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Comment by jfoutz | Hacker News Reader

My guess was to refuel spy satellites. I imagine those sats are tough and can survive a long time. But when they get low on gas they can only do station keeping. If you can count of fuel coming, there's a lot more freedom to shift the track a half a degree as needed.

It may be all electronic surveillance. I guess, you can count on satellites not changing after they're launched, so the electronics package would be good for a couple years. come back, get a new package for new surveillance.

Just delivering fuel though, has a lot of value, and you could keep using the same platform for a long long time. Seems to fit better with many multi year missions.

I'm sure somebody knows. But, you know, not me.

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On-orbit satellite servicing and refueling has not been performed as of yet, but we are currently working on it: https://sspd.gsfc.nasa.gov/restore-l.html

Well, Restore-L looks to service satellites not designed for service. If you knew the X-37 was coming, and you knew it was a flying gas station, i'd bet that problem is far far easier. You don't have to take the target apart in space and put it back together. On the other hand, an easily accessible common connector seems like something we could have standardized on and implemented 15-20 years ago.

Again, i have no evidence of any of this. But it's my favorite pet theory.

Agreed. Most major satellites are now designed with potential reservicing in mind, at least to some degree.

> On-orbit satellite servicing and refueling has not been performed as of yet

Declassified on-orbit satellite servicing and refueling has not been performed as of yet. I wouldn't be shocked if the X-37 has refueled a NRO bird or two (or just simulated it) as a test.

While it's not entirely impossible that some classified mission has done some basic reservicing of a DoD bird, I know from working on Restore-L that we will be the first ever to do what we are doing, namely autonomous rendezvous and capture of another satellite in LEO and reservicing.

The X37 does not have the mechanical tools or sensors required to perform the kind of reservicing Restore-L is doing.

Wouldn't those that try to track satellites notice this?

Hubble fixes? Also it seems that quite a few shuttle missions were satellite servicing missions including relaunching sattlites that failed to get into the correct orbit: https://en.m.wikipedia.org/wiki/STS-49

Yeah, the SSPD (NASA office behind Restore-L) started with the Hubble reservicing missions

So I think what you meant was, unmanned servicing has not been performed yet?

Yeah, that's more correct

Refuelling sats won't ever be a thing. There is no real need. Any refuelling vehicle will need it's own propulsion/rcs system and a docking scheme. Once docked and/or latched onto the target ... job done. The refuelling vessel becomes the new orbital manoeuvring system for the depleted sat. Cost wise, that makes more sense than having a large tanker bouncing around between clients. With the switch to ion propulsion total fuel may also not be the limiting factor. Ion thrusters can become very inefficient and/or useless after years in space. Flying up and bolting on a new rig is simpler than trying to actually service/replace such parts.

Refueling satellites will absolutely be a thing :) Restore-L is going to do just that in 2020-2021, and do it autonomously to boot.

I work on Restore-L and believe me, there is a huge need for on-orbit satellite refueling and reservicing. The vast majority of satellites reach their end of life due to depletion of fuel, not due to electrical problems or sensor issues. This will be a huge business one day.

But will sats be refueled or will they simply have new service modules attached to them, bypassing all the tricky plumbing issues?

They will be refueled.

https://sspd.gsfc.nasa.gov/restore-l.html

I thought Restore-L was one of the missions who's funding was cut in the budget proposal. I'm partly funded by PACE, which is toast.

Turns out we are funded. PACE may be funded as well actually, but there's no clear indication either way. I was at the all-hands a few weeks ago where it seemed to be a bit more grim but lately there has been some talk of PACE surviving.

i don't think it's refueling anything. for one it has a pretty small payload, but more importantly it has a low orbit (~320km). there's some decent speculation here:

http://www.airspacemag.com/space/spaceplane-x-37-180957777/

tldr possibly a test bed for new smaller electronics packages designed for new smaller satellites

Eh, you're probably right. Those spy satellites have a very elliptical orbit. Probably only a few seconds when they could be close.

It sounds cool, and I can think of a few ways that could work, and it would be super useful. So I'm sticking with my personal conspiracy theory. But yeah, it's a low likelihood of being true.

I think you might be right on this one.

Recent US spy satellites such as PAN (https://en.wikipedia.org/wiki/USA-207) have started using much, much more aggressive manoeuvring strategies in order to do line-of-site microwave dish spying and spying on commercial sats.

This is unusual for "geostationary" satellites, as it wastes precious fuel. If there is no restriction on the amount of fuel used, they can stay up a lot longer than a normal satellite could.

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