Why I've Turned Against Nuclear

JoshNH4H · 2013-12-11 11:18:21

Although I have in the past been a strong proponent of Nuclear power for an early Mars mission and for subsequent missions, over time I have come to see more and more reason to use photovoltaic panels in early missions and then transition later to Concentrated Solar Power systems produced from local resources.

I do not, however, do this based on the technical merits. It is still my firm belief that nuclear fission is a massively promising technology with the potential to revolutionize the way we live our lives, and could become so with a relatively small development effort. I am still strongly of the opinion that a nuclear power source could be built with no moving parts and be a low-mass, safe, and reliable

I am also of the opinion that if we want to go to Mars now, nuclear is the wrong powersource to choose at any stage.

Let's say PV turns a 3-5 tonne reactor into a 10 tonne PV system for an increase of 7 tonnes to the surface of Mars. Multiplying by four to get the (approximate, with significant safety factor) increase in the mass to LEO, you get 28 tonnes. At a cost of $2,500/kg (See Falcon Heavy), that corresponds to an increase in mission cost of $70 million.

The last time the US tried to develop a nuclear reactor (the SP-100, designed in the late '80s as a part of the Reagan Strategic Defense Initiative) it cost $420 million ($800 million 2013) over the course of ten years, and development to completion would cost more than that.

Compare to the ongoing research and development of Space and Mars rated solar panels, which do exist (albeit in much smaller quantities) and would need to be scaled up from existing models. Because solar panels are inherently modular this would not be that much of an issue.

If we want to leave soon, we need a simple, low-cost development program that produces usable hardware. Because we will not be importing power for very long, because solar power of some kind or another is probably going to find a wider variety of uses (applications from big to small, in orbits out to Mars or perhaps farther), the investment in small nuclear reactors, taken only for its value to the space program, is not worth it.

Terraformer · 2013-12-11 12:32:18

What about LENR?

...

Joke, just looking for a reaction.

I agree with going with solar, because I want to start as we're going to be going on, and also because getting hold of a nuclear reactor is going to be difficult if you're not a sovereign state - can you imagine the insurance that will be demanded?

JoshNH4H · 2013-12-11 13:57:52

The logical next question is how to store power. There are two aspects to power storage for a Martian PV system. The first is power storage to even out the diurnal cycle, and the second is power storage to serve as a backup in the case of a global dust storm. People are quick to propose batteries, but batteries typically store a pretty low amount of energy per kilo. According to this source, it's 600 kJ/kg.

We're going to be looking at energy storage more on the order of 4 GJ to even out the diurnal cycle. This corresponds to about 6700 kg of batteries, which is a lot, especially considering that there will be other mass items. Because the requisite solar panels are lighter than the requisite batteries (assuming a mean peak insolation of 425 W/m^2, and the standard space-qualified GaAs cells with 28% efficiency, 4200 m^2 of cells (think a square 65 m on a side), and assuming an increase in mass of 50% over the mass of the panels for structure (Those panels are .84 kg/m^2), the panel assembly will mass 5300 kg.

At this point, just for diurnal cycle batteries and panels, and support for the panels, we have 12 tonnes. Obviously this is a number that we would like to see much lower, but accounting for various other components (For example, when you have a field of solar panels this large you need a bunch of wiring, probably a literal tonne, plus equipment to set up and unroll, plus "other stuff" and margin. Let's say the total mass works out to be 15-18 tonnes.

I'd like to note that this estimate is not very different from what I proposed while supporting nuclear power. However, I bet improvements could be made.

To start, thin films are not the way to do it. Believe it or not, their masses are not much lower if at all than the space-rated solar panels; They use less silicon which makes their costs lower but that doesn't end up making them all that much less massive.

What might be a way to do it would be to use inflatable concentrating mirrors. Only slight internal pressurization would be needed, to be provided by some compound that is a gas at martian temperature, stored as a pressurized gas or liquid for transit.

If the mirrors are troughs instead of dishes, and oriented east west, built with the Compound Parabolic Concentrator design, they should be able to concentrate sunlight by a factor of about ten while still being tolerant to positioning errors.

