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It's worthwhile watching the launch of the Chinese Long March vehicle: https://www.nasaspaceflight.com/2019/06/china-first-sea-laun...

They appear to shoot the entire vehicle out of a cannon-like container, then air-ignite the booster. I can't think of another launch vehicle that does this. The US did this sort of launch for the Sprint anti-ballistic missile: https://www.youtube.com/watch?v=msXtgTVMcuA

It's worth noting that's Long March 11, which is a completely different vehicle to the Long March 5 (the one which will launch China's robotic Mars mission(s)) with the only commonality being that they're both Chinese.

Long March 11 is based on solid rocket motors and is much smaller than Long March 5 (roughly equivalent to a Delta IV Heavy or an expendable Falcon 9) which uses kerosene and oxygen for the first stage and hydrogen and oxygen for the second stage.

That's a "cold launch" in ICBM terminology. It was popular during the 1980s - the U.S. Peacekeeper MX and Soviet SS-18 (among others) used it, as did Soviet VLS tubes and every SLBM.

There is a nice SS-18/Dnepr launch video: https://www.youtube.com/watch?v=XwvNuZLASdE

The sequence goes like this: - the missile is ejected from the silo by mortar system, that generates a huge amount of gasses under the missile to push it out, acting on a piston part located right under the missile - the missile jumps out of the silo and the piston is ejected sideways via a small solid rocket motor - some wiring harnesses and what looks like guide wheels is ejected from the missile - the first stage engines of the missile (in this case liquid & hypergolic) are ignited and the missile starts to climb

This technique keeps the silo pretty much intact, which is nice for an ICBM acting as a space launch vehicle. Also IIRC for war use, it was theoretically possible to reload the silo and fire another missile before a retaliatory strike could destroy it, causing all kinds of havoc in cold war scenario planning.

Frankly, I'd like to see some kind of maglev-based launch platform that propels the rocket up the side of a mountain, and then lets the rocket's own boosters take over.

How about a very similar concept, but implemented as a deep vertical shaft in the ground? The initial acceleration could be provided by electromagnets with the rockets only kicking in once the vehicle reaches ground level?

The tubular structure of most large rockets is well suited to withstand many gs of load along its axis. It's also quite fragile wrt side forces and bending. Making it stronger makes it also heavier.

A device that can carry several tons to GEO and to start in a slanted position along a mountain would be a very different beast than a usual rocket.

To say nothing about building several miles of an excessively straight maglev bridge along a mountain which is likely not that straight, and also highly visible.

If it’s accelerating along the longitudinal axis, then the slant doesn’t matter. It’ll never experience more than 1g orthogonal to the axis.

The problem is getting out of the thickness of the lower atmosphere. That’s why rockets go up before they go sideways.

That wouldn't fit on most ships.

Yes, I've often found that events using "mountains" are intended to occur on land.

Insert obligatory "we're going to need a bigger boat" comment here.

Very cool.

>They appear to shoot the entire vehicle out of a cannon-like container, then air-ignite the booster.

They have an interesting launch platform, maybe they are trying to limit the damage to equipment? As it is their strategy seems relatively gentle to their launch platform. This could give them faster turnaround on launches.

Don't submarine missiles work like this?

Most man-portable anti-aircraft and anti-tank missiles work like this as well, for obvious reasons.

Yes, but man-portable, AA and anti-tank missiles, and sub-launched ballistic missiles, are not carrying quarter-of-a-billion dollar satellites. Typically, you don't want launch vehicles to have to withstand heavy loads not related to actually flying vehicles into orbit. Ground support stuff is not supposed to impose design loads, but I would imagine that firing the launch vehicle out of a cannon would actually impose high enough loads to cause engineers to design to those loads.

What happens if the rocket fails to fire - I mean, it's a rhetorical question, I can imagine what happens.

It makes a big splash into the ocean?

That's a missle, and lauching like that don't make sense for rockets.

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