Mars and nuclear power

[JonClarke]

Advocacy for NTR and other nuclear space applications skirt round these issues, focussing on the supposed propulsive and power supply advantages. However they cannot be ignored, the following items I suggest are minimum standards. <br /><br />1. Test facilities for NTRs must be redeveloped. I doubt if the Russian facilities are operational and Jackass Flats will be inadequate. It is not acceptable to test NTRs in the open air any more and let radioactive clouds blow across Los Angles, as happened in 1965.<br /><br />2. Both surface power reactors and NTRs run on highly enriched fuel. It the current and foreseeable climate this will require very high levels of security, similar to those associated with nuclear weapons. Much more intense than needed for current RTGs and RHUs. This will impact on cost, management, access to the mission, and require stringent security and recovery procedures. This also raises the political liability of the technology. <br /><br />3. The security issues means that for the foreseeable future any nuclear mission to mars will be government. No private organization or company is going to be allowed to get its hands on highly enriched fissile material. Advocates of primate Mars missions must take note.<br /><br />4. Reactors will be launched cold. They must be able to contain their fuel in the event of maximum credible accident between the pad and orbit. Once NTRs are activated they must be able to contain the core in the event of a maximum credible accident which is a core meltdown followed by a 14 km/s entry. Surface power units must also be able to contain their core in the event of a maximum credible accident.<br /><br />5. While the technical problems of early NTRs were solved (minor matters like internal disassembly followed by ejection of core fragments through the exhaust), the issue of exhaust radioactivity was never solved. Erosion of fuel elements led to an exhaust plume contaminated by uranium and worse a whole range of fission <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Thank goodness, he's nearly finished.....<br /><br />Nuclear surface power is a viable but not essential option for Mars surface power supply and. It will be essential for some locations. However the technology is less mature than solar and a considerable number of borader issues need to be addressed.<br /><br />NTR is potentially useful but not essential for going to Mars. However it very immature technology and will need a very expensive and extensive test program. There are a whole range of unresolved technical and non-technical issues associated with it.<br /><br />My view therefore is there is no need to develop nuclear technology for Mars missions. However, if the technology exiosts when we plan them, and if its use is appropirate, then my all means it should be used.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[krrr]

<font color="yellow">Josh raised the argument that “Aerocapture is also impractical if you use solar panels for power. Using aerocapture results in nearly 50% fuel savings, so that must be counted against a solar option as well…”</font><br /><br />For SEP-powered cargo missions, there is no need for aerocapture. The SEP tug would either release its cargo near Mars for a direct landing, or spiral into a highly elliptical orbit from which the cargo would gently aerobreak into a lower orbit.<br /><br />In the case of a manned spacecraft, if aerocapturing is used, it must be built for that anyway. Somewhat streamlined, enforced on the leading edge etc. Again, the other option is to enter a highly elliptical orbit by conventional means, then aerobreak into LMO.

 

[mlorrey]

No, Josh, this isn't so, except in the very long term. The facts are that a 3-5 degree rise in Mars' avg temp will cause an outgassing of CO2 from rocky carbonates that will cause a runaway effect that will feed on itself over a 20-30 year period, resulting in an atmosphere of between 250-300 millibars of CO2, and a new average temperature of 15-20 deg C, that will be stable for the next 10,000-50,000 years. This sort of climate compares favorably to that of Lhasa, Tibet (though you'd need to wear a loose oxygen mask, you could work in shirtsleeves), and should last long enough for mankind to build a more permanent solution, in the form of production of long term CFC compounds, and CO2 eating plants that exude them naturally. This would result in a thicker O2 atmosphere protected by natural CFCs.<br /><br />Building nuclear plants all over the planet is also needed, to provide a long term source of heat that Mars lacks in its less dense core.<br /><br />This is all well explained, if you care to actually do some homework, by ordering up Martyn Fogg's seminal textbook on the topic: Terraforming: Engineering Terrestrial Worlds, which you can obtain through Amazon or Borders.