I propose that this will make it possible to cut the mass of the panels by a factor of three, to 1,800 kg.

Something we don't talk about as much is using fuel cells and electrolysis. While somewhat less efficient than Lithium Ion batteries, storing the energy chemically promises significant reductions in the mass that needs to be brought down. Elecrolysis can be expected to have an efficiency around 75%, and fuel cells around 80%, for a total efficiency of 60%. The fuel cells used on the shuttle had a specific power of 60 W/kg (Given the developments in fuel cells since the 80s, I'd say we could do much better than this), and an electrolysis unit is probably around 150 W/kg.

Of course, the 80 kW of the Zubrin reactor is needed to generate methlox for rocket fuel; The ISRU unit is estimated to be 500 kg in Mars Direct; By increasing its capacity from 80 kW to 500 kW, one would expect this to increase to 3 tonnes. When the crew is there one would expect the required power consumption to be much lower. Let's say 10 kW. This will necessitate eight times less mass in batteries, for 900 kg of batteries.

The total system mass is therefore 1,800 kg of panels and inflatable mirrors, 900 kg of batteries, 2,500 kg of additional fuel production equipment, for 5,200 kg total.

However, rather than use batteries for the people, there's another solution: We could use an internal combustion engine. 10 kW is 15 horsepower, which should result in a generator massing under 200 kg. This could double, combined with perhaps 500 kg of batteries, as a dust storm backup. That is to say, excess methane produced In situ could be used in the case of a dust storm for power.

Therefore, we have a total system mass of 5 tonnes. It will probably be more massive than a nuclear reactor, and it will be more difficult to make this system reliable (It after all has three major subsystems, and at least one of the backup systems has to be functional at all times) than a nuclear reactor, which in the natural course of its operation is nearly invulnerable to any martian weather event and could reasonably be expected to simply work. However, I believe that the same course of argument applies here as Zubrin originally used to argue against a nuclear rocket:

Dr. Robert Zubrin wrote:

In particular, [Baker] wouldn't buy the idea of using nuclear propulsion as the basis for the first Mars missions. Its development would cost too much, he argued, and public acceptance would be a problem. I didn't accept those arguments; on a sustained human Mars program the cost of developing a nuclear rocket engine would be paid back in reduced launch costs after only two or three missions, and if the public wanted a sustained Mars program, they would come to accept nuclear propulsion on that basis. But, Baker said, if you insist on using nuclear propulsion starting on the very first mission, you'll delay the whole program, perhaps fatally.
That point struck home. I felt very strongly that a humans-to-Mars program had to be done on a rapid schedule. Fast schedules reduce program cost: cost equals people multiplied by time. Moreover, every year any major program has to go before Congress for continued funding where it faces risk of termination, often caused by deals or interpersonal frictions that have nothing to do with the program itself. Every time a program goes before Congress for funds it is forced to play another game
of Russian roulette. You can only expect to be lucky so many times.
...
Nuclear propulsion, I conceded, might have to wait but the Mars mission couldn't. By all means, use nuclear propulsion whenever it should materialize; it will increase mission payload capability and cut launch costs (by about a factor of two). But don't delay the mission until you've got it. Go as soon as you can with what's at hand. Improvements can come later.

By replacing "Nuclear Propulsion" with "Nuclear Power" the argument remains cogent and a powerful argument for the use of a lesser, but still sufficient technology. I would add that this is true whether Congress is funding the mission or not.

JoshNH4H · 2013-12-11 14:02:49

Terraformer wrote:

What about LENR?
...
Joke, just looking for a reaction.

I presume you saw my posts on the Mars Settlement Facebook page. In any case, such conspiracy pseudoscience is not to be encouraged.

Terraformer wrote:

I agree with going with solar, because I want to start as we're going to be going on, and also because getting hold of a nuclear reactor is going to be difficult if you're not a sovereign state - can you imagine the insurance that will be demanded?

