Re: Zeppelin Spaceship
- Matt Kramer wrote (11/25):
> [Responding to PT Galt 11/25]Also, to my surprise, I learned recently that while some of the
> I like the idea. There are a few things that could be
> improved, though.
> > A heavy-lift, high-altitude zeppelin lifts off,
> > carrying a 100-ton cargo-bearing spacecraft.
> > The zeppelin is filled mostly with helium,
> > but contains a bladder of hydrogen running down the
> > center of its gas envelope. Being surrounded by
> > nonflammable helium, the hydrogen is
> > not a threat of a Hindenburg-type disaster.
> Actually, that's not necessary. Contrary to popular
> belief, hydrogen was not actually responsible for the
> Hindenburg's demise (see
> http://www.ttcorp.com/nha/advocate/ad22zepp.htm ).
Hindenburg passengers were killed by a diesel-oil fire aboard, and
others as a result of jumping from the ship, all those that rode the
flaming craft to the ground survived. Since hydrogen at atmpspheric
pressure is so diffuse, gaseous hydrogen does not generate much heat
per unit volume (or surface area, of a person or object near the
fire), and the gas disperses fairly rapidly.
> So the helium could be omitted. However, the hydrogenYes, now that you mention it, it would probably take considerably
> wouldn't be very useful as a fuel in its gaseous state
> anyway--so maybe helium would be better, if it's
> cheaper, even though it's heavier.
more energy to compress or cool the hydrogen into a useful fuel (and
therefore, mass for the fuel to provide that energy) than it would
take to just carry the ship fully-fueled in the first place,
regardless of whether the zeppelin uses hydrogen or helium.
The helium, though heavier atomically, provides about 90% as much
lift as a comparable volume of hydrogen. The main problem I see with
helium is that it's a non-renewable resource derived primarily from
natural gas fields in the US. The Hindenburg used hydrogen largely
because the U.S. government didn't want to supply the Nazis with
helium, especially in the light of the military role zeppelins played
in World War I. Since the United States government would likely be
less than enthusiastic about providing a necessary resource for a
libertarian-oriented space project, I think a hydrogen zeppelin might
be a better way to go.
> > As the ship rises, the hydrogen is used to power itsWhen I was writing this, I was aiming for an ideal use of resources
> > engines and/or compressed as fuel for the spacecraft.
> > This allows the helium to expand as the ship reaches
> > higher altitudes without stressing the zeppelin's
> > airframe while saving the weight that would otherwise
> > have been required for the fuel the hydrogen is
> > replacing.
> So you have liquid oxygen and hydrogen stored then?
and energy in which little to nothing is wasted. However, as you
correctly point out, the gaseous hydrogen in the zeppelin's envelope
wouldn't be of much use as a fuel (which is why it's also safe to use
to lift the zeppelin). It would therefore be more energy-efficient
to simply vent the helium or hydrogen to climb to higher altitudes.
For powering the motors, I'd aim for a combination of solar power and
hydrogen fuel cells. For this purpose, hydrogen can be stored in
metal-hydride cells which release the hydrogen when warmed above a
certain temperature (the exact number escapes me at the moment, I
think it was something like 67 degrees) or in hydrocarbon form such
as natural gas.
The engines could also be powered by biodiesel (diesel fuel generated
from biomass) or some other non-fossil fuel. If all fuels for the
project (both the zeppelins and the rockets) can be produced locally
by renewable means, we would not be dependant on access to fossil
fuels produced in potentially hostile nations.
> I like this idea. A lot. It makes me wonder why itThanks. Here's why, IMO: Up to the present, space programs have all
> hasn't been tried before?
been government projects. Since WWII, zeppelins have had little
military utility (though they are now being considered as heavy-lift
military cargo vessels, high-altitude communications platforms, and
for reconnaisance). Ballistic missiles, OTOH, were/are the ultimate
symbol of military supremacy and national prestige. To my knowledge,
the Saturn V was the first rocket designed and built specifically for
civilian space travel. All previous spaceflights and satellite
launches were accomplished using modified ballistic missiles.
When Kennedy called for the Apollo program, resources were shifted
from other (IMO) viable approaches to manned spaceflight such as the
X-15 program to the area most relevant to Cold-War military needs and
national prestige: rocketry. There was, and is, no
institutionalized "zeppelin lobby" in the U.S. comparable to
ballistic-missile contractors like Morton Thiokol (sp?) and
Since ICBM's were already in manufacture in the '60's, it made a kind
of sense to use those technologies rather than try something
radically different like a zeppelin/lifting-body spaceship combo or
SSTO. In a race to put a flag and footprints on the Moon, disposable
ballistic missile-type rockets were the best option. They're a lousy
option if the goal is to create cheap, widespread access to space and
permanent settlement there. But then that has never been the goal of
the US or any other nation.
- Matt Kramer wrote (11/26):
> I realized today that I said something massivelyDoes this apply at high altitude, such as in the stratosphere? I can
> stupid [in my last post]. You can't use hydrogen
> at all, never mind the Hindenburg, unless you blast
> off the rocket far, far away from the zeppelin.
> The blast-off reaction is extremely exothermic...
> And you'd have to make the zeppelin out of extremely
> durable material, even if you used helium. It'd
> just melt otherwise.
imagine this would be a problem launching vertically and/or at close
to sea-level atmospheric pressure (e.g. the titanic controlled
explosion it takes to get a space shuttle off the ground). At
stratospheric level, the air is much thinner, thus much less
conductive of heat and shock waves (unless my limited understanding
of atmospheric physics is very wrong. >grin<).
If the spacecraft is being dropped horizontally from the zeppelin, it
could fire its engines at a more modest thrust, enough to give it
forward motion and aerodynamic lift, gradually accelerating as it
moves away from the zeppelin and arcs into a climb. Unlike a ground-
launch, it does not need to ignite its engines with enough thrust to
lift its mass straight up initially. As someone else has pointed
out, there have been launches of small rockets from high-altitude
balloons. I'd expect that by the time the rocket goes to full
throttle, it would be at least as far away from the zeppelin as a
space shuttle is from the crowds watching it.
In short, I don't think a zeppelin-launched rocket would need
to "blast" off.