 

[josh_simonson]

>An operating nuclear reactor needs cooling and thus a large radiator surface. You can’t dump this or fold it away. This is not incompatible with aerocapture but requires a different type of heat shield, typically a very large coolie hat rather than the bionic currently popular.<br /><br />The design of the radiator is much looser than the design of solar panels, as far as the material used, ect. Perhaps it would be possible to build a radiator that can also be used as a heat shield for aerocapture?

 

[josh_simonson]

There are books about alien pyramids and monuments on mars too, but that doesn't make them true. Scientists can't even make accurate assertions about such stuff on earth, dispite the ease of gathering data.

 

[henryhallam]

It might be a bit tricky to design a radiator that COULD fold away, but if you can do that then maybe the reactor can be shut down or run at very low power for the brief aerocapture phase. Though I suppose that would be the same time you would want to use the rocket engine, if it were one of those combined-cycle jobs.

 

[JonClarke]

"The design of the radiator is much looser than the design of solar panels, as far as the material used, ect. Perhaps it would be possible to build a radiator that can also be used as a heat shield for aerocapture?"<br /><br />That's an interesting suggestion.<br /><br />remember that a radiator is a complex and delicate structure (take a look at the one in your car). It's not going to take much stress or heating either.<br /><br />But I assume you could use a large radiator for aerobraking, much as some Mars probes have used solar panels abd Magellan used its antenna and panels at Venus. The problem is that it takes a large number of passes to achieve this, so not really practical for a human mars mission. <br /><br />But it could be a very good idea for a nuclear probe probe going into orbit round Titan. Would it also work for Jupiter or Saturn (although saturn would require multiple passes through the rin plane which would be very iffy). Certainly food for thought.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[gunsandrockets]

"The reality is much more complex...For example a study of the power system for the NASA DRM 3.0 (http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?1999/TM-1999-208894.html), came to the conclusion that a 160 kW reactor system would require 12 tonnes, including all systems."<br /><br />Very interesting report. Thanx for the link.<br /><br /><br />"One difficulty is that the design of solar and nuclear power systems is often approached differently. For example 160 kW for DRM 3.0 study above was determined by adding all the estimated demands, regardless of whether they are ever likely to be concurrent. However the previously referred to Kerslake study (http://www.grc.nasa.gov/WWW/RT1999/6000/6920kerslake2.html) showed that by intelligent and efficient management of loads the same mission (could be met by a solar power system that supplies less than 50 kW continuously and masses 8 tonnes."<br /><br />Well that's an interesting way of describing those two reports.<br /><br />The nuclear power report you linked to described supplying the power needs of a manned Mars base built up over a period of ten years that included three separate manned missions to Mars. The solar power report you refer to (which I first linked) describes a power mission of about 3 years for a single manned mission to Mars. They are not directly comparable jobs.<br /><br />Plus the nuclear report you brought up (thanx again) includes on page 2 this very interesting segment comparing power system options, including solar power options...<br /><br />"Both solar and nuclear power technologies were considered for the 160 kW power plant. A solar power system using non-tracking photovoltaic arrays and regenerative fuel cells for nighttime power is estimated to weigh 60 tonnes and have a stowed volume of about 1500 m3 (Hoffman, 1997). The DRM Mars cargo lander, capable of delivering a maximum of 65 tonnes and 625 m3 to the surface, would be undersized for the solar power system. Alternatively, a 160 kW nuclear po

 

[JonClarke]

Kerslake is directly equivalent to the Mason. Both are designed to supply power for the DRM. Mason, as do the authors of the DRM, simply total the power needed by all the different phases. Kerslake recognises that the demands can be managed sequentially for substantial savings.<br /><br />The Mason study, while very useful with respect to surface nuclear power options is simply wrong when it comes to the solar option. The fact that it says it needs 60 tonnes to provide 160 kw is proof of that. That is 375 kg a kW. Kerslake shows they need ~180 kg a kW. <br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[gunsandrockets]

