Spacecraft Status

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SpaceOps 2004 Montreal, Canada May 2004 Flying
the Earth Observing Constellations Angelita C.
Kelly Earth Science Mission Operations (ESMO)
Project/Code 428 Systems Engineering Branch/Code
581 NASA Goddard Space Flight Center Greenbelt,
Maryland U.S.A. 20771 Warren F. Case Computer
Sciences Corporation Lanham/Seabrook, Maryland
U.S.A. 20706 Acknowledgement This paper
reflects discussions with the members of the
Morning and Afternoon Constellation Operations
Teams.
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Topics

• Introduction
• Earth Observing Constellations
• Morning Constellation and Lessons Learned
• Afternoon Constellation (A-Train)
• Operations Challenges
• Operations Coordination
• Summary

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Introduction

• Mission Of NASAs Earth Science Enterprise (ESE)
• Develop an understanding of the total Earth
  system and the effects of natural and
  human-induced changes on the global environment.

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What is a Constellation?
In regard to Earth Observations . . .
A constellation is a group of satellites which
move in essentially the same/similar orbits in
close proximity, such that they over-fly the same
geographical regions at about the same time. The
Earth observing constellation satellites
discussed here are in repeating, sun-synchronous
orbits at an altitude of 705 km.
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Why Fly As A Constellation?

• Constellations form single virtual platforms
  which enable coincident observations
• Increase synergy between satellites Instruments
  on multiple satellites can observe the same scene
  at about the same time,
• Facilitate coordinated validation and calibration
  efforts, and
• Explore the utility of coordinated observations
  proposed for future missions.
• The sum is greater than the parts

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Earth Observing Constellations

• Morning Constellation
• All 4 satellites are on-orbit (Landsat-7,
  followed by EO-1, SAC-C, and Terra)
• Ascending equator crossing times near 1000 Mean
  Local Time (MLT)
• Afternoon Constellation (A-Train)
• EOS-Aqua is the only member currently on
  on-orbit.
• Other missions will follow CloudSat, CALIPSO,
  PARASOL, Aura, and OCO.
• Descending equator crossing times near 1330 MLT

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Morning and Afternoon Constellation Phasing

Tracking Station Key AGS Alaska Ground
Station SGS Svalbard Ground Station LGS
Landsat Ground Station TDRSW TDRS-WEST
(geo-synchronous)
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Morning Constellation
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Morning Constellation Science Requirements and
Mission Design

• Landsat-7 (Apr. 1999) and EOS Terra (Dec. 1999)
• Prior to launch, the Project Scientists and
  Project Managers signed an agreement to maintain
  the satellite orbits relative to one another in
  order to enable synergy among the instruments.
• EO-1 and SAC-C were launched together in Nov.
  2000.
• EO-1 is a technology demonstration satellite that
  flies in formation one minute behind Landsat-7,
  producing images of the same ground location
• EO-1 and SAC-C science teams agreed to cooperate
  to promote NASA/Argentine research initiatives in
  remote sensing.

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Operations Coordination Example EO-1 / Landsat-7
EO-1 flies in tight formation with Landsat-7 (MLT
separation of 1 minute 1 sec). EO-1 plays
follow the leader with Landsat-7, so
coordination is critical

• Ground Track Control (GTC) maneuvers
• EO-1 worked with Landsat-7 to get their
  operations to target GTC maneuvers for Tuesdays,
  allowing EO-1 to plan Formation Flying burns for
  Thursdays.
• Inclination maneuvers
• Original plan was to wait until Landsat-7
  completed their inclination burns before
  performing the EO-1 burns. To be more efficient,
  EO-1 now performs 1/2 of its burn prior to the
  Landsat-7 burn and completes the remaining 1/2 of
  its burn after the Landsat-7 burn is complete.

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Morning Constellation Operations Coordination

• Constellation operations coordination evolved
  after the satellites got on orbit.
• Coordination agreements were formally documented
  in the Morning Train Coincident Observation
  Implementation and Operations Plan, September
  2002.
• Lessons learned from the Morning Constellation
  are being applied to the Afternoon Constellation
  (A-Train).

