Camillus said:
It's not just a matter of energy coming in you've got to radiate out the energy that your vessel produces. Even an unmanned craft will need to run its computers, sensors and communications which means power and waste heat. That's got to go somewhere and realistically the only way you can get rid of it is by radiating it.
Sure. But you put your heat sink facing a narrow-angle aperture pointing out the back, aimed at the darkness of empty space. Chances of sighting are slim to none.
Is it? I would have thought that a shiny object in front of a terrawatt light source would be fairly easy to spot.
That's a natural instinct, but it's wrong. Don't think of it as a shiny object, think of it as a mirror. What you see when you look at a mirror isn't the mirror itself, but whatever the mirror is reflecting. From large distances, the angular divergence is VERY small, so you're talking about something close to a line projection. Light from the sun will hit a few surfaces of your missile in a very narrow solid angle arc, and be deflected in a very narrow solid angle arc. Only someone in that very narrow solid arc will see light reflected from the sun. Everyone else will see reflections of deep space, and a reflection of deep space on a background of deep space is invisible. This is somewhat counterintuitive because on earth, many shiny objects are also rounded (so a narrow solid angle from the sun is reflected into a large solid angle), and because the object itself takes up a large solid angle from the viewer's perspective.
This idea of using flat surfaces to minimize visibility is not new. The F117 stealth fighter works on exactly this principle. It sometimes "glitters" on enemy radar, when they catch a reflection, but most of the time they see nothing, and they can't track it with any accuracy from those glitters.
No, tracking and predicting the trajectory of a thrusting spacecraft is trivial. Once you engage your engine I can measure the spectrum of the output of your drive to estimate thrust. My semi-acive sensors will lock onto you and measure acceleration. From those two pieces of information I have your mass and shortly after that I know with a reasonable degree of certainty where you're going and how long it will take for you to get there.
Roughly speaking, but that's not enough. You need EXACT precision for an intercept, because anything you send out to meet it will have an enormous relative velocity and an incredibly tiny window of oportunity to act. We're talking many kilometers per second here - getting within tens of feet at those relative velocities is close to impossible. Think, for example, about the problems of current anti-ballistic missile technology. It's trivial to get approximate tracking, but that's not good enough. You need tracking down to feet, and you need to do it at huge relative velocities. Doing that with only data from the first half of a trajectory is impossible.
If by "long ranges" you mean outside the solar system then you might be partially right but you have to remember that in between burns your craft is radiating all the heat its engines, power plant, crew, life support and electronics generate. If you've helpfully made yourself really reflective then you're also visible to my semi-active sensors.
No, no, and no. Remember: missiles, no crew, VERY minimal power output during cruise. Main engines for initial thrust can in fact be a separate stage, so as soon as they're expended you drop them and don't worry about the heat. What minimal heat you do need to expell you let out the back side from a narrow aperture hole, a hole that you can point in whatever direction you want. And the shiny surface, well, we already went over that. A network of sensors might pick you up occasionally - it might pick up bright flashes of light now and then for a small fraction of a second, getting an accurate range on an object from one flash visible from only one sensor (because only one sensor could pick up that reflected beam from the sun at a time) is impossible. So they might know you're still coming, and have estimates for location, but that's not good enough for an intercept.
Interception at long ranges will be relatively easy because your missiles are easy to track. Remember that once they begin thrusting they will become extremely visible and their path is predictable.
Not with enough precision. Your main thruster burn is easily trackable. But after that, even a mechanical shove for disconnect (which you can't track accurately) that imparts a few feet per second relative velocity between the warhead part and the engine is going to mean that by the time intercept range comes up, your error is going to be huge.
I agree that interceptors will be "first pass" devices but the high velocity works in their favour because a scattering of debris in the path of an object will work quite effectively to destroy it (remember that once speeds exceed 3 km/sec the energy contained in an impact is equivalent to it's mass in TNT).
It's not that easy. You need to keep the cloud dense (meaning the chance to pass through it without impacting something is small), so you can't actually make it that big. And I think you're seriously underestimating how much error you're going to have. One foot per second error on your tracking is going to make an intercept like this impossible, and I can't see how you can expect to have better tracking than that.
Lasers are likely to have a range of a few hundred thousand kilometres. Unless your missiles are closing at velocities close to c there's more than enough time to target and hit them. Target counter-measures are probably going to make it tricky and you might be able to overcome my point-defences by saturation but I am in with a fighting chance.
This relies on being able to track it from a huge distance, but I don't see that happening either. If you only know where it is within a cubic kilometer (REALLY not hard to get that kind of uncertainty in your tracking), there's no way you're going to be able to hit it. In fact, with a mirrored surface, you could be pointing your laser right at it and not know, because the reflected light isn't going to come back to you. Since the absoption is probably going to be less than 1% of power, and angular divergence is going to significantly broaden any laser you use by the time it gets this far, I just don't see this as being practical, especially since you almost certainly WOULD be facing multiple missiles (each of which would be at least several kilometers apart). Your laser aparatus to do anything at these kinds of ranges, is going to take much more resoures to make than each missile it might have a chance to defend against.
