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mcountryman

I had to picture someone opening a window and throwing it into orbit haha

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It's actually pretty cool. They have a space torpedo launcher:

https://en.wikipedia.org/wiki/Nanoracks_CubeSat_Deployer#/me...

What I haven't figured out is how they get the sats far enough away from the ISS orbit with only one push.

Relativity. At the moments before launch, the ISS and satellite are moving at the same speed. The launch gives extra velocity (positive delta-v??) which ever so slightly due to mass differences gives a tiny push against the ISS. So the satellite continues to pull away with its increase in velocity. See Newton's first law of motion.

However, after launch, the small satellite usually has no ability to course correct, and its orbit slowly decays to friction with the thin atmosphere. Meanwhile, ISS continues to course correct.

A minor nitpick but it's not relativity (as in Einstein's relativity,) it's just relative velocity.

The launch imparts velocity on the satellite but that velocity difference doesn't mean it flies in formation with the ISS a few hundred meters or a few kilometers apart. If they were launched in the direction the ISS is going (positive delta-v), that extra velocity means a higher orbit; if they're launched backwards (negative delta-v), it'll be a lower orbit. If it's launched sideways, it's either higher, lower, or same depending on delta-v but a different inclination (angle to the equator.) I couldn't quickly find where exactly the deployer is located but I'm guessing it's aft because it's the same module the ISS launches it's trash out of now (the Bishop airlock,) and I'm guessing they wouldn't launch anything in a fast decaying slightly higher orbit just to get hit by it a few cycles later.

The whole thing it's pretty cool, and it's quite new, it was installed only 3 months ago.

Wouldn’t sideways launch give an orbit that sometimes overlap with the original orbit or is there some maths that makes sure that never happens?

Yes, twice every cycle, just at an angle, assuming all other orbital parameters remain the same. That's also why no one sane would ever do it.

Are we assuming that the satellite is going to stay in the same orbit? The atmo drag will constantly be applying pressure on the cubesat so that its orbit will always being decaying.

I don't think atmospheric drag at 400km is large enough to decay the orbit by half the vertical height of the ISS in half a cycle, though. The ISS itself with it's comparatively huge surface area does orbital reboosts only about once a month or so.[1] Also, my original comment was quite simplistic - a launch with a negative delta-v with no other course correction would result in an elliptic orbit with the same apogee but a lower perigee (and the other way around with a positive delta-v.) Orbits are tricky that way.

[1] https://space.stackexchange.com/questions/9087/how-often-doe...

I assume the two confounding factors are (a) the satellite should be moving relative to the ISS at the speed it was launched, so it is going to take a while to come back around and (b) when it does come back around, it should only be going as fast as you launched it, so it shouldn't be nearly as dangerous as the typical orbital collision.

[Huh, if the cubesats are launched at 90 mph from the ISS (the speed of a fastball), it only takes ~12 days for them to come back around; that's quite a bit faster than I would have guessed, but still probably long enough for orbital decay and ISS adjustments to put them out of line.]

My understanding is that a transfer orbit requires two thrusts and otherwise, with only one push, all you've done is make for an eccentric orbit that still intersects your original one.

Again, I'm ignorant of these things but it seems like depending on atmospheric drag to provide for the additional correction is risking a lot.

It is, but the intersection point doesn't track the station. When you push an object retrograde (i.e. throw it out the back), two important things happen. One, you make it spend more time closer to Earth than it was spending before, meaning extra drag, which lowers that orbit's closest point to your orbit, ever so slightly. Two, objects in lower orbits move faster, contributing to drag, but more importantly, meaning that once you do one full orbit, the object will be somewhere else. It may still roughly intersect your orbit, but you won't be there when it does. Combining these two factors, you can give your object enough of a push that the two orbits stop intersecting before there's any risk of collision.

The eccentric orbit is the transfer orbit but yes, you need two thrusts to go from one circular orbit to another.

If you give it a few cm/s velocity, the separation distance grows over time.

> What I haven't figured out is how they get the sats far enough away from the ISS orbit with only one push.

What I don't understand here is how do they avoid the satellite hitting back the ISS? Once they are separated and non-propulsed, both orbits are elliptical with at least one point of intersection, and stay like that forever. If they have different period, it seems that the ISS and the cubesat might become arbitrarily closer in the future.

There are even manual deployments https://youtu.be/-hutA7In7GA

It's not that far off from the truth

Great, so they're essentially littering. I hope the Space Force Police pull them over to issue a citation. At least, this will burn up in the atmo rather than in a water system, or do they turn themselves into microparticles ultimately landing in the oceans? They really are litter

It's low orbit ~400km, the lifetime of these things is measured in weeks or months.

And the Earth picks up about 40,000 tons of space dust per year.

We've got a lot of work to do before our space "littering" can even dream of matching that level... and that's just a coincidental level that nature happens to have, not some sort of threshold for "real harm", which I'd guess to be multiple orders of magnitude higher.

So do McDonalds wrappers is my point.

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