Power for Mars Mission?

[bpfeifer]

It appears that all of NASA’s proposed manned missions to Mars call for nuclear power plants. I understand that this is because Mars receives less sunlight than Earth, making photovoltaic cells impractical. <br /><br />Is the nuclear requirement just for the base on the ground, or is it also for the spacecraft ferrying them between Earth and Mars orbits? Thanks.<br /> <div class="Discussion_UserSignature"> Brian J. Pfeifer http://sabletower.wordpress.com<br /> The Dogsoldier Codex http://www.lulu.com/sabletower<br /> </div>

 

[green_meklar]

Well, so far no one has invented a working nuclear drive. And about the only ways to use solar power to move would be an ion drive or a solar sail. So I think we can expect that, at least at first, the rockets behind manned Mars ships will be chemical rockets.<br /><br />As for the ground base I'm not sure. It may even use some solar power at first. Remember, the nice thing about solar cells is that they go on giving you power as long as you want, no matter where you are in the Solar System, whereas uranium eventually runs out. And with the time delays for Mars ships, we may end up needing more uranium than we could fly there from Earth.<br /><br />Although there is another idea that would be completely ineffective on the Moon but might work on Mars: Wind power! It's possible that, once the base gets going, they'll put up some windmills on the surface to catch some of the wind energy. Sort of like solar energy, only you use the atmosphere as your collector. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p>________________</p><p>Repent! Repent! The technological singularity is coming!</p> </div>

 

[JonClarke]

The NASA DRM 3.0 which is the baseline study, used solar power the transit and nuclear for the surface, with earth escape using an NTR. Dervitative missions of the DRM proposed other options, including keeping the NTR stage and providing power using a Brayton cycle turbine, and solar electric propulsion. Surface power options include RTGs with Stirling engine converters and solar arrays. <br /><br />So there are lots of power options. Which ones you chose will depend on the circumstances For short stay missions fuel cells should suffice.<br /><br />Of these options solar cells linked to batteries are most attractive for initial long-stay missions for power levels up about 100 kW as they are mature technology with excellent reliability, built in redundancies, and are easy to maintain. Efficiencies and power densities are already very attractive and both are improving through energetic research programs. <br /><br />Reactors are the most attractive for larger power requirements, probably associated with permanant stations where the mutliple reactors and extensive infrastructure development needed can be justified. They are also most attractive for missions to latitudes above 40 degress where insolation will fall to less than half equatorial values.<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>

 

[scottb50]

I think solar/water makes a lot more sense both in Space and on the surface of Mars. We need large quantities of water for human consumption as well as for radiation protection and most important, dealing with biological waste. <br /><br />Use filtration to remove most solids and solar power to create Hydrogen and Oxygen. Hydrogen and Oxygen power fuel cells and the purified water is returned to the clean water tanks. The same water could be used over and over and the mass needed would be less than what Nuclear reactors would require, especially when you consider you would have to carry a lot of water for a two year mission, especially if you had no method to recover some of it. <div class="Discussion_UserSignature"> </div>

 

[qso1]

bpfeifer:<br />It appears that all of NASA’s proposed manned missions to Mars call for nuclear power plants. I understand that this is because Mars receives less sunlight than Earth, making photovoltaic cells impractical.<br /><br />Me:<br />Depends on what you mean by power plants. There are nuclear propulsion systems and power systems. Propulsion is largely for getting a vehicle such as the ITV design you propose to mars. Nuclear thermal is the system of choice if you want something where a lot of technical experience is already available. Up to and including actual ground firings of NTR engines. There is also the VASIMR nuclear electric drive which has been developed within a laboratory and a prototype was proposed for an unmanned spacecraft a few years back but apparently the plans were shelved. Nuclear thermal advantages over chemical are mainly that one can get more payload for the same punch. A VASIMR based system is theoretically capable of cutting transit time to mars to roughly half what a chemical or NTR would require.<br /><br />On the ground, nuclear power systems would be a more practical solution to power for mars base systems but solar could be used as well. Although solar power would be a little less efficient at mars than earth. It works well on mars as evidenced by the current unmanned rover missions on mars. Where solar power becomes impractical are deep space missions to Jupiter and beyond.<br /><br />The ideal situation is a combination of power systems as JonClarke described. The reality however is that nuclear systems are expensive and going to mars will also be expensive. It's almost certain to be a tough sell to Congress who seem to be h**l bent on wasting far more money on deficits, and a public conditioned by the media to believe we could cut NASA funds and help cure disease and eliminate poverty. A public lead to believe NASA human spaceflight is a luxury America cannot afford. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[bpfeifer]

