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Terry Smith June 28, 2001

SuperNova / Acceleration Probe (SNAP). Command and Data Handling System. Terry Smith June 28, 2001. Command & Data Handling System Overview. 1 Generic C&DH Box with Mission-Unique Upgrades Buffers/Multiplexers/Compressors Integrated in Readout Electronics Real-Time Science Data Downlink

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Terry Smith June 28, 2001

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  1. SuperNova / Acceleration Probe (SNAP) Command and Data Handling System Terry Smith June 28, 2001

  2. Command & Data Handling SystemOverview • 1 Generic C&DH Box with Mission-Unique Upgrades • Buffers/Multiplexers/Compressors Integrated in Readout Electronics • Real-Time Science Data Downlink • Store and Forward Spectrograph Data • Single-String (2 year) or Dual Redundant (5 year) Options SNAP June 28, 2001Goddard Space Flight Center

  3. Command & Data Handling SystemDriving Requirements • Launch: October 2008 • Orbit: 57 RE x 19 RE, 40o incl • Life: 2 Years Minimum 5 years Goal • Science Data Acquisition Rate: 90 Mbps Peak 45 Mbps Average SNAP June 28, 2001Goddard Space Flight Center

  4. Command & Data Handling SystemDerived Requirements • Data Products (Data Reduction): None • Data Compression: Lossless Only • Telecommunication Contact Time: 80% of orbit • Telecommunication LOS Period: 24 hours • Real-Time Science Data Transmission: All Instrument Data • Science Data Record and Playback: Spectrograph Data Only • Spectrograph Data Storage: 74 Gbits • Simultaneous Record and Playback: yes • Downlink Data Rate: 55 Mbps SNAP June 28, 2001Goddard Space Flight Center

  5. Command & Data Handling System Science Data Reduction Analysis Histogram Data Products Memory Array represents CCD pixel grid 1 Accumulator register for each pixel 1 Gpixel = 16 Gbit array (16 bits per register) Rejected due to complications associated with Cosmic Rays: False data spikes on CCD, data filter not feasible Dithering: Spatial error on CCD Lossy Data Compression also rejected SNAP June 28, 2001Goddard Space Flight Center

  6. Command & Data Handling System Science Data Storage Analysis 100 % All Instrument Data Storage Science Data Acquisition Rate 45 Mbps Housekeeping Data Acquisition Rate 16 kbps Memory Error Detection and Correction Overhead (5%) 2 Mbps Total 47 Mbps Data Storage Retention (8 hours during LOS) 1.4 Terabits SNAP June 28, 2001Goddard Space Flight Center

  7. Command & Data Handling System Science Data Storage Analysis 100 % All Instrument Data Storage (continued) 1.4 Terabits SSR 2004 Rad-Hard DRAM Technology Projection: 64 Mbit or 256 Mbit SSR with 64 Mbit DRAM Size: 33 cm x 33 cm x51 cm Mass: 30 kg Power: 103 W Cost: $3.1 M SSR with 256 Mbit DRAM Size: 33 cm x 33 cm x35 cm Mass: 20 kg Power: 70 W Cost: $2.6 M SNAP June 28, 2001Goddard Space Flight Center

  8. Command & Data Handling System Science Data Storage Analysis 100 % All Instrument Data Storage (continued) 100 % All Instrument Data Storage rejected due to: SSR mass, size, power, and cost Relatively complicated operations Alternative: Downlink in real-time all science data while telecom is on-line (80%) Store and forward only the Optical and NIR Spectrograph data SNAP June 28, 2001Goddard Space Flight Center

  9. Command & Data Handling System Science Data Storage Analysis 100 % Spectrograph Only Data Storage Spectrograph Data Acquisition Rate 800 kbps Housekeeping Data Acquisition Rate 16 kbps Memory Error Detection and Correction Overhead (5%) 41 kbps Total 857 kbps Data Storage Retention (24 hours during LOS) 74 Gbits 24 hour retention period derived from orbit and ground station location SNAP June 28, 2001Goddard Space Flight Center

  10. Command & Data Handling System Downlink Data Rate Analysis Data Acquisition Rate: 45.2 Mbps CCSDS Protocol and RS-Coding Overhead (15%): 6.78 Mbps Stored Spectrograph Data Playback: 3 Mbps Total: 55 Mbps 74 Gbit Spectrograph Data Playback Time @ 3 Mbps: 6.6 hours SNAP June 28, 2001Goddard Space Flight Center

  11. Instruments Instruments Instruments Instruments Command & Data Handling System Selected Configuration and Rationale Flight Data System Command Uplink 2 kbps S-Band Communication System C&DH Unit Telemetry Downlink 1 kbps Instrument Electronics X-Band Communication System Wideband Downlink 55 Mbps Science Data 45 Mbps Spacecraft Data Bus and Hard-Lines Spacecraft Systems SNAP June 28, 2001Goddard Space Flight Center

  12. RS-422 Driver RS-422 Driver RS-422 Driver RS-422 Driver Command & Data Handling System Selected Configuration and Rationale Instrument Electronics Average (double for peak) Bursts 8 Mbps Readout Electronics NIR Spectrograph Data Rate Buffer Multiplex and Compress 400 kbps 1 1 Telescope Data Rate Buffer Multiplex and Compress Optical Spectrograph 8 Mbps 400 kbps Readout Electronics 1 1 200 Mbps 8 Mbps Data Rate Buffer Multiplex and Compress Readout Electronics NIR Imager 24 1 1 Gbps 40 Mbps Data Rate Buffer Readout Electronics Multiplex and Compress Fibre Channel Driver GIGACAM 128 1 8 Mbps 400 kbps Readout Electronics Data Rate Buffer Multiplex and Compress Star Guider 1 1 Control SNAP June 28, 2001Goddard Space Flight Center

  13. Command & Data Handling System Selected Configuration and Rationale C&DH Unit Command and Telemetry Lines Instrument Science Data KA-Band Com Interface S-Band Com Interface Spacecraft Data Bus I Q S S C&DH Discrete Inputs and Outputs Low Voltage Power Converter S-Band Uplink Downlink Memory 74 Gbits C&DH & ACS Processor Wide-Band Data Router Backplane Data Bus SNAP June 28, 2001Goddard Space Flight Center

  14. Command & Data Handling System RSDO Spacecraft Bus Accommodation • 1 RSDO spacecraft bus appears to meet the C&DH Requirements: SNAP June 28, 2001Goddard Space Flight Center

  15. Command & Data Handling System Specifications and Cost Summary • ItemMass kgPowerCost • Single-String C&DH Unit* 12 kg 25 W • Dual-Redundant C&DH Unit** 24 kg 30 W * 2 year life ** 5 year life SNAP June 28, 2001Goddard Space Flight Center

  16. Command & Data Handling System Issues and Concerns • No Data Retransmission Capability for Real-Time KA-Band Dropouts SNAP June 28, 2001Goddard Space Flight Center

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