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Comment by dingaling | Hacker News Reader

Satellites can be re-oriented into different orbital inclinations but that requires fuel and in the absence of a Shuttle fleet they cannot be refuelled. So despite movie depictions they don't go swerving hither and thither to follow a camel up a mountain track.

Such limited manoeuvring also requires planning and 90 minutes between passes. Lots of opportunity for bad guys to push their missile back into a hangar.

An atmospheric aircraft can follow an arbitrary course to take in as many targets as required, can be rerouted on a moment's notice and can approach from unexpected vectors to catch the target out in the open.

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> in the absence of a Shuttle fleet they cannot be refuelled.

Judging by the publicly-released payload specs for the DoD-operated Boeing X-37 spaceplane, it should be able to deliver about 2000+ L of hydrazine, compressed Xenon, or other suitable fuel in a single launch.

Edit: It looks like DARPA has been experimenting with "space gas station" experiments since at least 2007.

https://www.space.com/3644-prototype-satellites-demonstrate-...

> Satellites can be re-oriented into different orbital inclinations but that requires fuel

A LOT of fuel. So much so that even if lifetime wasn't an issue, it makes more sense to launch additional satellites in the proper inclination, rather than moving one.

I know that, in one instance, a company wanted to use the moon's gravity to change a satellite's inclination, as it was cheaper to all the way to the moon and back (and then circularize again). That maneuver seems to be patented, though.

Patents be damned, I use that in KSP from time to time. Can I claim prior art? If you're on a level orbit and you fly off to the moon, adjusting with a tiny bit of inclination so that instead of nearing the moon on the same plane but from above, you're suddenly in a highly inclined orbit on your way back. You can also use this to slow down/speed up depending on which side you approach.

Patent number/reference please? I’d love to use this as a test case in an orbital dynamics library I’m building.

I am fairly sure that "US 6116545 A" [1] is the patent in question.

[1] https://www.google.com/patents/US6116545

Sure, but don't we have drones for that now?

The high altitude spy planes (U2, SR-71) were mostly to prevent being shot down; surviving to return the film to base.

Drones don't need to bring film back, and it's not such a big deal if a few of them are lost.

If it can be shot down, I think that it's probably safe to assume that it won't be able to see anything particularly interesting. I'd expect something like Groom Lake to be surrounded by an impenetrable wall of interceptors and SAM sites.

Though I suppose that you could try to make your drones so cheap and in such volume that shooting them down becomes logistically and economically infeasible, but that's another strategy entirely.

> I'd expect something like Groom Lake to be surrounded by an impenetrable wall of interceptors and SAM sites

The whole idea of the SR-71 was that it went so fast that SAMs could just barely not catch up to it before they ran out of fuel. Any other plane couldn't outrun them, but the Blackbird? Well, Mach 3.4 will give you some breathing room.

The standard evasion tactic for SR-71 upon launched against was to simply accelerate.

That would be the only option. It's not like you can turn much you'd pass out or snap the airframe.

I imagine thought a little snake left/right might compromise getting the images that was the point of the mission.

Apparently it could also turn pretty hard. Mind, it's turn radius was huge, but at mach 3.2 it still meant pulling a lot of g's.

More to the point, it takes time to notice, track, lock and (in some cases) get approval to fire. That gives you seconds to minutes to not only fire but for the missile to reach the intercept point.

Missiles and radar tend to operate in a "bubble". Even with the Russian S200 system at 190 miles range, the time you spend in that "bubble" when you're at 70k ft is not often long enough to do anything. That also assumes the aircraft directly overflies the battery. You can play games like pointing the camera sideways and observing from an angle if you know there are going to be angry people with guns nearby.

Mach 3.4 was also fast enough that early radar systems couldn't track it. The plane would move far enough between radar pulses that it got filtered out as noise.

The state of the art advances. There are SAMs today that can shoot down ICBMs. I would guess that one reason the SR-71 was retired, besides the official line that it was expensive and made obsolete by satellites, is that it was no longer invulnerable as it had been when it was new.

Just speculating here on two points:

- There is no real need for SR-72 to be manned on all flights;

- Hypersonic plane would be very good for small (2m wingspan) drone delivery behind the enemy lines fast (in half an hour). This was already a concept with M-21/D-21, but now the drone part can be much smaller and one plane could carry more than 4 of those.

