On 23 Feb 2018 at 20:29, Jeff Zeitlin wrote:

> ... as posed in my previous question to the list, what do you use to
> get a ship from dirtside to space, without having to completely snap
> the suspenders of disbelief?

Well, you could leave the ship in orbit and ride some sort of shuttle
up and down. That's doable with WWII era tech if you want to work at
it. Maybe lower.

Given fusion reactors (hot fusion, not cold fusion) you can create
quite a rocket. If "raw" fusion rocket is a bit much for you (ie the
exhaust is basicly plasma from the reactor run thru an MHD "nozzle")
you can just use the reactor to heat liquid hydrogen to very high
temperatures and run it through a more normal nozzle.

The higher the temp of the exhaust, the better the Isp. That is, the
higher the exhaust velocity the less fuel you need for the same
acceleration.

Rotating orbital tethers can work but are kinda hard to explain.
Basicly a long rotating "cable" in orbit. You dock to the far end
(and an outbound cargo docks to the low end) and as the asssemblage
rotates you wind up in atmosphere at a more reasonable rate and the
outbound load winds up in space with more than orbit velocity.

Cable strengths depend on the loads handled and on how high & low the
pickup/dropoff points are. You also need to balance the in & out
loads (not exactly but somewhat close) to avoid messing up the orbit
of the "hub".

Usually set up so that the low end is stationary (only momentarily)
at some height above the ground. Anything from meters to kilometers.
Rotation rate and height of hub are chosen so the "touchdown" points
are equally spaced around the equator.

You can even have multiple tethers in the same orbit to increase the
frequency of trips upo & down. "layers" of tethers allow for getting
passed from ground to low orbit, and from low orbit to higher orbits.

Requires steady nerves or good automation to dock on either end. :-)

Beanstalks require *much* stronger cables and are a lot harder to
construct.

Dynamically supported structures like "orbital towers" Don't require
the strong materials but require a *lot* of power and if power is
lost they collapse on themselves with not pretty results.

Something like a Lofstrom Launch Loop doesn't fail as
catastrophically.

And then there are laser launch systems. Which can double as nasty
planetary defense stations.

More details are available at lots of places.
--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com