In many cases, even if you are a sovereign state, although any state that would be interested in launching a space mission also probably has access to one already.

JoshNH4H · 2013-12-12 10:07:29

I realized that I neglected to have an "other" category is my 5 tonne mass estimate. For the sake of argument, let's say that ups the mass to 6-7 tonnes.

louis · 2013-12-12 15:57:10

The mass discrepancy is far less. For one thing, you need a back up reactor. This is human beings we are talking about - you can't assume 100% operational ability. Either that or you have to take back up solar panel mass.

Also, nuclear reactors are not so good if you want to pursue a sensible policy of pre-landings. You'll need solar for those I would suggest. So why not take a lot of that solar panel mass in bite-soze pieces.

Of course once there, you can probably build reflective technology at no or little mass cost. It might be possible to begin that on the first mission.

JoshNH4H wrote:

Although I have in the past been a strong proponent of Nuclear power for an early Mars mission and for subsequent missions, over time I have come to see more and more reason to use photovoltaic panels in early missions and then transition later to Concentrated Solar Power systems produced from local resources.
I do not, however, do this based on the technical merits. It is still my firm belief that nuclear fission is a massively promising technology with the potential to revolutionize the way we live our lives, and could become so with a relatively small development effort. I am still strongly of the opinion that a nuclear power source could be built with no moving parts and be a low-mass, safe, and reliable
I am also of the opinion that if we want to go to Mars now, nuclear is the wrong powersource to choose at any stage.
Let's say PV turns a 3-5 tonne reactor into a 10 tonne PV system for an increase of 7 tonnes to the surface of Mars. Multiplying by four to get the (approximate, with significant safety factor) increase in the mass to LEO, you get 28 tonnes. At a cost of $2,500/kg (See Falcon Heavy), that corresponds to an increase in mission cost of $70 million.
The last time the US tried to develop a nuclear reactor (the SP-100, designed in the late '80s as a part of the Reagan Strategic Defense Initiative) it cost $420 million ($800 million 2013) over the course of ten years, and development to completion would cost more than that.
Compare to the ongoing research and development of Space and Mars rated solar panels, which do exist (albeit in much smaller quantities) and would need to be scaled up from existing models. Because solar panels are inherently modular this would not be that much of an issue.
If we want to leave soon, we need a simple, low-cost development program that produces usable hardware. Because we will not be importing power for very long, because solar power of some kind or another is probably going to find a wider variety of uses (applications from big to small, in orbits out to Mars or perhaps farther), the investment in small nuclear reactors, taken only for its value to the space program, is not worth it.

JoshNH4H · 2013-12-12 18:36:19

The mass discrepancy is far less. For one thing, you need a back up reactor. This is human beings we are talking about - you can't assume 100% operational ability. Either that or you have to take back up solar panel mass.
Also, nuclear reactors are not so good if you want to pursue a sensible policy of pre-landings. You'll need solar for those I would suggest. So why not take a lot of that solar panel mass in bite-size pieces.
Of course once there, you can probably build reflective technology at no or little mass cost. It might be possible to begin that on the first mission.

You don't need a backup nuclear reactor, because the space reactor has no moving parts, and once setup is not really vulnerable to failure short of being hit by a meteorite. The thing about a nuclear reactor with no moving parts (which is this design) is that once it works on the ground, nothing is really going to change that. With no cyclic loads, thermal cycling, extensive pre-flight testing, etc etc etc. you can be fully confident that your nuclear reactor will work. Perhaps a couple hundred kg of batteries would be needed, or more likely a small methlox generator (The engine will probably be about 40 kg, while the generator will probably not be more than 60 kg, for a total of 100 kg. Say 150 kg for the generator, including all the externalities.

I've also heard of natural gas being used in a fuel cell, which implicitly means that methane could be too. This would be more efficient and also probably have an even lower mass. You've been throwing around this "second reactor" argument for quite a while when there is really no reason to think that one would be necessary.

Is a second reactor more safe? Well, yes. But so is a second hab. Do you propose to send two of those? How about a second dedicated ERV, just in case? Or perhaps we should send a clone of each crewmember, cryogenically frozen, just in case the original should meet some fate?

