ISLAND ONE, a prime time family sitcom set on the High Frontier

> Now, for that acceleration tunnel. The aerospaceport is an
> artificial island on the equator

Equator is good, of course. But why an island? Every meter of
altitude decreases the delta-vee you need, and when you're paying
the rocket equation every bit counts. Plus, the first meter of air
at sea level has a lot more drag than the first meter of air you
encounter if you're starting from a kilometer or two above sea level.

> The important thing here is that NOTHING IS THROWN AWAY (even the
> ET's descendant is used over and over again)

While building colonies, I would be more inclined to have the fuel
tanks be material that can be used in orbit.

> The acceleration tunnel starts a hundred metres or more
> underground, and the shuttlecraft travels in a circle all the way
> around the circumference of this island

When you're dealing with circles, the equation to keep in mind is
a = v^2/r. You can go around a circle as many times as you feel
like to build up speed if you have a payload that's sensitive to
acceleration, but it's going to be exposed to the centripetal
acceleration to keep it curving around the circle. If your limit is
3g and your radius is 2.5 km, that gives

30 m/s^2 = v^2/2500m

30*2500 (m/s)^2 = v^2

v = ~273 m/s

I haven't plugged that in as u in the equation ANTIcarrot supplied,
but it sounds like the straight part is going to have to be a bit
longer.

--- In spacesettlers@yahoogroups.com, "Xenophile"
wrote:
>
> --- In spacesettlers, "ANTIcarrot." wrote:
>
> > From: Xenophile
>
> >> What I'm wanting to know is what if I don't want more than 3
G's,
> >> and am willing to settle for one tenth of orbital speed? How
long
> >> does my acceleration tunnel need to be?
>
> > Basic physics: v^2 - u^2 = 2*a*s
> > v = final velocity
> > u = initial speed
> > a = acceleration
> > s = distance
>
> It's my sucky math that has kept me out of the physical sciences
and
> engineering. I'm glad to have the chance to "virtually" hang out
> with folks who have the skills that I sometimes need, but lack.
IOW,
> thanks.
>
> > Rouding up G to 10m/s^2
>
> Seems reasonable. There's going to be some losses due to air
> resistance anyway.
>
> > Define orbital speed though. In LEO it's ~8kmps, but at GEO its
> > closer to 3kmps.
>
> LEO, so we're talking 8 kmps, or nearly 18,000 mph. Again, some
of
> that will be lost to the atmosphere.
>
> > One tenth of the former would require a tunnel 10.6km or 6.6
miles
> > long
>
> This is fantastic news! I was worried that ten miles might be too
> short. In fact, this is such good news that I'm going to spill my
> guts about my fictional launch system.
>
_
>
> The shuttlecraft consists of the "tank stage" and the "orbiter."
> Take a Space Shuttle External Fuel Tank. Deform it into the "tank
> stage." Add some landing fear, control thrusters, and a set of
> rocket engines at the butt end. These would be improved SSME's,
such
> as the (I think they're called) Cobra engines, only with another
> twenty years or so of development. It is a lifting body, looking
> kind of like a fat pumpkin seed from the side, and a delta from
above
> or below. It looks a little like the plane Steve Austin crashed
in
> the opening credits of _The Six Million Dollar Man_. There are no
> windows, but there are lights and such. Oh, and put a "well" near
> the front, on the topside, the same size and shape of your orbiter.
>
> Now, take an improved and modified and so on version of the
Shuttle
> Orbiter. This is the orbiter. Put it in the well, so that the two
> blend into one shuttlecraft. The shuttlecraft is shot out of the
> acceleration tunnel at about 0.8 kmps (1,800 mph).
>
> The tank stage takes it to 90% or more of orbital speed, then
drops
> away (a sliding panel covers the well and maintains the smooth
> contours). The tanks stage returns to the aerospaceport to be
used
> again. The orbiter continues to orbit, where it docks with the
> orbital cruiser, which is a passenger OTV. As soon as the
passengers
> have left, a new set of passengers, returning from space, boards
the
> orbiter. The orbiter undocks and returns to the aerospaceport.
>
> The important thing here is that NOTHING IS THROWN AWAY (even the
> ET's descendant is used over and over again) and that the orbiter
> spends less than five hours from passenger boarding at the
> aerospaceport to passenger unboarding at the same or another
> aerospaceport, at which point it can be re-readied for use. It
does
> not sit in orbit for days or weeks on end. It should be able to
> launch at least twice a day.
>
> Now, for that acceleration tunnel. The aerospaceport is an
> artificial island on the equator, five Km in diameter and with
thick
> walls on both north and south sides, walls that rise from beneath
the
> sea on the western shore to a height of 250 metres at the eastern
> side, each with a fifty metre diameter pipe-like structure
extending
> another Km out to sea, gradually curving up to a 45 angle and a
> height of 500 metres. There is a ring of aircraft terminals,
hotels,
> and other such structures just inside the walls, with the north
and
> south beaches loaded with tourists. The interior of the island is
> given over mostly to landing strips, with a few hangers and such.
> The acceleration tunnel starts a hundred metres or more
underground,
> and the shuttlecraft travels in a circle all the way around the
> circumference of this island (so almost 16 km, or a little over 9
> miles) and then out to sea while rising to that full 500 metre
> height. This is more than enough to achieve the 10% orbital
velocity