"The Mason study, while very useful with respect to surface nuclear power options is simply wrong when it comes to the solar option."<br /><br />So the Mars base report is to be trusted about it's analysis of nuclear power, but not to be trusted about solar power. Okay.<br /><br />" The fact that it says it needs 60 tonnes to provide 160 kw is proof of that. That is 375 kg a kW. Kerslake shows they need ~180 kg a kW."<br /><br />I remind you the solar power study examined the application of advanced thin film solar power technology to Mars surface power. Plus it did not include the 100% redundancy and auxiliary power systems included in the Mars base study.

 

[josh_simonson]

A space radiator is different from a car radiator because it must give off it's heat through infrared radiation instead of thermal conduction. That requires a relatively large, flat surface area of a material that emits IR efficiently, which is also a quality desired of a TPS so that more heat goes out instead of in. The RCC used on the STS would make a good radiator because it conducts heat well, and radiates it well too - it's also a useful TPS. <br /><br />I can't say for sure that'd be a great solution, but I see quite a bit of commonality between the two.

 

[JonClarke]

The Mason study was done by people who expertise was in nuclear power sources. That is why I take their numbers seriously.<br /><br />Landis and Kerslake and others are experts in solar technology. If they show that currently available technology can produce a solar power source for a fraction of the mass that Mason says, then I would take their judgement over Mason's. But I don't take anybody's numbers uncritically, I check them against information I have. <br /><br />Kerslake and others power studies use solar power technology already available to determine their numbers. Mason uses the specs for a reactor that is unbuilt. Which is going to be more reliable?<br /><br />You don't need 100% redundancy for a solar unit, unlike using reactors. Individual cells may fail, but not the whole array. To cope with the vagaries of the environment the array has built in all the redunancy it needs. They also degrade over time, but Mars is a far less hostile environment than LEO ansd this should be allowed for by the very generous margins that have been built in.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

A reactor that generates 100 kW of electricity is going to generate something like a mW of heat. That requires a very large and complex radiator. Not something you want to subject to a lot of stress, mechanical or heating. It's not something that has ever been built in space before either.<br /><br />The silica material of the shuttle is goping to be about the worst possible material for a radiator. They are very poor conductors. You want a good conductor, a high temperature alloy I suspect.<br /><br />Remember if you aerobrake using the radiators they have to undergo minimal heating, they still have to shed all the waste heat remember? If you overhead the radiator you start doing nasty things like pumping heat into the reactor faster than you lose it. Not good.<br /><br />So you would aerobrake nice and slow, just as you would using a big antenna or a solar array.<br /><br />Jon<br /><br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[darkenfast]

I really appreciate the summary of pro's and con's of NTR's, even if it is a bit depressing! I have a question regarding radiators. Assuming a suitable material exists, could a radiator consist of one (or more for redundancy) long loops of tubing? Just a long hose, held out by slow rotation of the spacecraft. Just prior to an aerobraking maneuver, the hoses would be reeled in. Propulsive maneuvers would have to be fairly gentle, of course. Just wondering.

 

[tap_sa]

<font color="yellow">"I really appreciate the summary of pro's and con's of NTR's"</font><br /><br />Ditto, excellent posts!<br /><br />A question about space reactor maturity: The Mason study assumed dynamic power-conversion using Brayton-cycle, has there been any examples of such (or any other type of dynamic conversion) flown in space? AFAIK everything flown so far has employed some form of direct thermo-electric conversion at rather poor efficiency.<br /><br />IMO one important feature that favours solar panel is the massive parallerism in the way it generates power. The Kerslake/Kohout solar array consists of thousands of 'strings', cells connected in series to produce desired 600V. If a micrometeor or something knocks out one cell, disconnect the string and operation can continue, albeit at slightly lower power. In the dynamic Brayton-turbine things tend to be binary, either everything works 100% or not at all. I believe this nature is enhanced in space/Martian operation where mass restrictions force a design with lesser margins, higher rpms etc. If the turbine looses a blade then the imbalance probably renders it useless and nearest metal workshop able to fix it is NN million miles away.<br /><br />I'd propose a scenario where both solar and nuclear power is used. Solar array for daytime activities when electrical power needs are highest. RTG for heating the base and providing enough electricity for lifesupport, comms and some low-energy research activities. No ISRU and other energy intensive activities during nighttime and dust storms. There wouldn't necessarily be need for fuelcell-energy storage, at least for initial missions. If the Mother of All Dust Storms hits then energy requirements are scaled down accordingly.

