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Jerry_Dub
2008-Aug-08, 10:21 PM
I am new to the forum, but I had a thought a day ago and I wanted to put it down on before it drifted away. It concerns long term space travel and powering it without resorting to as of yet non existent technology, a la Startrek or fusion etc.

Before I start, a little background. I am a recent Master's graduate in mechanical engineering, so space is a little out of my domain of knowledge, but my focus was on turbomachinery, propulsion and stationary gas turbines, heat transfer, and fluid mechanics.

So here is my thought, suppose we are trying to plan a manned extrasolar or deep solar exploration, how do we power this trip? Ignoring the affect of zero G on physiology or radiation and propulsive fuel, but only considering keeping the lights and heat on. Solar power is difficult because the insolation is proportional to the square of the distance from the Sun, so too far away from the Sun and the packed solar panels become too big to be practical.

How about chemical fuel? Well, first you would have to carry both an oxidizer and a fuel, a potential danger of fire and explosion. Advantages, you could use tried and true technology, internal combustion engines, either Diesel or Otto cycles, or even a gas turbine, waste heat could be used to keep the occupants warm. The disadvantage is what everyone knows who has driven a car or worked with industrial or aeronautical gas turbines, wear and tear.

Fuel cells are similar to the above, but with no moving parts. However, you are severely limited to fuel and oxidizer storage, but can generate useful products, such as water.

Now we come to the nuclear option, there are direct nuclear power cells, such as used for the Cassini probe, but these produce little power. I would think that a "typical" PWR, PBR, or BWR could be used to turn a steam turbine, which have a very long service life. Steam turbines have very simple systems and are very reliable. No gases are consumed or released and the system can be isolated from the people, a la nuclear submarines.

This is where the meat of my thoughts are. Some problems, first, if all the power and heat that is required is taken and there is excess heat to be released from the steam condensation, it must be released into space by radiation, without convection. However, the external temperatures of space are very low (4 K?), could we use water as a working fluid or would we have to use something else, such as CO2, something inert? Would there have to be a cascade system used to step down condenser temperatures to use a steam generator/ cycle, then an ammonia cycle, then a liquid CO2cycle , and then a cryogenic fluid cycle.

I know this sounds simple, but have we looked at boiling water in space/zero/mu gravity?

What are your thoughts? Anything blatant that I am missing?

mugaliens
2008-Aug-08, 11:13 PM
Nuclear

Magnetohydrodynamic pump

Low-temp plasma coolant

Radiator

No moving parts

Long life

Minimal external radiation

JustAFriend
2008-Aug-09, 02:26 AM
It's not like we dont already have the nuclear technology....
Every nuclear sub and aircraft carrier since the 1960s puts out more power that you'd need,
and the Navy's got a LOT of experience running the units for very long periods of time.

Heck, the military even came up with small palleted nuclear power plants to drop into Arctic
bases and DEWline radar stations to power them continuously with little or no human supervision.

I believe they've used (or at least experimented) with using liquid sodium as a heat transfer medium.

What we really need is a breakthrough in modest-sized fusion power and then everything will be a LOT easier....

ryanmercer
2008-Aug-09, 03:44 AM
What we really need is a breakthrough in modest-sized fusion power and then everything will be a LOT easier....

Now what we REALLY need, is Heinlein's device he used a few times... that converts any matter into pure energy :), banana peel providing enough energy to move a craft for weeks :) Wasn't something similar also in the Foundation Trilogy?

aquitaine
2008-Aug-14, 09:37 AM
Mr. Fusion should have been invented by now. :p