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CloudSat System Engineering Report [ Mission Performance]

CloudSat System Engineering Report [ Mission Performance]. Presented to CloudSat Science Team Ron Boain Project System Engineer 18 October 2006. Agenda.  Summary of mission activities since launch  Review of mission requirements related to science data collection

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CloudSat System Engineering Report [ Mission Performance]

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  1. CloudSat System Engineering Report[Mission Performance] Presented to CloudSat Science Team Ron Boain Project System Engineer 18 October 2006

  2. Agenda  Summary of mission activities since launch  Review of mission requirements related to science data collection  Review of mission performance against requirements CloudSat Science Team Meeting

  3. The A-Train  The Afternoon Constellation is comprised of Aqua leading, followed by CloudSat, CALIPSO, Parasol, and Aura.  All fly a sun- synchronous orbit at 705 km and 13:30 hours MLT and repeat their groundtracks in 233 revs or equivalently 16-days. CALIPSO CloudSat Science Team Meeting

  4. Mean Local Time Sun-Synchronous Orbit Earth's orbital velocity Earth's Orbit Earth Orbit ascending node () MLT ~ 22.5 13:30 hrs MLT = Mean Local Time of Ascending Node Sun CloudSat Science Team Meeting

  5. Ascent Maneuver Sequence (Not to Scale) Final Trim Operational Orbit Aqua CALIPSO Orbit Raise 2 CloudSat Orbit Raise 2 705 km CALIPSO Orbit Raise 1 CloudSat Orbit Raise 1 Checkout/Calibration Burns Separation Orbit CloudSat Calipso 690 km CloudSat Science Team Meeting

  6. Fuel Expenditure Accounting • Original fuel load at launch: 75.75 kg ~ V  200 m/s • Fuel used thus far for 20 maneuvers: 8.06 kg • 10.6% usage by mass • 20.93 m/s equivalent V • Fuel remaining: 67.8 kg ~ V  180 m/s • Remaining V commitments: • FF maneuvers 5.6 m/s • More Inclination maneuvers 10.0 • Co-maneuvers with AQ/CP 9.0 • EOM deorbit35+ • Total 59.6 m/s • Plenty of fuel for extended mission, etc. CloudSat Science Team Meeting

  7. Afternoon Constellation Control Boxes • Aqua, CALIPSO, and Parasol have independent control boxes • CloudSat’s control box is slaved to CALIPSO when formation flying • Satellite positions in the A-Train and Control Box dimensions specified in the ACOCP document CALIPSO positioned 73 s behind Aqua (CALIPSO is controlled to +/-10-km at the Equator crossing measured along the equator = +/- 21.5 sec) CloudSat Science Team Meeting

  8. CloudSat, Aqua, and CALIPSO in Formation Aqua Control Box Calipso Control Box CloudSat C.B. Circulation Orbit 30 sec (225 km) Circulation Orbit Circulation Orbit orbit ≈ 15 sec (112 km) 43 sec 43 sec (322 km) 116 sec (870 km) Aqua, CloudSat, and CALIPSO in their formation configuration. Aqua leads. CALIPSO follows but maintains its motion independent of Aqua within its control box. CloudSat is tied to CALIPSO's movement around its box. CloudSat follows a small circulation orbit, 2.2 seconds (16.5 km) along-track, positioned 12.5 seconds in front of CALIPSO. CloudSat Science Team Meeting

  9. MODIS Scanning Geometry Aqua S/C Scan Mirror 10 Detectors per scan MODIS Instrument 10º 10º Ground- track “Line of the MODIS Measurement Swath” 10 km 20 km Width = 2330 km cross-track along-track CloudSat Science Team Meeting

  10. Congruency of Aqua/CloudSat Measurements • Owing to CALIPSO's sun-glint avoidance requirement, CloudSat's orbit plane is shifted east of Aqua's plane an additional 1.93, or 215 km, at the ascending node When orbit control errors are taken into account, the maximum displace- ment of CloudSat's optical path relative to Aqua's is 18.8 at the equator For latitudes north and south of the equator, the displace- ment decreases to zero and then increases to its max at the next equator crossing CloudSat Aqua 55° 18.8 705 km Aqua GT CS Nadir MODIS Nadir Position MODIS Swath Width 1165 km (1/2 Swath) 240 km CloudSat Science Team Meeting

  11. Science Requirements Related to Formation Flying with Aqua • Congruency • Originally, a desire (not a requirement) to lay radar footprints on top of MODIS footprints looking along the same optical path through the atmosphere • However, sun-glint avoidance requirement (CALIPSO's) compromises accommodation of this desire near the equators (see later chart) • Requirement set as compromise: max cross-track separation ≤ 240 km between CloudSat's radar footprint and Aqua's groundtrack • Simultaneity • CloudSat and Aqua measurements are 120 seconds of each other • On average per the definition of formation flying control boxes the interval between a MODIS measurement and a corresponding CloudSat measurement of the same cloud field is approximately 60 seconds • Geometrically possible for some measurements to be as close as 15 seconds apart (see later charts), and as far apart as 101 seconds CloudSat Science Team Meeting