Thanks.<br /><br /> I did not intend to refer to propulsion systems, but only power for the other systems. It appears to me that solar energy certainly makes sense for the ITV or whatever vehicle carries the crew to Mars. <br /><br />I certainly like the idea of supplementing a surface mission with wind power. Has anyone done a serious study about it? I realize that Mars has high-speed winds, but with a lower atmospheric density, they should have less momentum.<br /> <div class="Discussion_UserSignature"> Brian J. Pfeifer http://sabletower.wordpress.com<br /> The Dogsoldier Codex http://www.lulu.com/sabletower<br /> </div>

 

[docm]

I remember reading of work being done on pebble bed modular reactors (PBMR) for spaceships, habs etc.. They're safe (can't melt down) and above all simple reactors. <br /><br />EDIT: it was called Project Timberwind and use fluid as a coolant instead of the helium gas proposed for earthbound PBMR power reactors. It succeeded, but was the victim of the usual funding cuts in the mid-90's <img src="/images/icons/tongue.gif" /><br /><br />Granted Timberwind was part of Star Wars, but its potential for Mars transit cannot be ignored. <div class="Discussion_UserSignature"> </div>

 

[mrmorris]

<font color="yellow">"I certainly like the idea of supplementing a surface mission with wind power. Has anyone done a serious study about it?"</font><br /><br />I'll do a quick study on it.<br /><br />On Earth -- For average atmospheric conditions of density and moisture contant: <br /><br />Power per sq. meter = .0006 V3<br /><br />Power = Mass of Air * Windmill Efficiency * Velocity3<br /><br />On Earth -- you could use this as follows:<br />Windmill efficiency = 42% <br />Average wind speed = 10 m/s (20 mph) <br />Power = 0.0006 x 0.42 x 1000 = 250 Watts per square meter <br /><br />Modifying this to Mars where the surface pressure is about 0.7% of the average surface pressure at sea level on Earth, we would get:<br /><br />Windmill efficiency = 42% <br />Average wind speed = 10 m/s (20 mph) <br />Power = (0.0006 x .007) x 0.42 x 1000 = 0.001764 Watts per square meter <br /><br />Pulling info from a NASA site (possibly outdated) on wind speeds on Mars, I found: <i>"Martian surface winds are normally quite light (between about 4 and 15 miles per hour [6.5Ð24 km/hour]). On occasion, however, surface winds gust to about 50 miles (80 km) per hour and, during dust storms can blow at over 300 miles (480 km) per hour."</i><br /><br />Let's assume we find a particularly windy spot on Mars where the wind speeds <b>average</b> 50 miles per hours rather than gusting to that level. <br /><br />50 mile/hour = 22.352 meter/second<br /><br />Let's re-run the above calculation using this (exaggerated) wind speed.<br /><br />Average wind speed = 22 m/s <br />Power = (0.0006 x .007) x 0.42 x 10648 = 0.01878 Watts per square meter <br /><br /><br />By contrast -- solar flux on Mars is 45% that of earth. On earth -- solar flux is ~1kW/m2 so it's approximately .45kW/m2 at Mars. A 35% efficient 1m2 PV panel would then produce about:<br /><br />.45kW * .35 = .157kW = 157 watts per square meter.<br /><br />Mind you that's o

 

[green_meklar]

Well, there goes my windmill idea. <div class="Discussion_UserSignature"> <p>________________</p><p>Repent! Repent! The technological singularity is coming!</p> </div>

 

[yevaud]

Very good indeed.<br /><br />It's the density that is critical here, I would think. Even if someone tried to build such a windmill on Mars, the surface area of the blades would have to be enormous. Something of a problem there. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[rocketman5000]

couldn't cloth blades be practical in that application similiar to early windmills from europe? <br /><br />Think the sail cloth windmills from holland.

 

[mrmorris]

<font color="yellow">"couldn't cloth blades be practical..."</font><br /><br />If cloth blades were more efficient than computer-designed composite blades... you'd be seeing them built today.

 

[rocketman5000]

I wasn't speaking of efficiency, I was talking about having the ability to use large diameter blades at a distant (Mars) location. It would be a lot easier to get cloth blades with a support structure to Mars than a windmill blade. One blade from a typical turbine takes up an entire tractor trailer on Earth.

