Servicing of the Hubble Space Telescope

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Servicing of the Hubble Space Telescope

• D. R. Soderblom, C. Biagetti,
• M. Reinhart, G. Chapman,
• P. Stanley

Space Telescope Science Institute Baltimore,
Maryland USA
2
What is HST?

• Orbiting optical and ultraviolet telescope,
  conceived in 1947, designed in 1970s, built in
  1980s, launched in 1990
• Designed and built for deployment and servicing
  from Shuttle
• Shuttle access forces HST into low-Earth orbit,
  at highest such orbit reachable by Shuttle (about
  600 km above surface)
• LEO means drag for large object such
• as HST, esp. at solar max. Orbit
• must be boosted regularly.
• LEO also means HST is within Earths
• magnetic field, reducing radiation
• background and allowing disposal of excess
• angular momentum.

3
Routine HST Operations

• LEO means HST goes in and out of shadow every 96
  min
• Most objects are occulted during a portion of the
  orbit, but with Continuous Viewing Zone at orbit
  poles (precessing at 56-day period)
• Regular passage through South Atlantic Anomaly
  forces temporary suspension of SI usage due to
  high backgrounds
• Ground system creates most-efficient possible
  schedule within given constraints using
  observations as specified by scientists, which
  contain additional constraints (usually
  restricted time of execution or the equivalent)
• Schedule construction is human-guided
  (semi-automatic) to achieve multiple and complex
  goals

4
Routine Operations (cont.)

• HST has sufficient autonomous capability to
  ensure that anomalies cannot threaten spacecraft.
  HST enters safemode when critical anomalies are
  sensed.
• Communication to and from S/C is through TDRSS in
  geo-synchronous orbit. TDRSS contacts
  pre-scheduled through NASA.
• Science operations schedules created to cover a
  weeks time, with commands up-linked about three
  times per day.
• Data downlinks daily to deal with volume ( 100
  Gbit/week).
• TDRSS ground station at White Sands, with link to
  GSFC then STScI.
• Archive at STScI contains all HST observations.

5
Servicing of HST

• HST designed for regular upgrades or replacement
  of critical components (solar arrays, gyros,
  RSUs, communication systems, science instruments)
• Intent has been to service approximately every 3
  years and there have been 4 SMs to date (SM1,
  SM2, SM3a, SM3b)

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SM Preparations

• Extensive and intensive documentation, training,
  and simulation, involving multiple NASA centers
• Astronaut preparation and training to deal with a
  specific manifest (list of items to be worked on)
  plus contingencies
• Preparation time 2 years

7
SM Initiation

• Multiple schedules constructed to deal with
  multiple contingencies
• Science operations continue if launch delayed
• Multiple entry points into schedule to allow for
  changes in exact launch time

8
SM Operation Overview

• Once launch is in progress, HST breaks into
  science program and places itself in suitable
  attitude for retrieval by Shuttle. Final
  maneuvers are done with real-time commands.
• Shuttle rendezvous with HST, approaches slowly,
  then grapples HST and attaches it at aft end to
  special fixture in Shuttle bay. Fixture allows
  for HST power and communication to come through
  Shuttle, and can rotate and position HST for
  convenient access by astronauts.
• HST ceases autonomous operation and depends on
  Shuttle. Ground operators at GSFC work through
  Shuttle controllers at JSC during course of
  mission to communicate with spacecraft.

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SM Operation Overview (cont.)

• SM proceeds. During daily EVAs, ground personnel
  shut down portions of spacecraft systems to
  prepare HST, monitor critical systems during the
  work, then restore systems and verify basic
  functionality.
• During non-EVA periods, ground personnel monitor
  spacecraft systems, prepare HST for next EVA,
  review previous shift for anomalies and otherwise
  ensure they and spacecraft are ready for next
  day.

10
HST Deployment

• After servicing complete and basic checkout done,
  HST is released from Shuttle, ordinarily after a
  burn to boost the orbit.
• Shuttle returns to Earth surface, HST reinitiates
  autonomous operation

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Servicing Mission Observatory Verification
(SMOV)

• An SMOV program is associated with each servicing
  mission
• A set of pre-planned, coordinated tests extending
  2-3 months beyond completion of Shuttle servicing
• Generic SMOV goals
• Timely recommissioning of the Observatory for
  science operations
• Commission newly installed science instruments
• Recommission existing science instruments
• Phased resumption of science operations in
  parallel with remaining SMOV activities
• Recommissioning of Observatory systems for normal
  operations
• Validation of other on-orbit replacements
  installations
• Early Release Observations (EROs)
• Demonstrate upgraded science capabilities to
  astronomical community and general public

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A Generic View of SMOV

• PHASE 2
• (1 2 weeks)
• Recommission existing science instruments
• Optical alignment focus - assumed OK
• Early release observations (EROs) optional
• Calibrations/characterizations minimal set
• Resume general science with existing instruments

• PHASE 1
• (1 2 weeks)
• Recover spacecraft subsystems
• Attitude, thermal, power, comm
• Activate science instruments
• Engineering check-out
• Thermal control
• Mitigate outgassing contamination risks
• Bright Earth avoidance
• High-voltage delay

• PHASE 3
• (2 10
  weeks)
• Commission new science instruments
• Optical alignment focus iterative process
• Early release observations (EROs)
• Calibrations/characterizations sensitivities,
• throughputs, flat-fields, photometry,
• geometric/thermal stabilities, etc.
• Start general science new instruments
• Science phased in as instruments/channels
• are commissioned