My point is that it's not necessary and increases cost while not decreasing the mission risk significantly.

In any case, logic dictates that rather than sending two 80 kW reactors to provide 80 kW, you send two 40 kW reactors; If one should meet with an unexpected failure, you still have half of the amount of energy you need and can spend twice as much time making fuel, which will still result in fuel production being completed before the fuel is actually needed.

Further, cycling the ISRU (In-Situ Resource Utilization) unit as you will have to as part of solar power will result in a higher probability of failure, and necessitates excess capacity on your ISPP (In-Situ Propellant Production) unit, which will be split into several identical subunits so as to be failure-tolerant.

In addition, because a nuclear reactor will mass in the 3-5 tonne range, it's small enough to land by itself. This is a factor of 3-5 larger than Curiosity, which is a very reasonable scale-up of the technology. Seeing as the Hab will mass significantly more I don't really see how this is even an issue, either from a technological or safety standpoint. Keep in mind that in the Mars Direct architecture you do have the option to re-send the entire system on the second launch window should it fail at the first.

Beyond this, that level of manufacturing is rather silly to incorporate in a first mission. It's a high level of risk for almost no return, just the kind of thing that is worth experimenting with but not depending upon.

It's interesting here that despite the fact that we're proposing systems that are now nearly identical, we're having the same argument we've had on the matter for the last few years

Regardless, I still hold that Nuclear Reactors are technically preferable, but only an issue insofar as the politics get in the way.

Quaoar · 2013-12-29 12:13:52

What about this NASA 500 KW small nuclear reactor?

http://spaceref.com/nuclear-propulsion/ … otype.html

It may be perfect to ISPP.

louis · 2013-12-29 14:27:18

JoshNH4H wrote:

The mass discrepancy is far less. For one thing, you need a back up reactor. This is human beings we are talking about - you can't assume 100% operational ability. Either that or you have to take back up solar panel mass.
Also, nuclear reactors are not so good if you want to pursue a sensible policy of pre-landings. You'll need solar for those I would suggest. So why not take a lot of that solar panel mass in bite-size pieces.
Of course once there, you can probably build reflective technology at no or little mass cost. It might be possible to begin that on the first mission.
You don't need a backup nuclear reactor, because the space reactor has no moving parts, and once setup is not really vulnerable to failure short of being hit by a meteorite. The thing about a nuclear reactor with no moving parts (which is this design) is that once it works on the ground, nothing is really going to change that. With no cyclic loads, thermal cycling, extensive pre-flight testing, etc etc etc. you can be fully confident that your nuclear reactor will work. Perhaps a couple hundred kg of batteries would be needed, or more likely a small methlox generator (The engine will probably be about 40 kg, while the generator will probably not be more than 60 kg, for a total of 100 kg. Say 150 kg for the generator, including all the externalities.
I've also heard of natural gas being used in a fuel cell, which implicitly means that methane could be too. This would be more efficient and also probably have an even lower mass. You've been throwing around this "second reactor" argument for quite a while when there is really no reason to think that one would be necessary.
Is a second reactor more safe? Well, yes. But so is a second hab. Do you propose to send two of those? How about a second dedicated ERV, just in case? Or perhaps we should send a clone of each crewmember, cryogenically frozen, just in case the original should meet some fate?
My point is that it's not necessary and increases cost while not decreasing the mission risk significantly.
In any case, logic dictates that rather than sending two 80 kW reactors to provide 80 kW, you send two 40 kW reactors; If one should meet with an unexpected failure, you still have half of the amount of energy you need and can spend twice as much time making fuel, which will still result in fuel production being completed before the fuel is actually needed.
Further, cycling the ISRU (In-Situ Resource Utilization) unit as you will have to as part of solar power will result in a higher probability of failure, and necessitates excess capacity on your ISPP (In-Situ Propellant Production) unit, which will be split into several identical subunits so as to be failure-tolerant.
In addition, because a nuclear reactor will mass in the 3-5 tonne range, it's small enough to land by itself. This is a factor of 3-5 larger than Curiosity, which is a very reasonable scale-up of the technology. Seeing as the Hab will mass significantly more I don't really see how this is even an issue, either from a technological or safety standpoint. Keep in mind that in the Mars Direct architecture you do have the option to re-send the entire system on the second launch window should it fail at the first.
Beyond this, that level of manufacturing is rather silly to incorporate in a first mission. It's a high level of risk for almost no return, just the kind of thing that is worth experimenting with but not depending upon.
It's interesting here that despite the fact that we're proposing systems that are now nearly identical, we're having the same argument we've had on the matter for the last few years
Regardless, I still hold that Nuclear Reactors are technically preferable, but only an issue insofar as the politics get in the way.