 

[mrmorris]

<font color="yellow">"I wasn't speaking of efficiency..."</font><br /><br />The problem at hand, however *is* efficiency. From the calculations in my post, a windmill on Mars would produce about .0007056 % the power of a comparable one on earth. Put another way, the area of the blade would have to be 141,723 times the area. Mind you, this is impractical no matter how efficient the windmill is. However, the numbers I used were typical for a modern windmill -- which typically use composite blades to minimize weight. If you switched that windmill to using cloth blade, whose support structure, etc. make them heavier than composities, and which have wind utilization efficiencies considerably lower, then your overall efficiency is very likely to halve. At that point we'd require ~300,000 times the area as a comparable windmill on Earth.

 

[vulture2]

The Mars Science Lab rover scheduled for launch next year will use an RTG (plutonium fueled) rather than solar cells, so as to be able to go to higher latitudes and function in any weather conditions. Could this be the first-ever nuclear powered land vehicle? (aka the atomic car)

 

[green_meklar]

I hadn't considered that, but it's quite possible.<br /><br />What I find interesting is how these current two rovers are <i>both</i> still going about seven or eight times past their design life. With the reasonable assumption that the mars science laboratory will last even longer, you have to wonder how long it is before we have a permanent robot presence on Mars (i.e., we launch landers faster than they wear out). <div class="Discussion_UserSignature"> <p>________________</p><p>Repent! Repent! The technological singularity is coming!</p> </div>

 

[JonClarke]

<i>The Mars Science Lab rover scheduled for launch next year will use an RTG (plutonium fueled) rather than solar cells, so as to be able to go to higher latitudes and function in any weather conditions. Could this be the first-ever nuclear powered land vehicle? (aka the atomic car)</i><br /><br />Possibly. The extensively tested but never flown Marsokhod was intended to have an RTG source. Whether one was actually tested with one I don't know.<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>

 

[green_meklar]

Looks like it was. <div class="Discussion_UserSignature"> <p>________________</p><p>Repent! Repent! The technological singularity is coming!</p> </div>

 

[spacester]

MSL is not scheduled for launch until 2009. <div class="Discussion_UserSignature"> </div>

 

[JonClarke]

I know. I was quoting the orignal post. <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]

Nice photos!<br /><br />I think the big orange box is a battery pack. An RTG would need cooling fins as ~98% of it's power output is lost as waste heat. <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>

 

[green_meklar]

Well, I've seen pictures of the Mars Science Laboratory and it doesn't seem to have any fins. On the other hand, if it's working on Mars, which is pretty cold, maybe having some extra heat around is a useful thing. <div class="Discussion_UserSignature"> <p>________________</p><p>Repent! Repent! The technological singularity is coming!</p> </div>

 

[mrmorris]

<font color="yellow">"Well, I've seen pictures of the Mars Science Laboratory and it doesn't seem to have any fins."</font><br /><br />Two things:<br /><br />1. The final format for the MSL power supply hasn't been chosen, so designing fins for it would be premature. At this time, they don't even know if it will be a standard RTG generator using thermocouples, or one use a Stirling engine to improve efficiency. That choice will *radically* change the size & placement of radiative needs.<br /><br />2. In general RTGs have been used in orbiters/probes rather than landers. Since they operate in vacuum, they would require much larger radiative space than a Mars Lander. Ergo -- MSL would have smaller fins than that of an RTG designed for vacuum operation.

 

[willpittenger]

What's special about a Stirling engine? The Wikipedia article with that name talks about pistons. So that can't be the right engine type. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[mrmorris]

<font color="yellow">"So that can't be the right engine type."</font><br /><br />Actually -- yes it is.<br /><br />Stirling engines use a completely different mode of operation than internal combustion engines. IC engines squirt fuel into a chamber, which then is combusted by either spark plug (gasoline) or compression (diesel). The resulting expansion of gas moves the piston generating torque. At the other end of the cycle -- the gas from the combustion are expelled and the process starts over again.<br /><br />By contrast, Stirling engines are sealed, and there is no gas entering or leaving. You can Google for specific details, but basically on one side, the sealed 'working' gas (usually hydrogen or helium) is heated, which causes the gas to expand and provide torque. As the gas expands it moves to another chamber where it cools and compresses. Stirling engines have a hot side and a cool side. The heat can be supplied by *anything* -- concentrated sunlight, a wood stove, or RTGs. Cooling can be supplied either by radiation, water cooling, etc.<br /><br />'Standard' RTG electricity generation using thermocouples is *very* inefficient. Using the heat from nuclear decay to power a Stirling engine can double or triple the efficiency. The downside is that thermocouples have zero moving parts and are therefore extraordinarily reliable. Stirling engines obviously have *lots* of moving parts and therefore provide a new failure point.