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

2. Command & Data Handling System Page 2 SNAP June 28, 2001 Goddard Space Flight Center  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 Command & Data Handling System Overview

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

4. Command & Data Handling System Page 4 SNAP June 28, 2001 Goddard Space Flight Center Command & Data Handling System Derived 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

5. Command & Data Handling System Page 5 SNAP June 28, 2001 Goddard Space Flight Center 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

6. Command & Data Handling System Page 6 SNAP June 28, 2001 Goddard Space Flight Center Command & Data Handling System Science Data Storage Analysis 100 % All Instrument Data Storage Science Data Acquisition Rate45 Mbps Housekeeping Data Acquisition Rate16 kbps Memory Error Detection and Correction Overhead (5%)2 Mbps Total47 Mbps Data Storage Retention (8 hours during LOS)1.4 Terabits

7. Command & Data Handling System Page 7 SNAP June 28, 2001 Goddard Space Flight Center 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

8. Command & Data Handling System Page 8 SNAP June 28, 2001 Goddard Space Flight Center 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

9. Command & Data Handling System Page 9 SNAP June 28, 2001 Goddard Space Flight Center Command & Data Handling System Science Data Storage Analysis 100 % Spectrograph Only Data Storage Spectrograph Data Acquisition Rate800 kbps Housekeeping Data Acquisition Rate16 kbps Memory Error Detection and Correction Overhead (5%)41 kbps Total857 kbps Data Storage Retention (24 hours during LOS)74 Gbits 24 hour retention period derived from orbit and ground station location

10. Command & Data Handling System Page 10 SNAP June 28, 2001 Goddard Space Flight Center 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

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

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

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

14. Command & Data Handling System Page 14 SNAP June 28, 2001 Goddard Space Flight Center Command & Data Handling System RSDO Spacecraft Bus Accommodation  1 RSDO spacecraft bus appears to meet the C&DH Requirements: Science Data Acquisition Rate Bulk Memory Size Wide-Band Output Data Rate C&DH Requirements 45 Mbps74 Gbits55 Mbps X Bus576 Mbps200 Gbits320 Mbps

15. Command & Data Handling System Page 15 SNAP June 28, 2001 Goddard Space Flight Center Command & Data Handling System Specifications and Cost Summary  ItemMass kgPowerCost  Single-String C&DH Unit*12 kg25 W  Dual-Redundant C&DH Unit**24 kg30 W * 2 year life ** 5 year life

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