2. Page 2 SNAP June 28, 2001 Goddard Space Flight Center Data Systems Topics  Overview  Driving Requirements and Assumptions  Selected Configuration and Rationale  Coverage  Signal Margin Summary  Component Power/Mass/Cost Summary  Risk Assessment  Issues and Concerns  Backup

3. Data Systems Page 3 SNAP June 28, 2001 Goddard Space Flight Center Data Systems Overview  Ka-Band downlink @ 55 Mbps continuously (except during eclipse) through a HGA to a ground network consisting of either:  Berkeley, CA; Lyon, France; Tokyo, Japan  Single gaps of 18 hours will occur each orbital period of 14 days  18 hour gaps are acceptable at once per orbit  S-Band T&C through omni antennas  S-Band ranging using DSN during early maneuvers, infrequently during the mission  Ground terminal sized for maximum range of 69 Re  On-board recorder sized for recording spectrograph data and housekeeping for 24 hours

4. Data Systems Page 4 SNAP June 28, 2001 Goddard Space Flight Center  Launch: Dec 2008  Mission Life: 2 year required, 5 year goal  Nominal Orbit: Prometheus 57Re x 19Re @ 40 deg  Stellar pointing  Instrument Data Collection Rates:  45.2 Mbps  Housekeeping rate = 16 Kbps  CCSDS compatible (@ 15%)  Data storage: 24 hrs/72 Gbits (see C&DH for details) Data Systems Driving Requirements & Assumptions

5. Data Systems Page 5 SNAP June 28, 2001 Goddard Space Flight Center  Data Latency: None  Infrequent commanding  Telemetry BER =10 -6  Rate 1/2 Convolutional/Reed-Solomon encoding  Inclination is primary driver  CCSDS compatible  Redundancy  Link margins : 3 dB  S/C is jitter sensitive Data Systems Driving Requirements & Assumptions

6. Data Systems Page 6 SNAP June 28, 2001 Goddard Space Flight Center Data Systems Selected Configuration & Rationale  Ka-Band  3 gimbaled 0.7m antennas  antenna movements between observation periods (every 100-400 seconds)  Beamwidth of 1 deg is large enough to provide adequate coverage without movement during observation periods (will stay close enough to main beam so as not to degrade the link)  located 120 deg apart  switchable by on-board command  20 watt TWT(2)- heritage is TDRS H  Ka-Band modulators(2)-modification to existing L3 X Band transmitter  Data rate = 55 Mbps continuous (includes science, Hskpg, CCSDS & R/S encoding)  S-Band  Omni antennas  Transponders(2)  Command rate = 2 Kbps  Telemetry rate = 1 Kbps

7. Data Systems Page 7 SNAP June 28, 2001 Goddard Space Flight Center Data Systems Selected Configuration & Rationale  Normal operations:  Continuous Ka-band transmission  Both S-band receivers always on  S-band transmitter on as needed  Ground terminals  Ground terminals are sized for maximum range of 69 Re  Ka-band autotrack will be required  Berkeley 11m (modified for Ka-Band)  All other sites 10m  Ka-band receive  S Band receive/transmit  Radomes highly recommended & included in cost

8. Data Systems Page 8 SNAP June 28, 2001 Goddard Space Flight Center Data Systems Selected Configuration & Rationale  Operational scenario 1(Berkeley,France,Japan)  Inclinations < 40 deg  Continuous transmission  Worst case maximum gap = 18 hours (average outage =12 hours)  per orbital period of 14 days(nominal period)  Operational workaround understood to be acceptable with spectrograph data(approx 816 Kbps) recorded on board & played back during visible periods

9. Data Systems Page 9 SNAP June 28, 2001 Goddard Space Flight Center Data Systems S/C Antenna Considerations  S-Band  Need 2 antennas to enable reliable command & recovery in case of loss of control & launch phase support  Best location is perpendicular to pointing axis(Z)  Ka- Band  Need 3 antennas in order to keep the antennas close to the spacecraft so that the dampening of the movement is quicker  Best location is perpendicular to the pointing axis

10. Data Systems Page 10 SNAP June 28, 2001 Goddard Space Flight Center Data Systems Selected Configuration & Rationale SNAP MOC Berkeley Science & Hskpg Command 2 kbps S-Band Cmd 55 Mbps K-Band science 1 kbps S-Band hskpg SNAP 11M K/S Japan/France 55 Mbps K-Band science 1 kbps S-Band hskpg 2 kbps S-Band Cmd 10M K/S

11. Data Systems Page 11 SNAP June 28, 2001 Goddard Space Flight Center Data Systems Selected Configuration and Rationale C&DH S-Band XPNDR OMNI 1 OMNI 2 CMD/TLM Data Storage: 9 Gbytes HGA Science Instruments HGA S-Band XPNDR Hybrid K-Band Modulator(2) Diplexer HGA K-Band Amplifier(2) Switch OBC

12. Data Systems Page 12 SNAP June 28, 2001 Goddard Space Flight Center SNAP Coverage Gaps (3 stations)

13. Data Systems Page 13 SNAP June 28, 2001 Goddard Space Flight Center SNAP Signal Margins (Max Range = 69 Re)

14. Data Systems Page 14 SNAP June 28, 2001 Goddard Space Flight Center Data Systems Component Power/Mass/Cost Summary

15. Data Systems Page 15 SNAP June 28, 2001 Goddard Space Flight Center Data Systems Risk Assessment  Construction, Maintenance and operation of 10M Ka/S-band stations: Low to Medium Risk  K-band Modulator: Modified design of current X-band transmitter: Low to Medium Risk

16. Data Systems Page 16 SNAP June 28, 2001 Goddard Space Flight Center Data Systems Issues and Concerns  During 5 year period the apogee/perigee/inclination will vary  Apogee up to 69 Re  Perigee down to 7 Re  Inclination down to 0 deg & up to 65 deg Shape of the orbit  If the inclination increases coverage gap times will increase (gaps greater than 18 hours will occur when the inclination increases above 40 deg.)  Location of apogee and perigee (dependent on possible inclinations)

17. Data Systems Page 17 SNAP June 28, 2001 Goddard Space Flight Center Data Systems SNAP Back-Up Charts

18. Data Systems Page 18 SNAP June 28, 2001 Goddard Space Flight Center SNAP Ka-Band 10 M Downlink (55 Mbps)

19. Data Systems Page 19 SNAP June 28, 2001 Goddard Space Flight Center SNAP S-Band 10M Uplink (2 kbps)

20. Data Systems Page 20 SNAP June 28, 2001 Goddard Space Flight Center SNAP S-Band Downlink (2 Kbps)

21. Data Systems Page 21 SNAP June 28, 2001 Goddard Space Flight Center SNAP S-Band Downlink (1 kbps)

22. Data Systems Page 22 SNAP June 28, 2001 Goddard Space Flight Center SNAP S-band Ranging Up-link

23. Data Systems Page 23 SNAP June 28, 2001 Goddard Space Flight Center SNAP S-band Ranging Downlink