NOTE Phases 2 3 can run concurrently
13
SM1

• STS-61, Endeavour, Dec. 2, 1993 for 9 days
• Primary purpose to restore optical functionality
  following discovery of spherical aberration after
  launch this was done with one new instrument and
  a set of corrective optics

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SM1 Agenda

• WFPC2 (still operating!)
• COSTAR, to feed corrected images to other 3 axial
  instruments (still in HST)
• GHRS redundancy kit, to recover full GHRS
  operations following an early circuit failure
• Rate Sensor Units (4 gyros) plus electronics (2)
• New solar arrays, same as original (ESA-supplied)
• Magnetic Sensing System (2)
• Computer co-processor upgrade

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SMOV1 First Servicing Mission Observatory
Verification

• Primary purpose was to demonstrate the
  restoration of the Observatory to its original
  optical specifications
• Calibration of new gyros (and recommission
  observatory control systems)
• Observatory focus and optical alignment
• Including COSTAR mirror deployment and adjustment
• Commission the new WFPC2
• Demonstrate corrected optics with set of EROs
• Recommission existing science instruments (using
  COSTAR)
• Faint Object Camera (FOC)
• Faint Object Spectrograph (FOS)
• Goddard High Resolution Spectrograph (GHRS)

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SM2 Agenda

• Replacement Fine Guidance Sensor
• New instruments STIS and NICMOS
• Solid-state recorder for data storage, to replace
  an existing tape unit
• Optical Control Electronics enhancement
• Reaction wheel assemblies
• Solar-array drive electronics
• Secondary S/C hardware

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SMOV2 Second Servicing Mission Observatory
Verification

• First Bright Earth Avoidance campaign
• Purpose Prevent (hypothetical) polymerization
  of
• contaminant molecules on telescope optics
• Avoid occultation by sunlit earth for initial
  SMOV period
• Recommissioning of existing science instruments
• WFPC2 ( 2 weeks), existing FGSs ( 1week)
• Commissioning of new FGS (10 weeks)
• Commissioning of NICMOS STIS
• (10-12 weeks)
• Complicated by unexpected problems
• NICMOS dewar expansion
• STIS NICMOS charge particle susceptibility

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SM3A Agenda

• Executed on emergency basis to replace failed
  gyros and other engineering hardware
• Replaced a Fine Guidance Sensor
• Added second Solid State Recorder

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SMOV3A Third Servicing Mission (Part A)
Observatory Verification

• SMOV3A was relatively simple
• No new science instruments
• Normal science resumed shortly after
• calibration of new gyros
• Completion of Bright Earth Avoidance period ( 2
  weeks)
• FGS2R commissioned

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SM3B Agenda

• New instrument ACS
• New solar arrays (modified Iridium) more power
  from smaller area
• Restore NICMOS by adding cryocooler
• Third-generation solar arrays more juice from
  less area more mechanically robust.
• Power control unit like replacing the main panel

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SMOV3B - Third Servicing Mission (Part B)
Observatory Verification

• Most complicated of all SMOVs
• All spacecraft/instrument HVs off during initial
  NICMOS cool-down
• Commissioned ACS
• Recommissioned NICMOS via newly installed NCS
• Anomalously long cool-down period greatly
  complicated SMOV plan
• Many replans carried out

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Lessons Learned

• Establish a dedicated SMOV working group of
  scientists, engineers, and operators to
  coordinate an integrated approach
• Plan within the normal scheduling system to
  reduce risk and cost
• Use success-oriented scheduling
• Plan for EROs
• Clearly define SMOV on-orbit requirements so you
  agree on when youre done
• Test the calendars and timelines
• Provide multiple critical paths
• Schedule think time
• Make the schedule insensitive to launch delays
• Do dry runs of real-time procedures

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The Next Generation of HST Servicing

• January 16, 2004 NASA Administrator Sean OKeefe
  announces that the Shuttle will service HST no
  more
• Are there good alternatives?
• Human servicing known to work and to be adaptable
  to circumstances
• HST designed for human servicing
• Related hardware and procedures well defined

24
Robotic servicing?

• Can robotic servicing work for HST?
• Despite lack of direct experience, significant
  development has been taking place in recent
  years.
• Many key hardware and system capabilities are
  available and space-qualified or nearly so.
• Robotic servicing for HST appears to be feasible.

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A Tour through the Cosmos with HST

• Why the upgrades?
• Entirely new science capabilities
• Extend the useful life of the facility
• Whats been accomplished?

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Jupiters Great Red Spot
Image Credit Hubble Heritage Team
(STScI/AURA/NASA) and Amy Simon (Cornell U.)
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CelestialFireworks
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)
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Sombrero Galaxy
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)
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Galaxy NGC 2787
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)
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Spirograph Nebula
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)
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Retina Nebula
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)
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Messier 15
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)
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Spiral Galaxy M64
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)
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NGC 604 in Spiral Galaxy M33
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)
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Spiral Galaxy Pair NGC 3314
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)
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Spiral Galaxy NGC 4622
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)
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Polar Ring Galaxy NGC 4650a
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)
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Planetary Nebula NGC 6369
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)
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Planetary Nebula NGC 6751
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)
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V838 Monocerotis Light Echo
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)
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Galaxy NGC 7742
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)
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Saturn
Image Credit NASA and The Hubble Heritage Team
(STScI/AURA)