IV. Spacecraft Changes PART A LUNAR DUST AND RADIATION DARKENING OF SURVEYOR 3 SURFACES

One of tile most conspicuous features noted by the astronauts during examination of Surveyor on the Moon and later during examination of the returned hardware in the Lunar Receiving Laboratory (LRL) was the change in color. The overall tan color was in sharp contrast to the stark white paint and shiny metallic surfaces of Surveyor before launch (and to that on the model used by the astronauts during training). Discoloration due to radiation darkening of the paint and to aecumuhtted lunar dust had been expected, tlowever, the expected patterns of radiation damage and conjectured patterns of dust accumulation were not evident on the returned hardware. The investigation to establish the causes of discoloration and the apparent absence of expected patterns has yielded information, primarily on the effects of hmar fines, which will be of value to future lunar operations. The white paint used on Surveyor was known to be subject to radiation darkening. The nature and rate of discoloration had been measured in simulation tests (refs. 1 and 2), and the effect verified from temperature measurements on Surveyor 1 (ref. ,3). Patterns of discoloration related to solar illumination geometry were expected because the magnitude of discoloration increases with total solar irradiation. The atmormal hmding of Surveyor 3 resulted in veiling glare and substantial loss of contrast in the pictures taken during spacecraft operation. This effect was attributed to dust on the mirror; the upper part of the mirror was significantly more affected than the lower, recessed part. It was reasonable to expect a similar coating of hmar dust on other surfaces of the camera, and with comparable variations in quantity. The astronauts observed dust contamination on the Surw_yor, but detected no directional pattern associated with the Lunar Module (LM) landing (ref. 4). No effects from the LM had been expected, as there was "... preflight consideration that the landing occur outside of a 500-foot radius of the target to minimize contamination of the Surveyor vehicle by descent engine exhaust and any attendant dust excitation" (ref. 5).