Coilgun Propulsion.... Realistic and Unrealistic

[Spacescifi]

Realistic: Shoot a ferromagnetic chunk of metal out fast enough and it propels your ship.

Unrealistic: Shooting that chunk of metal out so hard that it propels the spaceship like project Orion. Like the Kizinti lesson... only with metal slugs fired at high sublight speed. That would be space only use... and don't point your cannon at a planet either.

Both: IRL I reckon if one had a a coil cannon of such power, the mass of the necessary radiator fins and cooling equipment would cancel out the thrust to low levels  anyway. Still... interesting concept.

 

Praticality: IRL it may be practical for unmanned vessels, like asteroid mining drones.

 

What's easier? Refining chemicals for rocketry or just drilling and bagging metals before shooting out the back.

 

Limited fuel sure, but unmanned does not need ASAP flight dynamics anyway.

[.50calBMG]

Spacescifi threads... Always the same titles

[Scotius]

We won't use it for the same reason rockets don't shoot big steel bullets. It's impractical. And pointless. Hot expanding gases serve the same purpose without extra steps. Coilgun without chunk of metal inside = linear plasma accelerator.

https://en.wikipedia.org/wiki/Magnetoplasmadynamic_thruster

[kerbiloid]

A chunk of the metastable metallic hydrogen is also a chunk of metal, and has the same atomic mass as nonmetallic hydrogen being warmed.

So, coilgun + metastable metallic hydrogen pellets is a thing.

[DDE]

7 hours ago, Spacescifi said:

Praticality: IRL it may be practical for unmanned vessels, like asteroid mining drones.

Coilguns are for situations where you don't have any volatiles. It's simple as that. You can't "refine" a volatile out of dry rock.

[jimmymcgoochie]

Is anyone going to talk about the very obvious hazards of propelling your spacecraft with a relativistic projectile gun?

[Scotius]

2 hours ago, jimmymcgoochie said:

Is anyone going to talk about the very obvious hazards of propelling your spacecraft with a relativistic projectile gun?

Yeah. Some innocent cruises of your coilgun-ship, and several millenia later a sentient species in a galaxy far, far away will be making "Sir Glorp Lokdob is the deadliest son-of-a- bthig in Universe." memes.

[kerbiloid]

That's exactly what I always tell about the interstellar fly-by probes like Daedalus.

A one man's probe is another ... species apocalypsis.

[Spacescifi]

10 hours ago, Scotius said:

We won't use it for the same reason rockets don't shoot big steel bullets. It's impractical. And pointless. Hot expanding gases serve the same purpose without extra steps. Coilgun without chunk of metal inside = linear plasma accelerator.

https://en.wikipedia.org/wiki/Magnetoplasmadynamic_thruster

 

Wow.... so if sufficiently good plasma drives are made then this is the best ISRU drive ever.

 

Since ANYTHING can be turned into plasma, which means unlike conventional rockets you can use any kind reaction mass you want so long you heat it to plasma and eject it magnetically.

 

Even said in the wiki article that a beamed power version would have enough thrust to be an upper stage from low earth orbit.

Plasma drives are quite good, not torch but you do not really need torchdrives any way if your ship is big enough to roll sideways and generate sufficient g-force.

 

The main challenges are power and heat,  which can be helped with larger and longer engines to dissipate it as well as proper materials used.

 

Long story short, no proper manned spaceship will be small.... not for any prolonged voyage.

Edited October 15, 2021 by Spacescifi

[kerbiloid]

Plasma of different elements has different atomic mass and thus different momentum/energy ratio.

[Spacescifi]

6 minutes ago, kerbiloid said:

Plasma of different elements has different atomic mass and thus different momentum/energy ratio.

 

True... still... enough power will make up the difference.

 

 

Not totally related, but also a cool propellantless way to change trajectories.

 

Using solar wind and magnets only.

 

https://www.centauri-dreams.org/2017/12/29/the-plasma-magnet-drive-a-simple-cheap-drive-for-the-solar-system-and-beyond/

 

Spaceship drives gonna be big no matter what.

 

 

[Terwin]

1 minute ago, Spacescifi said:

True... still... enough power will make up the difference.

If you have arbitrarily large amounts of power, just use photons for reaction mass, as those can be generated directly and you no longer need to carry reaction mass...

[wumpus]

realisitic: shooting out an ion at extreme speeds so it gives some propellant.

Seriously.  Learn the rocket equation.  Don't bother with any other rocket science until you learn the rocket equation.  Nearly all rocket science stems from it.