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A terrorist wants to shoot a bomb down onto an unsuspecting high-value target, for instance Washington DC.

So, the terrorists somehow get a private space company to deploy what seems to be a normal, inconspicuous weather monitoring satellite. However, unbeknownst to them, the satellite is only a disguise, concealing a missile.

Once in space, the satellite/missile positions itself directly above DC. Once properly positioned, the missile sheds its satellite disguise, descends into the atmosphere, then guides itself straight down as fast as possible, directly on top of the unsuspecting target.

If it takes the missile 15 seconds to go from space to earth (120km at 8km/s), the President would never even get a notification anything was about to happen, and would therefore never get to go into the Presidential bunker.

How feasible is this? What safeguards do nations have to protect from this?

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  • $\begingroup$ Going straight down would be completely infeasible as it would require packing approximately 8 km/s delta-v on the missile (too much for a small missile), which would (assuming typical liquid fuel rocket) only allow for 16% of it to be anything other than fuel. De-orbiting by lowering perigee until you get caught in the atmosphere and using smart guidance systems and aerodynamic control surfaces to fine-tune re-entry is much more reasonable. $\endgroup$ – Jarred Allen Dec 15 '16 at 2:39
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    $\begingroup$ If you can put something in orbit and de-orbit it on target, a non-nuclear explosive payload is just lagniappe. The kinetic energy of the orbiter is more than sufficient to make big holes in things. See "kinetic bombardment" for more info, also Chelyabinsk meteor. $\endgroup$ – jamesqf Dec 15 '16 at 3:23
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    $\begingroup$ I recommend downloading and playing with Kerbal Space Program. KSP is a great place to play around with ideas like these and learn which ones work and which ones don't. $\endgroup$ – Cort Ammon Dec 15 '16 at 3:41
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    $\begingroup$ Or FTM Heinlein's "The Moon Is A Harsh Mistress", where the Loonies fight Earth by throwing rocks at them. $\endgroup$ – jamesqf Dec 15 '16 at 19:13
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    $\begingroup$ Satellites do not "position themselves". Satellites are in orbit, that is to say they are stuck in a circular/elliptic loop around the Earth with a speed of — at least — 27 000 kph / 18 000 mph. So a satellite cannot say "Ok, I will just head on over to Washington DC and stop there". No, the satellite will have to wait until the Earth has rotated underneath it so that Washington DC is in a good place for it to drop in. Also: no, the missile cannot drop straight down. The missile will have to fire its engine in the opposite direction of travel, and then make a long sloping de-orbit. $\endgroup$ – MichaelK Dec 16 '16 at 10:39
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As noted, this replicates an ICBM like weapon thought to have been developed by the former USSR; the FOBS (Fractional Orbital Bombardment System). Since both NORAD and the US ABM system were focused on detecting and stopping ICBMs launched over the great circle route over the North Pole, the Russians thought to launch warheads on other trajectories which might be mistaken for normal satellite launches, or coming over the South Pole, where they would either be undetected or detected too late to take action. It is also theoretically possible to loft the warhead in orbit and bring it down on target at a later time.

The main issue with your description is that objects in orbit do not remain "over" a point on Earth (except for points on the equator in the case of geosynchronous orbit), but will pass overhead on a regular basis (based on factors like orbital height and inclination). You will need to send a signal to the device in orbit to commence a retro burn to deorbit, and then, as noted in other answers, a heat shield to survive reentry and aerodynamic aids to fine tune the point of impact. As an aside, all this takes mass, and if you are trusting the kinetic energy of the impact to deliver damage, the more mass which needs to be consumed (rocket fuel, ablative heat shield) the less mass that will ultimately strike the earth.

This takes time, and NORAD or SPACE COMMAND might pick up the retro burn over the Pacific or North America (depending on the height and orbital inclination), and almost certainly start tracking the device as it re enters the earth's atmosphere and creates the superheated plasma sheath during its passage through the atmosphere. While with current technology there does not seem to be a way to intercept it (US ABM Interceptors are currently stationed in Alaska, so would not have a good shot at the incoming warhead), there is a possibility that future expansions of the ABM system and upgrades to systems like the US Navy Aegis Ballistic Missile Defense System might provide some limited protection.

Of course, once the deed is done, there will be a massive hunt underway for the culprits, and any nation which sponsored or sheltered the group responsible, as well as the group members themselves, will discover themselves facing the wrath of the United States and all the overt and covert power that cam be brought to bear against them, no matter how long it takes.

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    $\begingroup$ "superheated pasta sheath"??? in your penultimate paragraph. Somehow I suspect you meant "superheated plasma sheath". Superheated pasta suggests a thermal form of spaghettification. $\endgroup$ – a4android Dec 15 '16 at 6:54
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    $\begingroup$ Note to self: never answer a question using a smartphone.....The superheated pasta sheath is actually quite delicious, however. See the answer in fivestarchef stack exchange ;-) $\endgroup$ – Thucydides Dec 15 '16 at 13:55
  • $\begingroup$ AEGIS ABM is for hitting missiles on the way up, not on the way down. Frankly, I do not think that there will be any effective system for getting missiles on the way down, at least not in our lifetime. Space intercept is the only possibility, and even that is very hard given the speeds involved. Probably requires speed of light (i.e. laser) weapons to work. $\endgroup$ – kingledion Dec 15 '16 at 14:37
  • $\begingroup$ @kingledion: It's been done, e.g. navy.mil/submit/display.asp?story_id=91638 And also hitting a satellite in orbit: cnn.com/2008/TECH/space/02/20/satellite.shootdown $\endgroup$ – jamesqf Dec 15 '16 at 19:20
  • $\begingroup$ @jamesqf The Hebrides test was on the way up, not the way down. Given Terrier Orion's altitude limits, the 'space' intercept was only space in the nominal sense. Also the space shoot-down in 2008 was a non-maneuvering target with a known trajectory. AEGIS ABM has never shot down a target that was defending itself with countermeasures. $\endgroup$ – kingledion Dec 15 '16 at 19:52
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You are describing a Ballistic Missile

This is technology that has been around since the 50's. Rocket goes up, warhead, or many warheads, go down.

