Astronaut Highlights Greases Key Role in Space


DALLAS – Lubrication plays a key role in critical components aboard the International Space Station, and the space environment provides unique challenges, a U.S. Navy captain and former astronaut told the STLE 2015 annual meeting here.

NASA astronauts used grease in 2008 to lubricate a vital race ring component on the station, to reduce structural vibrations and drive motor current, Capt. Heidemarie M. Stefanshyn-Piper told the Society of Tribologists and Lubrication Engineers during her May 18 keynote speech, Historys Ultimate Lube Job: Lubricating the International Space Station.

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Selected as an astronaut by the U.S. National Aeronautics and Space Administration in 1996, Stefanshyn-Piper reported to the Johnson Space Center in Houston. She flew into space twice: Flight STS-115 on the space shuttle Atlantis in September 2006 and STS-126 on the space shuttle Endeavour in November 2008, logging 27 days and 15 hours in space.

The station runs on solar power gathered by eight large solar panels. To maximize efficiency, the panels must be constantly oriented toward the sun, so in 2006 and 2007 astronauts installed and activated two solar alpha rotary joint (SARJ) elements – one on the port side, the other on the starboard – that accomplish this by rotating 360 degrees on a 24-hour schedule.

A solar alpha rotary joint has two large main rings – a stationary inboard ring and an outboard ring that fits inside it and rotates. Trundle bearing assemblies on the inboard ring help reduce friction by contacting the race of the outboard ring and rolling against it.

Within a few months of the installation, astronauts on the space station noticed a lot of vibration coming from the starboard SARJ whenever it was running. Also, ground controllers could tell from data coming back, from the telemetry, there were higher current draws that were not normal, and were not expected – that was actually a bad thing.

Inspection of that SARJ revealed damage to the outer steel race with large quantities of magnetized debris present on both the race and trundle bearing assemblies.

A root cause investigation was launched. Stefanshyn-Piper was on flight STS-126, which was scheduled to resupply the space station in November 2008. So over the next year, the investigation team went into everything from what caused problem, why did one side have it, and the other side not have it, she said.

She recalled that NASA decided astronauts would need to replace all the trundle bearing assemblies on the starboard SARJ and then grease the bearing surfaces on both SARJs. She said one nuance not anticipated when replacing trundle bearings was the presence of debris. The debris was just a fine particle, because all these trundle bearings were literally grinding the metal surface away. You cant just vacuum dust in space, it doesnt work that way.

Grease proved handy for removing the debris, as everything sticks to grease, she said. When the SARJ was first designed in the 1990s, she noted, there wasnt a lot of knowledge on what grease does in a space environment. Luckily by 2007, there was more knowledge gained on grease, so it was determined that a Braycote compound would survive the environment, she said. So now we have a material, how do we get it up there?

Manufactured by Castrol, the Braycote line of high vacuum greases was developed to cover a wide range of temperature and chemical environments.

She noted that because of the Columbia shuttle accident in 2003, NASA had already developed what she liked to call space caulk guns to distribute material out of a tube, as part of repair procedures for the space shuttles wings. Using those tools for grease required modifying them to using grease. NASA also had to develop other tools for the job, such as a scraper, to be sure the tools would survive in the space environment. She pointed out also that crew members are working outside – it would be akin to caulking your bathroom wearing ski gloves, and putting a helmet over your head, and floating around.

Extensive crew training was also important in using the grease tools in space, including practice in a pool to help simulate the space environment. All the designs and preparation came together, and flight STS-126 launched on Nov. 14, 2008.

Over the next two weeks, three astronauts conducted four space walks, during which they cleaned and lubricated the starboard SARJ and replaced its trundle bearing assemblies.

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