ISP of 600,000!?

[thereaverofdarkness]

In the hard sci-fi anime Planetes, the Von Braun spacecraft is said to have an ISP of 600,000! Any ideas on how such a high ISP could be possible? It not only has an extremely high ISP, but a pretty awesome amount of thrust too, so it's not super slow like an ion craft. Something was said about its engine using mirror coils...

After the ship's ISP was mentioned by one of the show characters, someone remarked that it was 10,000 times the ISP they were using. So they were using engines with an ISP of only 60?? Are they referring to their reaction control thrusters maybe? Does any of this make any sense? Do the characters have any idea what they're spouting off about? Or are the show producers even trying to maintain a modicum of accuracy in these values? If this were any other show, I'd not be surprised by such ridiculous nonsense, but Planetes takes such great care in their realism that I'm not so sure they don't have some reasoning behind their figures.

What do you geeks think?

Edited September 17, 2013 by thereaverofdarkness

[maltesh]

Quick googling "specific impulse 600000" produced the following paper Antiproton Triggered Fusion Propulsion for Interstellar Missions which seems to indicate that an antimatter-catalyzed fusion nuclear pulse rocket can achieve 600,000 seconds Isp if the entire fuel pellet fuses.

Haven't watched any Planetes, so I have no idea what type of technology's available, though the "Tandem Mirror Engine" appears to be a reference to the Tandem Mirror Experiment in 80's fusion research.

[NGTOne]

Fission fragment rockets can have an Isp anywhere in the range of 100,000 to 1,000,000 (depending on design). Nobody's ever built one, but there's no technological reason that we couldn't (i.e. all the technologies required for them exist, and are reasonably well-understood and mature).

[Fractal_UK]

In the hard sci-fi anime Planetes, the Von Braun spacecraft is said to have an ISP of 600,000! Any ideas on how such a high ISP could be possible? It not only has an extremely high ISP, but a pretty awesome amount of thrust too, so it's not super slow like an ion craft. Something was said about its engine using mirror coils...

Specific impulse is just proportional to exhaust velocity, any engine that expells exhaust at 5,886,000m/s will have an Isp of 600,000. 6 million metres per second might sound fast but it's only 2% of the speed of light so it's definitely achievable. Any engine that exploits nuclear forces and uses the products directly as propellant, in other words, pure fusion engines, fission fragment engines, antimatter pion engines, etc could all have specific impulses in that range or better.

You could use the blackbody photons from a nuclear or antimatter reactor directly to generate thrust, in which case you'd have an exhaust velocity of the speed of light (Isp ~ 3x10⁷s) which is of course the theoretical maximum value of specific impulse.

[thereaverofdarkness]

Thanks for the replies! Wow, this stuff is amazing!

Any ideas what they might have been referring to with an engine with an ISP of 60s? I guess that would mean its exhaust velocity is only ~600m/s. That really does sound like a reaction control thruster eh?

[nhnifong]

How hard is the sci-fi in Planetes?

[NGTOne]

How hard is the sci-fi in Planetes?

Ultra-hard (with some allowances for future growth) - correct depiction of freefall, microgravity, and orbital mechanics, among other things.

[Specialist290]

How hard is the sci-fi in Planetes?

The whole thing was basically created to explore the question "What would happen if the Kessler Syndrome actually became a problem we had to deal with?"