Wow! You've just invented the first infallible machine.

SpaceNut · 2013-12-29 19:33:47

JoshNH4H I finally got to read the motor/generator post and find the motor can not be used as it is redlined at the 3600 rpm and would need to be able to reach 4500 so as to throttle the rpm down so that a natural 50 yo 70 cycle herts can be obtained by the generator head. I also see that the rated hours of run to maintenance needs iss also very low and would not allow for a continous run. Then the amount of fuel burn rate is not specified but it can be derived from the rpm/fuel mix ratio. The generator while it is rated for 9600 continuous I would run it at only 9000 to prolong its lifetime of useage.
Since we will be making methane on mars or some simular fuel I think that the residential standby generators would be a better fit. http://www.northerntool.com/shop/tools/ … generators
I think that 2 of the 60 kwatt size would be what we would want so as to have a back up for when we need to do maintenance.

JoshNH4H · 2013-12-29 22:30:16

Spacenut-

The current produced by the generator will probably be rectified to DC anyway, so the frequency is of little import. If for whatever reason they do choose to keep it as an AC voltage, it is trivial to install a belt or gear system to change the RPM of the engine. There's no need to redline, and we can run at an arbitrary rotation rate.

Louis-

I realize that my post was long, but I also provided for a non-fatal reactor failure. In any case I recognize that no mechanical system is perfect but it's possible to design a reactor that's about as good as you can get.

We are in agreement about solar, though, so I suppose there is little need to argue the matter.

SpaceNut · 2013-12-29 23:30:59

The generator head is a permanent magnet design which means that the slower the rpm is from the designed, the lower the power is that comes out of it. Pulleys and gears lead to wear items that we would not have for replacements. The Rectified and stored in batteries also means more loss as to get something useful means recoverting it back to ac for most uses. Not sure why we are talking about generation of power in this method, as the thread was about nuclear anyways....

JoshNH4H · 2013-12-30 10:11:42

Well, this is an energy storage method for solar power, which is my preferred alternative.

And anyway, two gears is not a major failure hazard. It's an entirely reasonable tradeoff, I would say.

Mark Friedenbach · 2013-12-30 20:16:58

I wonder how reliable those battery weight estimates are 20 years later...

JoshNH4H · 2014-01-01 01:43:19

I didn't use Zubrin's estimates, but rather sourced this from the wiki article on batteries, or Li-Ion or some such. The figures I used are current but conservative, in keeping with good mission design.

SpaceNut · 2014-01-01 11:40:16

Since Mars will be a methane or some other CO2 Hydrogen derived fuel that the backup generator would be powered by that and from the earlier post I went in search for the consumed rates for such devices.

I was shopping in my local Home Depot when I spied a brochure put out by GE for Home Generator Systsems which contained a table with the information.
For a unit capable of 15K watts weighing in around 1-4 ton range such as the 200A Symphony II which can power a Whole house from its 993cc Vangard V-Twin engine it would require 2.06 gal/hr of liquid propane or 170ft cubed/hr of natural gas.

It also appears from the table that for every 15k upward requires another 1.5 gals more/hr.

Could we stock pile that much fuel for future use if we did not have solar due to dust storms over a many month span and thenI assume this could be supplemetal energy as well so how fast can we make the fuel to run the genrator?

