Hubble Presentations
Albedo Level Photopolymerization
D. Hughes / Swales and Associates, Inc.
Background
- WF/PC-I Pickoff Mirror is contaminated.
- Throughput at Lyman-Alpha is negligible.
- STIS and other advanced instruments will view the Lyman-Alpha wavelength.
- Contaminant may be polymerized.
- Polymerization during the Servicing Mission is not a concern, but polymerization during HST operations would be.
Poylmerization Premise
- Ultraviolet radiation causes polymerization of hydrocarbon contaminants.
- The rate of polymerization is dependent upon radiation level and mass flux.
- Two exposures of the WF/PC-I Pickoff Mirror occurred: albedo levels during operations and direct sun during the Servicing Mission.
- Testing may reveal which is the likely cause.
Previous Research
- A simple model was able to predict accumulation within a factor of 2.
- Valid for 1 sun intensity.
- Prediction made for spacecraft using tested materials.
- Model suggests linear extrapolation to other mass fluxes; data does not confirm this.
Physical Model
Chemical Model
Test Objectives
- Determine the reaction rate as a function of mass flux and light intensity.
- Use this knowledge to set test parameters when attempting to duplicate WF/PC-I POM contamination.
Test Requirements
- Low background contamination levels.
- Cold chamber shroud.
- Open test configuration (one bounce).
- Variable light source.
- Pinhole filters to adjust to low light levels.
- Deuterium and Krypton lamps.
- UV detector and calibration method.
- Photomultiplier and NO detectors.
- Movable MgF2 window for calibration.
- QCMs for deposition and reemission measurements.
- Effusion cell with a shutter for rapid on-off capability.
Test Methods
- Find the rate constants using a pure material (to simplify analysis).
- Repeat for different UV intensities and mass fluxes:
- Internal to the HST.
- Servicing Mission on-orbit.
- Intermediate.
- Extrapolate to the required lamp intensity, given the mass flux available from a candidate source.
- Use the candidate source to contaminate a window. Verify the parameters were correct with a QCM.
- Analyze the window contamination.
Status
Mechanical and thermal systems are working.
Pure source (phthalate) and candidate on-orbit source have been identified.
Data Acquisition System is in place.
UV detector is performing poorly.
Results expected in early February 1995.
Return to Hubble Space Telescope Hardware Archive System