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Well, yeah, but you don't want any of that catastrophic failure stuff.

Why use a design where that's a possibility?

After all the beating this idea took today, I'm not sure if I still need to say that I went back over my calculations and found out that I was off by a factor of two _before_ accounting for efficiency...

So I won't.   

The sabatier reactor makes a lot of power, but cannot provide sufficient power for the needed production of oxidizer.

(Curses, foiled again!)   :bars3:

The Sabatier reaction, used for on site propellant production in the Mars Direct plan, releases a great deal of usable energy.  Even accounting for the energy use required to keep the process going continuously, a properly designed propellant plant based around a Sabatier reactor could produce enough power to run both itself and the ERV during the in-situ propellant production phase of a mars mission. 

That estimate does not require energy input from a full nuclear reactor (5kW, lithium cooled, etc.).  A set of RTG?s would still be required to start the Sabatier reactor and to maintain the ERV indefinitely after the Sabatier reactor shut down.  However, the mass of the RTG?s needed would be an order of magnitude less than a full nuclear reactor.  Additional hydrogen feedstock would be required, but not so much that it would outweigh a one to five ton nuclear reactor.  RTG?s have a better success record in space applications than full nuclear reactors and last longer.  (For comparison, the maximum lifetime of the longest operating RTG on a satellite ? the one on the Pioneer X probe ? hasn?t been determined after thirty years.  The longest lasting full nuclear reactor on a satellite didn?t make it to six months, with the average being closer to one month.)  Current RTG technology is already adequate for on site propellant production. 

In short, using the Sabatier reactor for power, employing the hydrogen fuel already along for the ride, can eliminate the need for a full nuclear reactor in an ERV.

Actually, thermoacoustics offers another technique besides fractionation by evaporation & condensation: thermoacoustic mixture separation (also being investigated by the folks at Los Alamos):

[http://www.eurekalert.org/features/doe/ … 092402.php]http://www.eurekalert.org/features/doe/ … 092402.php

Note that no physical state changes (or the energy needed for them) are required using this technique.  Thermoacoustic separation is a new transport phenomenon (like diffusion or osmosis), discovered in 1998.  It can be used for fractionation by producing a concentration difference between two ends of a tube containing a gas mixture.  Given a long enough tube and a loud enough sound source, this difference in concentration can approach 100%.  It requires no moving parts and is very forgiving in terms of temperature and pressure.  The degree of temperature control necessary for fractional distillation in the Martian environment would not be necessary. 

Thermoacoustic heat engines are quite versatile.  It is even possible to set up a cycle in which they can act as continuous operation compressors, lacking any moving parts more complex than a backflow valve.

Long tube lengths for thermoacoustic separation and thermoacoustic heat engines don't take up excessive space, because the tubes can be coiled like the tubing of a tuba or french horn.  The tubing can be made of plastic instead of the metal used by these researchers, which saves mass.

This looks like a very versatile technique. 

One difficulty I've had with the Mars Direct scheme is the fact that, in the fuel production stage, no one has ever provided a satisfactory answer for how the carbon dioxide reactant will be separated from the atmospheric intake.  Nor, apparently, has anyone taken the initial fuel production experiment to its logical conclusion and actually liquified the fuel gas generated by Dr. Zubrin's original Sabatier reactor experiment.

These folks at Los Alamos have provided us with two related technologies that can deal with both of those shortcomings.

CME

Hello GCNRevenger.

I should clarify.

I am not fundamentally opposed to all possible instances of any use of hydrogen fuel, thermal rocket propulsion, or any combination of the two.  You can, if you're willing to put in enough power, heat hydrogen to temperatures in excess of 700K -- the point at which its performance in a rocket engine becomes superior to any chemical propellant.  Mechanically, one can make such a propulsion system operate without a meltdown.  That's not my point. 

I've got no problem with nuclear power, either.  As long as it doesn't leak or disintegrate, a well shielded nuclear reactor is just one more heat source.  Most of what I've said can be applied to resistojets, heat beds, or any other type of thermal rocket.  That's not my point either.

My point is that there are better alternatives. 

My principle difficulty with hydrogen as a propellant is the amount of power you have to put into it to make it work as a superior propellant, when there are other propellants that will yield similar performance at a fraction of the heat flow. 

Two excellent examples are methane and ammonia.  Both have much higher molecular weights than hydrogen in their stable, room-temperature forms.  Fortunately, thermal rocket engines don't run at room temperature.  Methane and ammonia have relatively low specific heats -- closer to that of water than hydrogen -- and break down into much lighter molecules with relatively low molecular weights -- closer to that of hydrogen than water -- at temperatures in excess of 1300K.  And methane and ammonia require less than a third and less than a fifth, respectively, of the energy hydrogen requires to get to that temperature.  That means that if you were really interested in pouring in enough power to make a methane (or ammonia) thermal rocket's exhaust velocity comparable to that of a hydrogen thermal rocket, you could do it and still have some power left over.  You could produce higher thrusts using methane or ammonia as your propellant, at similar exhaust velocities, with a greater chance that your engine's heat exchanger would still be in one piece at the end of the day.

