Fear of nuclear power holding us back

[DarkenedOne]

I personally believe nuclear power is the future of space flight, however I believe that we are lagging in this technology due to people's fear of nuclear power.

Traditional chemical powered vehicles are simply not enough to get anywhere in space. Take the most powerful chemical reaction used on the space shuttle, the combustion of hydrogen. The chemical reaction between hydrogen and oxygen is the best rocket fuel for space travel because it produces a large effective exhaust velocities while having the lowest mass. However that effective exhaust velocity is still only 4,300 m/s. Now at first that may sound fast, but in space that is nothing. It takes a delta-v of around 10000m/s to get into LEO. It takes another 6000 m/s to get to the moon. That's a total of 16000 m/s to get to earth moon using the least amount of energy possible. According to Tsiolkovsky rocket equation a space craft taking off from earth going to the moon would have to carry 41 times its own weight in fuel. That would mean that around 97% of your spacecraft taking off from earth would have to be fuel. By comparison a 747 is about 50% fuel when fully loaded. The only way NASA is able to get there is to throw away the majority of their hardware by weight in these staged rockets. You see using chemical energy is going to get us no where no matter how much we perfect the technology.

Now there exists propulsion technologies that can offer the effective exhaust velocities in order to actually getting anywhere with a space ship that is not almost 100% propellant. Standard ion propulsion such as that used on the DAWN spacecraft produces effective velocities of between 15 and 40km/s. Using the Tsiolkovsky rocket equation we can see that such a system could potentially take off from earth and make it to the moon with less than 50% of its weight in fuel. The problem is that such systems require huge amounts of power. Solar power is only able to provide this type of energy over long period of time, which is ok for unmanned vehicles but not for humans. Nuclear power, being more than a million times more powerful then chemical is the only source of power that can provide that amount of power.

Problem is that nuclear power is greatly feared, and I believe that the fear has stifled NASA's technological advancement in the area. NASA's plutonium reserves for mission like the MSL are depleted, and there are currently no plans to establish a new supply, thus future missions will be restricted to solar power only, which will not cut it for many of NASA's operations. On top of that NASA has effectively stopped research on large nuclear reactors for manned space flight.

 

[thermionic]

I think itt was a money problem that shut down JIMO, not fear.

 

[Gravity_Ray]

I think your argument is somewhat correct. Certainly for any mission going to Mars or further, solar power is not very practical. Ion engines can be used, but they are the slow and steady type, which is not practical for a manned mission to Mars. However, nuclear power is not useful for getting us out of Earth gravity well. We will still need chemical engines for that, or something exotic like a space elevator.

But for a Moon or Mars base nuclear power will be indispensable. Also for getting far out in our solar system nuclear power is also needed.

But I think your 100% right that people fear this power in space, and that is too bad. Certainly if people were to understand that an RTG is very safe getting launched from Earth, and its oh so very practical and cost effective, there wouldn’t be such a resistance to it.

Maybe when the politicians see Energiya build a megawatt-class nuclear propulsion engine they will change their tune.

 

[Boris_Badenov]

Without Nuclear Power we will never leave Earth in any meaningful way.
Period.

We need to start using it in Space just like the US Navy has been using it in Naval Ships for 55 years.
The US Navy has accumulated over 5500 reactor years of accident-free experience.
(Nuclear-Powered Ships)

We will never be able to power really large ships, even in Earths orbit, without it.
NuclearSpace.com

 

[neuvik]

It is honestly fear holding nuclear energy proliferation back. Fear that drives costs to unsuitable levels to get any permits, inspections, machining, etc. Thanks to NIMBY and non growth groups...and apathy.

If the merchant marine (US) was given nuclear power we'd dominate the world, we have the best trained steam plant engineers; as opposed to the British who (once upon a time this was different) had to rip out many steam plants from their ships. Its a crying shame poor politics won out against sound science. The Savannah sadly was used as a test bed but not run as business would have. It was a show boat...but used to judge its place in industry, which made absolutely no sense. Our Artic bases need fuel, and its darn expensive too.

In Eureka, California we have a decomissioned nuclear plant....outside is a few gas turbines which now provied power. Just boggles the mind.

Heres hoping more people wise up. Because not to mention the space benifits...but there is just so much we need right now.

Edit: Savannah, woops!

 

[vulture4]

Havanna??? I think you mean the Savannah. But I'm sorry, I don't think it was practical; costs are too critical in the merchant marine. Agree we need nuclear power for space, particularly beyond Mars. But a reactor is much more powerful and actually safer to launch than an RTG. The RTG has plutonium fuel, which is very toxic, while the reactor has only uranium, which is a nuclear material but is essentially nontoxic and of very low natural radioactivity, until the reactor actually goes critical and begins to accumulate highly radioactive fission products. Normally the reactor is never run until the craft is in space, so at launch the hazard is minimal.

