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Frank Stocklin Ron Vento Leslie Ambrose June 28,2001

Frank Stocklin Ron Vento Leslie Ambrose June 28,2001. SUPERNOVA/ACCELERATION PROBE (SNAP). Data Systems. Data Systems Topics. Overview Driving Requirements and Assumptions Selected Configuration and Rationale Coverage Signal Margin Summary Component Power/Mass/Cost Summary

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Frank Stocklin Ron Vento Leslie Ambrose June 28,2001

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

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

  3. Data SystemsOverview • 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 SNAP June 28, 2001 Goddard Space Flight Center

  4. Data SystemsDriving Requirements & Assumptions • 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) SNAP June 28, 2001 Goddard Space Flight Center

  5. Data SystemsDriving Requirements & Assumptions • 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 SNAP June 28, 2001 Goddard Space Flight Center

  6. Data SystemsSelected 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 SNAP June 28, 2001 Goddard Space Flight Center

  7. Data SystemsSelected 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 SNAP June 28, 2001 Goddard Space Flight Center

  8. Data SystemsSelected 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 SNAP June 28, 2001 Goddard Space Flight Center

  9. Data SystemsS/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 SNAP June 28, 2001 Goddard Space Flight Center

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

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

  12. SNAPCoverage Gaps (3 stations) SNAP June 28, 2001 Goddard Space Flight Center

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

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

  15. Data SystemsRisk 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 SNAP June 28, 2001 Goddard Space Flight Center

  16. Data SystemsIssues 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) SNAP June 28, 2001 Goddard Space Flight Center

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

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

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

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

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

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

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

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