First Spacewalk Finished!

By Julianne Dalcanton | May 14, 2009 11:34 am

WFPC2 has been taken out of Hubble. The new super-fantastic imaging camera WFC3 is in! And better yet, it passed the “liveness test” (i.e. the patient is awake and talking to the nurses).

Even more importantly, the new data system is in, and also live! The need to repair this system was why they delayed the mission last November, so congrats to the engineering team for coming up with a successful fix in such short order. If this repair hadn’t worked, then there would have been no redundancy in getting data from Hubble back down to earth. There’s still lots of testing to be done (i.e. passing the liveness test isn’t the same thing as “working perfectly”), but so far, things look good.

Apparently, the repairs didn’t quite go as expected. I have previously described Hubble as the equivalent of having a 20 year old VW in space. If you’ve ever worked on old Beetles, you know that while they’re simple to repair in principle, you can spend half your time just trying to free rusty bolts. Turned out Hubble had the same problem, and the astronauts had a devil of a time freeing some of the bolts on WFPC2. They tried several tools (“Yo John! Get me a bigger wrench!”) and eventually had to go over the torque limits. But, whatever works!

Really great news all around.

  • Olli

    It certainly is an exciting week for us astronomers. With Planck and Herschel on their way, things seem to go pretty well so far.

  • Pingback: Ruimtewandeling 1: WFPC2 eruit, WFPC3 erin!bijAstroblogs()

  • Joshua Zelinsky

    So what would make the bolts in this case have trouble? There’s not much oxygen since it is in a vacuum so nothing should be rusting.


    Hubble is getting a new pair of “retinas”!

  • Julianne

    No idea — definitely not rust! I’m sure there will be a few engineering teams trying to understand it for the future.

  • joe


    This is from NASA’s Long Duration Exposure Facility research page about metal exposure in low-Earth orbit (LEO): “The effects of LEO exposure on metals includes meteoroid&debris impacts, cosmic rays, solar particles, solar radiation, thermal cycling, oxidation, and contamination.”

    Also partly relevant, from the Materials summary: “Silver-plated nuts from the intercostal clips showed no erosion or degradation of the protective silver coating. However, the nuts were tarnished, with the amount and color of the tarnish varying over each nut and between nuts. The tarnish consisted of silicone and silica/silicates from the decomposition of silicone and of amide material which may have originated from urethane paints. ”

    I don’t know what the A-latch bolt was made of, but thermal cycling alone could account for the freeze-up. The temperature diff between light and dark is hundreds of degrees F, and the bolt has been swelling and shrinking through that diff for 16 years. Or, the metal of the bolt could have reacted chemically with the metal of the threads it mated to. Or, some combination of both.

    I have a thirteen year-old car, and in the winter, when it is only 60 degrees lower than now (70F), I can’t turn the bolts on the battery terminal cables without an extension to the ratchet – plus my gloves aren’t pressurized and my feet aren’t strapped to a floating steel plate to keep me from flipping cartwheels when I apply the force. And the Earth isn’t screaming by at 17k/M/H, and I won’t die if I rip my coat. And I won’t ruin a billion dollar investment if I screw up.

    I watched the bolt sequence on NASA TV live, and I could tell it was extremely tense up there, and in MC. At one point, it will be in the transcript, a ground controller interrupted the astronaut with the wratchet and said the phrase, “game-ending activity.” He referred to the action of forcing the bolt without the torque limiter. The cap-com actually said if they broke the bolt, they would leave the old camera in place — no new wide field camera. That poor astronaut asked for advice about how to feel, with his fingers and arms, how much muscle equaled 57 pounds of torque three times, and the ground had nothing for him but, “give it a go.” Later they reassured him that he wouldn’t harm the mission, but veterans of air-to-ground comms know when the conversation is not about what it sounds like it is about (see Pete Conrad’s Apollo XII launch transcript).

    That’s the NASA we should be reading about on science page 1 – there is real drama in these missions, and real, exceptional talent and skill and fortitude. But just watch – some journalist will spin a story about how NASA took an hour to remove a bolt (instead of how ingenuity and engineering excellence saved the science).

  • Ben

    I have no direct knowledge of this bolt (or any bolt on Hubble) but as Joe says, thermal cycling and galvanic reactions are reasons that could increase stiction of a bolt. Remember that you can’t just put grease or anti-seize on a joint, as we would on the ground, because conventional lubricating compounds will outgas in space.

    Apparently, it’s a seven foot long bolt. That means a lot of the applied torque is likely taken up by torsion in the shaft of the bolt.

    Give journalists some credit. There may be some columnist somewhere who will write something dumb about this, but most journalists covering the mission, and most people paying even a small bit of attention, are impressed by the spectacle and skill of a maintenance spacewalk, and it shows in the news coverage.

  • Tod R. Lauer

    It is worth noting that WFPC1, which is mechanically almost identical to WFPC2, and lived in the same spot, came out with no difficulty after 3.75 years. They will get the instrument back and have a look at it. In any case, I remain in awe of what those guys can do in those suits and under those conditions. We owe them an awful lot…

  • Eric M

    Assuming the bolt is plated steel and the chassis aluminum, then the differential expansion is 11 ppm / degC. If the threads are 1mm wide and the temp range is 100 degC, the relative movement will be 1.1 um – not much, but not zero.

    The problem is comes from the alumina layer on the chassis. Under many thermal cycles, the hard crystals will eat into the soft underlying metal, roughening the interface. The effect is small, but it happens simultaneously along the entire length of the bolt, resulting in a stuck fastener.

  • Hiranya

    Wonderful news!

  • astropixie

    the new star trek was entertaining for a couple hours, but this mission to hubble has produced excitement for DAYS already, with no sign of slowing until the full mission is over! the folks up there are my favorite superheroes.

  • Peter Erwin

    I have previously described Hubble as the equivalent of having a 20 year old VW in space. If you’ve ever worked on old Beetles, you know that while they’re simple to repair in principle, you can spend half your time just trying to free rusty bolts.

    Appropriately enough, Andrew Feustel, the astronaut who finally got the bolt out, once worked as an auto mechanic, restoring old Jaguars.

    (Part of the fun of watching the live TV feed of the spacewalk was hearing the occasional bits of non-work-related conversation: “Hey, there’s big city down below.” “We should be over Australia, so that’s probably Sydney or Brisbane.” “Cool!”)

  • Joe

    The NASA video of what the control room looked like during the bolt sequence on wide field 2 removal:
    click on “Relief in the Control Room.”

    (NB., the passing around of a bottle of what appear to be antacid tablets, and a controller eagerly pouring himself one. :))


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