

Slingatron - build a railroad to space - binarymax
http://www.kickstarter.com/projects/391496725/the-slingatron-building-a-railroad-to-space

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czottmann
Backed.

Super-interesting concept, and the people at HyperV Technologies Corp seem to
know what they're talking about, so I am excited about this. For example,
their other KS project—the Plasma Jet Electric Thrusters for
Spacecraft[^1]—was successful both in funding and delivering what was
promised.

Also, you gotta love their pretty low-key / somewhat amateur'ish videos. ;)

[^1]: [http://www.kickstarter.com/projects/2027072188/plasma-jet-
el...](http://www.kickstarter.com/projects/2027072188/plasma-jet-electric-
thrusters-for-spacecraft)

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malandrew
Can anyone confirm whether the physics behind this makes sense?

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jccooper
Ballistic launch to orbit is... problematic. Getting something going fast
enough is tough (G loads, aero loads, material in the launcher, etc) but
doable. A really really big light gas gun should do, if the "Slingatron"
won't. Thing is, you cannot shoot something from the planet's surface to
orbit. Just can't.

If energy is too low, you're normal ballistic, and the projectile falls
somewhere downrange. If energy is too high, you escape from Earth's gravity
well, and you never see the thing again. (This might be fine for sending
materials to the Moon, though.)

What if the energy is just right? Well, you go into orbit with closest
approach at exactly your altitude. Which is you one orbit later... if aero
effects haven't already caused enough energy loss to run the projectile into
the surface, as they would on Earth.

(Side bar: even on the Moon or Mars, it wouldn't work well. Orbit at the
height of the highest lunar mountain would be very unstable, though it would
work better than on Earth! Might get a few orbits out of it before crashing,
if you can find a path without huge mascon changes, and if it doesn't hit your
launch facility. The top of Mons Olympus still has enough atmosphere to be
problematic.)

So you have to have high-altitude propulsion to alter your trajectory once you
get there, so you can orbit at a reasonable altitude. Which is why they note
that they need an onboard rocket. And that's unfortunate, because it throws
away the appealing simplicity of ground launch: passive payloads (and thus low
marginal costs). Now, alongside your space-gun you've also got to design a
mass-produced probably-expendable rocket system (with guidance) that can
survive wicked G loads. And so here come a lot of extra marginal and
development costs and a lower payload fraction. Does your gun-and-rocket
system still beat a 2/3-stage rocket? With enough volume it might, but where
do you get those customers?

I kind of like the idea of shooting your massive space-gun at an active target
that can do the orbital circularization for you; either a tug that refuels
itself from the projectile, or more exotically a rotating momentum exchange
tether. That on-orbit system adds additional development and capital expense,
in exchange for very low marginal cost. Which would be nice if you had the
volume--but nobody needs that sort of volume in space now (nor is likely to
for quite some time.)

But once some system with reasonable development costs and acceptable marginal
costs has paved the way, it might be a lovely system for bulk material
transport (probably mostly volatiles, like water, but maybe also metals for
construction).

