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Comment by marktangotango | Hacker News Reader

That's interesting, also a possible insight into what the X-37b mission is. Retrieving payloads, but what payloads?

The X-37B is much smaller than the shuttle (it was originally intended to fit in the shuttle's payload bay). It physically can't retrieve satellites of any significant size.

I'm really curious, do we have any idea whatsoever what the X-37 is being used for?

A big advantage of space planes is the ability to change orbit very quickly, could be used for reconnoissance or as a weapons delivery vehicle.

Only if they're in low enough orbits to make use of atmospheric drag. Such orbits decay quickly if the vehicle does not have boost capacity. Given the extremely long missions this thing flies - several missions over 700 days - it seems unlikely for it to make use of atmospheric drag. It might do so when in a highly elliptical orbit but even then it needs to perform a burn at apogee to keep it from re-entering before long.

There is value from the optionality of having a capability even if it isn’t regularly used.

That highly depends on who 'we' is.

Anybody really in the know is definitely not going to spill the beans. The payload is very small, the stated reasons it flew its missions are 'testbed' for various technologies. Which may well be all there is to it.

The links to the specific missions on the wikipedia page have some expert conjecture, based on observations by amateur skywatchers, so we have a good idea that it's being used to launch military surveillance and communications satellites, as well as being used to test new hardware. Which is all rather broad and generic, but if it were aliens, it's not like they'd tell us anyway.

Even if it were actually confirmed that OTV-1 launched a military surveillance satellite, we still wouldn't know how good it is at that other than some hard limits due to physics (mirror size and atmospheric interference).

https://www.youtube.com/watch?v=EQN4hId5psg

"Everything We Know About The US Air Force's Secret Space Plane - The X-37B" by Scott Manley

Obviously total speculation, but it's the right size to be a flying speed-of-light weapon platform. USAF have been interested in such tech for a long time. Some fun links:

- Directed Energy Directorate home page during the years 1999–2006: https://web.archive.org/web/20060831035044/http://www.de.afr...

- Directed Energy Directorate home page during the years 2009–2016: https://web.archive.org/web/20160428181404/http://www.kirtla...

- LASER Effects Test Facility fact sheet from 2002 showing a 50-kilowatt CO² LASER setting a test target on fire: https://web.archive.org/web/20070315131556/http://www.de.afr...

It seems small for any sort of directed energy weapon with a useful power output. There wouldn't be enough capacity for a big generator and heat radiators.

Right, short of a small reactor onboard, it seems unlikely to be able to store the energy or power densities required while in flight. Obviously there may be some unknown breakthrough that allows it...but I'm skeptical.

One common theory is it's being used to do close-up inspections of other countries' satellites. Bonus points if you can attach a magnetic limpet mine to them for future usage.

Wouldn't the mass change cause some kind of detectable change in the satellite's trajectory over time?

I don't think anything particularly detectable; they're so outweighed by the planet they're orbiting that the barycenter doesn't move measurably.

(To be clear, I'd imagine they're only doing the inspection thing right now, but I do suspect they're at least tinkering with on-orbit capture, refueling, disabling etc. with an arm.)

What if your satellite did some more manoeuvres for station keeping, wouldn't you notice the mass difference then?

Maybe. The mass of an explosive could be pretty small compared to the mass of a satellite. And even if you do notice that your (secret military) satellite is slightly heavier than the spec says, what would you do about it?

How expensive is it to attach a couple of space-rated external cameras to a modern satellite? This wouldn’t eliminate the threat but it would certainly remove the uncertainty. Presumably once you recognized the threat, then defending against it couldn’t be the hardest problem to solve.

It would not need to be very big mine though would it? A grenade would probably be just fine to eliminate the satellite from being useful. Something that small means it could carry a lot of ammo

Just something to put the satellite in a spin that is beyond what attitude control can recover from. Could be really tiny.

High energy elementary particle? ;)

> A grenade would probably be just fine to eliminate the satellite from being useful

Sure, but if You are lucky or smart enough, to use it close enough.

For example Soviet satellite-interceptors spent few years and made few attempts (each time with bigger explosive), before achieve enough cloud density .

It carries a negotiating table. Our telepresence on one side, the aliens['] on the other.

Or black box, so they will spend millennia to understand, what we want to say :)))))

Or... freak out and ATTACK!

What if the X37B was the imaging satellite?

Why would they build it to retrieve itself? That's very meta

Don't you get it. Its shuttles retrieving other shuttles all the way up!

Russian nesting shuttles?

This may be changing with rapid extension of satellite size towards the small end of the spectrum. Small size is now significant.

For example, a radar imaging constellation might consist of multiple transmit/receive satellites, each of which could be quite small (say, 1 - 5 cu. ft.). The X37B could accommodate that - especially after it snipped the solar panels off.

If that is its mission the answer is "small payloads" since the carrying capacity of the thing would be quite limited with its 2.1 x 1.2 m [1] payload bay. That leaves little room for the grappling arm or other mechanism needed to pluck a satellite out of its orbit.

I suspect it does not retrieve payloads but takes them up and down again. Which payloads? Good question. Experimental sensors meant for inclusion in next-generation reconnaissance satellites maybe?

[1] https://web.archive.org/web/20150321121050/http://www.boeing...

https://youtu.be/KZX1YCmzHEw?t=109

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