CloudSat System Engineering Report [Mission Performance] Presented to CloudSat Science Team Ron Boain Project System Engineer 18 October 2006
Apr 01, 2015
CloudSat System Engineering Report
[Mission Performance]Presented to
CloudSat Science Team
Ron Boain
Project System Engineer
18 October 2006
17 October 2006 CloudSat Science Team Meeting R. Boain 2
Summary of mission activities since launch
Review of mission requirements related to science data collection
Review of mission performance against requirements
Agenda
17 October 2006 CloudSat Science Team Meeting R. Boain 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
17 October 2006 CloudSat Science Team Meeting R. Boain 4
Mean Local Time
Sun
Earth
MLT ~ 22.5 13:30 hrs
Earth's orbitalvelocity
Orbit ascendingnode ()
MLT = Mean Local Time of Ascending Node
Earth's Orbit
Sun-Synchronous Orbit
17 October 2006 CloudSat Science Team Meeting R. Boain 5
Ascent Maneuver Sequence
Aqua
Calipso
CloudSat
690 km
705 km
Checkout/CalibrationBurns
CALIPSO OrbitRaise 1
CALIPSO OrbitRaise 2
Final Trim(Not to Scale)
CloudSat OrbitRaise 1
CloudSat OrbitRaise 2
Separation Orbit
Operational Orbit
Estimated Mass Left
846.89
CO 5/11/06 14:50:19 5 5.4 cm/sec 8.60% 20% 0.01927 0.02092722 846.8690728 846.87073
CLC 5/12/06 13:52:47 70 68.8 cm/sec -1.88% 14% 0.269786942 0.264714947 846.6043578 846.6009431
OLC 5/13/06 7:15:45 10 9.03 -9.70% 12% 0.038533556 0.034795801 846.569562 846.5624095
DNo1 5/22/06 11:24:05 320.09 304.084 -4.97% 10% 1.23296 1.171681888 845.3978801 845.3294495
DNo2 (+5%
counts)5/23/06 10:24:36 368 366.4 -0.43% 10% 1.417354121 1.411259498 843.9866206 843.9120954
OR1-A (+5%
counts) 5/25/06 20:45:44 181.1 181.4 0.19% 10% 0.6978952 0.699221201 843.2873994 843.2142002
OR1-B (+5%
counts) 5/25/06 23:13:31 257.4 258.7 0.50% 10% 0.99093 0.995835104 842.2915643 842.2232702
OR2-A (+4.6% counts) 5/27/06 10:12:21 142.291467 142.138 -0.11% 10% 0.5483152 0.54772302 841.7438413 841.674955
OR2-B (+4.6% counts) 5/27/06 12:40:32 121.518 120.266 -1.03% 10% 0.4679842 0.463163963 841.2806774 841.2069708
TINC (+4.8% counts) 5/28/06 10:55:33 66.5 64.01 -3.74% 10% 0.25635258 0.246764994 841.0339124 840.9506182
TM2 6/2/06 11:38:52 5 4.64 -7.12% 6% 0.0186177 0.01729212 841.0166202 840.9320005TM3 (+7%
counts) 6/15/06 13:36:50 5.5 5.63 2.30% 6% 0.0212 0.0216876 840.9949326 840.9108005
Brake (+5%) 6/28/06 7:19:55 0.4 0.54 35% 6% 0.0014871 0.002007585 840.9929251 840.9093134
DMU (+5%) 7/12/06 7:44:43 3.7 3.9 5.40% 6% 0.0142396 0.015008538 840.9779165 840.8950738
FF1 (-5%) 7/27/06 7:38:58 1.05 1.03 -1.70% 6% 0.003903689 0.003837327 840.9740792 840.8911701
PP1 8/21/06 7:20:53 0.4 0.347 -13% 6% 0.001487122 0.001293796 840.9727854 840.889683
1st Inc 8/26/06 9:05:56 224.2 224.3 0.02% 6% 0.864482273 0.86465517 840.1081302 840.0252007
2nd Inc 9/1/06 10:07:49 201.2 202.5 0.65% 6% 0.775954428 0.780998132 839.3271321 839.2492463
FF2 9/21/06 7:52:02 1 0.9688 -3.12% 6% 0.0037178 0.003601805 839.3235303 839.2455285
3rd Inc 10/12/06 10:01:46 128.946 128.508 -0.34% 6% 0.497380248 0.495689155 838.8278411 838.7481482
CloudSat Maneuver Summary
Burn IDPlanned DV
(cm/s)Achieved DV
(cm/s)Percent Error
(%)Acceptable Ball
Error (%)Estimated Mass Loss
Calculated Mass Loss
Calculated Mass Left
Burn time
17 October 2006 CloudSat Science Team Meeting R. Boain 7
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 deorbit 35+– Total 59.6 m/s
• Plenty of fuel for extended mission, etc.
