Constellation Operations

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The Earth Science Afternoon Constellation
Constellation Operations Lessons Learned For
Future Exploration
Space Operations 2006 Conference Rome,
Italy June 2006
Angelita C. Kelly / NASA Goddard Space Flight
Center Warren F. Case / SGT, Inc.
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Topics

• Purpose
• Earth Observing Constellations
• Morning Constellation
• Afternoon Constellation (A-Train)
• Unique Challenges
• Lessons Learned
• Summary

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Purpose
Describe the lessons learned by flying the first
5 missions of the Afternoon Constellation.
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Earth Observing ConstellationsWhy Fly
Constellations?
The Earth science community has long advocated
placing numerous instruments in space to study
the Earth and its environment.

• Constellations provide the opportunity to make
  coincident, co-registered, and near simultaneous
  science measurements.
• The satellites align their orbital positions so
  their instrument fields of views overlap.
• Earth science data from one satellites
  instrument can be correlated with data from
  another.

The whole is greater than the sum of its parts
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Earth Observing ConstellationsMorning
Constellation

• Four members with descending equator crossing
  near 1000 Mean Local Time (MLT).
• All 4 satellites are currently on-orbit.

• Landsat-7 nominal
• Terra nominal
• EO-1 lowering its orbit to satisfy re-entry
  requirements
• SAC-C raised its orbit to avoid a close approach
  with EO-1 and Landsat-7 in 2005, extending its
  lifetime in the process

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Earth Observing ConstellationsAfternoon
Constellation

• All 7 members have ascending equator crossing
  times near 1330 MLT.
• All but Glory and OCO are on-orbit (these due in
  2008)

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Earth Observing ConstellationsAfternoon
Constellation Phasing
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Earth Observing ConstellationsUnique Challenges

• The Earth Observing Constellations are unlike
  other satellite constellations.
• They present a number of unique challenges.

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Earth Observing Constellations Unique Challenges
(contd)
The Earth Observing Constellations are not a
homogenous mix of identical satellites. They
comprise several satellites with diverse
instruments that provide complementary
observations.
Aura
CALIPSO
OCO
Aqua
Glory
CloudSat
PARASOL
OCO - CO2 column
OMI - Cloud heights OMI HIRLDS Aerosols MLS
TES - H2O temp profiles MLS HIRDLS Cirrus
clouds
CALIPSO- Aerosol and cloud heights Cloudsat -
cloud droplets PARASOL - aerosol and cloud
polarization OCO - CO2
MODIS/ CERES IR Properties of Clouds AIRS
Temperature and H2O Sounding
(from M. Schoeberl)
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The Afternoon Constellation observational
footprints vary greatly
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Earth Observing Constellations Unique Challenges
(contd)
Most constellations are spaced around the Earth
to provide instantaneous, global coverage (e.g.,
GPS, communications, satellite radio, weather).
GPS Constellation
In contrast, the Earth Science Constellation
satellites orbit in close proximity so that
observations occur at about the same time over
approximately the same region. Due to the
relative closeness of the satellites (as small as
10 seconds), safety is an issue.
Morning and Afternoon Constellations
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Earth Observing Constellations Unique Challenges
(contd)

• The independent operations of the Afternoon
  Constellation are managed by multiple
  organizations (both U.S. and International
  Partners)
• The Control Centers are at widely distributed
  locations

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Constellation Management and Coordination Needed
Based on these challenges . . . There was a
clear need for Constellation management and
coordination. We need to keep the constellation
safe, thus enabling constellation science.
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Mission Operations Working Group (MOWG)

• In response . . .
• The Afternoon Constellation Mission Operations
  Working Group (MOWG) was formed with
  representatives from each mission
• The MOWG has been effective at addressing
  constellation management and coordination
  concerns
• Agreed on basic constellation operations
  philosophy
• Agreed on basic orbital configuration
• Agreed on WHEN and HOW we need to coordinate
  (during special/critical events, anomalies)
• Agreed on process for handling changes and
  conflict resolution

Each mission operates independently, but all
missions are committed to keeping the
constellation safe
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Mission Operations Working Group (MOWG) (contd)

• For the past 3 years we have learned a lot
  working together as a "constellation team
• Aqua, Aura, and PARASOL  provided a learning
  experience, exercising some of the agreed-upon
  interfaces and procedures
• Preparing for the launch and early orbit phase of
  CALIPSO and CloudSat provided recent lessons.

