Throughout my career, including with the Navy and NASA, we knew the importance of lubrication, declares Heidemarie Stefanyshyn-Piper. So this astronaut, engineer and U.S. Navy captain says she jumped at the opportunity to perform the ultimate lube job – lubricating the International Space Station.
Piper first flew to space in September 2006 on the shuttle Atlantis, to help build the International Space Station. During that 12-day trip she helped to mount an array of solar panels on the port side of the ISS to supply electricity for the stations live-in crew. These solar panels have a wingspan of 240 feet, and hinge on a Solar Alpha Rotary Joint, a 10-foot wide joint that pivots to keep the solar panels aimed at the sun as the ISS orbits the Earth. The panels also recharge the batteries that take over when the ISS is in total darkness.
In her May 18 keynote address to the Society of Tribologists & Lubrication Engineers annual meeting in Dallas, Piper recalled being selected as a NASA astronaut in 1996. She isnt an aviator, as many recruits in the space program are, and she lacked an aviators call sign. So her NASA colleagues gave her one: Xena, the Warrior Princess. She would go on to log more than 27 days in space, and complete five space walks totaling almost 34 hours.
On that first trip to space, watching as the pre-assembled solar panels unfurled, Piper and her fellow astronauts observed that some stuck (a phenomenon called stiction), but otherwise all seemed well. Nine months later, a different crew of astronauts flew in the Atlantis to deliver a second array of solar panels to the ISS, upping its power to 110 kilowatts. These also were coupled to a SARJ, this time at the starboard side.
Ideally, the combined solar arrays should have provided enough power to allow the ISS to double the size of its onboard crew. But by September 2007, it was evident that something had gone wrong. The panels were not delivering the expected power, and were not tracking as they should. There were higher current draws that were not normal – that was actually a bad thing, Piper said. Thats when NASA decided to conduct a root-cause analysis, to pinpoint the roots of the failure.
It helped, she told the STLE audience, that this was during an era when the U.S. space shuttle program was still active; they havent flown since 2011. One big advantage of the shuttle was that it had up-mass capability, and down-mass capability. That is, you could bring back material from orbit and do failure analysis.
In November, subsequent spacewalks confirmed the damage, and found that one of the SARJ had a damaged race-ring holding 22 bearings, Piper related. Back on Earth and hearing about the trouble, one of my first thoughts was, On which side was the ring that held the damage? It turned out that the fault was in the starboard side of the array, not the port side, which I had installed in 2006.
For the next year, a team of NASA investigators picked over the data, samples and systems, trying to figure out what had happened, and how to restore function to the damaged part. Everything involving space travel is done with extreme deliberateness, and at great cost, so this was actually a very compressed timeline, Piper observed. And as late as July 2008, they were still not finished with the investigation phase.
NASA engineers had narrowed the problem down from hundreds of possibilities to just one critical flaw: insufficient lubrication. The lubrication system for the starboard SARJ had failed on orbit, causing its race-rings hardened surfaces to begin to break up. The 12 trundle bearing assemblies that hold the two halves of the joint together were pressing too hard against one side of the joint, damaging the steel and grinding off metal filings that could make things worse.
The SARJs trundle bearings were designed to be replaceable, so that task would have been easy to accomplish. However, the entire 10 foot diameter race-ring was not expected to ever need repairs. Nobody had thought a hardened surface would grind on orbit, she pointed out. It also turned out that the bearing assembly contained a lot of debris, including very small particles. Trouble is, you cant take a vacuum cleaner out in space and vacuum up the dust. It doesnt work that way in space.
In November 2008, the space shuttle Endeavor took off on Mission STS-126, with Piper again on board. The plan was for Piper and her co-spacewalkers Steve Bowen and Shane Kimbrough to go out, remove the cover on the damaged SARJ, lift out the bearing assembly and clean off the metal shavings, then grease and replace some of the trundle bearings before finally replacing the cover. The SARJ then would be partly rotated, and the entire painstaking process repeated on the remaining bearings over two more spacewalks. For good measure, the port-side SARJ would get lubricated, too.
The mission had been preceded by months of training, practice and experimentation. Applying grease in space was relatively unexplored territory. First, NASA needed to create a tool to direct the grease exactly where it was needed and in exact quantities, regardless of weightlessness. It was decided that a modified space caulk gun would suit to handle the viscous material. The grease itself was Braycote 602, an inert grease from Castrol that is formulated for the extreme temperatures and vacuum conditions of deep space.
Another unknown was whether excess grease could be lifted off with a scraper. Of course, on the ground, grease sticks to a scraper – but this was going to be in space, Piper reminded. At each preparatory step, it became more clear that the task wasnt going to be business-as-usual. It was going to be like caulking a bathroom, but one where youre wearing ski gloves and a helmet, and floating in space.
Fast-changing light conditions would be another challenge. The orbital speed of the ISS is 17,000 miles an hour, and the spacewalks last almost seven hours. It takes one-and-a-half hours to orbit the earth, so we would be working in daylight or night for half of that time, back and forth. Temperatures rise and plunge along with the light levels, as well.
All in all, the astronauts would be handling a seemingly normal job in very abnormal conditions. It was going to be very different from working in your shirt-sleeves on the ground, with easy access to everything. So we did our training in a swimming pool. Even so, you still have some buoyancy and gravity – and things would be completely different in space, she said.
Our trainers also kept drilling into us: Dont get grease on anything – it leaves a dark spot. But, Piper stressed, what we did find is that in space, grease does get everywhere no matter how careful you try to be.
Sometimes, zero-gravity helps, and sometimes it doesnt. Offgassing helped the grease to exit the gun. But that same issue led to the infamous lost tool bag, she added ruefully.
It happened during the first spacewalk of the repair mission, as she worked alongside Steve Bowen: I reached into the tool bag and saw grease on my glove. With the words dont get grease on anything! ringing in her ears, Piper stared at the blob of grease staining her white glove, and realized it already had spread inside the bag. Trying to clean it, she let go – and realized too late that the bag was untethered and drifting away. Inside were two precious grease guns, scrapers, several wipes and some tool caddies.
As I watched the bag float away, I had a strong impulse to jump and grab it, but I knew that was a bad idea soon as I had it. Far more important was to regroup. I just said, Oh, no! and went on to call ground control, told them what had happened, and pushed on with the mission. While half of our grease guns went floating off in space. Piper finished the spacewalk by sharing Bowens tool bag; the two also improvised by using rags to wipe the grease into the bearings. Three more spacewalks finished the job, and the STS-126 astronauts went home.
Nine months later, so did the errant tool bag and its contents. They de-orbited and burned up in the Earths atmosphere.
Still, after the success of Mission STS-126, the International Space Station could rotate the SARJ and no other repairs were needed. Remarked Piper, Thats not to say that the solar array is operating like new. Its not, its refurbished – but it is giving full service.
Theres a lesson in this story, Piper concluded: Things will fail, so youd better find ways to deal with that.