That said, we haven't launched a reactor in a long time.

 

[bdewoody]

The Savannah is/was a beautiful ship. As it turned out very few nations would allow her to enter their harbors. So after only a few years of limited use she was tied up at Savannah, Ga. and allowed to deteriorate. I just read on Wiki that she is at Norfolk, Va. awaiting her fate.

I've heard comments from the uninformed that nuclear powered spaceships need to be banned to prevent the pollution of space. That always makes me grin.

 

[Boris_Badenov]

I've heard comments from the uninformed that nuclear powered spaceships need to be banned to prevent the pollution of space.

I have a small bowl of almonds & walnuts with honey every evening & just had a mouthful when I read that. I nearly choked. :lol:
If people want "space" free of radiation maybe we better start by turning the Sun off. Next we'll have to flip the off switch to the rest of the Universe. We'll have to clean up the Cosmic Microwave Background Radiation too.
Damned stuff is just everywhere. :ugeek:

 

[Boris_Badenov]

In the Bigelow Updates thread we are discussing the Big Bertha design. If 8 Big Bertha's in the long configuration are placed in a ring shape it would be around 300/350 in diameter & could support in excess of 350 people.
How many Solar Panels would be necessary to provide power for a station of that size?
How many Nuclear Reactors the size of a Hyperion Power Module (HPM) would be needed?
An HPM can deliver 25 Megawatts, enough for 20k average American homes.
I don't know how many solar panels we'd need to generate that kind of electricity, but I seriously doubt it would compare in mass to the HPM at 1.5 meters diameter & 2.5 meters in height.

 

[neuvik]

Havanna??? I think you mean the Savannah. But I'm sorry, I don't think it was practical; costs are too critical in the merchant marine. Agree we need nuclear power for space, particularly beyond Mars. But a reactor is much more powerful and actually safer to launch than an RTG. The RTG has plutonium fuel, which is very toxic, while the reactor has only uranium, which is a nuclear material but is essentially nontoxic and of very low natural radioactivity, until the reactor actually goes critical and begins to accumulate highly radioactive fission products. Normally the reactor is never run until the craft is in space, so at launch the hazard is minimal.

That said, we haven't launched a reactor in a long time.

Woops good catch! Fuel is about 45-48+% of a ships costs, so it takes a huge chunk out of profit. It is completly practicle for the merchant marine, and we are wanting them desperately. (theres a lot more reasons why, but emmisions is another reason)

Further on the Savannah, she was a beautiful ship no question about that, but along with the apathy that Boris and bdewoody mentioned about port restrictions...she was not run...or constructed in a way that would have made her equivalent to merchant ships. Combined cargo/transport ships are not a modle of efficiency, even before WWII most ships were either full cargo, or full passenger transport. So as a cold war era ship, she just did not fit in. Also steam ships would try and operate in cool water trade loops.


RTGs are perfectly safe, all that anti-plutonium hog wash force fed to us is just scare tactics based on no science what so ever. "Dangerous " things can be built to be safe. One of the US inspectors to North Korea, when NK was showing off its plutonium, asked if he could take it out of its containment. They allowed him too, and thats how he confirmed they did indeed create a small amount of plutonium, because it was warm in his hand.

 

[js117]

RTGs are way to weak in power to be used in large scale spacecrafts.
The New Horizons spacecraft going to Pluto uses a RTG and its power is 240 W, 30 V DC at launch, decaying to 200W
n 2015.

 

[js117]

Also I Would like to say Nuclear power on the ground or in space under President Barack Obama administration
is dead. Maybe not so much in space but on the ground it is.

 

[Astro_Robert]

Although a space based reactor would likely be less mass than a bank of solar panels for a given power level, when one considers various support systems (required for either) the ratio of mass wouldn't be quite as impressive.

I'm just trying to keep it real and am in favor of nuclear power. But the weight savings would be limited to the power generation portion only. Also required would be Radiators (probably next greatest mass usage of a power system), and Power distribution; both of which probably scale more with power consumed/delivered than with the source.

From a simple perspective the weight of a nuclear generator seems to be a slam dunk. When one considers all systems required for a given amount of power, the nuclear one probably still has a noticeable weight advantage, but also has a re-fueling/disposal issue which will make lots of people queasy for orbital applications. So I can't imagine ISS or its immediate successor gaining a reactor in the foreseeable future.

Hopefully, if NASA presses ahead with its Nuclear Sterling replacement for the RTG and continues drawing up plans for spaceships with MegaWatt (or 'multi-hundred watt' for that matter) class powerplants to support electric engines and sensors, then nuclear options for space will grow. For those unfamiliar with the NASA's Advanced Stirling Radioisotope Generator, it is a proposed slightly more powerfull successor to the old RTG's employed upto now for outer solarsystem exploration.