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Constellation Operations Lessons Learned

• Science teams need to communicate their
  constellation requirements early.
• Ensure all missions are willing to coordinate
  constellation requirements with each other.
• Start constellation discussions early enough to
  incorporate constellation requirements into the
  mission operations concept and spacecraft design.
• Analyze each missions maneuver capabilities and
  strategy.
• Implement a coordination system.
• Minimize number and complexity of constellation
  interfaces.
• Thoroughly test all constellation interfaces.
• Be prepared for changes in planned mission order
  of launches.
• Analyze each missions ascent plan.
• Analyze constellation contingency scenarios.
• Set up a mechanism to authorize constellation
  configuration changes and resolve conflicts.
• Coordinate end-of-mission plans.
• Maintain communications between teams.

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Lessons Learned 1Science teams need to
communicate their Constellation requirements
early.

• Science requirements drive the operations
  concepts for both the mission and the
  constellation design.
• To do coordinated observations, science teams
  must ensure their requirements are understood by
  the mission design team.

Example Science requirement Auras Microwave
Limb Sounder (MLS) instrument needs to view the
same air mass on the horizon that Aqua observed 8
minutes earlier by looking down. Solution Aura
orbits 8-15 minutes behind Aqua, offset 215 km
West.
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Lessons Learned 2Ensure all missions are
willing to coordinate constellation requirements
with each other

• The benefits derived from flying in close
  proximity to other satellites come at a cost.
• Mission teams must understand that coordination
  with other teams will be required.
• In nominal operations, little interaction is
  required
• It is usually only during special activities
  (e.g., inclination adjust maneuvers) and
  contingency operations that teams must
  coordinate.
• Agreements must be reached with all teams prior
  to a satellites entry into the constellation.

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Lessons Learned 3Start constellation
discussions early

• Start discussions early enough to incorporate
  constellation requirements into the missions
  operations concept and spacecraft design.
• Fuel allocations
• Staffing
• Glint constraints (relative to science
  requirements)
• What-if scenarios.

• Example
• Constellation-flying requires more fuel than
  free-flying.
• Formation flying with another constellation
  satellite requires even more fuel. CloudSat has
  enough fuel to do formation flying with CALIPSO.

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Lessons Learned 4Analyze maneuver capabilities
and strategy

• Evaluate the on-orbit maneuver philosophy for
  each mission
• Each mission needs to evaluate its on-orbit
  maneuver philosophy.
• A maneuver plan that works for a free-flying
  satellite may not be appropriate in a
  constellation environment.

• Example
• CloudSat must match CALIPSOs maneuvers in order
  to maintain their formation.
• A dangerous situation can occur if a scheduled
  CALIPSO maneuver is delayed. CloudSat must react
  immediately.
• CloudSat changed its maneuver strategy to
  schedule an automatic undo maneuver in case
  CALIPSOs maneuver is delayed. Once CALIPSO has
  maneuvered successfully, CloudSats undo
  maneuver is cancelled.

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Lessons Learned 5 Implement a Coordination System

• Develop a centralized coordination system to
  automate routine functions
• Orbital product exchanges
• Event notifications
• Ephemeris displays
• One centralized system relieves all organizations
  from developing multiple systems performing
  similar functions and redundant interfaces

• Example
• For both the Morning and Afternoon
  Constellations, NASA GSFC developed the
  Centralized Coordination System (CCS) to fulfill
  this requirement.

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Lessons Learned 6 Minimize number and complexity
of constellation interfaces

• Fewer interfaces ? Less coordination when
  problems occur, so minimize the number of
  interfaces.

• Standardize formats as much as possible (e.g.,
  STK).

Example Some of our products require format
conversions, increasing the complexity of the
task and introducing a potential source of error.

• Get buy-in and review from all interfacing
  organizations. Interface agreements must be
  reviewed and agreed-to by both management and
  operations organization.

Example An ICD, signed by management, was not
reviewed sufficiently by the people building and
operating the system. This caused late-breaking
changes to operational systems.
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Lessons Learned 7 Thoroughly test all
constellation interfaces

• Allocate time to conduct thorough interface
  testing prior to launch to identify any problems
  early.
• Where possible, incorporate constellation testing
  into existing mission testing to reduce
  additional impact to the mission.
• Agree on needed stand-alone constellation testing
  and simulations.
• These verify that agreed-upon constellation
  procedures are workable.

