Contamination

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Section 30 Contamination
. . . Michael Woronowicz Swales Aerospace
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Outline

• Contamination Perspective
• Thermal Balance/Thermal Vacuum Test
• Contamination-related equipment
• Measurements
• Pulsed Plasma Thruster
• Inertial Reference Units
• Delta Fairing Cleanliness
• Purge Requirements
• Cleanliness Maintenance
• Open Issues

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Contamination Perspective

• Contamination staff concerned with deposition of
  foreign materials
• Particulates
• Molecular films
• On sensitive surfaces
• Instruments
• Optics
• Thermal control surfaces
• Sources Considered for EO-1
• On-orbit
• Outgassing from non-metallic materials
• PPT operations
• During ground operations
• Contaminants in ambient atmosphere
• Residue from handling, testing

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T/V II Parameters

• Chamber 225 instrumentation
• 2 TQCMs (usually collected _at_ -65 C)
• 2 instrument scavenger plates (usually _at_ -65 C)
• Chamber scavenger plate _at_ 90 K
• Coldfinger (collected _at_ 90 K for 8 hrs)
• TQCMs measured outgassing rates from instrument
  interiors
• Kapton sheets isolated instrument outgassing
  from general S/C
• Differential measurements for aperture open vs.
  aperture closed indicate instrument internal
  outgassing rates
• Instrument scavenger plates intended to
  preferentially collect instrument NVR for
  chemical composition analysis ID

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T/V II TQCM Placement (ALI)
ALI Nadir Deck Heater Plate
Kapton Isolation Sheet
TQCM 1
Scavenger Plate (behind sheet)
ALI Outgassing Measurement Arrangement
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T/V II TQCM Placement (Hyperion)
Scavenger Plate
Kapton Isolation Sheet
TQCM 2
Hyperion
Hyperion Measurement Arrangement
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T/V II Initial Results

• Hyperion NVR mass loss rates condensable _at_ -65 C
• 1.6 x 10-7 g/s (outgassing mode, final hot
  plateau, 20 C)
• 1.4 x 10-6 g/s (outgassing mode, final hot
  plateau, 30 C)
• ALI NVR mass loss rates condensable _at_ -65 C
• 1.3 x 10-6 g/s (outgassing mode, final hot
  plateau)
• Other results, refinements currently still being
  processed
• Desorption demonstrated during TQCM warm-up to 0
  C
• during final T/V cycle hot plateau
• Post-test chemical analyses
• Same constituents and quantity as T/V 1 no
  unexpected contaminants have been introduced on
  spacecraft bus
• Instrument samples lost due to S-Band Transponder
  testing (during chamber re-evacuation event,
  7/19/00 cannot identify instrument sources
  (outgassing levels acceptable))

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Pulsed Plasma Thruster

• Concern over S/C degradation due to plume
  products from PPT firing
• uses Teflon for fuel ? fluorinated products
  possibly corrosive to S/C matls.
• some plume product fraction will be ionized
• Effects measured on S/C mockup with
  strategically-placed S/C materials during
  lifetime acceptance test
• Test performed in vacuum at NASA-Glenn
• Results indicate negligible degradation after 105
  pulses
• Reduce risk concerns by operating at end of
  mission

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IRU Helium Issue

• Inertial reference units (IRUs) absorb helium,
  changing required driving voltage
• IRU He desorption rate considerably less than
  absorption rate
• Exposure incidents during IT prompted purge
  modifications
• Research-grade bottled N2 replaced with LN2
  boiloff
• Relatively permeable teflon tubing replaced with
  impermeable Cu tubing
• Ambient air periodically monitored for helium
  concentration
• Assembly removed, placed under N2 purge at Swales
  during current MAP testing to reduce risk from
  elevated He concentrations
• Future risk includes possible exposure under
  flight vehicle environment
• This has been mitigated to the maximum extent
  possible by using stainless steel tubing on stand
  wrapped tubing in the fairing.

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Launch Vehicle Cleanliness

• Fluoroglide used on Delta II fairing separation
  rails
• Teflon spray application
• facilitates fairing assembly process
• creates particulate hazard during fairing
  separation
• seen on Globalstar-5 Globalstar-7 separation
  videos
• Concern regarding relative location of S/A CSS to
  fairing separation plane
• Minimize technical and schedule risk by using
  fairing w/o Fluoroglide
• KSC contamination personnel working issue with
  Boeing

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Fairing Separation Issue
Solar Array
Coarse Sun Sensors
Fairing
Fairing Separation Plane
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Purge Requirements

• IRU box
• Science instruments
• N2 boil-off (better than MIL-P-27401C Grade B,
  2mm absolute filtered)
• MIT-LL provided purge cart (all three
  instruments)
• Protects against accidental exposure to
  condensable hydrocarbons

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Cleanliness Maintenance

• Spacecraft cleaned during IT flow as work is
  performed
• External requirements (Visibly Clean, Sensitive)
• 1.86 obscuration (particulate), 2 mg/ft2
  (molecular)
• Current levels
• lt 1 obscuration, 1 mg/ft2 molecular
• Thorough inspection and cleaning performed at
  critical milestones
• Prior to Bay closures, following re-integration
  activity
• Before and after movement between facilities
• Before thermal vacuum test
• Before launch
• Spacecraft double-bagged when not in cleanroom

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Open Issues

• IRU Helium exposure risks with purge in place
• Helium usage in GSFC Building 7 complex
• Continuous monitoring in place via helium
  detector
• Launch vehicle environment
• Purge tubing changes at launch site
• Issue solved by adding a purge to the IRU
• Fluoroglide on Delta fairing separation rails
• Provide a fairing which is not lubricated with
  Fluoroglide
• Installation of a shield is also under
  consideration