[QUOTE=mks57]
The re-entry vehicles are covered in an ablative material, like carbon-carbon composites. They re-enter the atmosphere at hypersonic speeds. Unlike the Shuttle, there is no need to slow down to subsonic speed for a safe landing. I’ve seen some ICBM tests and the incoming re-entry vehicles look much like meteors. They are moving very quickly.
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Nitpick–first generation RVs, like the AVCO Mark IV, had a big metallic thermal mass (mostly alloyed copper) to absorb heat. The very tip of modern ICBM RVs is usually a reinforced carbon-carbon (RCC) material, but the main body of the RV is typically some kind of high temperature carbon phenolic tape lay-up. It is necessary to prevent ablation of the main body as much as possible because even slight geometic irregularities in the surface can result in undesirable spin or yaw impulses that will make a purely ballistic RV become inaccurate or unstable. The nosetip essentially sets up a shock wave which helps prevent ablation and convective thermal transfer to the main body. Older RVs like the Mark VI had a blunt body shape which helped to create a larger shock wave and allowed a larger payload (the Mark VI carried the 9MT W53 warhead on the Titan II, the largest ICBM nuclear package deployed by the United States) but was rather slow, making it vulnerable to interception, and tended to be less accurate. More modern RVs like the Mark 12A and Mark 21 used on Minuteman II/III and the now deactivated Peacekeeper have a more acute profile and a smaller tip, which allows much faster reentry (as mks57 says, they’re coming in faster than the eye can track) but requires careful design to prevent uneven tip erosion and loss of stability. There are also maneuverable RVs under development (and allegedly deployed by the Russians) which have articulating aerodynamic and lifting body surfaces, again presumable a RCC structure, that allow it to maneuver to avoid intercept or follow a non-ballistic terminal trajectory (useful for striking targets protected by ground features).
As for the OP’s question, the general scheme for a suborbital ballistic track is to get it to the target as quickly as possible. There may be other considerations, such as minimizing the probability of intercept or detection, which dictate other trajectories, like a fractional orbital trajectory used in FOBS or the depressed trajectories used by SLBMs, but in general you want to take the quickest–which is not necessarily the shortest–path, as well as making best use of your limited burn time on the rocket to acheive greatest range. You’d also prefer it to come as straight down and as fast as possible, minimizing time in the atmosphere (where aero loads will decrease the accuracy of the purely ballistic RV) and probability of terminal intercept, and the higher up it is during the mid-course flight, the harder it will be for a missile interceptor based in the target geography to reach. 800 miles isn’t really all that high when compared to the radius of the Earth; the problem with putting a payload into orbit at that altitude isn’t getting it up there, but generating enough orbital momentum to keep it in a stable orbit.
Orbital mechanics point of note: although the trajectory of the RV (once the rocket burns out and the RV is released) is strictly ballistic, it isn’t in the shape of a parabola unless you play some tricks with the geometry of the space it flies through. The shape of the orbit is actually an ellipse that intersects the surface of the planet. A parabolic orbit would actually have it in an escape trajectory, and it would never return.
There is a lot of creepily euphamistic terminology surrounding nuclear weapons and strategic weapons systems intended to conceal the fact that these are all weapons designed with the ostensible purpose of executing genocidal-scale death and destruction. Reducing the concepts to statistics and game theory concepts allows one to discuss them without sounding like General Turgidson, walking around with his arm protectively curled around binders entitled “World Deaths In Megatons” and making pronouncements like, “Mr. President, I’m not saying we wouldn’t get our hair mussed, but I do say that no more than ten to twenty million killed, tops…ur, depending on the breaks.”
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