Helium issue

[Esouder]

So it turns out the IMU is apparently sensitive to helium, which we use as a pressurant and maybe RCS propellant? In any case we will need to figure out what the deal is with this. We've made a little bit of noise about this to the rest of the team, so far, but nothing major.

1. What's the effect of helium on the device? Permanent disablement, something temporary, wonky readings?
2. What can we do about it?

[Esouder]

Had a brief chat with Dr. Mattison about this issue. He had a couple insights:

1. The IMU has some sort of internal seal that keeps the correct atmosphere inside of it (for MEMS reasons?), but it's not a perfect seal and helium can slowly diffuse through
2. Helium isn't likely to permanently break the IMU, but it might mess up the calibration and possibly make the device stop sending data if things go too far outside the range it's expecting. Most of the helium that might get in should be able to diffuse out by letting it sit for a few weeks.
3. We should be safe from helium as long as we're not venting or leaking helium directly into where the IMU is stored. Conformal coating or anything isn't super useful, as it probably isn't any better of a seal than what's inside the IMU already. It's more a matter of being careful, but Dr. Mattison suggests that just being 'around' the area of the rocket while we're, for instance, venting helium during an abort should be manageable.

Also in a suggestion from him, and something that we'd been thinking about for a little bit is that we don't really have a backup for the IMU. (or the GPS for that matter). I'm going to break this out into a separate issue.

[misprit7]

Obviously only one was planned for communication and it probably doesn't make sense to send both up, but just an FYI.

[Esouder]

Deleted a comment, it had Pablo's personal phone and address on it. It was an invoice that showed that we actually have two IMUs and we don't really need a backup in that case.