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Afternoon Constellation (A-Train)
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Afternoon Constellation Science Requirements and
Mission Design
While Constellation flying is a secondary
objective to the Aqua mission, coincidental
science requirements heavily influenced mission
designs for satellites that wanted to take
advantage of Aqua data

• Aura (to be launched next month) will be phased
  to be 8 minutes (in MLT) behind Aqua to observe
  the same atmospheric region.
• CALIPSO and CloudSat (to be launched together in
  2005) will fly in tight formation (12.5 2.5
  seconds) and within 2 minutes of Aqua, enabling
  coincident data from the CloudSat radar, CALIPSO
  lidar, and Aqua instruments.
• PARASOL (to be launched in 2004) will fly one
  minute behind CALIPSO and will provide
  measurements of the polarized and
  multi-directional reflectances coordinated with
  data from the other satellites
• OCO (to be launched2007) will fly 15 minutes
  ahead of Aqua and will correlate global space
  carbon measurements with other A-Train data.

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Constellation Operations Challenges

• Satellite safety is the prime consideration --
  need to avoid dangerous close approaches/collision
  s
• The satellites are managed by multiple
  organizations (in both U.S. and its International
  Partners)
• Control Centers are at widely separated locations

Operations coordination is essential!
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Afternoon Constellation Control Center
Coordination
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Operations Coordination Approach For the
Afternoon Constellation
Based on lessons learned from the Morning
Constellation, NASA Goddard Space Flight Center
formed the Afternoon Constellation Mission
Operations Working Group (MOWG) comprising
mission representatives. The MOWG is addressing
the following

• Agreements
• Operations coordination concept
• Pre-mission analyses
• Operational guidelines
• Pre-launch simulations
• Tools to facilitate communication and coordination

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Constellation Member Responsibilities
Each mission team maintains its satellite in its
respective position in the Constellation relative
to other satellites and operates its satellite
independently, but all have a collective
responsibility to ensure the safety of the
Constellation.
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Constellation MOWG Progress
Through the MOWG, Constellation team members have

• Defined the orbital configuration
• Agreed on the information to exchange in order to
  monitor the constellation status
• Defined a zone of exclusion (ZOE) for each
  satellite (i.e., the area surrounding a satellite
  which is considered a no trespassing zone)
• Agreed to follow a set process for resolving
  conflicts and anomalies
• Established guidelines for new missions wishing
  to join the constellation

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Afternoon Constellation Orbital Configuration
(Baseline)
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Coordination Tools
NASA Goddard Space Flight Center will deploy a
constellation coordination system to make
constellation monitoring as autonomous as
possible.

• All constellation missions will provide
• Their latest orbit data
• Current status
• The system will provide warnings of potential
  close approaches.
• Missions will verify their actual status,
  coordinate with the other missions as needed, and
  take appropriate action to avoid a dangerous
  situation.

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Constellation Coordination Process
ESMO constellation coordination system
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Operations CoordinationSignificant
Accomplishments

• All mission teams now have a better understanding
  and appreciation of each missions science
  requirements for coordinated observations
• Aqua flight operations and science teams have
  agreed to tighten the Aqua Ground Track Control
  (GTC) requirement from 20 km to 10 km to
  enable CALIPSO and CloudSat missions to achieve
  better science results.
• Increases frequency of Aqua maneuvers
• At the request of CALIPSO and CloudSat, Aqua
  agreed not to perform inclination maneuvers
  during their lifetime to help conserve fuel for
  CALIPSO and CloudSat science operations.
• Significant change to original Aqua inclination
  maneuver plans Aura will need to match the Aqua
  maneuvers.

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Summary

• Constellation operations enhance the overall
  science.
• Operations coordination is critical to the safety
  of all constellation satellites
• If done correctly, operations coordination must
• Start early (before mission designs are set) and
• Minimize the impact on individual mission
  operations

Constellations present special challenges to
operations but its worth the additional effort
because you get better data for the scientists.