GW Johnson · 2014-01-01 12:19:29

A nuclear power plant on the order of what fits inside a submarine has proven to be a very reliable system. Some are steam turbine drive, others have generated electricity for electric drive. There have been no reactor failures since SSN-571 Nautilus ca. 1954. Only SSN-575 Seawolf had a sodium-cooled system, and it got replaced with pressurized water after a year or two. The only engineering problems have been leaks in the steam loops that drive the turbine. Even the turbines are now very, very reliable, as long as scheduled maintenance and repair are done at intervals of decades. I'd say a pressurized-water nuclear power plant generating electricity could run very well without much trouble for decades. They already do, if done to USN, not commercial, standards.

We developed low rpm electric motors decades ago, for use in submarines without reduction gears, starting in Tench-class fleet subs in 1944, and by refit in the older Balao's and Gato's. These not only proved to be quieter, they were also more reliable. They're still in the modern nuke boats that have electric drive. You're talking thousands of horsepower (or KW) at about a hundred rpm. This sort of thing could turn wheels about as easily as propellers. But you pay for it, they're big, and heavy. Doesn't matter, having such a technology available to you on Mars would be well worth it.

Scaled down a bit, this same electric drive system with low-rpm motors has been in diesel-electric locomotives since about 1933. So you don't have to transport marine weights and volumes, the railroad stuff is a lot smaller. In fact, the same technology is small enough to fit inside road cars and trucks, and has been since about 1973. So, if you want an electric-drive truck to run of graded dirt roads on Mars, yes we can build such things. As has been true since the beginning, it's all about the battery and how you keep it charged.

To run a truck on tires on a gravel road is a lot "draggier" proposition than we have on the paved highways here. You have lower gee, for a lower normal force, yes, but the effective friction coefficients are going to be around 3 to 10 times higher than we see for tires on pavement. So, even at reduced speeds and reduced gee, you will still need around 10-ish KW to move a big rig (or mobile habitat) on Mars. It's even worse if the road is not graded (going overland without roads). That's an awfully big solar panel on a smallish vehicle; plays havoc with design layouts.

Putting the nuke on the vehicle has two serious problems: radiation and size. Nukes never scaled down. About the smallest size into which a naval system fits is a 9 or 10 meter diameter submarine compartment about 2-3 times as long. That's why nuclear trains, and nuclear road vehicles, have never been built. Land with a nuke plant to start your first base. You can add stationary solar to the other sites you think advantageous later. It'll take a mix of both types to get started.

You might use chemical energy storage for the electric-drive vehicles, of which the most efficient is the fuel cell. The truly practical ones use hydrogen and oxygen (my, isn't it convenient there's buried ice all over Mars?). The others that use hydrocarbons are very complicated, and have never been put into service, for a variety of very good reasons. But hydrogen-oxygen has been in service, for a long time now. And I think that points the way you should go.

Put a solar-powered electrolysis plant on top of every buried glacier, and add both compressed-gas and liquified-gas infrastructure at these sites. Use them as filling stations for your electric-drive surface vehicles that use the (easier-to-deal-with) compressed gases. Transport with those vehicles the liquified gases to those sites where your LOX-LH2 flight vehicles operate. Pave the roads (a whole 'nother issue) as fast as practical, to reduce surface transport energy costs.

Hey, that's part of how a base might evolve into a permanent settlement.

GW

JoshNH4H · 2014-01-02 00:34:02

GW-

From an engineering, minimal-new-designs standpoint you're more or less right (Although I think you're talking about things that we were discussing in another thread?). However, as reliable as nukes are, from a programmatic standpoint if I were in charge at this point I'd try to go without.

Spacenut-

Do you have any idea what that corresponds to in terms of kg of meth/lox? That sounds like the kinds of figures we'd need to say if this were workable or not.

For fuel production, dust storms aren't a big issue: You simply stop production during them and replace it with more production later. If you plan to be totally done by the time the crew launches from Earth this is no issue at all.

