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"The Moon is a Harsh Mistress" by Robert Heinlein involves some of that. But how difficult would it be to intercept the payload safely outside the atmosphere?

"The Moon is a Harsh Mistress" by Robert Heinlein involves some of that. But how difficult would it be to intercept the payload safely outside the atmosphere? Seems it would be easier than intercepting an ICBM.

ben_w 8y ago
I get the impression it would be harder, because ICBM launches are really obvious (to current equipment) and you can at least make a good guess about their ballistic path, while anything of that size launched from the moon would be invisible until it had almost hit you. While it is often said that stealth is impossible in space, that tends to assume the appropriate tech has actually been manufactured rather than sitting in a lab somewhere waiting for a purchase order. Radar, even lidar, is going to have awful signal-to-noise ratios and almost all of the return signal will be stuff that bounced off the moon rather than any projectile. Even the lunar retroreflector turns 10^17 photons out into one photon back, according to Wikipedia, and that’s about as far from stealth as you can get. Edit: I suppose one could reasonably argue that any industrialisation of Luna would, as a result of my own argument, make governments choose to put loads of effort into appropriate defence technology. On the other hand, I’m told trench warfare was more accident than deliberate planning in WW1, so perhaps governments would be as myopic as ever even with a massive space gun on the moon.
- piannucci 8y ago
  Once it gets within a few tens of megameters, pulsed radar systems could easily distinguish an incoming projectile thanks to the 2.4 second round-trip-time to the moon. Metallic objects have ideal visibility. If you are concerned about solar thermal radio emissions bouncing off the moon and reducing SNR, that could be an issue -- a phase-of-the-moon bug in the system, if you will. But based on what I’ve overheard from friends working on 21-cm radar teaching telescopes, I doubt the luminosity of the continuous background is high enough to pose a big problem, assuming you have a decently large antenna. I’m more concerned that there’s nothing much you can do to redirect such an object in the few hours it takes to fall on your head. By that time it will have reached 4km/s.
  - ben_w 8y ago
    Good to know. In that case, I’m not concerned by the first n (n<5000 ish, varies by nation), but the relative ease by which an attcker can just keep going until the target run out of missiles to shoot at the attacker’s projectiles.

ben_w 8y ago

I get the impression it would be harder, because ICBM launches are really obvious (to current equipment) and you can at least make a good guess about their ballistic path, while anything of that size launched from the moon would be invisible until it had almost hit you. While it is often said that stealth is impossible in space, that tends to assume the appropriate tech has actually been manufactured rather than sitting in a lab somewhere waiting for a purchase order. Radar, even lidar, is going to have awful signal-to-noise ratios and almost all of the return signal will be stuff that bounced off the moon rather than any projectile. Even the lunar retroreflector turns 10^17 photons out into one photon back, according to Wikipedia, and that’s about as far from stealth as you can get. Edit: I suppose one could reasonably argue that any industrialisation of Luna would, as a result of my own argument, make governments choose to put loads of effort into appropriate defence technology. On the other hand, I’m told trench warfare was more accident than deliberate planning in WW1, so perhaps governments would be as myopic as ever even with a massive space gun on the moon.

piannucci 8y ago
Once it gets within a few tens of megameters, pulsed radar systems could easily distinguish an incoming projectile thanks to the 2.4 second round-trip-time to the moon. Metallic objects have ideal visibility. If you are concerned about solar thermal radio emissions bouncing off the moon and reducing SNR, that could be an issue -- a phase-of-the-moon bug in the system, if you will. But based on what I’ve overheard from friends working on 21-cm radar teaching telescopes, I doubt the luminosity of the continuous background is high enough to pose a big problem, assuming you have a decently large antenna. I’m more concerned that there’s nothing much you can do to redirect such an object in the few hours it takes to fall on your head. By that time it will have reached 4km/s.
- ben_w 8y ago
  Good to know. In that case, I’m not concerned by the first n (n<5000 ish, varies by nation), but the relative ease by which an attcker can just keep going until the target run out of missiles to shoot at the attacker’s projectiles.