 

[SteveMick]

If the nuclear-electric power plant proposed for the JIMO probe is any guide; nuclear electric is
far more massive than solar electric. Large (100ft. dia. plos) low mass solar concentrator mirrors in tandem with concentrator type triple junction solar cells such as those made by Spectrolab have a specific power of a little over 1KW/kg and efficiency over 40% for the entire system. Waste heat can be dumped by the tubes supporting the concentrator(s) doubling as the radiator.

When making a comparison between solar and nuclear it is good to compare any proposed nuclear system to a solar concentrator based system and then keep in mind that only concentrator mass goes up with distance from the Sun and at 1 AU the concentrator may be less than 10% the mass of the solar cells. This means that even out to Saturn's distance it has a specific power of around 10kg/KW and there are ways to reduce even this by more than a factor of ten by forming sub visible light wavelength diameter holes in the reflective material. By comparison the JIMO reactor based system had a mass of around 10,000 kg for 100KW elec. or 100kg/KW - ten times worse than solar at Saturn at hundreds of times the cost.
Nuclear thermal propulsion does have an advantage in thrust per unit mass over solar thermal but requires a different kind of reactor as I understand it than that needed to make electricity and the solar thermal has a higher exhaust velocity, wildly lower cost,and can easily use the same concentrator for propulsion directly or concentrator PV electricity cam run a plasma propulsion unit. The concentrators can double as antennas for comm or radar or as a radiotelescope.

As for a Moon base, aluminum oxygen batteries using solar heat to regenerate the aluminum after it becomes alumina is far, far, more versatile and wildly cheaper than a reactor. The batteries can be used for vehicle power for instance, and of course for periods when the Sun is unavailable.

Nuclear was going to make electricity "too cheap to meter" It was not fear that made that vision fail. Nuclear is still subsidsed by the Price Anderson Act providing insurance at taxpayer risk. If the equivalent subsidy had been put into solar that vision would now and forever be true.

Steve

 

[DarkenedOne]

If the nuclear-electric power plant proposed for the JIMO probe is any guide; nuclear electric is
far more massive than solar electric. Large (100ft. dia. plos) low mass solar concentrator mirrors in tandem with concentrator type triple junction solar cells such as those made by Spectrolab have a specific power of a little over 1KW/kg and efficiency over 40% for the entire system. Waste heat can be dumped by the tubes supporting the concentrator(s) doubling as the radiator.

There are a few things wrong with your solar concentrator idea.

First of all the solar radiation at Jupiters distance from the Sun is 55 watts/m^2. At 40% efficency that drops to 22 watts/m^2. Do the calculation and you would need a mirror with an area of 4545 square meters to equal the reactor's 100kW. Your dish would have to be 38 meters or 124 feet in radius in order to have the same power. There are few dishes on earth that big let allone in space. It is clear that you did not factor in the weight of the concentrator when you made your calculation because when you factor in the supporting structure as well as for the reflective material itself needed for a dish that large the mass grows significantly.

Second of all is the logistics. No such structure has ever been deployed from a rocket. such a large structure has never been put into space period. The only way I think such a large dish can put in space is to have it assembled in ordit, and I am not talking about simple docking. Building such a structure in space is simply a ability that we do not have with our current technology. Then you have to figure out what you are going to do in the shade.

There is a good reason why people say solar power beyond Mars is simply impractical. Lastly the planned power from JIMO reactor was 300kW not 100kW

When making a comparison between solar and nuclear it is good to compare any proposed nuclear system to a solar concentrator based system and then keep in mind that only concentrator mass goes up with distance from the Sun and at 1 AU the concentrator may be less than 10% the mass of the solar cells. This means that even out to Saturn's distance it has a specific power of around 10kg/KW and there are ways to reduce even this by more than a factor of ten by forming sub visible light wavelength diameter holes in the reflective material. By comparison the JIMO reactor based system had a mass of around 10,000 kg for 100KW elec. or 100kg/KW - ten times worse than solar at Saturn at hundreds of times the cost.
Nuclear thermal propulsion does have an advantage in thrust per unit mass over solar thermal but requires a different kind of reactor as I understand it than that needed to make electricity and the solar thermal has a higher exhaust velocity, wildly lower cost,and can easily use the same concentrator for propulsion directly or concentrator PV electricity cam run a plasma propulsion unit. The concentrators can double as antennas for comm or radar or as a radiotelescope.

At Saturn's distance the solar radiation is 16 watts/m^2 and 6.4 watts/m^2 at 40% efficiency. That means that you would need to collect light from an area of 15625m^2. That is the 3 times the area of a football field. Sorry, but such a craft is simply impractical.

This spacecraft has to be something that can be deployed from a reasonable HLV.

