Hubble Space Telescope

(HST) Archive System

NASA Langley Research Center
Hampton, Virginia

HST Contamination Meeting

Space Telescope Science Institute
Baltimore, Maryland
May, 1995

The HST Contamination Meeting covered contamination-related topics relevant to the operation of the HST scientific instruments. The first presentation is the only one discussed in this archive section, as it provides results from WF/PC-I contamination studies, and other returned hardware. It is a confirmation of the data reported at the HST Returned Hardware Evaluation Symposium held at GSFC in December, 1994.

• As part of the HST Returned Hardware Program, the 1216-1608 Angstrom reflectivity of the WF/PC-I pickoff mirror was found to be degraded. It was measured in an ambient (nitrogen) tent and in vacuum.
• A Tiger Team and then a Failure Review Board were appointed to study the impact to HST.
• This section summarizes key Failure Review Board findings.

• Flight WF/PC-I Pickoff Mirror:
  • Showed large degradation below 1600 angstroms
  • Measured at 45 degrees and normal incidence
  • Measured first in nitrogen tent, then in vacuum
  • Spare pickoff mirror also measured
  • Compared to pre-flight data
• Flight Aperture Window:
  • Showed some degradation below 1600 angstroms
  • Measured in nitrogen tent
  • Compared to pre-flight data

• Energy calculations indicate Earth albedo UV strong enough to photopolymerize the contaminants of the pickoff mirror (Based on IUE data)
• Contaminants did not come off in vacuum, and had a reflectivity curve consistent with UV polymerization
• Contaminants were removable under high temperature or with certain cleaning methods (evidence of partial polymerization)
• Contaminant chemistry generally consistent with results from spare FGS outgassing test
• No historical data that support charged particles as energy source

• General:
  • Minimize exposure of UV optics to the bright Earth during servicing mission instrument changeout. For the 1997 mission, it is important that the open STIS instrument aperture not be unnecessarilly pointed at the bright Earth.
  • Characterize, as well as possible, the environment to which the science instruments are subjected during a servicing mission with witness mirror(s) and/or with onboard QCM measurements. The time resolution of the QCM measurement would provide considerably more information regarding potential contamination sources.
• If the Spare Fine Guidance Sensor is Flown:
  • Clean it to the same cleanliness level that the original Fine Guidance Sensors are at now after five years of outgassing.
  • Perform UV monitoring of STIS, WF/PC-II, and the remaining COSTAR channel as part of the Servicing Mission Orbital Verification (SMOV). The monitoring should occur frequently enough to assess build up of contaminants soon after the mission is complete.
  • If an FGS is removed, its pickoff mirror should be preserved both during the servicing mission and during ground processing. This includes minimizing exposure of this mirror to the bright Earth during the servicing mission.

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