Thanks for your time.

CME

Hello CC.

There are a lot of plastics that will be just as difficult to work with as you say.  However, polyethylene and polypropylene are not among them.

Neither of these plastics evaporate readily in vacuum, so they can be worked with in the open.  Both have relatively low melting points -- around 100C.  Rather than pressing them, they can be pooled, drawn or blown like glass. 
Special shapes with exact tolerances will require heavy molds, though.  And some sort of press will be needed to work the plastic, but to form melted liquid, not solid blocks of plastic.

Polyethylene withstands cold very well.  It's brittleness temperature (the temperature at which its strength is reduced by half) is -90C.  Polyethylene is also resistant to sunlight and very strong.  (High density versions compare favorably to aluminum and kevlar.)  It's a common material for children's playground equipment.

Polypropylene is not so good in cold, and it eventually breaks down and turns brittle in sunlight.  It's brittleness temperature is just 0C.  But it has a unique property: It is almost immune to thermal stress.  Changes in temperature do not crack or warp it.  Polypropylene pipe can be used for liquid nitrogen, and polypropylene dishes are safe in hot dishwashers where polyethylene dishes would be deformed by the heat. 

Polyethylene is useful enough to justify taking some with us when we go to Mars.  However, if you absolutely must chose between the two, choose polypropylene.  It can be made on Mars directly from the propane byproducts of a Sabatier Reactor, using a second catalyst chamber.  This eliminates the need to take a block of it with you from Earth. 

CME

Wouldn't the bends (decompression sickness) be a problem with running around naked outside?  The pressure is low enough that all gases -- not just nitrogen -- would start to come out of solution in your body.

I for one wouldn't want my kids to see me carried in with an embolism.

CME

Hello Clark.

You wrote:

And the answer is, ultimately, that I have no answers to any of the questions you ask.  These methods alone are not long term solutions.  They are acts of desperation. 

People also jump out of burning buildings as acts of desperation.  How would that address the problem of survival?  How would that deal with the fire undermining the structure of the building?  How can a person throw themselves from one impending doom to the next?

I have no answer for that, either.  I only know that both things happen, and seem quite similar in the amount of forethought given to each.

They happen often enough that we can reasonably expect them, regardless of whether or not they are reasonable.

CME

Hello Clark and Scott.

Clark, the best form of central government for dealing with potential strikes and revolts among essential personnel is a dictatorship.  For example, here in the United States of America, it is illegal for railroad and electrical power plant employees to strike.  If they try it, the government immediately sends in its own negotiators for binding arbitration, and if that doesn't work the companies are authorized to fire and replace everyone.  In time of war, military force is authorized.  This is very helpful for the preservation of social order.  Whenever a strike or revolt is threatened, the threatened companies simply lock out all of their employees and holler "STRIKE!"  In comes the government, and the whole messy matter is cleared up in no time, with none of the messy business observed in other industries where the workers' unions decide who goes on strike and who doesn't. 

Very clean, very orderly.

Scott, some of the most prevalent problems with bureaucratic heirarchies stem from their inefficiencies in passing information from one point to another within their own structure.  Does the Los Horcones community have typical and/or unique methods of passing information within its structure, and are there any problems common with them? 

CME

It seems that every time someone a discussion of potential government forms for Martian colonies, two contrasting notes appear: 1) Drastic economic shortages will be a fact of life in the first Mars colonies; and 2) Let's use forms of governance favored by societies enjoying the luxury of economic plenty.  Something must be done to remedy or reconcile this. 

Regarding Walden Two as a model for government, the social management style Dr. Skinner expounded on has actually seen extensive use in several places in the business community.  Bureaucratic decision making structures follow similar mathematical models whether in business or government. The results of those experiments (directed at running businesses with measurable economic outputs rather than societies with less tangible outputs, but still indicative) lead me to believe that a society based strictly on the methods described by B.F. Skinner will quickly come to resemble the well known group from another fictional tale:

Dilbert. 

Beware of any kind of government that both requires a lot of interference and refuses to tell you how it's going to work from one day to the next.

Regarding the economics of a Mars base, I think we have a lot to learn from the poorer cultures of the world.  For example, the national economy of Argentina has collapsed over the past few years.  But Argentinian economics has not.  Barter has replaced money-driven economies in many places, and it often not the bare minimum "I want that and I'll give you this for it" that one might expect.  Since there's so little money to work with, many of the Argentine people are trading in markets and clubs that apply modern economic principles to the barter system, printing trade tickets, establishing exchange rates, etc.  These barter clubs are more like Sam's and Walmart than a barter session with your next-door neighbor.  And they are building a sort of currency/money system as well.  Barter Club vouchers are currently a harder currency than the Argentine peso and stand to replace it for many purposes if the national economy does not recover.

I suspect that the first Martians will look not to the US Federal Reserve Board but to the Argentine Barter Clubs for their first economic plans.

CME

Shaun, I merely meant that the pranksters who make these crop circles often sign their work.

I'm afraid it may take a little more than lining your cap with gum wrappers.

http://space.com/busines....31.html

It turns out the reason there have been no research results is that there is no research.

CME :angry: