> While railgun, gas gun or any other type of projectile system makes for
> easier earth to orbit travel, the reality is there is not much you can
> do about the orbital inclination. Once such a large system is
> constructed, it is pretty much stuck where it is.
> Some will counter that you can 'dogleg' to the proper orbit once you
> achive primary orbit, but it takes a vast amount of energy to do this.
> For example (albeit a bad one), if the shuttle used all of it's onboard
> fuel, it could only change its orbital inclination by 3 degrees. Not
> enough to do anything meaningful.
I have trouble with the idea that being stuck in some orbit
is a tragedy, in itself. For a space station, clearly it's not a
problem. And the vast bulk of truly useful stuff in space is
still probably geosynchronous communication satellites.
Freedom to go anywhere doesn't mean much when there's
an awful lot of nowhere between the "meaningful" places.
And it's pointless in cases where the real design criteria is
maintaining a certain fixed orbit.
But let's say you want to change orbits. If you can ship fuel
to orbit at $200/lb, what happens to your objections? If that
fuel is xenon, and the thrusters are ion drives, and you *do*
have a lot of time, what happens to the on-board energy
requirements?
The issue really isn't energy -- it's what sort of tradeoffs you're
willing to live with. If you want something to be very expensive,
simply require that it do whatever you can think of, as fast as
physically possible (rather than whatever you can settle for,
as soon as it really needs to be done.) When I hear the
objection to gun-style launch that you can't easily point
the gun, I just sigh, and say, "point in the same direction as the
nearest satellite TV dish, then to where you think the
space station is right now." For large orbital facilities, how
many orbits will really matter?
And, yes, your example really is a bad one: the Shuttle doesn't
have much onboard fuel capacity because it was never intended
to deviate much from any orbit it was pointed to from the ground.
For an intraorbital ferry, it would be hard to come up with a
worse design. Designs for actual intraorbital ferries, unsurprisingly,
look nothing like the Shuttle. Most of those designs have fallen
prey to the daunting economics of rocket resupply -- they would
need to replenish their fuel and their ablative shielding from
somewhere, somehow. And that somewhere and somehow are
Earth and rockets, respectively. Both fuel and ablative shielding
are highly G-force resistant, hence reasonable payloads for gun-
style launch.
-michael turner
[EMAIL PROTECTED]
> Joe L.
>
> On Sat, 2003-09-13 at 21:05, Michael Turner wrote:
> > Larry asks if balloon launch makes a difference for launch.
> > In LEO, the potential energy from altitude is only about
> > 10% of the kinetic energy in orbital-speed motion, and
> > balloons can only get you 20 miles of altitude where what
> > you really need is more like 200. At very high altitudes,
> > there is the advantage of starting with less atmosphere
> > to punch through, but basically we're talking about low
> > single-digit percentages of cost and benefit.
> >
> > At least one X Prize contestant is going with a balloon
> > lower stage (or would that be "upper stage"? I'm all confused
> > now.) However, the X Prize isn't about reaching orbital height,
> > much less the far more difficult goal of orbital velocity. So
> > the advantages of balloon lift for the X Prize goal line
> > (100 km of altitude) are worth considering.
> >
> > For gun-style launch (railguns, light gas guns, ramacs),
> > firing from very high in the atmosphere might help.
> > The optimal launch angles for firing from the surface
> > (presumably high in the mountains) take into consideration
> > atmospheric losses for a trajectory designed for the least
> > amount of kick-motor correction to establish true
> > orbit -- i.e. an orbit that doesn't reintersect the
> > atmosphere. This still means about 500 m/sec delta V,
> > however. And about 20% loss to the atmosphere of
> > initial (muzzle) velocity. If one could fire a projectile
> > from the upper atmosphere, a trajectory much closer
> > to tangent with the Earth's surface would reduce the
> > fuel requirements for the kick motor -- in fact, a few
> > small propulsive detonations might do the trick.
> > (no big deal for a projectile that might have had to
> > take thousands of Gs in the gun-launch acceleration.)
> > From 20 miles up, you might get far less atmospheric
> > resistance from a flat launch angle than you get
> > from 3 miles up with a 60 degree angle.
> >
> > Unfortunately, suspending any gun-launch system
> > in the upper atmosphere means an awful lot of
> > balloon lift capability. You probably want to have
> > large facilities up there for some other reason already,
> > and what would that purpose be? Maybe some
> > kind of proto-space hotel? Reached by some
> > kind of proto-space elevator?
> >
> > In short: I used to think that balloon lift was a
> > great unexplored direction in launch technology.
> > I shoulda done the math. It's interesting,
> > practical for certain niches, but very speculative
> > for anything requiring orbit, and probably
> > out of the question for human orbital launch.
> >
> > -michael turner
> > [EMAIL PROTECTED]
> > ----- Original Message -----
> > From: LARRY KLAES
> > To: europa
> > Sent: Sunday, September 14, 2003 8:26 AM
> > Subject: Re: The cheap way to the stars - by elevator
> >
> > Interesting - would launching a rocket from a high-altitude
> > balloon make a difference in terms of payload capacity and
> > distance?
> >
> > Larry
> >
> > Earth is very blue, and there's nothing I can do....
> >
> > ----- Original Message -----
> > From: wmarcus
> > Sent: Saturday, September 13, 2003 3:42 PM
> > To: [EMAIL PROTECTED]
> > Subject: Re: The cheap way to the stars - by elevator
> >
> > Larry
> >
> > How about a zeppelin, without the lead it might float
> > up to heaven. :-}
> >
> > Robert Palmer
> > ----- Original Message -----
> > From: LARRY KLAES
> > To: setipublic
> > Cc: BioAstro ; europa
> > Sent: Saturday, September 13, 2003 12:57 PM
> > Subject: The cheap way to the stars - by
> > elevator
> >
> >
http://www.guardian.co.uk/spacedocumentary/story/0,2763,1041360,00.html
> >
> > The cheap way to the stars - by escalator
> >
> > David Adam, science correspondent
> >
> > Friday September 12 2003
> >
> > The Guardian
> >
> >
> > If climbing a stairway to heaven sounds like
> > too much hard work, then a conference of 70
> > scientists and engineers opening in Santa Fe
> > today may offer hope of a more leisurely way
> > into space.
> >
> > In two days of discussions, the scientists aim
> > to turn into a reality an ambition that has
> > been around for at least a century: the
> > creation of a space elevator that would
> > deliver satellites, spacecraft and even people
> > thousands of kilometres into space along a
> > vertical track.
> >
> > Engineers say that recent advances in
> > materials science - particularly in the
> > development of carbon nanotubes - mean that
> > such a system, which first gained widespread
> > attention when the science fiction writer
> > Arthur C Clarke described it in his 1979 novel
> > Fountains of Paradise, is no longer pure
> > science fiction.
> >
> > Mr Clarke - who once said a space elevator
> > would only be built "about 50 years after
> > everyone stops laughing" - was due to address
> > the scientists at the Santa Fe conference
> > today by satellite link from his home in Sri
> > Lanka.
> >
> > The American space agency Nasa is no longer
> > laughing. It is putting several million
> > dollars into the project under its advanced
> > concepts programme.
> >
> > At the heart of a space elevator would be a
> > cable reaching up as far as 100,000km from the
> > surface of the Earth. The earthbound end would
> > be tethered to a base station, probably
> > somewhere in the middle of the Pacific ocean.
> > The other end would be attached to an orbiting
> > object in space acting as a counterweight, the
> > momentum of which would keep the cable taut
> > and allow vehicles to climb up and down it.
> >
> > A space elevator would make rockets redundant
> > by granting cheaper access to space. At about
> > a third of the way along the cable - 36,000km
> > from Earth - objects take a year to complete a
> > full orbit. If the cable's centre of gravity
> > remained at this height, the cable would
> > remain vertical, as satellites placed at this
> > height are geostationary, effectively hovering
> > over the same spot on the ground.
> >
> > To build a space elevator such a geostationary
> > satellite would be placed into orbit carrying
> > the coiled-up cable. One weighted end of the
> > cable would then be dropped back towards
> > Earth, while the other would be unreeled off
> > into space. Mechanical lifters could then
> > climb up the cable from the ground, ferrying
> > up satellites, space probes and eventually
> > tourists.
> >
> > The biggest technical obstacle is finding a
> > material strong but light enough to make the
> > cable; this is where the carbon nanotubes come
> > in. These are microscopically thin tubes of
> > carbon that are as strong as diamonds but
> > flexible enough to turn into fibre. In theory,
> > a nanotube ribbon about one metre wide and as
> > thin as paper could support a space elevator.
> >
> > No scientist has yet succeeded in making such
> > a fibre, but Rodney Andrews, a carbon nanotube
> > expert from the University of Kentucky will
> > tell the conference: "Until some of the basic
> > science concerning how to connect nanotubes
> > together and transfer load between them in a
> > composite is understood it will remain
> > elusive, but a lot of progress is being
> > made."
> >
> > Brad Edwards, a space scientist who has been
> > developing the space elevator concept for
> > several years, said there was still a lot of
> > scepticism to overcome. "Initially, people
> > look at me like they're trying to work out
> > whether or not I'm pulling their leg," he
> > said.
> >
> > Dr Edwards says the original satellite used to
> > send up the cable should provide enough
> > tension in the cable for the first vehicles to
> > climb into space, each of which would then be
> > added in turn to the counterweight. These
> > lifters would clamp caterpillar tracks to
> > either side of the cable and would be powered
> > by converting laser light beamed up from the
> > ground into electricity.
> >
> > "None of it is really extravagant," said Dr
> > Edwards, who estimates it would take about
> > $7bn (£4.4bn) to turn the concept into
> > reality. He hopes to have a final elevator
> > design hammered out by next year.
> >
> > He said the floating base platform would be
> > placed hundreds of miles from aircraft routes
> > and shipping lanes and would be in a region of
> > the sea where storms, lightning and high waves
> > are rare.
> >
> > The biggest hazard could be space junk, but Dr
> > Edwards said the floating platform would be
> > moved around to steer the cable out of the
> > way. He says it would slash the price of
> > access to space 400-fold, and could allow
> > cheaper, faster travel to other planets.
> >
> > One unlikely problem could be capturing the
> > public's imagination. "When we actually start
> > launching this it's going to be kind of
> > boring," Dr Edwards said. "There's no smoke,
> > there's no pillars of fire and there's no loud
> > rumbling noises. There's just this thing that
> > slowly ascends the ribbon into space."
> >
> >
> >
>
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