General

• Planning for HST-SA1 PFIP started in 1991.
• STSA-1 PFIP to be seen in connection with EURECA-SA PFIP.
  • ST-SA1: flexible array, 43.3 months in orbit.
  • EURECA-SA: rigid panel design, 10.8 months in orbit.
• Smooth Transition from EURECA-SA to HST-SA1 PFIP
  • EURECA-SA PFIP: July 1993 - Decmber 1994.
  • HST-SA1 PFIP: December 1994 - May 1995.
    • Final Report: July 1995.
• General investigation approach is identical for both programs.
• Experience from EURECA PFIP helped to further optimize the HST-SA1 Investigation Program.

• Evaluation of system performance
  • In-flight performance against specification (mechanical, electrical)
  • Comparison of data (pre-flight, on-orbit, post-flight)
• Evaluation of changes in materials properties
  • Insulation strengths, embrittlement, µ-cracks, alpha, epsilon, etc.
• Explanation of on-orbit failures
  • Short / open circuits, boom buckling, tension sensor, etc
• Evaluation of design related degradation mechanisms
  • Power, loss factors, low cycle fatigue of connectors, etc.
• Refinement of models for space environment
  • Radiation, ATOX, µ-meteorite, etc.
• Design recommendations for future solar arrays

• Deployment/Retractions
  • Comparison of performances
  • Electrical continuity during deployment
  • Synchronization, blanket tensions
• Inspection of Bi-Stem Booms
  • Surface condition, marks, deformations, particles
• Gear Wear, Wear of Ceramic Gear Carrier
• Assessment of Lubricants, Fluid Reservoirs, Fluid Creep
• Static Adhesion
• Fretting on all Clamps/End Stops
• Electrical Contacts, Brush/Commutators
• Motor Currents, Speed Torque Characteristic

• Thermal / ATOX Protective Coatings
  • Generally all coatings and surface finishes showed discolorations, where exposed to Sun (except aluminized Kapton material).
  • Top layer of one MLI segment on PDM arm experienced splitting starting from nitting and venting holes.
  • Teflon^® tape used for PDM harness cracked in some areas (sun direction only).

• Secondary Deployment Mechanism
  • Deployment/retraction went very smooth.
  • 3 stops were implemented for synchronization measurements.
  • Total deployment time 6 minutes 34 seconds (both microswitches operated).
  • Handling error during retraction triggered microwitch (float).
  • Bi-stem boom diameter increased by 2%.
  • Bi-stem boom showed evidence of radial movement between elements.
• Primary Deployment Mechanism (PDM)
  • Primary deployment/retraction function and PDM locking device test successful.
  • EGSE glitch during PDM deployment operation (EGSE drive electronics for the motor).

• No delamination of the GFRP stiffeners.
• The piano hinges are in good shape.
  • No rupture of hinge loops was observed.
  • 3 hinge pins moved towards blanket in board end.
  • In one case the hinge rod penetrated the sliding protection substrate (no protection on BDA/IBA pins).
• No degradation/delamination of insulation strip/tape.
• All bridge pieces are in good shape.
  • No sign of degradation.
  • No sign of overstressing or distortion.
  • No evidence of ATOX attack.
• No sign of substrate degradation/delamination (bubbling).
• All solder joints are in good condition (no sign of degradation).
• All repair techniques were successful (no sign of degradation).

• All coatings have been successful in protecting from ATOX.
• RTV-S 691 (silicone adhesive, front side).
  • Bus Bars (silver) overcoat has darkened in color from fairly bright red to a brownish tinge.
  • Meander bars (silver) overcoat has darkened in color from fairly bright red to a brownish tinge.
  • Blanket and edge stiffeners (GFRP) changed as the silver overcoat, but darkening is more pronounced.
• DC 93500 (silicone adhesive, front and rear side).
  • There is no obvious degradation of substrate integrity.
  • There is no obvious change in appearance where the substrate is shielded from direct sunlight.
  • Areas directly exposed to sunlight (UV) caused in some areas severe darkening of DC 93500 (i.e. IBA).

• Survey of both blankets and mechanisms.
  
  
  • Scanned area is approximately 65 squared.
  • More than 40000 impacts of particles > 10 µm expected.
  • More than 1000 impacts of particles > 80 µm expected.
  • SPAs were inspected by Mare Crisium (MC) and DASA, using different inspection methods.
  • Data evaluation in progress.
• MC results
  • 672 impact features greater than or equal to 1.2 mm recorded on SPA front sides.
  • Solar-cell grid finger spacing is 1.2 mm.
  • 270 impact features recorded on rear-side.
• DASA results
  • 3862 impact features recorded on SPA front sides.
  • Blanket rear side recording difficult due to different surface morphology (only > 500 µm particles recorded).
  • 738 solar cells (silicon) damaged.
  • 149 solar cells with "dents" in silicon due to rear side hits (no cracks).
  • 1316 cracked cover slides (crater with no further damage not considered as a crack).

• The blankets and solar cell network is in good condition.
• The blankets are in a good bonding state.
  • No delaminations of the carrier substrate were visible (test planned in vacuum).
• Exposed RTV coatings how different degrees of discoloration.
• No significant change of thermo-optical properties.
  • i.e. SCA, rear sides.
• SCA interconnectors are in good shape.
• No surprise concerning the number of broken cells.
• The electrical degradation of solar cells was somewhat less than expected.
  • For future power predictions loss factors should be revised.
• The post-flight system performance of the mechanisms was smooth and as expected.
• Materials and coatings for the protection against ATOX and UV are suitable for long duration missions in LEO.
  • FEP requires special integration precautions when used (procedure TBD).
• Unexpected Findings (until now).
  • Radial movement of bi-stem elements.
  • Cracking of flexible data harness on OBA/DBA interface.
• Thousands of particle impacts were recorded on the arrays with almost 200 penetrating the blankets.
• Despite the numerous clearly visible impacts there is no indication that any meteoroid or debris impact has caused any of the observed failures or other unusual power degradation.
• The results from the PFIPs is a great help in refining the environmental models and the understanding of damaging effects of impacting particles.
• PFIP is on Schedule.
• SA-PFIPs for EURECA and HST have already proven to be very valuable for ESA and its future solar-array projects.
  
  Teflon is a Registered Trademark of DuPont
  

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