When the people are around, power consumption has to be lower, but it also has to be more constant. This is where burning methane comes in, and this is why there needs to be extra, or the capacity to produce more in the case of a dust storm.a

GW Johnson · 2014-01-02 14:33:04

I saw in the discussions some fears that the reactor might fail, I guess based on incidents like Three Mile Island, Chernobyl, and now Fukushima. The US Navy nuke program has a sterling track record, so I thought I’d offer some of the experiences and data.

As for surface transport, you have electric drive, and you have mechanical drive. We could easily do electric drive, using the marine and RR technologies and a suitable battery or battery-substitute. Actually, chemical storage and a fuel cell is the best.

For mechanical drive, that’s just an engine and a transmission. The heat of combustion of LCH4 with LOX is known, but I don’t have the number available. You’ll need a diluent gas to cut chamber temperatures a bit. The best combustion engine to couple to a variable-speed requirement is piston, not turbine. Operating on a smooth paved highway at steady cruise, you could expect around 15-to-20% energy conversion efficiency. Maybe 25% peak, but I’ll believe it when I see it. Start/stop rough-ground, you might get around 5-10% energy conversion efficiency, and that’s only if you don’t stop and idle a lot.

With LOX-LH2 you could do exactly the same piston mechanical drive, but we already know that trade works out far better as fuel cell electric drive. Don’t forget the diluent gas: we can handle 2000 C pulsed flames, but not 3000 C.

GW

JoshNH4H · 2014-01-02 14:42:03

GW-

Fair enough. I myself have never held that opinion. I agree with you that nuclear reactors are immensely reliable. Having said that, failure on a ship that's a few days' journey from the shore looks a bit different than it does from Mars.

For motion, I would expect fuel cell-electric motor to be the most efficient in all cases, although perhaps not the most lightweight.

How does one define the efficiency of an engine, anyway?

SpaceNut · 2014-01-02 20:33:26

not sure about the mix ratio comparison for methane versus methanol lox burn perhaps these links can help.

http://www.researchgate.net/publication … d_pressure

Methanol to Gasoline process
http://en.wikipedia.org/wiki/Gas_to_liquids

http://www.fischer-tropsch.org/DOE/DOE_ … 4-t9-A.pdf

GW Johnson · 2014-01-04 11:10:24

For purposes of the kinds of discussions we are having here, engine efficiency is just the overall energy conversion efficiency: shaft power output divided by the heat release of the chemistry powering it. Your car is at the very best around 25% efficient by that measure, usually closer to 15%, assuming you drive around without rat-racing on paved roads, and that you don't pull heavy trailers, either. Off-road, around a third of those figures. Pull a heavy trailer, and you'll further cut those reduced efficiencies in half.

To figure fuel-oxidizer ratios, you have to balance the chemical equation (which does require knowledge of product species as an input). Quite often, you have to do this running fuel-rich. The coefficients are the molar proportions. The ratio of input oxidizer coefficient to input fuel coefficient is the molar oxygen to fuel ratio. If you multiply those balance coefficients by the corresponding molecular weights, the oxidizer-to-fuel ratio is then by-mass. The "r" you see in most rocket propellant combination data presentations is oxidizer-to-fuel ratio by mass. It's generally not stoichiometric, but fuel-rich, as I said. That's driven by where Isp maximizes, and that balance is chamber pressure-sensitive, which is why recommended r is a function of design chamber pressure.

GW

SpaceNut · 2014-03-22 17:41:19

This might be the way to go solar still. Engineers create origami-inspired solar array for space deployment

Their folding solar array is designed to be compact at launch and expand to around 10 times its size once it's deployed in outer space.
Sporting 1-cm thick solar panels on a thin flexible membrane, the array will fold down to a diameter of 2.7 m (9 ft), and unfold to about 25 m (80 ft) across.
While this array is expected to generate 150 kW of power, the researchers aim to create one that can generate 250 kW for use in satellites or space stations. It's an ambitious plan, especially when you consider that the eight solar arrays currently in use on the International Space Station generate a total of 84 kW of power.
"The 25 m (80 ft) array is designed to fit inside an Atlas V rocket for launch," Zirbel tells us. "It hasn't been designed for any specific satellites, but we expect to deploy it with a perimeter truss, such as the AstroMesh from Northrop Grumman."

