CloudSat System Engineering Report [ Mission Performance] Presented to CloudSat Science Team Ron...

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


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


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


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


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.


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


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.


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


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 displacement 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


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


• 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


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


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


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


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


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


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


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)


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


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


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 System Engineering Report [ Mission Performance] Presented to CloudSat Science Team Ron...

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