2
$\begingroup$

Im trying to find a way to get a torch-ship up to some 0.x % of lightspeed with a ion-thrust like engine.

Let assume power is a non-issue, unless its becoming absurd (it makes no sense to propel a mountain of propellant) in a human viewpoint time-frame. The upper tech-limit to this endeavor is nuclear fusion.

Could such a engine be made, kept running and meaningful propel a ship up and down from c Within a human lifetime? If yes, how would such a engine work and look?

Improve this question
$\endgroup$
6
  • 1
    $\begingroup$ No. Ion drives have absolutly terrible Thrust to Power ratios. Modern Ion drives give you 1 Newton / i think 5 kW. Pushing anything heavy with Ion drives just wont happen. You would need a GW scale powerplant (Electrical, not thermal output) and the mass of that plant will put your acceleration to around 0 m/s². $\endgroup$
    – ErikHall
    Commented Mar 10 at 21:01
  • 4
    $\begingroup$ If you haven't already check out the Atomic Rocket Website (link below). It contains an extensive list of space propulsion alternatives along with the technical pros and cons of each. Link here projectrho.com/public_html/rocket $\endgroup$
    – Mon
    Commented Mar 10 at 22:24
  • $\begingroup$ Agreed with ErikHall, ion drive typically has lousy specific impulse, higher Isp means higher efficiency in the conversion of mass of the propellant into delta v. Ion drive would takes forever to get to the desire speed despite it costs next to nothing. $\endgroup$
    – user6760
    Commented Mar 11 at 6:56
  • 1
    $\begingroup$ You haven't really defined what you expect "torchship-like acceleration" to be. 10G? 1G? 0.1G? Project Rho has one suggestion which is >300km/s delta-V and >0.01g acceleration, but that's a little low by softer scifi standards though quite a bit more achievable. You also haven't really said what you mean by "ion drive". Is this purely electrostatic propulsion? electromagnetic? Do you include plasma thrusters? Is an IEC fusion rocket or mag-orion an "ion drive"? A little more detail would be appreciated! $\endgroup$
    – Starfish Prime
    Commented Mar 13 at 9:44
  • 1
    $\begingroup$ Is there any particular reason you want an ion drive? Perhaps a better question would be to formulate your requirements and ask what kind of drive might fit those parameters? $\endgroup$
    – Gillgamesh
    Commented Mar 14 at 20:34

1 Answer 1

Reset to default
4
$\begingroup$

The problem with ion thrusters is not just that they require an absurd amount of power, but they require electrical power, and equipment to transfer that power from electrical machinery to the exhaust plasma. So you not only need ~40 gigawatts of electrical power to produce a single SpaceX Raptor's worth of thrust, you need to convert that power from whatever your power source is with many gigawatts of waste heat from conversion losses, and transmit it all to and through your engines via electrical conductors and more power conversion/regulation machinery, then the engines themselves are only around 60% efficient so you've got another 16 or so gigawatts of waste heat to get rid of.

So, your ion thruster ship is evaporating due to the waste heat it produces long before it's producing true continuous-acceleration torchship levels of thrust.

The specifics are of course unknown, but a real fusion torch drive would operate much more like a conventional chemical engine, generating the power by fusion within the plasma being used as reaction mass and using magnetic fields to direct that plasma in the desired direction for thrust without making any effort to convert or handle it in any other form. The machinery would instead be designed to absorb as little of the power output as possible, and may incorporate regenerative cooling similar to chemical engines, which are already able to operate at quite extreme power outputs.

Improve this answer
$\endgroup$
3
  • 3
    $\begingroup$ "So, your ion thruster ship is evaporating due to the waste heat it produces long before it's producing true continuous-acceleration torchship levels of thrust" Is it just me or is anyone else getting the physics of Santa Clause Christmas parcel delivery vibes? ;) $\endgroup$
    – Pelinore
    Commented Mar 11 at 3:09
  • 1
    $\begingroup$ @Pelinore you're nowhere near the amount of heat Santa would generate $\endgroup$
    – Separatrix
    Commented Mar 11 at 9:31
  • $\begingroup$ @Separatrix Well, his sled would flash into ash in under a second iirc, mere seconds if I'm not, but I still get the vibe ;) $\endgroup$
    – Pelinore
    Commented Mar 11 at 9:34

Not the answer you're looking for? Browse other questions tagged .