 

[cuddlyrocket]

"A reactor that generates 100 kW of electricity is going to generate something like a mW of heat."<br /><br />This heat itself may be useful used directly - for example for space hearing etc.<br /><br />One use, for later missions where a larger base is to be developed, would be for baking bricks - a common ISRU construction material in design studies.<br /><br />The use/non-use of 'waste' heat is another factor to be taken into account in considering nuclear or solar for individual mission.

 

[mlorrey]

Right on. On Mars, there is no such thing as "waste heat"...

 

[nibb31]

I would think that you would need to find ways to preserve the Martian environment from human contamination as much as possible, and that includes generating lots of heat or gas. This is not from a purely ecological perspective (there might not even be an ecology to preserve) but for scientific value. It would be like contaminating scientific samples.<br /><br />For example, have you seen the latest news about dormant bacteria that might be surrounding the probes we sent to Mars? This can compromise any future findings about indigeneous bacteria on Mars.<br /><br />There are many unknown chemical and physical processes that occur on Mars, some that we have absolutely no idea about. This is a different planet where there are bound to be different meteorological and geological phenomenae (sp?) than on Earth. We don't want to compromise processes that we don't understand and that might teach us a lot.<br /><br />Therefore, whatever the energy source used, it has to be as clean as possible.

 

[mlorrey]

BS. Any bacteria found in the future will have DNA scanned. It will be very easy to tell from that whether its a terran interloper or a native species.<br /><br />"whatever the energy source used, it has to be as clean as possible"<br /><br />This is the sort of foolish absolutism that was so effectively disparaged in Robinson's Mars trilogy. "The Intrinsic Value of Rock" is about the stupidest but most obviously typical sort of statement you'd get from the moonbats.<br /><br />Mars is not going to be explored to satisfy your scientific curiosity and sense of purity. It is going to be explored because it will eventually be terraformed into someplace that humans can live. That is the only really valuable reason to go there.

 

[nibb31]

"It is going to be explored because it will eventually be terraformed into someplace that humans can live. "<br /><br />Is it? Sources please. It seems to me that the goals of the ESAS plans are scientific/political. Am I missing something? <br /><br />There are much nicer, easier and more profitable places to colonize before going to Mars, although that would be nice science fiction.

 

[mlorrey]

read the part about avoiding having ones eggs all in one's basket, especially with human threats like nuclear war, and external threats like asteroid/comet strikes, that ending the exclusivity of earth as sole habitat for humans is the essential core of manned space exploration. There really is no reason for humans to go anywhere if we don't intend to stay there and build civilization there in the near future.

 

[josh_simonson]

>The silica material of the shuttle is goping to be about the worst possible material for a radiator. <br /><br />Yup, that's why I was talking about the RCC. Carbon conducts heat well (which is why diamonds are sometimes called 'ice'). The RCC has reflective and insulating layers under it to protect the shuttle from the heat that conducts through the carbon.

 

[scottb50]

A prime example of what would be faced on the moon and Mars is exhibited on the Shuttle. The entire payload bay door inner surfaces are radiators to get rid of heat. Heating is not a problem, cooling is. <div class="Discussion_UserSignature"> </div>

 

[henryhallam]

On the Martian surface things are a bit easier than in free space since there is an atmosphere, albeit thin, to carry away heat by convection.