Latch blamed for Webb vibration test issue


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A latch that hadn’t closed properly has been identified as the cause of the anomaly that halted vibration testing of the James Webb Space Telescope in December.

At the committee meeting, Smith said the problem was tracked down to a latch designed to hold in place one of the wings of JWST’s primary mirror, which consists of 18 hexagonal segments. Those wings are folded into place to fit within the payload fairing of the Ariane 5 that will launch JWST, then deployed into place once in space. The latch, he said, consists of two plates with serrated teeth a few millimeters in size. “The thought is that the teeth, when they closed it, they didn’t quite seat,” he said. “So during the vibe [test], the teeth clapped together on the order of a millimeter or two, and that was what made the noise.”

Engineers were able to replicate the noise by placing the plates slightly out of alignment in the lab and subjecting them to similar vibrations, giving them confidence that was the cause of the anomaly.

I love how the Webb program manager also says that Webb is “on budget and on schedule.” That claim could only be true if you make believe that the budget was always $9 billion and the launch date was always supposed to be 2018 instead of the original $1 billion and 2011 launch date.

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4 comments

  • diane wilson

    Government procurement procedures encourage underbidding, cost overruns, and over-optimistic schedules. In that sense, JWST has met its objectives. If they’d told anything like the truth, it would never have been built. SLS is also on track to meet its schedule delay and cost overrun commitments.

    What makes JWST worth continuing is that nothing like it has never been built before, and it will provide capabilities that we’ve never had before. We didn’t know how to build JWST until we built it. That’s the real difference between JWST and SLS. SLS is more of the same, old, same-old, built with scrapped parts. There’s no justification for it.

  • LocalFluff

    @diane wilson
    I agree. Astronomers will always require high risk high cost investments in unique instruments. That’s what is needed to challenge current theories. And there cannot be much economies of scale or such applied, because each major space telescope has to be a unique being of its time in terms of the technology available and the science questions asked. Launching a copy of Hubble Space telescope today would be a bad investment.

    Space based astrophysics today reminds me about some myths of the ancient world. Where there existed one and only one item which was magically superior in its class. Be it a horse or a hammer or a spear. Or Woden’s sacrificed eye at the bottom of the well of knowledge.

    It’s hard to have efficient competition when designing unique gadgets. The buyer is pretty much stuck with the the only one who can do it, and there will be monopolistic pricing. The only limit is where other branches within the same budget complain effectively. And as consuming the JWST has been, it has had strong support, as far as I can tell. And there are Nobel prizes to be discovered beyond the horizon there. Very prestigious. Big motivator.

  • wayne

    diane wilson-
    Good stuff.

    I believe the phrase we’re looking for is, “Good enough for Government work.”

  • PeterF

    Wayne-
    The phrase “Good enough for Government work.” became popular during the United States Civil war. It meant that any product that met US government specs was of the highest quality. Good enough for government work was a statement of pride a manufacturer could make if their product could be said to be of the highest quality anywhere in the world.
    It only became a shameful indictment of shoddy work when the “New Deal’ socialists of the 30s changed the meaning.

    Anyway, I heard that there was a thirty meter telescope looking for a new location. I wonder if it could be attached to a Bigelow habitat and placed in MEO? The engineering problems can be solved. Its only rocket science after all. Not difficult like “climate science”

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