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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
----- Original Message -----
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
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 -----
Sent: Saturday, September 13, 2003
12:57 PM
Subject: The cheap way to the stars -
by elevator
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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