There are orifice equations, but guessing the size of the orifice(s) is the black art. Systems are almost never as gas tight as we think they are. We once fretted about overpressure in a box once; the first time the box was purged and "sealed" it went back to ambient pressure in under a minute. If your box is at all leaky, it's likely to have dumped the majority of the pressure before you even release the satellite from its launch vehicle.

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Yeah, I don't really worry about the overpressure in the box, I'm sure that it is pretty "leaky" and it will dump the air pretty quick; but I still need to do a venting analysis to include it in the report as a requirement from the client.

I'm trying to guess what this analysis would turn up. Is it to determine excess forces on the satellite or the effect on orbital velocity? Is it to include the effects of ionizing radiation on the escaping gas and the effect on the electronics or overall electrical charge on the satellite?

Again, there are orifice, crack gas calculators on the web: https://www.lmnoeng.com/Gas/GasLeakRate.php

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it'll vent well before orbit !

There are FEA tools for doing this ... decompression analysis.

On the face of it it seems a "pointless" anlaysis ... the question should be easily with a picture and an opinion "how can this thing support internal pressure ?"

There is a minor technical question about air currents as the payload compartment adjusts to outside pressure. I'd've thought this was more a question for the payload compartment, where your involvement would be to provide a model of your payload component then they run the fully assembled payload compartment.

There's a way to punt the question back ... what is the pressure profile (over time) in the payload compartment ?

Possibly you could show that your box cannot support even a small pressure difference, like 0.1psi, with the surrounding compartment ?
But I think the real question is, again from the payload compartment, what loads does your box experience as the rocket climbs (and depressurises) ? The payload compartment is depressurising, not your box. This will create loads on your box, probably peanuts, but this is a box that needs ticking.

It would be interesting to get a previous analysis report covering this requirement.

another day in paradise, or is paradise one day closer ?

The various payload designs we've come up with don't even have boxes for the electronics; after all, what would they actually do, aside from adding to the weight? The only functional utility might be to keep fingers out, but we're supposed to be in a clean room environment anyway, so ought not be too many fingers poking about. In our case, we have optics and sensors, so the quicker the satellite vents, the better, and the sooner bakeout can be completed.

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The pressure profile in the payload compartment/fairing is the one from Ariane 6 launcher [https://www.arianespace.com/wp-content/uploads/202...] chapter 3.2.8. I tried to find a previous analysis report but I could not find anything.

I think I will do a static pressure analysis on the box based on maximum depressurization rate (considering that value times a safety factor, the pressure difference between inside and outside of the box at a certain point in time), this should tell me if the box will withstand the pressure drop. For the venting I will calculate to see if there is any possibility of the flow being obstructed/chocked, based on A. Mironer, "Venting of Space Shuttle Payloads)", article.

that is, IMHO, amazing. "surely" the pressure distribution with the payload compartment varies with the payload ?

yeah, I get what you're trying to show, but I still think a picture of your "leaky" box should be enough.

I'd love to see a previous report. How do you even set up this analysis ? I know something of decompression analysis, a pressurised fuselage venting into a lower pressure volume. I looked at your link quickly ... section 3.2.8 seems applicable ? But that "only" says pressure in the payload volume over time. If the pressure falls by 0.1bar in 5 seconds, what does that mean to your "leaky" box ??

and IR ... I'm using "box" in it's non-shape specific sense ... I could've said "widget".

another day in paradise, or is paradise one day closer ?

maybe it's enough to apply 0.1bar (or 2psi) to each face of your "box", as a conservative estimate ?

another day in paradise, or is paradise one day closer ?

Thoughts...

I would suspect that micro vent holes... covered/backed by metallic foams to bleed-off EE energy to the metal body structure... could be built into satellite base-mounts that would vent most/all of interior gasses during launch. Then this system of metallic foams and micro-holes would prevent any arcing/static/corona from entering the satellite body... much like fuel vent flash/explosion suppression grids do. AND this would also allow predictable long-term venting of ANY gasses/ions on a discreetly-aligned 'thrust' orientation.

Regards, Wil Taylor
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An interesting video dealing with, among other things, venting of air in a satellite payload that is far more delicate than I would expect a typical electronic box would be: https://youtu.be/Pu97IiO_yDI?t=558