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Envisat Spacecraft in orbit performance Francois Spoto Envisat Satellite system manager (EOP-PPS)

Envisat Spacecraft in orbit performance Francois Spoto Envisat Satellite system manager (EOP-PPS). Acknowledgements.

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Envisat Spacecraft in orbit performance Francois Spoto Envisat Satellite system manager (EOP-PPS)

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  1. Envisat Spacecraft in orbit performanceFrancois SpotoEnvisat Satellite system manager (EOP-PPS)

  2. Acknowledgements • This presentation capitalizes on detailed performance information gathered by Astrium (UK, Germany, France), ESTEC (Envisat Project) and ESOC (Flight Control Team, Flight Dynamics System) teams. • Special thanks to John Simpson,Bill Johnson,E.Schutte and M. Horblin from Astrium for their major contributions. • The relevant reports are identified within the presentation for reference.

  3. Table of content • Spacecraft power and energy management • Spacecraft thermal performance • Spacecraft Attitude and Orbit Control • Spacecraft pointing performance • Spacecraft data handling and software • Spacecraft telecommunications • Time correlation and datation performance • Orbit prediction and restitution performance • Conclusion

  4. Spacecraft power and energy management Operational scenario: ASAR high rate mode 10’ in eclipse & 20’ in sunlight, wave else where 2 XBS channels on over Kiruna, 2 SSRs with 100% duty cycle, SM in SYSM with permanent thrusters cat-bed heating

  5. Spacecraft power and energy management (BOL) Power at SADM Available: 7318 W Required: 5260 W Shunt Power (lost) (Sun) ; 880 W Losses : 244.1 W Sun 35.60 V Ecl 30.01 V Margins Sun only ; 1932W Averaged :Sun+ Ecl ; 1209W Power at Junction Point Power available (sun): 6948 W Power required (sun) : 5016 W Power required (ecl) : 2617 W Battery 15.72% dod Recharge Power : 1519 W Discharge Power : 2545 W Sun 35.08 V Ecl 29.4 V Service Module (inc losses) Sun ; 729.7 W Ecl ; 633.7 W PEB (inc losses) Sun ; 221.4 W Ecl ; 297.5 W Instruments (inc losses) ASAR Sun ; 752 W ASAR Ecl ; 752 W Global Mission (Sun) ; 915 W Global Mission (Ecl) ; 862 W

  6. Power at SADM Available: 6901 W Required: 5260 W Spacecraft power and energy management (EOL) Shunt Power (lost) (Sun) ; 880 W Losses : 244.1 W Margins Sun only ; 1515W Averaged :Sun+ Ecl ; 948W Sun 34.90 V Ecl 28.61 V Power at Junction Point Power Available (sun): 6531 W Power required (sun) : 5016 W Power required (ecl) : 2617 W Battery 15.72% dod Recharge Power : 1519 W Discharge Power : 2545 W Sun 34.38 V Ecl 28.0 V Service Module (inc losses) Sun ; 729.7 W Ecl ; 633.7 W PEB (inc losses) Sun ; 221.4 W Ecl ; 297.5 W Instruments (inc losses) ASAR Sun ; 752 W ASAR Ecl ; 752 W Global Mission (Sun) ; 915 W Global Mission (Ecl) ; 862 W

  7. Spacecraft power and energy management Solar Array performance Power Available at SADM (BOL) Predicted = 7175W (refer to TN.25000.0080.MA) Estimated (from Junction Point Measurements) = 7318 W Delta = +143 W Power Available at Junction Point (BOL) Measured=7200W Power Available at SADM (EOL) Predicted = 6767 W (TN.25000.0080.MA) Estimated (from Junction Point Measurements) = 6879 W Delta = +112 W Power Available at Junction Point (EOL) Projected = 6946W

  8. Spacecraft power and energy management • Conclusions: • SA generates 7318W (143W in addition to predictions) • Predicted 1515W of power margin EOL to support a full mission operational scenario • Average battery DOD = 11.2% with 8 healthy batteries • Average battery temperature is cycling around – 3 deg C (heaters activate every 8 orbits with a threshold of –5 deg C)) • Average K factor for energy recharge = 1.1 in average • Additional information can be found in PPF-MMB-TN-0768, issue 1, May 2002

  9. Spacecraft thermal performance • SM and PLM TB tests and correlated thermal models have been used to predict in orbit temperatures at unit level, heater power demand, and heater duty cycle. • The sole mission critical anomaly experienced in orbit was the failure of the Thruster 9 heater mat (mounted at FCV level, implementing both HW and SW controlled heaters and thermostat): the cat-bed heaters of the A Thrusters are now switched on permanently to warrant hydrazine temperature > 2 deg C. • The heaters duty cycle is less than predicted: in a few cases, the upper temperature switching limit was raised by 5 deg C. • The Satellite thermal control system functions nominally with a large margin wrt to temperature limit of the units. • More detailed information can be found within PPF-MMB-TN-0766, issue 1, May 2002.

