This seems to be a solid rocket booster with moving parts. Isn't that the worst of both worlds? Lower ISP than liquid fuelled rockets due to the propellant choices and higher manufacturing complexity than a solid rocket booster...
Meanwhile the high thrust options we have are all very heavy, which means we have to carry more fuel, which means we need a bigger rocket, which means have to carry more fuel, and so on. The sum of this infinite series is finite, but it is still large.
If this tech lowers the weight of the first stage, it might actually RAISE the ISP of the rocket overall, even if it lowers the ISP of the engine itself.
The rocket equation doesn't account for thrust. It's terms are mass and ISP (or exhaust velocity).
>If this tech lowers the weight of the first stage, it might actually RAISE the ISP of the rocket overall, even if it lowers the ISP of the engine itself.
ISP is depends only on exhaust velocity. Changing the mass of the rocket cannot effect it.
Only sort of true. If you naively apply the rocket equation like you're imagining, you would predict a nonzero final velocity for a hypothetical rocket that has enormous ISP but thrust less than its weight. This is true if the rocket is starting out in orbit, but it's totally wrong when you're on the ground. Starting from the ground, you also have to fight gravity, so you care more about (thrust - weight) / mass.
It's very accurate when those things contribute little, and totally inadequate for modeling spaceflight if any are significant.
There are more complex versions that account for those things, but 'the rocket equation' is always understood to mean Tsiolkovsky's equation.
https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation
If you want to be more specific, e.g. include gravity then you can't say "the rocket equation".
> If you want to be more specific, e.g. include gravity
> then you can't say "the rocket equation".
[1] https://www.nasa.gov/mission_pages/station/expeditions/exped...
If we used aerospikes, then it would be a different matter.
Out of curiosity, if g was much greater, could it be infinite? What order of magnitude would g need to be for that to happen?
So there's definitely a quite low maximum gravity allowing practical space access.
As a corralary it should be finite as long as you're not inside a blackhole.
It should be asymptotic up to that point. Mathematically infinite at the horizon and then completely unbounded inside it (in the sense that it converges to infinity versus not converging at all ( see a "flat" universe versus hyperbolic)).
The moon is practically made of alumina-oxide solid fuel propellant. Along with its lack of atmosphere and low gravity, it would be preferable to use the literal dirt that is everywhere on the ground to loft precious refined or manufactured products into orbit instead of more efficient yet much more valuable cryofuels.
It also would have a very good shelf life, and a brutally simple machine can have the kind of reliability people would kill for in space. For most missions you'd need something with better ISP, but for some applications it could be just the ticket.
Granted it's not currently as simple as conventional solid rocket motors, but that will probably improve as they work out the kinks. The fact that it eliminates structural mass continuously is almost like a CVT for spacecraft; the staging doesn't happen in big, clumsy chunks, it gradually sheds mass all the way down to the payload.
i.e. a small amount of extra complexity for a big new feature.