Fusion drives stats

[jedidia]

Well, I'm not asking for the stats per se, I can find those pretty quickly. What makes me wonder is why there are so huge performance differences between different kinds of fusion drives.

a D-T fusion drive is projected to have an ISP of 22,000 and a thrust of roughly 100,000 newtons, with an energy output of about 16 MeV.

a He-D drive has a higher total energy output, an incredible isp, but my granny could probably apply more thrust to a spaceship.

where do these huge differences come from? In my (VERY limited) understanding, it should be possible to rig a D-T fusion drive to provide low thrust/high ISP, and an He-D drive to provide high thrust/low ISP.

 

[Urwumpe]

Remember:ISP depends not only on the fuel used, but also how you use it. For example think about different mixture ratios or nozzle shapes.

If I remember correctly, the Black Dart main engine peaks at 86000 m/s specific impulse (He3-fusion, little hydrogen injection), but produces only very little thrust... I used some handwavium in the construction, I admit it, but in general, the energy balance is sound.

 

[jedidia]

Hmmm... how much Handwavium would it take to construct a variable magnetic nozzle to allow "gear-shifting" on a fusion drive?

 

[Linguofreak]

Hmmm... how much Handwavium would it take to construct a variable magnetic nozzle to allow "gear-shifting" on a fusion drive?

Unknown. We're far enough from single gear fusion drives that we can't really say how much more it would take to allow shifting.

Remember that, as of now, we don't even have operating fusion power plants...

 

[Urwumpe]

Remember that, as of now, we don't even have operating fusion power plants...

But controlled fusion explosions.

---------- Post added at 09:44 AM ---------- Previous post was at 09:43 AM ----------

Hmmm... how much Handwavium would it take to construct a variable magnetic nozzle to allow "gear-shifting" on a fusion drive?

Pretty much a lot in terms of switching power. You need to counter the pressure of the exhaust during the expansion, and that in any gear...

Without switching the power, it is simpler, but still a lot of handwavium.