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Comment by cpgxiii | Hacker News Reader

Where exactly is that storability not needed? In the VLS cells of USN warships? In the missile canisters of field-mobile SAM batteries being driven cross-country (which, for survivability on the modern battlefield need to be moving a lot more)?

The only real cases a non-storable SAM/ABM is viable are where the target being protected is so small and so known that (1) all missile infrastructure on/near the target is vulnerable and (2) sufficient advance warning is available to handle liquid fuels as needed. There is really only one case of this: Guam. I think there is a case that a dedicated unique-to-Guam liquid-fueled SAM/ABM farm would go a long way to addressing stockpile and magazine depth concerns.

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> There is really only one case of this: Guam

Every U.S. base has this need. Stored munitions take out the first wave. That buys time to fuel the plentiful replacements.

Which means US servicemen handling extremely dangerous chemical oxidizers under fire. This stuff reacts explosively with everything, including common metals and anything organic.

Admittedly, it allows you to sidestep the regulatory hassles with handling those chemicals in the US, we can order troops to do all sorts of non-OSHA bad ideas, but wouldn't it be easier to just do the dangerous chemical handling on US soil, on a 9-5 in factory?

> Which means US servicemen handling extremely dangerous chemical oxidizers under fire

Fueling and oxidizing is automated now. The only risk would be the oxidizer being struck. But that isn’t super different from storing any ammunition.

> wouldn't it be easier to just do the dangerous chemical handling on US soil, on a 9-5 in factory?

No, it’s not. Particularly when you factor into the risk calculation the inevitability of exhausting those stockpiles in a conflict.

Man, this is such a weird hill to stand on.

Are we talking HTP+Kerosene or UDMH+N2O4 here? The article said HTP in which case you have 1% breakdown to water per year which will be an ongoing problem for stockpiles. N2O4 is nastier but more stable when contained.

Either way, you're going from "dangerous chemistry in the plant" to "dangerous chemistry in the plant, through a global logistics network, and in operations". The solid rocket fuel is pretty stable after it's built, just don't light it on fire or drop it too hard. Room temperature oxidizers are terrifying.

> a weird hill to stand on

To be clear, I know a good amount about rockets and less about missiles. I’m standing on this hill. I won’t die on it.

> Are we talking HTP+Kerosene or UDMH+N2O4 here?

I’m thinking kerosene or even methane. UDMH is a toxic mess.

> you have 1% breakdown to water per year which will be an ongoing problem for stockpiles

Sort of? It’s a nuisance. Not a dealbreaker. Certainly not an issue compared to running out of munitions.

> to "dangerous chemistry in the plant, through a global logistics network, and in operations"

The dangerousness of an energetics plant is not comparable to that of managing HTP. (And at a certain point, LOX becomes economically competitive for base protection.)

> solid rocket fuel is pretty stable after it's built, just don't light it on fire or drop it too hard

It’s great while you have them. Then you run out. That’s the current situation. Lots of perfect for a while, and then rationing while the enemy gets free hits.

Put two militaries against each other, one which can mass produce and fuel liquid rockets against one with fewer solid ones, and the former has an attrition advantage while the latter has a readiness one. If one only has solid-fueled rockets being made at a tiny clip, where the AP all comes from one plant, they become an easy adversary to defeat.

>> Are we talking HTP+Kerosene or UDMH+N2O4 here?

> I’m thinking kerosene or even methane. UDMH is a toxic mess.

Methane is absolutely out because of pressures/temperatures involved in keeping it liquid for any useful length of time. It would require both significant on-site gas storage as well as a gas compression plant to produce liquid methane on demand, both considerable additional targets (and very fragile ones at that). Kerosene + additives (e.g. RP-1 and JP-8) is the only really viable storable "friendly" hydrocarbon.

In practice, Hydrazine/UDMH + N2O4 is going to be much easier to handle safely than you think (Hydrazine itself is probably safer to handle than Ammonia, and there's a lot of Ammonia handled out there). You fill and seal the tanks at assembly, and outside of rare leaks the handling is fairly benign. Most notably, basically every major military has, as some point in the 20th century, done so - including aboard USN carriers, famously a very skeptical customer from a handling standpoint. Even today, every single F-16 (about 2000 in active service with about 25 operators around the globe) carries Hydrazine in the onboard EPU, and those operators are prepared to service (and handle leaks) safely.

While they aren't pleasant chemicals by any stretch, Hydrazine/UDMH + N2O4, by virtue of its immediate hypergolic behavior, is actually quite well-behaved from a fire/explosion safety standpoint, which is practically a larger concern than toxic fumes (consider how many other things in and around a combat environment can produce toxic gasses). Hydrazine/UDMH + N2O4 ignite promptly on mixing, and thus don't accumulate in an explosive mixture to be ignited later like alternative fuels and oxidizers.

I feel like the whole point is what's most economical/practical. Liquid engines are better than solids on specific impulse, throttling/relighting, this is great if you're going to orbit but solids are better for transport/storage and the downsides are minimal for interceptors or boost-stage for ramjets.

What liquid situation changes that? What liquid would be more economical? My instinct is towards minimizing operations outside of the US, keep it simple stupid and just go solid, but could it actually be reasonable to have, say, sealed containers of fuel/oxidizer of whatever type inside the missile and you "pull the pin" to uncap them and start mixing in the ignition chamber?

> could it actually be reasonable to have, say, sealed containers of fuel/oxidizer of whatever type inside the missile and you "pull the pin" to uncap them and start mixing in the ignition chamber?

No. The economics really shine if you can mass produce dry engines and then fuel them on site, ideally with locally sourced or even on-based manufactured oxidizer (if you’re going LOX).

Barring that, though, not being limited by AP would make the last comment’s hydrazine path acceptable.

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