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Old 10-25-2009, 02:50 AM   #1
Ulzgoroth
 
Join Date: Jul 2008
Default [Spaceships] Fuel versus reaction mass

I'm wondering just how this stands with fusion and antimatter rockets. Particularly in relation to air rams.

A chemical or nuclear pulse rocket has both-in-one. Others usually don't. An electrical thruster uses whatever feeds it power as fuel. Nuclear rockets, except nuclear salt water, have a built in reactor (with how much endurance, anyway?) providing a lifetime supply of fuel.

Fusion rockets could fuse their reaction mass...considering that they're plasma thrusters, they must be directly exposing the reaction mass to fusing material at least. But then there's air ram mode. It still has to fuse something, but it doesn't burn off anything from its tanks. Is the fusion reaction fuel negligible compared to reaction mass? Is it assumed to be able to fuse the air?

Antimatter rockets, of course, use the antimatter which is included in their tankage as fuel. That may be a negligibly small mass (except for the pion drives, of course), but it's essentially the entire cost of fuel. So how do antimatter air rams work? They can replace the reaction mass, but obviously that does nothing to stretch the antimatter supply. Maybe they should carry extra antimatter for air ram mode?
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