17 October 2006 CloudSat Science Team Meeting R. Boain 8
Afternoon Constellation Control Boxes
15” Aqua Orbit
15 min max
Aqua is maintained in a control
box of ± 21.5 s
±21.5”
15”
±21.5”
Parasol is maintained in a control box of ±21.5 s
±21.5”
Calipso is maintained in a control box of ±21.5 s
CloudSat is maintained 12.5 ±2.5sahead of Calipso
Aura is maintained about 15 min behind Aqua
15”
Aqua, CALIPSO, and Parasol have independent control boxes CloudSat’s control box is slaved to CALIPSO when formation flying
CALIPSO positioned 73 s behind Aqua (CALIPSO is controlled to +/-10-km at the Equator crossing
measured along the equator = +/- 21.5 sec)
• Satellite positions in the A-Train and Control Box dimensions specified in theACOCP document
17 October 2006 CloudSat Science Team Meeting R. Boain 9
CloudSat, Aqua, and CALIPSO in Formation
orbit
116 sec(870 km)
30 sec(225 km)
43 sec
(322 km)43 sec
Aqua Control Box Calipso Control BoxCirculation OrbitCirculation Orbit
CloudSat C.B.
Circulation Orbit
≈ 15 sec(112 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.
17 October 2006 CloudSat Science Team Meeting R. Boain 10
MODIS Instrument
alon
g-tra
ck
cross-track
20 k
m
10 k
m
Scan
Mirr
or
10 D
etecto
rs
per s
can
Aqua S/C
“Line of the MODIS Measurement Swath”
Width = 2330 km
10º 10º
Groun
d-tra
ck
MODIS Scanning Geometry
17 October 2006 CloudSat Science Team Meeting R. Boain 11
Congruency of Aqua/CloudSat Measurements
CloudSat
MODIS Swath WidthMODIS Nadir Position
705 km
55°
1165 km(1/2 Swath)
CS Nadir Aqua GT
240 km
• 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
Aqua
18.8
For latitudes north and southof the equator, the displace-ment decreases to zero andthen increases to its max atthe next equator crossing
17 October 2006 CloudSat Science Team Meeting R. Boain 12
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
17 October 2006 CloudSat Science Team Meeting R. Boain 13
• 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
Lidar footprint(Dia= 70m)
Radar footprint(Dia= 1400m)
CloudSat Groundtrack
Position of footprints relative to groundtrack
2000 m
15 seconds(
113 km)
Goalconditionmet
Time delayedLidar footprint
Science Requirements Relatedto Formation Flying with CALIPSO
17 October 2006 CloudSat Science Team Meeting R. Boain 14
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
17 October 2006 CloudSat Science Team Meeting R. Boain 15
Measured AQ/CS Cross-track Separation
0 5 10 15 20200
210
220
230
240
Days Past 09/22/06
Cross-track Separation (km)
240
200
x
200 t
● Requirement for cross-track separation between Aqua and CloudSat ≤ 240 km
17 October 2006 CloudSat Science Team Meeting R. Boain 16
Measured AQ/CS Along-Track Separation
0 5 10 15 2055
56
57
58
59
60
Days Past 09/22/06
Along-track Separation (sec)
60
55
x
200 t
● Requirement for along-track separation betweenCloudSat and Aqua≤ 120 seconds
17 October 2006 CloudSat Science Team Meeting R. Boain 17
Measured CS/CP Along-Track Separation
0 10 20 30 40 500
5
10
15
Days Past 09/27/06
Along-Track Separation (sec)
15
0
y τ( )
x
Yrq τ( )
500 τ t, τ,
● Requirement for Along-Track Separation between CloudSat andCALIPSO: 10 sec ≤ x ≤ 15 sec
● Along-track separation between CALIPSO and CloudSat; measured data inblue● Formation-Flying Maintenance maneuver will be scheduled before 10 sec boundary violation occurs ● Red line is a quadratic fit to data
17 October 2006 CloudSat Science Team Meeting R. Boain 18
Measured CS/CP Cross-Track Separation
0 10 20 30 40 501
0.5
0
0.5
1
Days Past 09/27/06
Cross-Track Separation (km)
1
1−
y τ( )
x
500 τ t,
● Requirement for Cross-Track Separation between CloudSat andCALIPSO: -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
17 October 2006 CloudSat Science Team Meeting R. Boain 19
Measured Difference Between CS/CPMean Local Times
0 5 10 15 2010
11
12
13
14
15
Days Past 09/22/06
Difference in MLT (sec)
15
10
x
200 t
● Requirement for difference in MLTbetween CloudSat and CALIPSO =12.5 ± 0.5 sec
17 October 2006 CloudSat Science Team Meeting R. Boain 20
Total Mission History of Requirements Compliance
Past and Projected Location w.r.t. CALIPSO
9
10
11
12
13
14
15
16
2-Jun 16-Jun 30-Jun 14-Jul 28-Jul 11-Aug 25-Aug 8-Sep 22-Sep 6-Oct 20-Oct
Date
Seconds from CALIPSO
#REF! Leading Boundary (sec) Braking threshold (sec)
Constellation box front (sec) Past Separation Control box center (sec)
Projection with maneuver(s) (sec) Constellation box back (sec) FF maneuver location (sec)
17 October 2006 CloudSat Science Team Meeting R. Boain 21
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
17 October 2006 CloudSat Science Team Meeting R. Boain 22
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
17 October 2006 CloudSat Science Team Meeting R. Boain 23
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.