terry smith june 28, 2001

Terry Smith

June 28, 2001

Command and Data Handling System

SuperNova / Acceleration Probe(SNAP)

Command & Data Handling System

SNAP June 28, 2001Goddard 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


Overview




Driving Requirements

Launch: October 2008

Orbit: 57 RE x 19 RE, 40o incl

Life: 2 Years Minimum5 years Goal

Science Data Acquisition Rate: 90 Mbps Peak45 Mbps Average




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



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



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




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




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




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



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



Instruments

Command & Data Handling System Selected Configuration

and RationaleFlight Data

System

Spacecraft Data Bus and Hard-Lines

Science Data45 Mbps

X-Band Communication

System

Instruments

C&DH

Unit

Spacecraft Systems

InstrumentsInstrument

s

Instrument

Electronics

S-Band Communication

System

Command Uplink 2 kbps

Telemetry Downlink

1 kbps

Wideband Downlink55 Mbps




and Rationale

8 Mbps

Telescope

NIR Spectrogra

ph

Optical Spectrogra

ph

NIR Imager

GIGACAM

Star Guider

Readout Electroni

cs

Readout Electroni

cs

Readout Electroni

cs

Readout Electroni

cs

Readout Electroni

cs

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

Data Rate

Buffer

Data Rate

Buffer

Data Rate

Buffer

400 kbps

400 kbps

8 Mbps

40 Mbps

400 kbps

1

1

1

1

1

Multiplex and

Compress

Multiplex and

Compress

Multiplex and

Compress

Multiplex and

Compress

RS-422 Driver

RS-422 Driver

Fibre Channel Driver

RS-422 Driver

Control

BurstsAverage

(double for peak)




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 I Q

KA-Band Com Interface



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 Mbps 74 Gbits 55 Mbps

X Bus 576 Mbps 200 Gbits 320 Mbps



Command & Data Handling System Specifications and Cost Summary

Item Mass kg Power Cost

Single-String C&DH Unit* 12 kg 25 W

Dual-Redundant C&DH Unit**24 kg 30 W

* 2 year life

** 5 year life



Command & Data Handling System Issues and Concerns

No Data Retransmission Capability for Real-Time KA-Band Dropouts

terry smith june 28, 2001

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