Satellites are quite limited when you need to make fast decisions. Hypersonic plane will move about 7 times slower than an optical recce satellite, yet it can maneuver very fast if you need to relocate the imaging area and can get at least 10 times closer to the target. Instruments can be selected/improved even after the first flight of the plane -- not true for the satellites.

I always imagined spy satellites in a 'string of pearls' kind of configuration. Rather than having 1 in some specific orbit, have 4 or more in the same orbit. your 90 minute return time gets cut to ~20 minutes or less. Obviously, i have no information either way.

There's no need to imagine. The quantity and orbits of spy satellites are public knowledge since there's no way to hide anything in space. The exact capabilities of each satellite are classified but but we can guess how good their sensors are just based on physics. Currently it costs so much to build and launch a spy satellite that we can't afford to put a bunch of them strung out in a single orbit, but maybe that will become practical eventually as launch costs decline.

> The quantity and orbits of spy satellites are public knowledge since there's no way to hide anything in space.

The "Misty" satellites came up on HN last week related to the SpaceX launch and failure.

https://en.m.wikipedia.org/wiki/Misty_(satellite)

http://www.armaghplanet.com/blog/the-real-mystery-satellites...

"A week after launch, reports were released from the Soviets that six bits of debris had been detected suggesting an explosion had occurred. The Pentagon announced that any debris would decay after six weeks. The amateur astronomers and observers that were tracking this object only catalogued five out of the six pieces. Six months later an unidentified satellite was discovered in orbit on a similar trajectory to that of the classified payload was released, leading the satellite spotters to suspect it was the missing piece, nick-named Misty. However a couple of noticeable manoeuvres later, Misty disappeared again. Perhaps the ‘explosion’ was a decoy to put Misty into place unbeknownst to the Russians."

Planet is doing this with many satellites today. They are much smaller than DoD projects so it's much cheaper.

Here's a diagram of their style orbit: https://www.planet.com/docs/spec-sheets/spacecraft-ops/monit...

404'd

that's a weirdly specific shuttle refueling point, dingaling. satellite servicing of any kind was very rarely attempted much less regular refueling. We can and do change orbits using onboard fuel without ever refueling - sure it's limited. Saying the shuttles supported refueling and hence maneuvering spy satellites are no longer a thing is very far from reality.

1. The Space Shuttle flew a large number of lengthy, classified missions.

2. The Space Shuttle suffered from many costly design compromises due to its excessively large hangar bay.

Given #1 and #2, there are four likely kinds of classified missions that the Space Shuttle undertook.

1. Stealing Russian military satellites.

2. Returning American military satellites to Earth.

3. Launching American military satellites into unpredictable orbits.

4. Refueling American military satellites, which allowed them to change to a new, unpredictable orbit.

It's entirely possible that the Space Shuttle only engaged in some of these tasks... But it's difficult to conclude that given the very odd design of the space shuttle, and the very lengthy missions that it undertook, that no satellite servicing/orbital shenanigans took place.

Yes, satellites can change orbits using on-board fuel reserves, but due to the tyranny of the rocket equation, those reserves are limited - and are unlikely to allow a very large inclination change (Inclination changes are incredibly fuel-expensive.)

The Space Shuttle certainly didn't steal any Soviet satellites. The Soviets had radar too. It's physically impossible to do anything like that in space without getting caught. Furthermore the Shuttle couldn't get higher than LEO so many satellites were simply out of its range.

Likewise there is no such thing as an unpredictable orbit. Orbits are predictable, by definition. Any country with a good set of radars, telescopes, and IR sensors can find the exact orbit of every single satellite.

The Space Shuttle was certainly used for launching American military satellites into regular predictable orbits. They might have done a refueling mission at some point as a proof-of-concept but even that seems unlikely considering that it's always cheaper to just build and launch a new satellite.

The shuttle did not fly a large number of missions to begin with... It was so unreliable (fatal accidents every fifty launches!) that it never had a chance. The SpaceX model of reusability looks a lot more likely to deliver.

If SpaceX succeeds at lowering launch costs then it would be easier to launch many small and disposable spy satellites than ever to bother refueling one.

Nonetheless, the point is that satellites are limited as to opportunities due to limited availability and limited time windows. This does argue that there ought to be a role for an SR-71. I'm not sure there's much of a role for an SR-72, but certainly for the SR-71 there ought to be.

Yeah, but a low, slow, cheap drone has all those advantages anyway. There's no need for a hypersonic space plane.

What's the point of having people in this?

To operate it.

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