## Sunday, October 3, 2010

### Space Railgun

The most efficient way I can think of to move a large amount of mass to space is to have a site with many solar panels, and many deep cycle batteries, and a massive railgun. In existing rockets, 91% of the weight must be dedicated to fuel. Fuel which will instead by in the batteries. We would launch something along the lines of a 10 ton cargo container. With some kind of docking port.
Randall Monroe's XKCD suddenly becomes terribly relevant here, as Mr. Monroe used to be a NASA consultant. Accordingly, he brings me a chart of how much force I need to apply to escape various planets in the solar system. Escaping Earth's gravity is essentially the same as moving 5,478 6,379 km straight up. From this, I can calculate energy.
10 tons * 6379km / .1 s ^2 = 5.87 x 10^11 newtons. Quite a lot of force, for sure, but only 9% of what would be needed if it were a traditional rocket. And, this can be used over and over. Every few months, we can launch another cargo container, until either the batteries or solar panels break down, and if we replace one of those after every launch, the system will run indefinitely. (Solar panels last for about 20 years before requiring replacement. Batteries depend on the manufacturing, but I give them 5 years. We can replace a component once a year, or if we're paranoid, once a month. More than enough capacity left, so every launch should succeed.)
The best part of this system is that it would bank sunlight until launch day. You can't launch every day: there are narrow windows when you can get to your destination with the most gravitational assistance from the other planets, and reach your actual destination in space rather than drifting forever into the void. In the meantime, the system is not idle so much as gathering energy. Energy it will use when the time is right.
I'm hoping that this will reduce space launches costs by a factor of ten. Not as good as a space elevator, but a definite improvement. Did I write this before? I feel the strangest deja vu....

TwoYaks said...

Another problem with a railgun from earth is replacement of the rails. It would have to be very regular, since each launch would cause pitting and scorching of the rails.

There's also the issue of acceleration being too great for living squishy things. Not so good for manned spaceflight.

A rail gun in space works a bit better (though still has the acceleration issues), so maybe people could space-elevator on up to an orbiting rail gun, which flings you towards Phobos, or whatever destination you had in mind. At least, I think a railgun in space can't scorch... IIRC, it's oxidation driven?

TCG said...

Perhaps you are thinking of a massive coil gun instead whereby the projectile 'floats' inside the magnetic coils ,much like a maglev thus not needing any rails and thus no friction to be replaced.

OTOH to get the most benefit from it, much like rockets we're supposed to stick them on the equator... and there are not so many countries stable enough for such a massive project.