Example Pre-mission simulations for CloudSat and
CALIPSO identified some incompatible formats.
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Lessons Learned 8 Be prepared for changes in the
planned mission order of launches

• Mission B may launch before Mission A, even
  though Mission A was to launch first. This may
  have consequences.

• Example
• CALIPSO/CloudSat were to launch before PARASOL,
  so they received more attention from the
  Constellation MOWG. CALIPSO/CloudSats launch
  was delayed, so some Constellation testing with
  PARASOL did not happen.
• Fortunately,
• The Constellation entry risk for PARASOL was
  lower since CALIPSO/CloudSat were not yet
  on-orbit
• PARASOL did not have any constellation-related
  anomalies during ascent, and
• CNES did an excellent job of keeping the other
  mission teams informed.

• Application
• We benefit in preparing for the Glory and
  Orbiting Carbon Observatory (OCO) missions in 2008

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Lessons Learned 9Analyze each missions ascent
plan

• Analyze each missions ascent plan in relation to
  rest of Constellation to ensure safety.
• The most risk to the Constellation occurs for the
  final injection burns, although the entire ascent
  (including contingencies) needs examination.
• Have a third party evaluate ascent plans
• This was done for the CALIPSO and CloudSat
  ascents
• Conduct ascent simulations, including recovery
  from an anomalous situation.

• Example
• Ascent simulations showed the need for teams to
  coordinate more via telecons during the launch
  and early orbit (LEO) phase.

• Application
• Glory and OCO ascents will be analyzed and
  coordinated with the rest of the constellation
  teams.

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Lessons Learned 10Analyze constellation
contingency scenarios

• Each mission team performs contingency analysis
  for their own satellite, but not those involving
  other satellites. Credible constellation
  contingency scenarios must be analyzed
• Identify the most likely contingencies.
• Analyze the ability of each mission to react to
  contingencies
• Develop procedures to mitigate the risks.
• Get all teams to signoff on the procedures
• Simulate the contingency procedures to verify
  their efficacy.
• If and when contingencies do occur, the response
  and resolution will be timely, efficient, and
  effective.

• Example
• If one satellite goes into safe-hold and starts
  drifting, it eventually could threaten another
  Constellation satellite. A collision between the
  two could create a debris field that could
  threaten all missions. Contingency procedures
  were developed and signed off by all teams so
  there will be no confusion over a missions
  actions in a contingency situation.

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Lessons Learned 11Set up a mechanisms to
authorize constellation configuration changes and
resolve conflicts

• Establish an approval process for planned
  constellation configuration changes.
• Establish a process to resolve conflicts.

• Examples
• Aquas original ground track control requirement
  was 20 km.
• CloudSat and CALIPSO science teams asked Aqua to
  change this to 10 km to improve the science.

• 2. To maintain its mean local time (MLT)
  requirement, Aqua originally planned to conduct
  inclination adjust maneuvers in Spring 2005.
• CloudSat and CALIPSO mission teams asked that
  Aqua perform these maneuvers earlier in order to
  save fuel for their missions.
• In both cases, Aqua was able to accommodate the
  requests.

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Lessons Learned 12 Coordinate End-Of-Mission
Plans

• A mission must ensure that its exit from the
  constellation does not present a close approach
  risk to nearby satellites.
• The end of mission plan must be reviewed by the
  other constellation members several months before
  the mission begins exiting the constellation.

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Lessons Learned 13 Maintain Communications
Between Teams

• Facilitate and encourage communication between
  the mission teams throughout the mission life
  cycle.

• Example
• Remember also that Points of Contact usually
  change after launch. Be sure to identify points
  of contact for both the planning/development
  phase and the on-orbit phase, then involve both
  groups in the communications flow.
• Issue periodic updates based on personnel changes.

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Summary

• Start early. Talk with science teams. Develop
  an operations concept for a constellation of
  diverse satellites and organizations.
• Understand individual mission capabilities.
• Get the mission teams to communicate and work
  together as one constellation team.
• Get signed agreements for coordination,
  especially for the handling of contingencies.
• Develop a coordination system to exchange data.
• Minimize complexities, but always be prepared for
  changes and contingency situations.

We hope that these lessons prove useful for other
constellations.