PSR Section 23

1
Section 23 Contamination
. . . Michael Woronowicz
2
Outline

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

3
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 and testing

4
TB/TV Parameters

• Chamber 238 instrumentation
• 2 TQCMs (usually collected _at_ -35 C)
• scavenger plate _at_ 90 K
• coldfinger (collected _at_ 90 K for 10.25 hrs)
• TQCMs placed above nadir deck to measure
  outgassing for general external requirement
• one faced upward near Hyperion aperture
• another faced downward near ALI
• Demonstrate contaminant desorption during TQCM
  warmup to satisfy instrumenters concerns

5
TB/TV TQCM Placement
Nadir Deck Heater Panels
S-Band Antenna
TQCM 1
X-Band Antenna
TQCM 2
ALI
Hyperion
6
TB/TV Contamination Results

• Hot thermal balance TQCM requirement (1.3 ? 10-8
  g/cm2/hr deposition _at_ -35 C) easily met (by
  factor of six)
• continued to monitor outgassing throughout test
• Desorption readily demonstrated during TQCM
  warmup to 40 C
• near end of hot T/B plateau
• during final T/V cycle hot plateau
• final TQCM frequencies indicated slight net loss
• Post-test chemical analyses performed on
  coldfinger indicated little deposition (at edge
  of resolution)

7
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 materials
• 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

8
IRU Helium Issue

• Inertial reference units (IRUs) absorb helium,
  changing required driving voltage
• Ambient Helium in Bldg 7 highbay high enough to
  cause IRU voltage to exceed operating
  specifications
• IRU Helium desorption rate considerably less than
  absorption rate
• Nitrogen purge to IRU box halted He absorption
• Special Topic discussed on PSR Day 2
• This was our most significant contamination issue

9
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

10
Cleanliness Maintenance

• Spacecraft cleaned during IT flow as work is
  performed
• external requirements
• 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
• before and after movement between facilities
• before thermal vacuum test
• before launch
• Spacecraft bagged when not in cleanroom

11
Open Issues

• No open issues
• No contamination liens
• Ready to ship