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Comment by ozborn | Hacker News Reader

I'm surprised SpaceX hasn't put together a proposal for ground-based ICBMs using a Falcon variant, seems right up their alley... I'm guessing the government doesn't want to be any more beholden to Elon and/or it's technically harder to convert than I realize?

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American ballistic missiles are all solid fuel, which avoids the need to babysit liquid fuel. For liquid, you either need to keep cryogenic propellant and/or oxidizer constantly topped up, or use a hypergolic fuel (which are almost universally quite nasty). Solid just sits in the silo until you push the doomsday button. Falcon is a liquid fueled rocket with a cryogenic oxidizer (liquid oxygen), so it'd make for a poor ICBM.

In fact, the US miltary doesn't have any liquid-fueled rocket engines of any type unless perhaps you count the very small engines that refine the trajectory of a MIRV bus after the end of the boost phase of an ICBM or SLBM.

And liquid-fueled rockets are all SpaceX knows.

Liquid-fueled setup is largely unsuitable for ICBMs. Want something that can sit in the silo for years and then be immediately available - so solid rocket motors are the way to go, plenty of other defence companies that are specialists in this.

The missiles are designed, built, and installed by the contractor. They are managed, operated, and controlled by the USER. USAF.

Over a 50 year life. With very strenuous time to launch requirements. By staff that is well trained, but not well experienced.

An ICBM is a lot different that putting a payload in orbit. Needs to sit for 10 years, with 21 year old technicians performing the maintenance. And then launch when desired, on short notice, perhaps with portions of the support systems inoperative.

A lot of engineers working at space companies are there precisely because they don't want to work on weapons systems.

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