  10. Spacecraft thermal performance • SM Temperature uncertainties (measured in orbit versus predicted)

  11. Spacecraft thermal performance • PLM Temperature uncertainties (measured in orbit versus predicted) with the payload in operations

  12. Spacecraft Attitude and Orbit Control • The AOCS operates fully nominally (all sensors and actuators show nominal performance, without anomalies) • Critical B units have also been tested OK: gyros 3 and 4, STD B • All spacecraft AOCS modes have been tested satisfactorily, excluding safe mode (eg Orbit Control Mode in plane or out of plane, Fine Control Mode, Stellar Fine Control Mode), and the Satellite is operated in SYSM for nominal operations. • SFCM in plane manoeuvres are performed every 20/35 days (ground track dead-band maintenance within +/- 1 km), and inclination corrections through OCMs about every 4/6 months. • SOE-ENV.RP.0560.ASTR (AOCS performances during Leop and commissioning phase) and PPF-TN-24300-2934-ASTR (UMS performance during in flight acceptance) can be consulted for detailed information.

  13. Spacecraft pointing performance • The platform pointing performance reported by FDS at ESOC is better than +/- 0.015 deg/axis (0.010 deg on pitch, around x axis) with no measurable bias. • The overall hydrazine consumption is currently 29 Kg (including the phasing with ERS2), with a remainder of 285 Kg prior to achieve the end of mission (estimated lifetime of 8 years with 2 safe mode, and 9 years without) • Independent pointing characterization using payload instruments has been performed: good and coherent pointing performance (see next table from document PO-RP-ESA-GS-1342 )

  14. INSTRUMENT IN-ORBIT MISPOINTING (deg.) PRE-LAUNCH BUDGET (deg) PRE-LAUNCH SPECIFICATION (deg) MERIS Roll = 0.0251 Pitch = -0.0022 Yaw = 0.0247 Roll = 0.0295 (Equivalent to a Total Pitch = 0.041 Radial error of 1205m) Yaw = 0.0333 Total Radial < 2000m ASAR Elevation = Not Estim. Azimuth = -0.0174 Normal = 0.0015 Elevation = 0.0298 Azimuth = 0.0612 Normal = 0.0658 Elevation = 0.1048 Azimuth = 0.1424 Normal = 0.6127 MIPAS Elevation Rear = 0.025 Elevation Side = TBD Elevation Rear = 0.0926 Elevation Side = 0.0881 El. Rear = 0.052 El Side = 0.052 GOMOS Roll = 0.008 Pitch = 0.016 Yaw = -0.0490 The above generates a Cone Error = 0.052 Roll = 0.0713 Pitch = 0.0769 Cone Error = 0.1048 Cone Error = 0.2740 Spacecraft pointing performance

  15. Spacecraft data handling and software • The SM OBDH and CFS software operate perfectly (a few CFS patches have been up-linked to update surveillance thresholds, timings, or because of the FCV 9 thermal anomaly) • The PLM OBDH operates perfectly. • The PMC software was subject to three anomalies leading to payload safe mode. These anomalies have been understood and corrections have been up-linked by patch. The PMC operates nominally since mid June 2002. Note that an updated and fully validated software version (V38p1) is being up-linked week 37. A version V38p2 is being prepared to address a ‘live” data recording mode for troubleshooting. • Instruments software (ICU and secondary processors) operate nominally. In a few cases (MERIS, DORIS) the ICU entered refuse mode due to SEU and lack of adequate memory scrubbing. These software have been updated by patch and prove now to operate nominally.

  16. Spacecraft data handling and software • Many SEU hits between 11-03-02 and 18-06-02 concentrated on the South Atlantic Anomaly • Clear time correlation when comparing occurrence dates with the SOHO CELIAS Proton Monitor data • SW scrubbing functions have been tuned or patched where ever required to complement EDAC

  17. Spacecraft telecommunications • S band telecommunications: • DMT1 is used operationally (DMT 1 and DMT2 receivers in hot redundancy, transmitter of DMT 2 in cold redundancy) • The S band link budget with Kiruna at AOS 5 deg is as follows (refer to ENVI-ESOC-OPS-TN-1008-TOS-OF, Envisat in flight link budget analysis for detailed information): : • TC uplink, BER of 10-6, 52.4 dB • TM downlink, BER of 10-6, 20.5 dB

  18. Spacecraft telecommunications • X band telecommunications: • The 3 communication channels have been used and proved to operate nominally. The mission is currently conducted using channels 1 and 2. • The X band link budget with Kiruna at AOS 5 deg is as follows (refer to ENVI-ESOC-OPS-TN-1008-TOS-OF, Envisat in flight link budget analysis for detailed information): • TM downlink, BER of 10-6, 5.3 dB Note: the XBS data quality of the first orbit of the day (low elevation) is Often degraded by the GS “auto-track mode” using S band, causing numerous ISPs CRC errors. Use of “programmed track” on that orbit avoids the problem.