  12. Requirement on simultaneity of radar and lidar measurements: Measurements of the same cloud fields taken 15 seconds Requirement/goal on spatial overlap of radar and lidar measurements: Footprints must pass 2000 meters edge to edge Equivalent to controlling CloudSat's groundtrack to being within ±1 km of CALIPSO's lidar track Goal for footprints to overlap at least 50% of the time Science Requirements Relatedto Formation Flying with CALIPSO Position of footprints relative to groundtrack Lidar footprint (Dia= 70m) 15 seconds (113 km) 2000 m Time delayed Lidar footprint Radar footprint (Dia= 1400m) Goal condition met CloudSat Groundtrack CloudSat Science Team Meeting

  13. Measured Data for Requirements Verification • Propulsive maneuvers are used, as needed, to keep CloudSat within its control box and compliant with formation requirements • Last Formation-Flying Maintenance maneuver: 09/21/06 • Next maneuver predicted for ≈10/25/06 • Longest recent period, uninterrupted by an along-track impulse, was between 09/22/06 and 10/10/06 • An inclination adjust maneuver by CALIPSO on 10/10/06 imparted a small in-track impulse altering along-track motion, slightly but noticeably • Data has a discontinuous derivative at these points • Therefore for this discussion, trajectory data collected over the interval 09/27/06 to 10/10/06 is shown here as means to demonstrating Formation-Flying requirements compliance over interval with no maneuvers CloudSat Science Team Meeting

  14. Measured AQ/CS Cross-track Separation ● Requirement for cross-track separation between Aqua and CloudSat ≤ 240 km CloudSat Science Team Meeting

  15. Measured AQ/CS Along-Track Separation ● Requirement for along-track separation between CloudSat and Aqua ≤ 120 seconds CloudSat Science Team Meeting

  16. Measured CS/CP Along-Track Separation ● Requirement for Along-Track Separation between CloudSat and CALIPSO: 10 sec ≤ x ≤ 15 sec ● Along-track separation between CALIPSO and CloudSat; measured data in blue ● Formation-Flying Maintenance maneuver will be scheduled before 10 sec boundary violation occurs ●Red line is a quadratic fit to data CloudSat Science Team Meeting

  17. Measured CS/CP Cross-Track Separation ● Requirement for Cross-Track Separation between CloudSat and CALIPSO: -1 km ≤ x ≤ +1 km ● Cross-Track separation between CloudSat and CALIPSO; zero is CALIPSO's groundtrack ● Measured data shown in blue ● Quadratic fit (in red) to data enables estimation of next FF Maintenance maneuver before requirement is violated CloudSat Science Team Meeting

  18. Measured Difference Between CS/CPMean Local Times ● Requirement for difference in MLT between CloudSat and CALIPSO = 12.5 ± 0.5 sec CloudSat Science Team Meeting

  19. Total Mission History of Requirements Compliance CloudSat Science Team Meeting

  20. Spacecraft Pointing Error • A spacecraft pointing error was discovered through data analysis after formation establishment • 1.7 deg forward, in-track and 4.4 deg right of forward • Cause was an incorrect quaternion loaded in spacecraft memory • Radar's footprint was not positioned at the spacecraft nadir but was displaced 21 km along-track ahead of nadir and 1.6 km to the right of the groundtrack • A computer memory upload has replaced the incorrect quaternion with a correct one and pointing is now slightly off-nadir (0.16 deg ahead, in-track) per the recommendation of the CPR Team • Algorithms created to enable CIRA to both re-process the data collected while pointing was in error and to account for the 0.16 deg point bias now established CloudSat Science Team Meeting

  21. Conclusions  CloudSat has achieved its nominal operational orbit in a state of Formation-Flying with CALIPSO and Aqua per the mission requirements  A total of 20 propulsive maneuvers have been executed since the launch in order to achieve the op orbit and to maintain the spacecraft within its Constellation control box, per agreement with Constellation members - The Orbit Analyst Team continues to monitor the spacecraft's motion relative to the Constellation, most especially CALIPSO, and to executes additional maneuvers as necessary - Plenty of propellant remains for an extended mission  Measured trajectory data (routinely available on the web) demonstrates that CloudSat is under control and is meeting its requirements - The spacecraft falling to a safe-hold represents the greatest threat to a control box violation CloudSat Science Team Meeting

  22. Question for SWT • Given that the instrument continues to operate and funding is provided for an extended mission, where should CloudSat be positioned in the A-Train after CALIPSO executes its inclination change maneuver and drifts away? • Tight formation with Aqua along Aqua's groundtrack, i.e., remove the 215 km sun glint displacement? • Positioned in the buffer zone between CALIPSO's box and Aqua's box? With or without sun glint displacement removed. CloudSat Science Team Meeting

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