> Is there really any hope for low cost to orbit without using nuclear power
> or ground based launchers (like mass driver/spacegun and laser launch)? My
> impression was that orbit is expensive not because of NASA but because
> chemical rockets out of Earth's gravity well just suck.
from the sea should be a beautiful sight (if you are not caught by the
tsunami :-). Or perhaps a nuclear canon - build a capsule filled with
respiratory liquid, put some crazy enough people inside, drop it in a hole
kilometers deep and nuke-shot it to space at escape velocity. (I have some
hope that the respiratory liquid would counteract acceleration - after all,
rat fetuses can withstand 1000gs when in water -
http://www.angelfire.com/my/theory/g.html. ) Unfortunately, nukes are not a
very popular option nowadays - unless you really don't *care* about whether
an option is popular or not, and that brings China to the scene again.
As for chemical rockets, maybe that argument favoring BDBs is right and all
that we need is economics of scale.
And what about the space elevator? I think that it is too a kind of "ground
launcher", as you say, in a way...
Lucio
> (...)
>> Is there really any hope for low cost to orbit without using nuclear
>> power
>> or ground based launchers (like mass driver/spacegun and laser
>> launch)? My
>> impression was that orbit is expensive not because of NASA but because
>> chemical rockets out of Earth's gravity well just suck.
cost of launch is high in large part because the rate of launches is
low. The cost of any given service is the fixed cost (the price you pay
for stuff like launch pads, ground crew, etc) and the marginal cost
(the cost of the launcher itself, if it's expendable, otherwise just
fuel and flight preparation costs). As it stands launchers have huge
standing armies and fly rarely. Therefore the fixed cost is spread over
only a few flights. Increasing flight rate would help a great deal. In
addition launchers aren't designed for low cost operations (bizarre as
that may seem). The legacy of missiles quickly adapted as launchers is
still with us.
It's not really a technical issue at all. It's a matter of economics.
There are a lot of ways to bring down launch costs, but all have one
thing in common: they require a high launch rate in order to be
worthwhile. Big Dumb Booster or Reusable - it doesn't matter. If the
launch rate is high enough you can justify the investment in
streamlining operations, bringing costs down dramatically.
As a point of comparison, the aviation industry runs at a cost that's
about 4 times the cost of the propellants. If we could get to that
point with rockets a trip to orbit for a vacation could be had for
~$50,000. I know I'd be saving right now if I could get what Tito had
for only $50K.
......Andrew
--- In ssi_list@... Lucio de Souza Coelho
right and all
> that we need is economics of scale.
>
> And what about the space elevator? I think that it is too a kind
of "ground
> launcher", as you say, in a way...
>
> Lucio
IMHO, progressing beyond chemical launch systems is many decades
away, thus for us to find CATS we either make incremenetal advances
in launch engineering or revolutionary leaps in fuel technology.
The best we have now is LH/LOX which imparts a theoretical specific
impulse of 454 and an exhaust velocity of 5,072 m/s.
If research at LLNL into Metallic Hydrogen proves it to be
metastable and means can be devised to manufacture it in quantities,
then we'll have a fuel with a specific impulse of 1,800 and an
exhaust velocity of 17,658 m/s.
http://www-phys.llnl.gov/H_Div/GG/metalhydrofact.html
http://www.aip.org/enews/physnews/1996/split/pnu263-1.htm
Right now fuel/oxidizer is a small component of laucn cost. If the
tolerances of the vehicle can be lessened by using a more robust
fuel, then even if the fuel is more expensive perhaps we can find
cost savings in the rest of the system to more than offset the fuel
cost increase and then, finally have cheap access to space.
TangoMan
> >> My impression was that orbit is expensive not because of NASA
but because
> >> chemical rockets out of Earth's gravity well just suck.
>
> This isn't at all accurate, though it's a commonly held belief.
The
> cost of launch is high in large part because the rate of launches
is
> low.
turnaround a shuttle? If the variable costs of shuttle launches was
made available and the fixed cost of the standing army was held
steady, how many more could we launch per year?
Or do they have to take as much time as they do now to rebuild the
shuttle prior to every launch. IOW, is the shuttle truely a reusable
launch vehicle or is it so extensively rebuilt between launches that
it is only marginally reusable?
TangoMan
> Given the existing infrastructure of NASA, how quickly can they
> turnaround a shuttle? If the variable costs of shuttle launches was
> made available and the fixed cost of the standing army was held
> steady,
launches per year. I did read somewhere that the opportunity cost of
these extra launches is something ridiculously low like $150 million;
but I don't recall where I read that.
> how many more could we launch per year?
Unfortunately I don't believe that you can add more than 2 extra
launches with the Shuttle launch system.
The CAIB report has some details on shuttle turn-around time
and extent of rebuilding. I was quite surprised - a lot of the
external tiles and frame of Columbia were "original equipment" -
it's mainly the engines that have to be rebuilt every time,
although I heard elsewhere the longest turnaround time had
something to do with loading and unloading payload...
Maximum launch rate (pre-Challenger) was 9 in one year, with
4 orbiters; if I got the right numbers from the CAIB report it's not
the rebuilding of the shuttle (which takes just over 2 monthns)
that is the main barrier to launching more often.
>
> IMHO, progressing beyond chemical launch systems is many decades
> away, thus for us to find CATS we either make incremenetal advances
> in launch engineering or revolutionary leaps in fuel technology.
the systems level (which NASA seems allergic to considering) are both
on the horizon.
> The best we have now is LH/LOX which imparts a theoretical specific
> impulse of 454 and an exhaust velocity of 5,072 m/s.
LH2 is a bad fuel from a systems perspective. The density is so low
that the tanks have to be *huge* - the foam that fell from the forward
attach point of the shuttle to the tank came from the junction of the
top of the LH2 tank with the intertank. The LH2 tank takes up the whole
lower section of the ET - check out
http://history.nasa.gov/SP-407/p38.htm> and bear in mind that the
volume of the O2 tanks looks deceptively large due to the long ogive
section at the front. With a hemispherical cap at the front the length
would be about 30% shorter.
That huge tank means additional weight. Also LH2 is a deep cryogen,
which means expensive external insulation and the need for intertank
insulation, both of which are heavy (the shuttle intertank section
weighs ~7 tons, IIRC). LH2 also requires special materials throughout
the fuel plumbing system, increasing expense and often weight.
One alternative that has been proposed (and which I rather like) is
propane cooled to LOX temperatures. The ISP is >360 sec and you can get
rid of the intertank insulation, as well as having a much smaller tank
due to the higher density. Propane has many of the advantages of
hydrogen without the density and deep cryogen issues.
......Andrew
> One alternative that has been proposed (and which I rather like) is
> propane cooled to LOX temperatures. The ISP is >360 sec and you can
get
> rid of the intertank insulation, as well as having a much smaller
tank
> due to the higher density. Propane has many of the advantages of
> hydrogen without the density and deep cryogen issues.
>
> ......Andrew
They are considerably cheaper, really available and they reduce the
size of the rocket... Another great choice is kerosene which is
liquid at room temperature. If you look at the atlas/centaur it uses
Kerosene/LOX in the first stage and LH/LOX in the second stage. I
guess the theory is that you don't need to send all the carbon up
into orbit only to be burned once you get there. Besides, Kerosene,
as dose propane, will freeze solid in space or in the upper
atmosphere.
The most interesting thing is - the atlas centaur was developed in
the sixties and it was one of the best launch systems ever
developed. The idea to use Hydrogen stemmed from a belief that it
was a modern high-tech fuel. Which, for better or for worse, is true.
Jeffrey