louis · 2014-03-22 20:03:25

SpaceNut wrote:

This might be the way to go solar still. Engineers create origami-inspired solar array for space deployment
Their folding solar array is designed to be compact at launch and expand to around 10 times its size once it's deployed in outer space.
Sporting 1-cm thick solar panels on a thin flexible membrane, the array will fold down to a diameter of 2.7 m (9 ft), and unfold to about 25 m (80 ft) across.
While this array is expected to generate 150 kW of power, the researchers aim to create one that can generate 250 kW for use in satellites or space stations. It's an ambitious plan, especially when you consider that the eight solar arrays currently in use on the International Space Station generate a total of 84 kW of power.
"The 25 m (80 ft) array is designed to fit inside an Atlas V rocket for launch," Zirbel tells us. "It hasn't been designed for any specific satellites, but we expect to deploy it with a perimeter truss, such as the AstroMesh from Northrop Grumman."

Yes, sounds very good to me. These PV panel systems will only need to see us through a few years on Mars before the colonists develop their own systems e.g. solar reflectors to power steam boilers.

Antius · 2014-05-09 07:34:42

The reliability of a 100kWe nuclear reactor with no moving parts would appear to be no more precarious than 4000m2 of solar panels, which would be fragile and vulnerable to dust contamination.

None the less, I would agree that the development costs of the SP-100 could be substantial, probably hitting the $billion range. Certainly worthwhile for a permanent base or colony, where you need a lot of affordable power. But for initial missions relying on stored propellants, the cost nbenefit ratio may very well be different.

New Mars Forums

Announcement

#1 2013-12-11 11:18:21

Why I've Turned Against Nuclear

#2 2013-12-11 12:32:18

Re: Why I've Turned Against Nuclear

#3 2013-12-11 13:57:52

Re: Why I've Turned Against Nuclear

#4 2013-12-11 14:02:49

Re: Why I've Turned Against Nuclear

#5 2013-12-12 10:07:29

Re: Why I've Turned Against Nuclear

#6 2013-12-12 15:57:10

Re: Why I've Turned Against Nuclear

#7 2013-12-12 18:36:19

Re: Why I've Turned Against Nuclear

#8 2013-12-29 12:13:52

Re: Why I've Turned Against Nuclear

#9 2013-12-29 14:27:18

Re: Why I've Turned Against Nuclear

#10 2013-12-29 19:33:47

Re: Why I've Turned Against Nuclear

#11 2013-12-29 22:30:16

Re: Why I've Turned Against Nuclear

#12 2013-12-29 23:30:59

Re: Why I've Turned Against Nuclear

#13 2013-12-30 10:11:42

Re: Why I've Turned Against Nuclear

#14 2013-12-30 20:16:58

Re: Why I've Turned Against Nuclear

#15 2014-01-01 01:43:19

Re: Why I've Turned Against Nuclear

#16 2014-01-01 11:40:16

Re: Why I've Turned Against Nuclear

#17 2014-01-01 12:19:29

Re: Why I've Turned Against Nuclear

#18 2014-01-02 00:34:02

Re: Why I've Turned Against Nuclear

#19 2014-01-02 14:33:04

Re: Why I've Turned Against Nuclear

#20 2014-01-02 14:42:03

Re: Why I've Turned Against Nuclear

#21 2014-01-02 20:33:26

Re: Why I've Turned Against Nuclear

#22 2014-01-04 11:10:24

Re: Why I've Turned Against Nuclear

#23 2014-03-22 17:41:19

Re: Why I've Turned Against Nuclear

#24 2014-03-22 20:03:25

Re: Why I've Turned Against Nuclear

#25 2014-05-09 07:34:42

Re: Why I've Turned Against Nuclear

Board footer