Spike Jones wrote:
>
> jeff davis wrote:
>
> > ...wherein we find launch costs estimated at $600/Kg (in
> > 1990 dollars) for a 200 kg payload. I
> > believe--someone care to confirm?--that this is
> > substantially cheaper than than current launch costs
> > using conventional, ie multistage rockets, methods.
>
> Yes however there are still substantial problems. In theory
> we should be able to find a way to round out the orbit, but
> I haven't seen anything really convincing. Mike Lorrey pointed
> out that it is possible to harden electronics to 1400G. We
> still need to carry some fuel and some means of keeping the
> orbitter pointy end first while we burn that orbit adjust
> fuel, which would need to be a substantial fraction of the payload,
> depending on the angle we left the atmosphere.
Since your projectile is already hardened for 1400 g's, make the fuel an
explosive shaped charge (or several charges) to optimize density,
perhaps using that theoretical N60 nitrogen fullerene explosive (which
as I recall is 100-125% more effecient than PETN).
=================\\
DDDDDDDDD||payload >>
=================//
where D are shaped charges and the "=" is the casing.
>
> > It would seem to me that for any payload capable of
> > withstanding the rigors of such a launch method--bulk
> > payloads of food, water, fuel, and building materials
> > immediately come to mind--
>
> Nuclear fuel would be good perhaps, since it is so
> dense. Water might be a bit problematic since its
> density is low enough that the payload ballistic
> coefficient of the shell goes down.
>
> I was once interested in a rail launch where a
> human is sent up, submerged in water. I got
> into this after putting a number of minnows in
> a centrifuge at 100 G for 10 minutes. They all
> survived. {8^D
I'm not surprised. USAF G tests once showed a person suitable harnessed
and equipped with G suit could withstand momentary 30+ G accelerations.
The only real difficulty in water immersion is dealing with possible
nitrogen narcosis (bends) produced by relief of acceleration. Using
helium/oxygen mixes as deep sea divers do is an obvious solution, along
with breathing hyperoxygenated fluids.
>
> My design for a rail launched
> human capsule didn't work out with a reasonable
> rail length, unless you can go up the side of one of
> the worlds tallest mountains. This can be problematic,
> for as soon as you propose it, some silly prole will
> argue that mountains are sacred, yakkity yak and
> bla bla.
Kilimanjaro. Pay the Kenyans enough bux and they'll fall all over
themselves.
>
> > the economic advantages of
> > gun launch present a striking commercial opportunity.
>
> > ...would seem a promising means to that end.
>
> > So I have to ask, "Where's the problem?. Why hasn't
> > anyone done this?"
>
> Its hard. Even after ya know how to do it. {8-]
The problem is that its so '19th Century' an idea that ignorant money
people automatically assume its an insane idea.
BTW: did Bull's barrel segments get destroyed after the war or are they
still sitting in some British scrap heap?
>
> > Also, sometime back I read that the PV solar panels
> > for the Internation Space Station generate 65 kw and
> > cost $500,000,000.
>
> Ja, those things are pricey. They are specialty PV
> panels, able to withstand launch environment, orbit
> environment and still demonstrate 3 nines reliability
> after 5 yrs in orbit.
Primarily because you've gotta keep a similar setup running in a vacuum
chamber here on earth with more run hours than the one in space accrues.
>
> > parabolic dish made of minimum thickness styrofoam
> > and coated with a film of appropriate reflective
> > material.
>
> Styrofoam wont hold up in earth orbit for even a few
> days. Atomic oxygen and UV will eat it up. But I
> hear what you are suggesting. The convincing studies
> to date have been on mylar balloons which are metallized
> by vaporized aluminum on orbit. Then the reflective surface
> holds up after the mylar surface is oxydized away. Ill see if
> I can find URLs that refer to it.
Take the mylar balloon to inflate to produce the surface, then use an
ion deposition system to thicken one side of it up.
