4 ms·

Kinetic impactors are not missiles. Repeat: Kinetic impactors are not missiles. https://en.wikipedia.org/wiki/Kinetic_bombardment https://en.wikipedia.org/wiki

Kinetic impactors are not missiles. Repeat: Kinetic impactors are not missiles. https://en.wikipedia.org/wiki/Kinetic_bombardment 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.

rocqua 9y ago
> They don't follow a trajectory. They might just travel straight down from a geostationary orbit 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.
- daemin 9y ago
  I am wondering, what kind of impact would the wind have on these projectiles? Or even on ballistic missiles? 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).
  - nradov 9y ago
    Wind and other transient atmospheric conditions have a major effect. That's why individual unguided projectiles can't reliably hit a target more than about 4 miles away, and even at that range you have to be really lucky. The range from LEO to surface is a lot longer.
    - ethbro 9y ago
      If you were going to use this as a first or second strike kinetic weapon platform (and prepared to tap dance around the "no militarization of space" treaties by claiming it's an aircraft), then your biggest asset is orbital velocity. It's sitting up there doing 7-8 km/s. 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?"
      - nradov 9y ago
tomdz 9y ago
>They don't follow a trajectory. They might just travel straight down from a geostationary orbit So you're just going to target the equator then?
- pc86 9y ago
  It's gotten a pass for too long.
nradov 9y ago
This is 100% wrong. You don't understand orbital mechanics. Everything follows a trajectory until force is applied. When you release something in orbit it doesn't fall down. It continues orbiting until an attached rocket motor does a de-orbit burn. Rocket motors are subject to manufacturing variations plus there are a lot of atmospheric effects on the way down to the surface so any missile would require a sophisticated guidance system to have any chance of striking a target.
- pavement 9y ago
  Prove to me that a rocket simply MUST be burnt, to set an orbiting mass in motion. 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.
  - nradov 9y ago
    You are still 100% wrong. Magnetic induction wouldn't be be practical because it would disrupt the satellite's orbit. Inert gasses are too heavy to be practical for the amount of delta V needed. You're just making things up and missing basic physics concepts.
    - pavement 9y ago
      You're imposing constraints where there are none, and declaring physical law as an insurmountable barrier, because you are sourcing all materials involved as terrestrial in origin, and insisting on reusability. 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.

rocqua 9y ago

> They don't follow a trajectory. They might just travel straight down from a geostationary orbit 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.

daemin 9y ago
I am wondering, what kind of impact would the wind have on these projectiles? Or even on ballistic missiles? 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).
- nradov 9y ago
  Wind and other transient atmospheric conditions have a major effect. That's why individual unguided projectiles can't reliably hit a target more than about 4 miles away, and even at that range you have to be really lucky. The range from LEO to surface is a lot longer.
  - ethbro 9y ago
    If you were going to use this as a first or second strike kinetic weapon platform (and prepared to tap dance around the "no militarization of space" treaties by claiming it's an aircraft), then your biggest asset is orbital velocity. It's sitting up there doing 7-8 km/s. 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?"
    - nradov 9y ago

tomdz 9y ago

>They don't follow a trajectory. They might just travel straight down from a geostationary orbit So you're just going to target the equator then?

pc86 9y ago
It's gotten a pass for too long.

nradov 9y ago

This is 100% wrong. You don't understand orbital mechanics. Everything follows a trajectory until force is applied. When you release something in orbit it doesn't fall down. It continues orbiting until an attached rocket motor does a de-orbit burn. Rocket motors are subject to manufacturing variations plus there are a lot of atmospheric effects on the way down to the surface so any missile would require a sophisticated guidance system to have any chance of striking a target.

pavement 9y ago
Prove to me that a rocket simply MUST be burnt, to set an orbiting mass in motion. 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.
- nradov 9y ago
  You are still 100% wrong. Magnetic induction wouldn't be be practical because it would disrupt the satellite's orbit. Inert gasses are too heavy to be practical for the amount of delta V needed. You're just making things up and missing basic physics concepts.
  - pavement 9y ago
    You're imposing constraints where there are none, and declaring physical law as an insurmountable barrier, because you are sourcing all materials involved as terrestrial in origin, and insisting on reusability. 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.