> Charley,
> If we could get affordable space
> travel without nuclear power I'm all for it.
>
The CIS can provide cheap launches to LEO using
existing chemical launchers.
The next breakthrough will be the supply of oxygen to LEO obtiaoned from water ande/or silicates on the Moon
and the asteroids.
Over 80% of the system mass for a rocket is in the mass of the oxidizer.
Getting oxidizer from Luna and asteroid thus reduces the system launch weight requirement by 80%.
A vehicle intended for Mars or the asteroids can be
launched with a fuel tank full of kerosene, but the oxygen tank empty. It gets partially loaded with oxidizer in LEO. It can then go on to Luna where it can received a full load of oxidizer. From Luna the
delta-vee required to get anywhere in the solar system is quite small.
The trajectory involved from Luna is to to a trans
Earth injection, accelerate towards Earth and do a close Earth fylby, doing a kick burn at perigee, to
increase the velocity by about 10%, and achieve
Earth escape velocity.
Via this approach the vehicle can carry a large surplus of fuel and oxidizer to cover any required mission abort contingency scenarios, e.g. return to Earth before
reaching Mars/asteroid.
As we discussed before, the oxidizer could be stored as
H20/H202 and electrolyzed/catalyzed as required.
Hall thrusters would be a good way to augment the delta-vee for an interplanetary vehicle.
> You mentioned Hall thrusters. Like any plasma engine
> they are high isp and low thrust. If you could build
> one large enough to lift a rocket where would you get
> the power to run it? I still don't see any way except
> with a nuclear reactor.
>
Like Ian said, Hall thrusters only work in vacuum.
Cheers,
Charles R.
In regard to "It can then go on to Luna where it can received a full load
of oxidizer." It is silly to go the surface of Luna, rather than to a low
lunar orbit (LLO) or a highly eccentric Earth Orbit (HEEO). Why use lots of
fuel and oxidizer to land on the Moon and then more to take off, to get back
to where you were?
Sincerely,
Jay Huebner at jhuebn@...
> In a message dated Thu, 8 Nov 2001 9:21:52 PM Eastern Standard
Time, Jim Lemmon writes:
>
> > Charley,
> > If we could get affordable space
> > travel without nuclear power I'm all for it.
> >
> This can be achieved most easily using chemical propellants.
>
> The CIS can provide cheap launches to LEO using
> existing chemical launchers.
>
> The next breakthrough will be the supply of oxygen to LEO obtiaoned
from water ande/or silicates on the Moon
> and the asteroids.
>
> Over 80% of the system mass for a rocket is in the mass of the
oxidizer.
>
> Getting oxidizer from Luna and asteroid thus reduces the system
launch weight requirement by 80%.
transporting that O2 defeats the gains of the system. That is, unless
you are planning multiple Mars shots (and I mean more than 10). Of
course, once that system is in place, it allows for multiple
missions, beyond just Mars trips.
Using a NTR, you do away with the need for an oxidizer COMPLETELY.
king_rodent (the frumpy bastard)
A vehicle intended for Mars or the asteroids can be
launched with a fuel tank full of kerosene, but the oxygen tank empty. It gets partially loaded with oxidizer in LEO. It can then go on to Luna where it can received a full load of oxidizer. From Luna the
delta-vee required to get anywhere in the solar system is quite small. The L-1 point would be a particularly good place for this kind of staging operation. RobertZubrin, in his attempts to get people to stop thinking about the moon and think about Mars instead, makes the disparagement that even if fuel was laying around on the lunar surface in tanks, it wouldn't pay to land and fuel up there. Of course he doesn't address the far more sensible scenario that you outline here. If one avoids landing the dead weight of the vehicle on the moon, and instead merely lifts the fuel needed into orbit with some tanker which can rendezvous with the vehicle, then lunar fuel (or even just oxidizer, as you propose) definitely offers a tremendous advantage.
Mike Combs
Jay...
I am disappointed in you.
You know very well that I did not mean landing on the surface of the Moon.
We have been debating the ideal staging post, and as
you know, my favorite option is currently L-1,
but there are some benefits to using L-4/5 or
possibly a HEO.
Which is your preference, and why ?
To say that "Over 80% of the system mass for a rocket is in the mass of the
oxidizer." without saying what the rocket system is just plane nuts. A
nuclear thermal rocket using hydrogen as the reaction mass uses no oxidizer.
It has no chemical fuel and the oxidizer mass is zero. Please stop sending
nonsense.
Jay,
Most of us on this list know how nuclear propulsion systems work, such as NERVA, Orion, Timberline.
Most of us understand that the oxidizer mass fraction is 0% for those systems.
My apologies if this was not clear from my post, on this list it is typically not necessary to explain some of those details.
It seems that you are not alone in missing my point of the 80% mass fraction number, so I shall ellaborate.
Specifically, I think it is clear that our nuclear discussions are focussed on NERVA type systems of late, which would use H2 reaction mass.
If we assume that unlimited oxygen is available in LEO from lunar/NEO sources, then we can ignore the mass fraction of O2. The comparison between nuclear and chemical then reduces to a comparison of the Isp of chemical versus nuclear, for a given mass of hydrogen or hydrocarbon fuel.
I must admit I forget the respective Isp numbers, NERVA is I believe something like 1000 compared to maybe
200 for a chemical system ? I am sure somebody will post better numbers.
The nuclear rocket has a slight overhead disadvantage (versus chemical) in terms of the weight of the nuclear reactor and associated hardware, for a large load of hydrogen this becomes insignificant.
The performance of nuclear systems is certainly several times higher than for chemical systems. And the capital cost of the infrastructure required to manufacture oxygen is significant. Actually, getting oxygen from water is not so difficult, simple electrolysis will suffice, so if water is available on Luna or NEO's then we are in great shape for some major developments.
Of course, the investment for extracting oxygen from silicates is a lot higher.
In the near term there are no oxygen facilities in space currently. This means that for a one or two off mission to Mars a nuclear system is really essential, which IMHO means it probably will not happen, because of the political problems.
That means that the Mars folks should join us in trying to develop oxygen production facilities in space, for that is our best hope of getting to Mars as well as for achieving a spacefaring civilizstion.
Cheers,
Charles R.
That means that the Mars folks should join us in trying to develop oxygen production facilities in space, for that is our best hope of getting to Mars as well as for achieving a spacefaring civilizstion. Very true. And the unfortunate reality is that many in the Mars camp can't look at lunar/NEO resource development in orbital space as anything other than something which would delay the first expedition to Mars.
Mike Combs