Re: Uranium-239 Radioisotope Rockets
- From: sjv2006@xxxxxxxxx
- Date: Fri, 24 Oct 2008 00:00:33 -0700 (PDT)
On Oct 21, 8:44 pm, Willow <wrschlan...@xxxxxxxxx> wrote:
Uranium 239 has a half life of just over 20 minutes. It is routinely
created with existing technology, but it has never to my knowledge
been separated out within 20 minutes of being created. Instead it
decays to Plutonium which can then be fissioned for energy.
I propose to build 3,000 nuclear reactors that use liquid deuterium as
both a moderator and coolant similar to the kiwi rocket reactor which
ran at 4 GW. It is possible for such a reactor, in principle, to
create 1 kg of Uranium 239 within 20 minutes. Given 3,000 such
reactors (and say each one costs just $1 million to build and then
some to operate) it is possible for around $3 billion to create 3,000
kg of Uranium 239. I call the idea "flash-nukes" because it flashes
out the Uranium-239 radioisotope.
3,000 kg of half-decayed U-239 will have a power output of over 222 GW
and with nine giant turbopumps, each with 10 times the pumping
capacity as the liquid hydrogen turbopumps in the space shuttle, it is
possible for a 1,750,000 kg rocket to accelerate from the surface of
Earth at 3 g's until it runs out of fuel. Assuming a specific impulse
of just twice the space shuttle main engines, which is very
reasonable, we can easily send a 10% usable payload (175,000 kg second-
stage) on a trajectory towards Mars.
Using six such rockets it is possible to do a manned two-way mission
to Mars with 7 people. Three are needed to land an Earth Return
Vehicle and associated support equipment including a nuclear reactor
and equipment to mine Mars water ice and turn it into liquid hydrogen
and oxygen for propulsion for the trip back to Earth. One is a habitat
with supplies for 3+ years (we use dried food, locally mined water is
used). One is the crewed vehicle from Earth, and doubles as the Mars
base (to be buried with dirt for radiation protection).
The sixth rocket to Mars is sent last, when the crew is ready to
return. It's a Mars Return Vehicle, which the Mars Ascent Vehicle
boosts up to and docks with; the crew is transfered and then the MRV
returns to Eath (it's fueled up with propellant from Earth).
Now a radioisotope rocket is NOT a crazy idea. It's real, it's been
done before. It eliminates the need for a fission reactor which needs
radiation shielding to shield the crew from the neutrons. It may have
radioactive exhaust. A radioisotope rocket has no fissioning, no
neutrons, and no radioactive exhaust. It just works, it's relatively
easy too!
Can anyone out there help me calculate the cost of performing six
missions every three years, so that just when a crew wants to leave
they are "relieved" by a new crew? I assume it would cost only 1.5
billion plus another billion US dollars for unrelated infrastructure.
Now if we look at the cost of the U-239, assuming we run 3,000 x 4 GW
nuclear reactors for 20 minutes, that's 1.44e16 J. At 5 cents/kWhr
that works out to a cost of just 200 million dollars.
Now the rocket has a mass of 1,750,000 kg.
I know it takes energy to produce liquid hydrogen but suppose the
rocket costs $200 per kg on average. I have no idea what it would be
made from, but $200 per kg sounds pretty reasonable to me - at least
form a physics stanpoint. Some specialty parts might be needed, but
how low can it go in principle?
200 million dollars plus $200 / kg * 1,750,000 kg equals 350,000,000
dollars. Thus I assume each rocket will cost 750,000,000 dollars. We
launch on average (or at least pay for) 2 per year. Hence I expect a
1.5 billion dollar budget gets you to Mars with an additional 1
billion for infrastructure costs (such as people's salaries).
Can anyone out there provide some hints about this idea - has it been
done before, why not, is it feasible? Maybe I am off by an oder of
magnitude in cost estimation. If so, a manned mission to Mars would
cost 15 billion dollars. This is in line with what using an Ares I and
several Ares V rockets would cost to get to Mars.
The idea is to have filaments of U-239 (3,000 x 1kg filaments) in a
ten huge "combustion chambers", each with 300 kg of U-239. Liquid
hydrogen is pumped in, it boils and is exhausted at twice the specific
impulse of the space shuttle main engine. This allows for great
performance.
How to make the U-239? I propose a deuterium nuclear reactor with
natural uranium. It's a flash-nuke, running way beyond melt-down at a
4 GW like the kiwi nuclear rocket reactor. The deuterium will allow
U-235 to fission without enrichment being necessary. All those
neutrons will transform U-238 into U-239. 1 kg of U-239 can be made in
20 minutes in theory, but I don't know how to do it in practice.
Anyone have any ideas?
---
One issue is, you have to separate the second stage from the first
stage somehow because the first stage is going to melt down when it
runs out of liquid hydrogen coolant. My target was for only 13,500 m/s
delta-V, enough to go from the surface of Earth to a Mars trajectory.
At 3g's acceleration, this takes 7.65 minutes. So we have enough
hydrogen for 8 minutes or so, then we separate and the first stage
does a nuclear melt-down! Does that bother you?
Another issue is I propose to launch from Antarctica. It's a legal
nightmare. Where do you think I could launch from in principle if it
were possible? Any countries out there that would want a nuclear
rocket?
Finally there is cost. How to get a 2.5 billion dollar budget,
increasing with inflation each year? That is the real show stopper
here. I was thinking only a new technology could generate revenues
that high, preferably an energy technology. 2.5 billion dollars a year
is equivalent, at 2 cents/kWhr profit, to 15 GW. If you had a 15 GW
plant of some sort, you could in principle sell energy and if you
divert 2 cents/kWhr to the space project, you could pay for it.
We really need a new energy technology and a lot of investors. Solar
power is my favorite, especially solar power troughs. One can
calculate the cost of thin aluminum reflectors (mirrors) and if that's
all a solar power trough was, we'd be in business! Unfortunately we
need to transfer the heat to a fluid which then boils water and turns
a turbine, all that adds to the cost. In principle is it possible to
get the budget we need? Say we had 25 billion dollars to invest, then
could we start colonizing Mars? Lets see how far fetched this is with
a calculation.
To get 15 GW, we need a surface area (assuming 25W/m^2 on average) of
25 km x 25 km. That's a lot of aluminum and remember aluminum is not
all a solar power trough is made out of! But just for a lower limit
estimate, can you do it with 25 billion dollars? If we sell the energy
for 5 cents/kWhr, we can spend 1 cent on maintainence, 2 cents go to
the investors, and 2 cents to the space project.
25e3*25e3 m^2 is the surface area of our solar power project. In
principle, suppose the reflectors are 5000 kg/m^3 and 0.001 m thick.
Then we have a mass of 3,125,000,000 kg just for the reflectors (this
assumes it's flat and not parabolic, hence it's a real lower limit).
In order to afford the project with a $25 billion budget, we need our
solar power project to cost just $8 / kg. This is not outside the
realm of possibility, it's just a little far fetched by today's
standards.
I really think solar power can pay for Mars colonization.
Wow. Talk about doing things the hard way...
.
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