Discussion of The Rocket Equation and Different Types of Rocket Propulsion

[scaesare]

Would be ironic if the way we discover extraterrestrial life is to find PTFE floating around in their star systems! Paging JWST...

Given that it's estimated that every living being on earth has PTFE in its system, that might unfortunately be an effective method...

 

[JB47394]

There are apparently other Pulsed Plasma Rocket designs out there. There is a Slashdot post of a Gizmodo article, and one of the comments on Slashdot talks about firing uranium out the back of the thing. The commenter provided a link and, sure enough, there's a paper describing how that would work. It quotes the same performance as the Howe Industries work, so they may be going after a uranium fuel instead of Teflon. Perhaps Teflon doesn't scale to this level.

https://www.sciencedirect.com/science/article/abs/pii/S0094576522001187?fr=RR-2&ref=pdf_download&rr=881aca248c9d05bc

Here's the Slashdot comment that I was working from. Reading the whole thing is worth your time.

TL/DR: it's a gun that shoots fission plasma like little nuclear bombs. A 2,2kg projectile containing low-enriched uranium (LEU) and a moderator is fired (once per second) by a coilgun through a a flared 522kg 33cm-long LEU barrel (with the barrel flaring out in a HEU section at the base) at 1600 m/s (requiring 5MW of power), where it hits criticality. By a third of the way through the barrel its interior is already 1eV / 11605K, then is boosted to 500 eV by the HEU section as it leaves the barrel into a parabolic magnetic nozzle to direct the plasma. The fact that the projectiles move through in pulses makes it easier to cool the barrel, given that the thermal power present in the first third of the barrel is 5,4TW, and in the latter section, a peak of 46TW; obviously you're not going to withstand that continuously! 1% of the power from the explosion is recovered via coils, returning 29MW to the system, to power the gun and any other spacecraft needs. The result - 100kN of thrust at 5000 sec Isp, would be enough to lift 10 tonnes of mass from the surface of the Earth (not that you'd use it on the surface), and has a propellant efficiency 14x that of Starship's Raptor engines.

Obviously, this rocket is dirty, but almost everything from the explosion will have a velocity higher than the escape velocity of the solar system, so so long as you're not pointing it directly at Earth, it doesn't matter. Not that one engine firing in the direction of Earth would matter all that much anyway, but...

 

[ecarfan]

it's a gun that shoots fission plasma like little nuclear bombs.

Your summary had me from the get go. What a great concept! Very innovative thinking.