# Sad feeb needs help with magic pixy-dust stardrive math

1. Nov 25, 2008

### Bailywolf

I'm working on a bit of speculative fiction, and I don't want to grossly embarrass myself- despite a few specific black-box departures from the strictly possible, I want a rough sense of physical verisimilitude... I need to work out the physics of what, when the setting specific fluff is stripped away, amounts to a full conversion drive. Drop matter in the front, get energy out the back with as close to perfect efficiency as to make no difference. This is the magic pixy-dust part (both in and out of the setting itself).

So far, I've found the best info by considering it like a matter/antimatter engine without the antimatter- any old matter will do, from nine tons of surplus plastic baby-doll legs to interstellar hydrogen gathered by a magnetic scoop (and hopefully, beating the Bussard drag problem).

I want my imaginary ship to operate at relativistic velocities, but my sad sad liberal arts brain chokes on the classic rocket ship equations.

The ship is going to be big- really big. Miles long. Millions of tons.

I'm trying to figure out how much mass I'd need to push it to a respectable percentage of C VS how long that might take VS how much mass I could scoop out of the interstellar medium along the way to top off the tank.

I've given google a workout, and found most of the easy to locate explorations of interstellar rocketry, but I'm having trouble adapting most of these treatments to my specific case.

Can anyone help a Creative Writing major out?

-B

2. Nov 26, 2008

### Savant13

You have a couple of options here. Antimatter might be good to start off with, but it's going to be a pain to produce on the road. If you insist on using antimatter, here is a link for an http://en.wikipedia.org/wiki/Antimatter_rocket" [Broken] A Bussard Ramjet uses an electromagnetic field to collect interstellar hydrogen, which is used to power a fusion rocket.

Last edited by a moderator: May 3, 2017
3. Nov 26, 2008

### Bailywolf

I'm not talking about AM- AM rocketery descriptions are just the closest thing to the math I'm trying to work out here. The pixie dust comes in the form of a full-conversion engine rather than a Matter/Antimatter annihilation engine. My best-guess would be that this would function in a similar fashion to an AM rocket without the tricky biz of creating and storing all that explodey antimatter.

The Bussard is a classic- Niven made good use of it in his early Known Space stories, but the physics are a little dodgy because of the drag on the ship's ramfield caused by the very interstellar stuff it scoops up.

With my magic conversion drive, I was trying to get around the AM issue and the ram field issue so rather than using the hydrogen for a fusion (pick your flavor) engine, it would just get dumped straight through the conversion torus, and vroom off she goes.

Because the drive can work effectively on any mass and part of the pixie dust of the engine directionalizes just about all the converted mass, it becomes a question of figuring out the rocketry equations which... frankly... I suck at.

-B

Last edited by a moderator: May 3, 2017