  19. Spacecraft telecommunications • Ka band telecommunications: • The Ka band antenna pointing function has been validated (azimuth and elevation) and shows good functional performance. • An end to end data relay characterization will be performed with Artemis in geostationary position (current plan: Mid February 2003 – Artemis altitude elevation is nominal at 15 km/day) • Decision to use scientific data relay through Artemis operationally in complement to X band will be made based on the outcome of this characterization.

  20. Time correlation and datation performance • Time Correlation Product algorithms: • Time Correlation Products (SBT ref, UTC ref & Step Size) are computed for every Kiruna pass using time stamp of each TM frame. • TM frame time stamps can have random 3 different jitters of: 0, ±7.5 µs, or ±16 µs due to Kiruna demodulator. • Baseline TCP algorithm: Leads to errors on the computed UTC ref values of up to ±2.5 µs and errors on the SBT Step Size of ±20 ps (a least square fit function rounds the errors). • Current temporary TCP fix: The CCU USO frequency is very stable so a fixed SBT Step Size is currently used, occasionally updated manually. Since launch this has evolved from 3906249776ps to 3906249783ps (a change of 7ps). • New TCP algorithm: Currently under final testing. This removes the demodulator jitter, giving UTC ref and SBT Step Size accuracies much better than the Time Correlation Product resolution of 1µs and 1ps respectively (UTC ref accuracy is ± 0.6 µs, and SBT step size accuracy is ± 1 ps).

  21. Time correlation and datation performance • Accuracy for the datation of Satellite events with new TCP algorithm: • ICU OBTs are 258.8 µs behind SBT due to OBDH delays (i.e. when OBT=SBT ref in the ICU, UTC=UTC ref + 258.8µs). When using the TCP this bias must be applied with the instrument time biases (already known to the CAL-VAL groups). • Satellite datation and time correlation performance proven by comparison between the Envisat calculated UTC of BCP2 with the DORIS TAI of the BCP2: identical to within ±10µs (the DORIS time accuracy). • With the new TCP algorithm, the following performance is achieved; • UTC ref bias uncertainty (including orbit prediction error) < ±10µs • UTC ref error (including TCP resolution) < 0.6µs • SBT Step Size error (incl TCP resolution and CCU USO drift) < 1ps. • ICU OBT to SBT synch accuracy (FM tests + DORIS data) < ±10µs. Over one orbit, the uncertainty on the UTC of a Satellite event is < ±22.1 µs. over one orbit and < ±42.6 µs over one day

  22. Orbit prediction and restitution performance • The prediction and determination of the Envisat orbit is performed routinely by FDS at ESOC to support Satellite acquisitions by GS, mission planning, and fast delivery data processing. • It uses S band tracking (range and range rate generated by the Kiruna MPTS) • Orbit predictions are available 1 day in advance with the following performance: • Along track < +/- 25 m (+/- 900m spec) • Across track < +/- 1 m (+/- 15m spec) • Radial < +/- 0.5 m (+/- 25 m spec)

  23. Orbit prediction and restitution performance • Orbit restitutions are available after 1 day (3 previous days of orbit data are processed) with the following performance: • Along track < +/- 2 m (+/- 60m spec) • Across track < +/- 1 m (+/- 15m spec) • Radial < +/- 0.5 m (+/- 15m spec) • The DORIS Navigator performance (real time) provides the following accuracy: • Along track < +/- 0.40 m • Across track < +/- 0.44 m • Radial < 0.30 m

  24. Orbit prediction and restitution performance • The DORIS MOE (off line after 1 day) provides the following accuracy: • Radial < 0.05 m (confirmed by laser ranging using LRR) • The DORIS POE (off line after a few days) provides the following accuracy: • Radial < 0.04 cm • Note the Satellite velocity residual based on the Doppler measurement by Doris is 0.5 mm/sec

  25. Conclusions • A fully operational Satellite running on its nominal redundancies (platform and payload module). • Comfortable performance margins related to power,thermal, pointing. • Ka band terminal final characterization awaiting for Artemis readiness. • Proper documentation of the Satellite performance available as a reference. • An Envisat spacecraft lessons learnt workshop will be organized with D-TOS in October/November 2002

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