>
> > For comparison purposes, at 10% conversion efficiency,
> > and 1300 watts/sq meter, you can get 65 kw out of a
> > dish a mere 13m in radius. (And a dish of 100m radius
> > delivers a healthy 4 mega watts.)
>
> The problem with the biggie dish is the conversion at the
> focal point. Since we are materials limited to max temperatures
> below about 4000K, there might not be any big advantages
> to making one huge reflector.
Well, normally you get about 250 deg F in space in normal sunlight in
earth orbit, which is 394 K, so you can focus ten times the normal
sunlight on your heat sink. The big advantage of focusing energy is that
PV cells work more efficiently the more sunlight you shine on them.
Krystall, Inc. of Issaquah, WA had this demonstrator I saw a few years
ago of a cylinder of GaAs/GaAnt multi-layer cells converting power off
of a natural gas burner stack. They were developing a hybrid electric
car and portable generators using said setup. They were getting several
kW of power from I'd guess about 24 sqare inches of solar cells.
El cheapo system I can think of: several large (2 meter dia) umbrella
mechanisms that have a gold plated steel mesh fabric focusing on a few
square decimeters of high efficiency solar cells.
I say screw all the heavy duty testing and 3 nines performance
requirements. Spend the money on shipping up twice as many as you need
instead and test em in orbit, keeping those with bad components as
scavenge items to repair those that fail in the future.
>
> > Two immediate obsevations. Weightlessness would seem
> > to allow an EXTREMELY large dish,
>
> Right, it does. So how do we convert the energy once we
> concentrate that much of it?
PV is fine for 5-10 times concentration levels, there is also a liquid
metal thermal system that the USAF's Phillips Lab developed for an OTV
vehicle.
>
> > and the hard vacuum
> > of space seems to suggest that the reflective surface
> > would not be subject to oxidative degradation.
>
> Only if we get waaaay up there. Unfortunately the
> leo environment has atomic oxygen, highly reactive
> and at high speed relative to your orbitter. Its pressure
> is very low, of course, but there are still jillions of
> collisions per square cm per second, and materials
> break down after a while. If we can lift the stuff
> a couple thousand km, this problem goes away,
> and then we merely need to contend with radiation.
Gold does not react easily with this atomic oxygen, which is why it is
the envelope of choice for many satellites.
>
> > I envision the dish as spin stabilized to keep it
> > pointed at the sun,
>
> Sure but you still need to adjust the axis of rotation
> a degree a day to account for its orbit about the
> sun. {Assuming you have it orbitting in the earth's
> neighborhood.} So spin stabilization doesnt solve
> everything. But a degree a day isn't that hard to do,
> and the propellant required is estimated thus: it takes
> as much angular momentum to change a rotating body
> pi/2 as it had to start with, so you need to turn 2 pi per
> year, so estimate the moment of inertia of the dish and
> the necessary rotation rate, multiply to get the angular
> momentum and you need 4 times that much per year.
Unneeded. There are these long metal magnetic posts that are used in
satellites to orient them to a magnetic field. Hooking one of these up
to a clockwork mechanism, a reaction wheel, and some PV sensors to
detect the direction of the sun and you could keep it oriented without
any fuel use.
>
> Perhaps that argues against getting *too* carried away
> with the size of the dish, since moment of inertia increases
> as the 4th power of the diameter of a disk in general.
>
> More later on that, gotta go.
>
> > Maybe I'm just talking out my asteroid, but hey, I'm
> > havin' fun.
>
> Me too. Speaking of which, shall we start a Lorrey-esque
> subgroup to discuss this, or will the extropians indulge us
> by allowing us to post orbit-gun and inflatable dish stuff
> on the main list? spike
Well, Spike, I'm still waiting on your help with the XLSim
spreadsheet... ;)
This archive was generated by hypermail 2b30 : Sat May 11 2002 - 17:44:15 MDT