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Comment Re: Hypersonic flight is the application du jour (Score 1) 131

I honestly don't get why the military keeps working on new hypersonic missiles when WE ALREADY HAVE HYPERSONIC MISSILES and have had for the last 50 years.

There's a big difference between weapons that achieve hypersonic speeds via a big rocket booster, and AIR BREATHING hypersonic weapons. In rocket fuel and explosives alike only about 25-33% of the mix is fuel - the rest is oxidizer. Thus, anything that breathes air - that gets its 02 for "free" from the atmosphere - is MUCH lighter and smaller than a ballistic rocket booster. This matters a lot when you're trying to load missiles onto, say, a warship, with strict tonnage and volume limits. Or an aircraft, for that matter. The big race right now is to develop working, reliable air-breathing scramjet weapons.

Ballistic hypersonics are a big deal again themselves for different reasons. The first is the "hypersonic glide vehicle," or HGV. Boosted with a normal ballistic missile, then it just glides on the residual energy. Unlike a MIRV, which just adjusts trajectory out of the atmosphere and then falls more or less ballistic, a boost-glide HGV can steer and maneuver in the lower atmosphere and make a significant part of its approach at below-the-radar altitudes. Even though it slows considerably, if you only have a few seconds to engage it once it pops over the horizon, the residual speed it has is more than enough. That's a game-changer and a significant improvement on Ye Olden RV.

The second reason is that missiles are really, really, REALLY good these days. Even as late as the 1990s, in Desert Storm, the US was using the old and much-hated AIM-7 Sparrow missile, who's record in combat was regrettable at best. 70 years after the USAF gleefully ditched guns for missiles on their "Century Series" fighters, air to air missiles have finally achieved the accuracy and reliability they over-enthusiastically expected of them when they were new. When the Tomahawk cruise missile was new, it was fairly good at penetrating air defenses simply by being "something small flying low." That was enough. Now, it's more or less considered a target; if your weapon isn't stealthy or at least low/reduced RCS, it's going to eat an interceptor going up against any decently modern air defense systems.

For poorer countries that aren't tech leaders who are looking to beef with the US, that means that previously uneconomical options are now cost-effective... such as rocket-boosted hypersonics. Yes, rockets are heavy, huge and expensive as hell, but if the warhead gets through and one hundred cruise missiles do not, they are cost-effective. See China for an example of this philosophy put into action.

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