Projectiles have to survive atmospheric reentry. Wiki says that modern icbms have a reentry speed of 4km/s, vs 28km/s for x-37.

Doesn't have to be an ICBM or some type of rocket - a kinetic energy weapon (giant lawn darts from space) could be effective, but without nasty radioactivity afterwards.

Are there materials dense enough to be useful for this, and thermally non-conductive/stable enough to withstand the heat of reentry?

Tungsten carbide and uranium cement have been postulated. https://en.wikipedia.org/wiki/Space_weapon#Orbital_bombardme... Interestingly, these are not prohibited by any treaties. The US Air Force estimated a 1-foot (.3 meter) diameter tungsten pole would impact ~Mach 10. It would weight 9 tons and have the same destructive force as 7.5 tons of dynamite, but it would only take 15 minutes to get anywhere in the world and there would be no ICBM launch warning. https://en.wikipedia.org/wiki/Kinetic_bombardment#Project_Th...

If I remember rightly (it's been a while since I read up on them), they proposed using tungsten rods initially. Not sure if they'd still go down that route, or whether they'd use something a bit more exotic (carbon nanotubes is always the go to answer for exotic-scifi style things).

28 km/s? It would be more than escape velocity (11.2 km/s), where did you get that? Low earth orbit is around 8 km/s. Still not totally the same as and ICBM, but could be done.

But why would you stuff the rods in an X-37B? You could just launch a light satellite without all this re-entry stuff and you'd get many more rods for the same mass... or then you could use a smaller launcher.

The X-37B is basically a reusable payload fairing, a very heavy one at that. Oh well, it isn't even that because the rocket requires another outer expendable payload fairing.

I was completely wrong on the velocity, mixed the types and didn't even think about the weird number. I should rely on wiki less.

X-37 is an ICBM (with a guided glide mode). Airplane go boom.

Didn't think of that. In that case a specialized icbm would be better. As space-x shows you don't need wings to be accurate from orbit.

Nasa should really drop this winged approach. They can't because they have experience and scientists on that field, and change is hard.

NASA has. The shuttle program is deceased. This isn't NASA's.

http://www.nasa.gov/exploration/systems/index.html#.UvE53R_E...

Who said the X-37 has to survive though? That can do a 180 and decelerate using the main AR2-3 at the cost of a decaying orbit then drop the payload at 4km/s.

That would be about Mach 10 weapon launch. I don't think that's been seriously studied or tried in practice. That would be quite a technological achievement all by itself, aside from everything else the thing can do.

Of course the vehicle is going to be destroyed anyway, so just carry the payload all the way down till it goes boom or whatever, unless you were hoping to launch multiple warheads. The problem is the whole vehicle is very light, so you're not going to fit a B-52 worth of payloads in a vehicle who's launch weight is, I believe, lighter than a GBU-43. My point being that if vehicle plus payload at launch is lighter than a GBU-43, there's not much point in being concerned with how many GBU-43 it can be dropped if it can only carry a fraction of one anyway.

The main problem is its hard to think up a mission profile where a cruise missile wouldn't be cheaper and more effective.

I'm not an expert but I will state that x-37 in orbit doesn't have 23km/s delta-v. I think wiki for similar vehicles can confirm that: http://en.wikipedia.org/wiki/Delta-v_budget

Its a hydrazine monopropellent, or so they say, so an Isp of 250 or so would be impressive. Someone with a lot more time on their hands can tell you the mass fraction required to get 23 KM/s outta a 250 second Isp and its going to have about as many 9's as reliability marketing material. So yeah, thats not happening.

Don't forget aerobraking which can knock a big chunk off that delta-v.