Surprised nobody's mentioned this possibility as it usually comes up re: the X-37B. Terrifying but I think not out of the question given the strategic potential of such a weapon.
That is utterly terrifying.
1. Surprise. All land-based launch sites are actively monitored all the time, giving countries advance warning when a missile is launched. Submarine launches cut down this warning time, but still light up radar and thermal all over the place. A kinetic impactor falling from LEO can hit its target before the enemy even reports up the chain of command (we're talking single digit minutes).
2. Lack of radioactive fallout while still having larger destructive force than conventional munitions. If you need to destroy an entire air base far behind enemy lines, but don't want nearby population centers to be irradiated, you're looking at pretty bad options today, compared to a kinetic bombardment.
3. You can't really intercept a kinetic impactor. We have the technology right now to shoot small rockets right out of the sky, and at least a chance of intercepting ICBM payloads. With a kinetic rod, though, intercepting it wouldn't really do very much - it's just a big chunk of mass moving really fast. The best you could do is break it into smaller pieces that are still moving really fast.
https://en.wikipedia.org/wiki/Kinetic_bombardment
These are not things that get fired. You don't launch them.
They don't follow a trajectory. They might just travel straight down from a geostationary orbit, depending on implementation. Yes, a guidance package might be necessary (depending on target discrimination, and precision, which in warfare isn't always required). They aren't gliding like smart bombs though.
At the speed of re-entry, and with possibly just 100 short miles to close, a defensive interceptor would be unwarned, have to acquire possibly many targets (one need not drop only one). Intercepting vehicles would have to close on a target in an arc representing a distance longer than the hypotenuse of the right triangle between the kinetic slug, the interceptor's launch site, and the defended target.
The slug is simply released with no indication of ingress. From a geostationary orbit, it just starts getting closer very fast. Cover it with EM absorbant, non-reflective material, and there's even less hint of activity, until the re-entry burn at approximately 60 miles altitude. Unless the target itself is equipped with interceptors, and lots of them, it will be difficult to notice and recognize in time, and even harder to catch and defeat.
That's not how orbiting works. If you want your projectile to travel straight down, you need to cancel all it's orbital velocity. For geostationary orbit, that's 3km/s of delta V needed.
Obviously, you can de-orbit with less delta-V, but then guidance starts becoming necessary.
> The slug is simply released with no indication of ingress. From a geostationary orbit, it just starts getting closer very fast. Cover it with EM absorbant, non-reflective material, and there's even less hint of activity, until the re-entry burn at approximately 60 miles altitude.
There is going to be some kind of burn to start de-orbit, you could simply monitor for that.
I would imagine a nuke having such a large explosion that missing the target by a kilometre won't matter too much. But with a kinetic projectile that kind of deviation would not be acceptable (unless we are talking about seriously big projectiles, like in Tunguska etc).
Obviously you don't want to do a powered de-orbit for reasons mentioned (you burn fuel & lose kinetic energy). However, if you're flying low enough, couldn't you aerobrake your projectiles after release and have them de-orbit themselves?
For comparison, the X-41/51 scramjet programs appear to be aiming at the mach 5-9 region. So less than 1/2 as fast.
As complicated as the materials science and guidance has to be for any X-71-based projectiles, slowing down and terminal guidance (ablative coatings and sacrificial control surfaces) seem like easier problems than boosting up to ridiculous velocities.
As for tracking, you get the heat bloom as it aerobrakes, but if you manage to keep it coherent through re-entry then the ridiculous speed largely moots that.
At 5 km/s, with a prograde orbit, you're from Istanbul to Beijing about 24 minutes (by my sleepy calculations?). The exercise seems more of a question of "How steep can you dive (aka how much heat can you handle)?" than anything else.
PS: Well, and "How the hell do you communicate-with / sense-from a platform surrounded by air that hot?"
Of course that's all pointless because a ballistic missile launched from Earth could accomplish the same mission at a far lower cost with greater reliability and survivability.
Regardless of what orbit you start from, you dip into the atmosphere, deploy your payload from there, voila.
Now anything you dropped has to deal with a furnace of superheated air, and the question of whether it's possible to have control in those conditions, but it's definitely going to de-orbit.
And the atmosphere is going to supply most of the energy, rather than direct retro burns from the delivery vehicle.
So you're just going to target the equator then?
Propellant is a conventional means, but certainly not the sole means. Magnetic induction could eject a slug from an orbiting platform, or inert gases could jettison to induce motion. Burnt fuel isn't a requirement.
You insist on a rocket motor. But you just resist the idea of this form of orbital weaponry.
A large enough asteroid could enter into earth's gravity well and chart a straight line to impact.
You presume preconceived concept of a weapons platform already in orbit, controlled from the ground, or by a terrestrial entity. But a weapon of lunar origin might insert into the atmosphere differently. As with any weapon, an approach to target should be the least defensible path. After atmospheric re-entry, when position is given away, you'd want the penetrator to travel as perpendicularly to the target as possible, but prior to that moment, any stealthy approach is game.
I'm not 100% wrong. You're 100% obstinate.
Magnetic induction would also apply opposing forces to the launch satellite, but that doesn't matter if the launch satellite is just as disposable as the slugs that destroy the target.
Inert gases are too heavy, only if the weapons program tries to collect them on the ground and launch them into orbit.
I'm obviously making things up, because this is a system open to invention, given that it doesn't actually exist yet. This concept is less practical, if you operate within existing constraints, using only rocket propellant to boost objects into orbit, and then subsequently de-orbit them.
Game changers emerge, when new ways of operating in space appear. Even if this is "less practical" right now, after the introduction of adjacent technologies, as an existing concept it could suddenly become practical. For example, with the introduction of a space elevator, boosting such a weapons system into orbit is less costly. Then, more of its components become readily disposal at practical values.
I'm not required to operate within existing economic constraints, to consider ideas that are not actually limited by physical laws.
Never underestimate passionate nerds and their ability to notice unusual things!
> I'd be a lot more worried about them being dropped from stratospheric balloons - maybe not so useful for full scale bunker busting but extremely cheap to make and almost indefensible against as a strategic strike system.
If you meant to speak from the point of view of a revolutionary (why?) and note that stratospheric balloons would be a cheaper way of killing revolutionaries than ICBMs or Rods from God, sure, I agree. There are a million ways to shoot fish in a barrel. Forgive me for assuming your point-of-view party was militarily capable.
Eventually by the late 1980s they developed the Myasishchev M-17 balloon interceptor aircraft, with a dorsal cannon-turret and able to loiter for hours at 22km. Still not quite sufficient.
Now increase the balloon altitude to 50km and they should be safe against any opposing force with early-2000s levels of military capability.
Something similar has already been used here since WW1.
Don't discount the PR disaster that would ensue from the US using nukes in any scenario other than retaliation for a nuclear attack. Nukes used in anger would likely mean worldwide condemnation, sanctions, and pissed allies complaining about fallout.
But if you think it is, there's a big advantage of kinetic weapons over ICBMs, namely that they are a lot more credible as a first strike weapon. ICBMs launches are quite detectable, allowing counter strikes (hi there nuclear deterrence).