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I'm watching this clip of a Russian anti-sat or anti-ICBM rocket launched from a silo and of course note that its early acceleration is much higher than for large spacecraft launchers. Why isn't cargo that can survive the high acceleration, given a push from a non-carried energy source, explosive or magnetic or beamed or sonic or... there are many ideas?

This question about an initial push to the rocket, as opposed to the more common but more radical ideas to completely replace rocketry. The delta-V required to enter LEO is about Mach 30 at sea level. If a gun blast can give that a Mach 3 start, that's pretty valuable in the rocket equation. And when optimizing design for this, perhaps for example the rocket engines could be better optimized for vacuum since they pass through most of the atmosphere in a few seconds.

Given the historic prominence of artillery in early rocketry, going back to Conrad Haas of the 16th century when it comes to documented rocketry development. Like multi-stage powder rockets and putting rockets on the back of birds, fascinating stuff! (Not that he ever advocated barrel launched rockets, so maybe it instead shows the long going split between rockets and barrels in the artillery tradition?) Continuing to Wernher von Braun who first worked for the artillery, both in Germany and then again in the US, isn't that right? Given that, why hasn't Jules Verne's canon concept for how to go to space been successful in the form of a kick-off that doesn't add to the mass launched? Is there a more practical potential in it for the emerging dedicated small-sat launcher market? I've never heard of any investments in canons giving rockets an assist, so I wonder what the main problem is.

LocalFluff
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  • While your clarification of the difference stands, that doesn't invalidate relevance of the linked answer. Anti-ICBM rockets need to get to the target fast - can't afford wasting time at low initial speeds, but that comes at cost to almost every other trait, like payload mass, total delta-V or structural overhead to withstand the acceleration. – SF. Jul 03 '19 at 12:15
  • Two main problems: 0 to Mach 3 over the length of a barrel means extreme acceleration - useless to all but the most sturdy of cargo. This can be mitigated with a longer barrel, but that comes with more drawbacks. Mach 3 in sea-level atmosphere means extreme drag, reducing the benefit gained from the initial launch. – Jack Jul 03 '19 at 12:17
  • @Jack But the air defense rockets launched at high acceleration (I don't know when they reach Mach 3, but they accelerate a whole lot faster than large launchers), they probably contain some pretty sophisticated electronics and sensors. That's stuff that planetary astrophysicist would make use of as air defense against our conspiring enemies of disknowledge on Uranus (especially Oberon according to a Facebook trend). – LocalFluff Jul 03 '19 at 12:50
  • When you compare the energy of motion, Mach 3 is only 1 % of the energy of Mach 30. – Uwe Jul 03 '19 at 13:09
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    " von Braun was able to pursue a career as a rocket scientist in Germany due to a "curious oversight" in the Treaty of Versailles which did not include rocketry in its list of weapons forbidden to Germany" from Wikipedia. Thus Wernher von Braun did work on military rockets, but never on artillery using gun barrels. – Uwe Jul 03 '19 at 13:12
  • You should read about project HARP. – Uwe Jul 03 '19 at 13:28
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    @LocalFluff yes, air defence rockets have high accelerations (see Sprint for an extreme example), but they are self propelled - ie. a rocket - and accelerate over a larger time and distance. Anything that is 'fired' out of a gun has much higher accelerations. Back of the envelope maths: 100g acceleration (way too high for most scientific instruments) gets us to ~Mach 3 in 1s and requires a ~500m barrel (way too long to be practical) – Jack Jul 03 '19 at 14:41

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There are 3 main reasons:

  • Cost
  • Safety
  • Increase in dry mass

Otherwise its a great idea. The cost thing is fairly straight forward, just crawling along form storage to the pad required a 2,721 ton US$14 million monster, and that peaked at 2 mph. Even if you where prepared to tolerate a significant g-load, what ever structure is getting your rocket to decent speeds is going to be tall, subject to high loads and speeds. Its also going to be bespoke/produced in small numbers. AKA expensive.

Safety is less obvious. Apart form the obvious bit where firing anything out of a gun to a significant speed doesn't scream safe, there are problems with having a very small window to determine a startup failure and no real abort modes.

Probably the least surmountable problem is the increase in dry mass. Any significant acceleration above what ever the rocket was going to have in the first place is increased structural requirements which is increased dry mass which is a major problem.

So far nothing with a "cannon" type approach has managed to make this balance work net positive. However stratolaunch was a promising alternative of a very similar idea. Shame it's died, but something like it may happen again.

ANone
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  • I don't see how this could be categorically so. Up to some speed, initial acceleration of a ground based power source certainly must be adding something. Earlier acceleration is more productive in covering distances. And launch pad operations seem expensive and risky as they are, a gun barrel approach might improve that. Artillery failures are much less common than rocket failures. – LocalFluff Jul 03 '19 at 13:08
  • @LocalFluff: it certainly does add something. I have often thought it was a shame there wasn't a way to get the early speed for exactly this reason. I think the artillery analogy is miss-leading though. The solid lump of metal in the shell isn't comparable to a rocket. Or at least no one has yet managed to make it economic yet. But stratolauch is proof that the idea of early acceleration best not being done by a rocket is not inherently a bad idea. – ANone Jul 03 '19 at 14:12