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X-Ray Calorimeter Mission. Communications Ron Vento Blake Lorenz 2 – 6 April 2012. Topics. Overview Functional Configuration Driving Requirements and Assumptions L-2 Orbit, Mission Timeline, and S/C Attitude Data R ates and Storage Selected Configuration and Rationale
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X-Ray Calorimeter Mission Communications Ron Vento Blake Lorenz 2 – 6 April 2012
Topics • Overview • Functional Configuration • Driving Requirements and Assumptions • L-2 Orbit, Mission Timeline, and S/C Attitude • Data Rates and Storage • Selected Configuration and Rationale • Functional Configurations • Signal Margin Summary • Cost/Mass/Power Summary • Backup
Overview • Ka-Band for science and data dumps via DSN 34 meter • Data dumps at 20 Mbps • One 7.7 minute contact per day require to dump data. • Twice a month a 33 minute contact required for addition of peak data • S-Band TT&C via HGA to DSN 34 meter • 2 kbps command • 8 kbps telemetry • S-Band TT&C via omni to DSN 34 meter • 1 kbps command • 2 kbps telemetry • Ranging for orbit determination • 60 minutes per day required for transfer phase; 30 minutes per day on orbit • S-Band thru TDRSS for launch and LEO critical events • 1 kbps command • 1 kbps telemetry
Functional Configuration decrypter S S/Ka-band Transponder Hybrid Diplexer S S-Band omnis PA switch K S decrypter S C&DH PA S Diplexer switch S/Ka-band Transponder Hybrid S switch ISOLATOR Ka-band TWTA SWITCH S / Ka HGA Triplexer K Ka-band TWTA
Driving Requirements & Assumptions • Launch: 25 March 2022 • Nominal Orbit: Earth-Sun L2 orbit (Lagrange point ) • ~800,000 km to 1.2 Mm Halo and/or Lissajous orbit • Attitude: Stellar pointing • Orbit determination via DSN ranging • Ranging required • One 60 minute period/day during transfer orbit • One 30 minute period/day when on orbit • Timing requirement of 100 μs at L2 • Latency: 72 hours for nominal data • Telemetry BER: 10-6 • Nominal Instrument data rate: 76.1 kbps • Peak science collection rates up to 6 hours at 1.804 Mbps forbright object observations at random intervals (assume twice a month) • RF communications - observations continue during downlink
Driving Requirements & Assumptions Flight Mirror Assembly (FMA) • Launch on Falcon 9 • 3 years Mission life • 5 year goal • Launch Date – 25 Mar 2022 • Class B Mission • Science Payload • 1.3 m diameter X-ray Flight Mirror Assembly (FMA) • 9.5 m focal length • X-Ray Micro-calorimeter Spectrometer instrument (XMS) XMS Instrument
L-2 Orbit L2 Earth-Sun angle: 7 to 34º Lunar Orbit L2 Transfer Trajectory E To Sun Courtesy - JWST 800,000 km amplitude L2 Orbit w/180 Day Orbit Earth L2 Distance:1.5x106 Max Range: 1.8x106 • L2 800,000 km semi-major axis halo orbit • 0% solar or lunar obscuration throughout 10 years • Essentially the same orbit as JWST
Instrument Data Requirements • Storage Size Requirement 48 hours including 12 hours of peak rate and 36 hours of average rate (this is called 48-hour-peak-volume) + up to 1 day of missed passes (ie., an additional 24 hrs of average data rate) ____________________________________________________________________________ = A TOTAL of 12 hours peak plus 60 hours of avg data (94.3 Gbits) (122.7 Gbits w contingency) (Assumed 100% efficiency for this 72 hour storage sizing) • Downlink / Latency Requirement • Data collected at average rate must meet 72 hour latency requirement • Size to downlink 48-hour-peak-volume over period of 2 weeks above the avg. rate required for data latency of 72 hours • Allows for 2 bright source observations (peak) per month • 5 year Mission Data Composition Requirement • 98.3% of the time data collected at low data rate • 1.7% of the time data collected at peak data rate
Data Rate and Storage Analysis • Data Storage: 130 Gbits for 60 hours nominal data plus 12 hours of peak data
Selected Configuration & RationaleKa-Band • Ka-band used for data dumps • Two DSN S/Ka-Band transponders • Two 10 watt Ka-Band TWTAs • Data will be LDPC rate ½ encoded • (If rate 7/8 encoding is used a 15 Watt TWTA will be needed ) • QPSK modulation will be used for Ka-band (Residual carrier for S-band when ranging) • Gimbaled 0.5 M dual frequency high-gain antenna • On the Earth pointed axis • Transmit data rate of 20Mbps to DSN 34 meter • Multiple rates can be included if lower or higher rates needed • A 30 minute contact is required every day for ranging. • 95% rain availability is assumed • Redundancy except for the antenna systems • 8 minutes required to transmit data simultaneous with the 30 min ranging contact • The peak data can be accommodated during a ranging contact with an additional ~3 minutes
Selected Configuration & RationaleS-Band • S/Ka-band communications using DSN 34 m • S-Band for TT&C • 5 watts RF using 5 watt power amplifiers via omnis or the HGA • Use omnis • 2 kbps telemetry • 1 kbps command • Use HGA • 8 kbps telemetry (rates up to 250 kbps are achievable) • 2 kbps command • Use TDRSS for launch and LEO critical events • 1 kbps command • 1 kbps telemetry • Ranging: One hour contact per day during transfer orbit and one 30 minute contact per day when on orbit, alternating between north and south locations
Functional Configuration 1 kbps tlm1 kbps Command (launch & LEO) TDRS Ka-band: 20 Mbps telemetry S-band: 8 kbps Tlm 2 kbps command,& Ranging Timing requirement 34M MOCC White Sands complex DSN Command Command Housekeeping Science & Hskpg
Link Margin Summary TDRSS guarantees support with a margin of >0 dB S-Band return links use residual carrier (worse case) for ranging.
DSN Support • Launch and early orbit • Continuous tracking for the first 48 hours • DSN 34M/Transfer orbit • Two 30 minute contacts/day • 24 hour support before and after each mid course corrections (Two corrections planned) • 100 days to orbit • Orbit insertion • DSN 34M/ Mission orbit • One 30 minute contact /day • The peak data can be accommodated during a ranging contact with an additional 3 minutes • Pre-pass time: 45 minutes • Post-pass time: 15 minutes
Total Costs • Total mission costs for 5 years: $15.1 M (Excludes timing system and FTEs • Launch and early orbit: $155 k • TDRSS costs: $55 k • 2 hours SSA support: $15 k • Documentation: $40 k • DSN 48 hours support: $100 k • DSN 34M/Transfer orbit: $588 k • 0ne hour contact/day: $331.5 k • 96 days to orbit • Two mid course corrections: $171 k • Orbit insertion: $85.6 k • DSN 34M/ Mission orbit: $4.55 M/5 years • One 30 minute contact /day: ($910 K/year) • Spacecraft cost: $9.76 M
. Back-up Slides Ka-band (HGA) to 34 meter (at 20 Mbps) S-band (HGA) to 34 meter S-band 34 meter to HGA S-band omni to 34 meter S-band 34 meter to omni TDRSS return link (SSAR) TDRSS forward link (SSAF)
