Nov 6, 1998

Living in space is tough, even for spaceships

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Mir scientists discuss space exposure tests


November 6, 1998: Life in space can be tough not just on humans. Spaceships have to weather a severe environment, too, as they endlessly circle the globe. So in addition to biomedical experiments on humans, NASA has run the equivalent of biomedical experiments on Russia's Mir space station in preparation for launching the International Space Station.

Right: One of the Passive Optical Sample Arrays (POSA-1) is seen after being attached to the U.S. docking module on Mir in 1997.

"Primarily, we were looking at the space environment," said Rachel Kamenetzky, a materials engineer with NASA's Marshall Space Flight Center. "We knew we might encounter some contamination from Shuttle dockings, EVAs, and outgassing of space components." As it turned out, "contamination had a far greater effect than the natural environment on our samples." Speaking to the second day of an interim results symposium on science aboard Mir, Kamenetzky described some of the results from the Mir Environmental Exposure Program (MEEP) that were attached to the docking module on Mir.


Left: Numbered flags indicate the locations of the two POSA arrays and two other exposure sample experiments on the docking module.

Two of the payloads - the Passive Optical Samples Arrays (POSA-1 and 2) - were built like a traveling salesman's sample case. The astronauts took the cases outside the airlock and opened them so that one tray of samples faced Mir and the other, identical tray faced into space.


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The samples included thermal coatings like those that will be used in the ISS's radiators, metals, and other materials.
Web Links

Shuttle-Mir research Including space biology, materials sciences, and other fields.

Shuttle-Mir Increment 6 and Increment 7 activities and science described.

Microgravity Program Office at Marshall Space Flight Center

First phase of Shuttle-Mir science harvest to be discussed - Interim science results symposium planned - story posted Nov. 3

Space Travel Increases Some Health Risks - This week's Mir Science Results Symposium discusses changes in the human body resulting from space flight. (story posted Nov 4)

Living in space is tough, even for spaceships - Mir scientists discuss space exposure tests (this story)

"We tried to use samples that would be applicable to ISS," Kamenetzky explained. The samples were exposed from March 1996 through October 1997 when a later Space Shuttle mission returned them to Earth.

While the samples are still being analyzed, Kamenetzky said some changes were quickly obvious. Determining the sources can be a challenge because the various elements of Mir are up to 12 years old.

One of the sample trays showed traces of silicone-based contamination, a common problem in space since many gaskets and other materials are made of silicone plastics. She said that the deposits probably came from a new solar array stowed on the docking module that had not yet been deployed. The arrays were still folded against the side of the docking module.

The trays also had two surprises. Plate surfaces facing the solar array, and coated with Z93, a widely used thermal coating that will be applied to the ISS radiators, darkened. "Z93 is a good space-stable coating," Kamenetzky said. "The issue is contamination. There is not a good way to clean a surface once it is in orbit. Once it's contaminated, you have to replace it."

The change in radiative properties is a concern because ISS is expected to operate for up to 20 years. And in disassembling the sample cases, Kamenetzky said that the scientists found evidence of atomic oxygen erosion behind the trays in one case. Atomic oxygen - or AO - is the space-age equivalent of the universal solvent. AO is formed by sunlight splitting oxygen molecules into oxygen atoms that merrily combine with most chemicals they encounter - including a lot of spacecraft materials.

In this case, Kamenetzky said, AO apparently eroded silver coatings on nut plates that held the trays in place.

Another of the MEEP payloads was a sophisticated Optical Properties Monitor developed by AZ Technology of Huntsville. AZ President Don Wilkes explained that an active monitor is needed in space because passive samples - like those in the two POSA trays - can be altered simply by re-exposure to air when they return to Earth. Passive samples also do not tell when contamination happened.

"Mir offered a unique opportunity to study the environment around a large space station," Wilkes said.

The Optical Properties Monitor crammed several instruments into a volume about the size of a foot locker. Their focus was on a carousel containing various samples - mostly optical and thermal coatings - that were rotated under the instruments to measure how they changed with time in space once a week.

The OPM demonstrated the usefulness of an active monitor, as samples' optical properties see-sawed with varying atomic oxygen and ultraviolet radiation levels, and even recording one event that deposited a coating 38 nm thick on Dec. 16, 1997. Most of the coating baked off a few days later. Wilkes' team is also studying darkening of the multilayer insulation on the outside of the monitor case.

The Mir results conference concludes today with a review of biotechnology, combustion science, and materials sciences experiments.


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Microgravity Program Office at Marshall Space Flight Center

Life and Microgravity programmatic information from NASA headquarters.


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Author: Dave Dooling
Curator: Bryan Walls
NASA Official: John M. Horack