Re-entry is at 8 km/s or so. Plenty fast, almost impossible to shoot down even with today's technology.

Accuracy is more or less classified, but is probably in JDAM range: 10 meters; definitely no worse than 100m.

Story wise, there are plenty of these things hanging around if the terrorists can shoot one off using stealing/blackmail/hacking, whatever.

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  • $\begingroup$ Well, my thought was that most missile defenses, like NORAD, are watching horizons (I think), rather than directly above, say, Washington DC. So, could terrorists manage to sneak the missile to be positioned directly above the target if it's not rocketing through space, but rather very slowly inching into position. Is that feasible? $\endgroup$ – Thom Blair III Dec 15 '16 at 2:51
  • $\begingroup$ @ThomBlairIII NORAD will see the launch, but that doesn't mean they can stop it. There are no effective anti-ICBM missiles anywhere in the world. Think about this: it takes about 15 seconds for an ICBM to drop from outer space onto its target (120 km at 8km/s). What weapon on earth can hit a target on that short notice? By the time they know where the weapon is headed, its almost already there. $\endgroup$ – kingledion Dec 15 '16 at 2:59
  • $\begingroup$ The 15 seconds to impact is my point, except that if the missile is deployed from a commercial spacecraft, rather than launched from earth, it might not be seen by NORAD as a threat, since it's not shooting across space with it's engine going full speed. Can NORAD or any other space-based system detect a missile floating sneakily into position above earth targets? If not, there would be no warning at all, ever, before it hit the target. In fact, no one would even know where the missile had come from...any country or group could have launched it, since no inbound trajectory was ever detected. $\endgroup$ – Thom Blair III Dec 15 '16 at 3:02
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    $\begingroup$ @ThomBlairIII Yes, they are always looking for IR signatures of launches. Its hard to put something in orbit with a rocket undetected. And they'd also track any commercial space launch once it got to space, since NORAD has plenty of satellite interests too. $\endgroup$ – kingledion Dec 15 '16 at 3:07
  • $\begingroup$ So, then the only question left is whether or not they have space-based weapons for destroying weapons deployed from space. Does anyone? $\endgroup$ – Thom Blair III Dec 15 '16 at 3:09
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This doesn't work very well.

What you have to realize is that the weapon has to decelerate just as much as it accelerated to get into orbit. This will take a great deal of fuel, so the final impact body will be quite small. The useful term here is the payload fraction. The Space Shuttle is good example. It takes a liftoff weight of 2,000,000 kg or so to put 130,000 kg into LEO, for a payload fraction of about 0.065. Apply that to a 1 ton (1,000 kg) "weather satellite", and you get an impacting body of about 65 kg. The situation is a bit clouded by the fact that you presumably don't want a multi-stage deorbiter, but it's clear that 65 kg is optimistic, not to say unrealistic.

At 10 g's, retro burn time is only about 81 seconds and begins 32 km before the vehicle would pass over the target if there were no burn, so this is happening pretty much out of view of most radars.

Furthermore, this simply produces a satellite which is (temporarily) essentially stationary and which then begins free-falling, and ignoring atmospheric effects will take about 157 seconds, with a final velocity of about 1500 m/sec. Of course, you can't actually ignore such effects, and descent will really take a good deal longer. In order to get an 8 km reentry velocity will require double the total thrust (8 km/sec to stop the vehicle, and another 8 km/sec vertical speed) - you can't combine the two if you want a vertical reentry. So the impacting body will be even smaller. Like, in the neighborhood of 4 kg. And it won't hit an anything like 8 km/sec - remember atmospheric drag effects. You're right, though, to think that there is simply nothing looking straight up over DC, so there will be very little warning.

You may well feel that 1500 m/sec (about Mach 15) is pretty unimpressive. Well, that's because it is. Unfortunately, you'll get maximum impact velocity, about 8 km/sec, if you think of the final orbit as being a very slight ellipse, with closest approach being 120 km less than the maximum. Unfortunately, this will produce a very shallow approach angle which is in principle easily detected, not to mention producing a whole lot of drag and slowing your impactor down trementously. Fortunately for your story, the approach angle can be from the southwest, and there aren't a lot of radars pointing in that direction.

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To your first question:

As other answers have pointed out, it's not feasible. You have to have an appreciable amount of sideways in your orbit in order to, well, orbit, so going straight down isn't an option. This then turns the question into : how can we stop an ICBM that's undetectable until 15 seconds before it hits?

The answer to that question is simple:

M.A.D.

We already have safeguards in place to stop this kind of attack: notably that once one group starts doing it every other group will. Current ICBM technology is pretty much unstoppable once launched, though there have been many attempts at building systems to do just that, and if someone drops a warhead on the president's head you can be pretty sure that someone elsewhere in the chain of command is going to retaliate in a pretty spectacular fashion.

As everyone knows this and nobody wants the world to end up a hideous war zone no major world power will want to try this kind of thing. And if you've got a rogue terrorist group that wants to end the world and is capable of building and launching an ICBM without being detected first then frankly your world is going to burn anyway.

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