Shooting it down
by Tom Temple
Feb 15, 03:29 PM
Have you guys heard about this?! Basically, there is a bus full of poison that is going to fall out of the sky and we have essentially no idea where. So we’re going to say “to hell with orbital debris” and try to blow it up. (We are going to hit it pretty low so most of it should burn up pretty soon. But we’re blowing it up—it’s going to go everywhere. Some of it will stay for a while. China’s recent, high-orbit mess will be around for a very long time.)
Wow! Everybody in Aero/Astro is excited to see what happens with this. We’re about to see what we can actually do. This is like missile defense except we get two months to aim. Shooting down a satellite whose position is very accurately known is pretty hard. One that’s out of control is substantially harder. The problem with active tracking should become appearant if you think about the non-inertial reference frame issue; the physics are pretty hard. Docking with it might be doable, hitting it will be harder. To avoid this we can attack it at an angle where we don’t have to chase. The downside of this is that it means the relative velocited involved are enormous something like 8km/sec on the satellite 6km/sec on the missile. It’s not a sure thing by a long shot. Luckily, we get to try more than once It should be easier than a hitting a missile though, it being bus sized and all.
note: Not everyone understands that we are planning on actually physically hitting it, i.e., we aren’t planning on using explosives. That turns out to be the best way to impart a lot of energy into something when you’re both in space and there is like a billion joules of kinetic energy available. This is also how the missile defense system works.
Feb 15, 03:43 PM
What, no comment on the conspiracy theories about how the real reason we’re shooting it down is because of all the classified goodies on the thing?
Other than that, I’m relatively uninformed:
1.) Do we shoot at this thing close range? I mean, do we fly a plane at really high altitudes to launch the projectile, or do we launch our projectile from the ground?
2.) Does the distance travelled by the projectile even make a difference, unlike in darts?
3.) How dangerous is this thing really? I’ve heard reports that the gas really isn’t dangerous; that it dissipates really quickly and that for it to hurt people you’d have to inhale it constantly for like hours. The debris isn’t really that big of a danger is it?
Feb 15, 05:05 PM
1) It gets shot from the ground an aircraft carrier. This missile is more like a spacecraft than an aircraft missile. It’s got four stages and can go nearly LEO velocity.
2) The missile seeks the target in IR so distance doesn’t exactly matter. In theory it can acquire the target ~500km away (once they are both in space).
After looking around, I’m with Joran. It’s not that dangerous. The kinetic energy would be tens of kilograms of TNT. The hydrazine has enough energy to start a respectable fire although noone has been talking about that. Scott, is it hard to catalyze or something? The chemical exposure risk does seem impressively minor.
I don’t think the technology conspiracy angle is very likely although it is possible since it is a very new satellite. I would suppose that their main reason is to test the missile defense system. They’ve been working on this stuff for a while and China did just shoot down a satellite.
More interesting, now that I think about it: Isn’t this is the sort of stuff that the current administration does first and then tell’s us about later? After looking at that missile’s record, I think they are very confident in a hit. That we are hearing about it now suggests to me that there is some PR going on.
Feb 20, 03:53 PM
So Tom, what do you make of the decision to delay the shot due to weather?
That doesn’t really bode well for this as a proof of concept for a missile defense system, does it? Unless North Korea only has missiles that fly when it’s sunny…
Feb 20, 08:27 PM
Eh, I’m not too surprised about that regardless of how you look at it. It is a hard thing to do and they don’t want to miss. So they’ll wait for favorable conditions. You’re right in terms of hitting enemy missiles, but actually hitting real enemy missiles isn’t really on the near term agenda, is it.
Sort of related, it’s really exciting to be in Aero/Astro at MIT. It reminds you of how amazing this whole space project really is. I just got to watch some pretty real footage (the equivalent of the NASA channel on cable if you’re so lucky) for the Atlantis mission that just finished. Putting people in orbit (and getting them back again) still entails strapping them to some of the biggest rockets we can make and having them go exactly where we want them to. They are accelerating at 3G for two minutes!