> the plane change from the pre-positioned orbit to one that intersects with the target? Sorry if this is a dumb question, but is it really that bad?
Yes. The closer you get to the surface the faster the orbit which means while you have less orbital energy to kill on approach you need more birds to cover a given area. (To communicate how unintuitive orbital mechanics can be, consider that thrusing "up" or "down" (radial in or out) doesn't actual increase or decrease your mean altitude [1]. You have to fire retrograde, which means a long, swooping, predictable, observable (and thus avoidable) approach to intercept unless you're Project Orioning it [2].)
> guy your responding to has mostly deleted their posts
They were repeating a conspiracy theory around SpaceX's actual purpose being to create a space-based missile defence system. The proof being there are senior people who were involved with the latter who have been around SpaceX. It's total nonsense somewhat orthogonal to why space-based missile defence is between difficult and stupid.
The core concept of boost-stage (i.e. in the atmosphere) space-based intercept isn't physically fucked. It's just that every case where one presents it, ground-based interception--including at the boost phase--does better. You can hide your interceptors better. For any given cost, you can deploy more of them (and more early-warning/targeting satellites). And even primitive ASAT can reliably punch a hole in it.
The only benefit is political/PR, because it sounds cool--that doesn't rule it out. But it isn't something SpaceX is working on much less was founded for.
(Space-based midcourse (i.e. in vacuum, while the warhead coasts) interception is stupid on all levels. It's a slightly more difficult version of blanketing the skies in drones for intercept--except you have more volume to cover and have planes which send off a screaming signal every time they change course.)
Yes. The closer you get to the surface the faster the orbit which means while you have less orbital energy to kill on approach you need more birds to cover a given area. (To communicate how unintuitive orbital mechanics can be, consider that thrusing "up" or "down" (radial in or out) doesn't actual increase or decrease your mean altitude [1]. You have to fire retrograde, which means a long, swooping, predictable, observable (and thus avoidable) approach to intercept unless you're Project Orioning it [2].)
> guy your responding to has mostly deleted their posts
They were repeating a conspiracy theory around SpaceX's actual purpose being to create a space-based missile defence system. The proof being there are senior people who were involved with the latter who have been around SpaceX. It's total nonsense somewhat orthogonal to why space-based missile defence is between difficult and stupid.
The core concept of boost-stage (i.e. in the atmosphere) space-based intercept isn't physically fucked. It's just that every case where one presents it, ground-based interception--including at the boost phase--does better. You can hide your interceptors better. For any given cost, you can deploy more of them (and more early-warning/targeting satellites). And even primitive ASAT can reliably punch a hole in it.
The only benefit is political/PR, because it sounds cool--that doesn't rule it out. But it isn't something SpaceX is working on much less was founded for.
(Space-based midcourse (i.e. in vacuum, while the warhead coasts) interception is stupid on all levels. It's a slightly more difficult version of blanketing the skies in drones for intercept--except you have more volume to cover and have planes which send off a screaming signal every time they change course.)
[1] https://space.stackexchange.com/questions/44608/what-happens...
[2] https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...