Isolation

Today had an unexpected hiccup–we found a devil amongst the details.  In the morning, Jane, Alan, and Zach continued with the final harnessing.  Steve completed the battery boxes.  I worked on a bit of thermal analysis before installing the rest of the shield pieces with Alan.

One completed battery box.

After lunch, though, Jane was taking a look at the shields and the cryostat-side harness to make sure everything was fitting right.  When she checked with a multimeter, though, she found an electrical connection between the cryostat and the gondola!  To minimize electrical noise, the detector-cable-card cage chain is electrically isolated from nonessential parts of the gondola, typically with insulating spacers.  Since there is precious little play in the shields or the detectors, we were fretting about how to find and remove the electrical contact.

By this point the whole group was taking a look at things, and it got worse–the card cages themselves weren’t isolated from the gondola!  So, potentially we had problems on both ends of the chain.  On closer inspection, we found that the metal card cages were directly touching to the metal rails holding them.  We had to interpose an insulating layer to give us the isolation we needed.  After brainstorming about cutting mylar film or using Kapton tape to insulate the rails, we asked ourselves why we didn’t have this problem in the New Mexico flight–the isolation check was part of our preflight checklist.  Eventually, we figured out that we had omitted half of the fiberglass washers surrounding the bolts which attach the rails to the card cages!  I had simply misremembered how they were mounted.

Those little washers are what we forgot.

Fixing that oversight took a couple of hours and involved removing all the card cages from the ebay (again!).  The good news was that adding the washers isolated the cryostat from the shields as well, so the shields don’t have to be moved.  We’re back up and running as we expected again.  As our old family saying goes, if you don’t have it in your head, you’ve got it in your feet!  It does underline the importance of regular, step-by-step testing.

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4 responses to “Isolation

  1. Heyah! Wow, I didn’t know this blog was here. This is so awesome. I’m here in Alice, any chance I could come out when you do the launch and take pictures? Thank you so much for this blog!

    • Hi Anne! The launches take place on the airport runway, so access is strictly controlled by the federal police. There are ID requirements for the few of our personnel who will be allowed to go airside to do preflight checks. However, I don’t know of any reason one couldn’t watch from outside the fence! Watch this space for launch news, and I’m glad you’re enjoying the blog!

  2. Your photos are amazing. I love seeing this stuff; the science is beautiful. If we could watch from the fence, that would be cool – we have good camera lenses. And mostly I just want to see the big balloon. Total sucker for that sort of thing. :)

    My husband (also an amateur photographer) was psyched that you were in town when I told him today, and said he’d take time off work to go take photos if you launched on a weekday. Do you have an estimate on when you’re going to give it a try yet?

    • Thanks, Anne! Launch attempts for the first group, TIGRE, could start as early as next week. The catch is that it can take weeks of trying before the surface winds are low enough to inflate the balloon. We’ll be starting work every day at 2 or 3 am, aiming for a launch just after sunrise. Launch scrubs can and do happen right up until inflation begins. I’ll pass on what I know here, though!