As for a Moon base, aluminum oxygen batteries using solar heat to regenerate the aluminum after it becomes alumina is far, far, more versatile and wildly cheaper than a reactor. The batteries can be used for vehicle power for instance, and of course for periods when the Sun is unavailable.

You realize the moon has night times that are 13 days long. Do have any conception of how much battery you would need simply to live let alone conduct operations for that long on battery power. Let's assume the moon base is the size of the ISS, which requires 110kW. 110kW over 13 days comes out to 34320000 watt*h in need energy. According to wiki the aluminium oxygen batteries have a specific energy of 1300w*h/kg, which means you would need 26400 kg of battery in order

Nuclear was going to make electricity "too cheap to meter" It was not fear that made that vision fail. Nuclear is still subsidsed by the Price Anderson Act providing insurance at taxpayer risk. If the equivalent subsidy had been put into solar that vision would now and forever be true.

While solar power has a great deal of potential for providing energy for satellites in Earth orbit, it has serious short comings when it comes to space flight beyond Earth. Nuclear power has made many missions in space possible where solar power could not. Solar power tech will continue to progress, but it will always be limited by amount of sunlight you get. Unlike solar power, nuclear power, the same power that drives the Sun itself, is self-contained and therefore will work equally well everywhere in the solar system and beyond.

 

[SteveMick]

Thanks for the thoughtful repsonse and yes I am aware of how large of a concentrator mirror was required. A few years back we had quite a discussion about this right here in this forum. Even in my post you'll see I stipulated mirrors in excess of 100ft. diameter.
In the early nineties an inflated antenna of 40 ft. dia. was deployed from the Shuttle. If it had been aimed at the Sun it would have essentially been a solar concentrator that weighed in at 40lbs. including the inflation system if I remember correctly. I mention this because it is of the general type I've been advocating for quite a few years now, with one important difference. I beleive I originated the idea of space based insitu-form with degradable elements in which following on-orbit inflation, exposure to UV light from the Sun alternately causes some parts to harden while others vaporize. Using this tech which was proposed for the cancelled "Starfire" program, but what I had and have been advocating is much more extensive involving even the mirror material itself. With this technique I believe very low mass and fairly accurate mirrors of considerable size can be formed.

BTW I believe that antennas of around 300 ft. in dia. are currently doing some spy work from GSO.

I should have mentioned that the alumina is heated in the presence of hydrogen and the resulting water has to be split back to H2 and O2 to complete the cycle. Aluminum - air batteries have a fantastic energy density as you noted and I appreciate you figuring up how much mass of battery is required. I should have made myself more clear -
The batteries are formed(perhaps entirely) from Lunar regolith so the mass is in no way a problem. Any nuclear system will need backup power and you'd probably still want to charge up some Al -O2 batteries.

I will concede that the JIMO power system was probably not the lowest mass example of the general type - it was after all designed by submarine builders, but its 9 billion dollar cost was probably more representative of what to expect. My projections of concentrator mass may be a little rosy - or not, but they'd have to be off by an order of magnitude before nuclear electric systems even compete - at 100's of times the cost! Also, near the Sun solar thermal and/or electric can't be beat and many trips to Mars and beyond can use Sun approaching trajectories to great benefit.

DarkenedOne wrote:
" While solar power has a great deal of potential for providing energy for satellites in Earth orbit, it has serious short comings when it comes to space flight beyond Earth. Nuclear power has made many missions in space possible where solar power could not. Solar power tech will continue to progress, but it will always be limited by amount of sunlight you get. Unlike solar power, nuclear power, the same power that drives the Sun itself, is self-contained and therefore will work equally well everywhere in the solar system and beyond"

The entire point of my post, or at least a main one was that large low mass solar concentrators are a game changer. You can argue about the highest practical specific power they can have, but I do not believe deployment issues are a signifigant problem. One of the first sattelites Echo-1 was an inflated sphere over a hundred feet in diameter. The sizes get large but the forces on the concentrator can be kept small. I've suggested actuator based active control to assist this. I agree its difficult to picture such large delicate structures, but you'll need big antennas to have decent communication from Neptune anyway.
I agree that beyond the solar system, solar doesn't work.... directly. Actually with the high efficiency of solar concentrator PV, lasers could send power to another concentrator at great distances, but that's another story.

Steve

 

[Valcan]

Dude no offense i like the idea of solar lasers for sending power or propelling a cargo ship on the slow roll to a distant part of the solar system but its

a) kinda limited

b) insanly dangerous

c) Its a laser..a huge laser in space capable of burning warships.........its not happening.

I like the idea of laser propulsion for some things but for mos thuman travel in space no.

 

[SteveMick]

The idea about solar lasers came from an idea by the late Dr. Robert Forward who in the early Sixties came up with an idea to use enormous light sails propelled by ridiculously high power(45TW) solar lasers in orbit around Mercury (where the solar intensity is about ten times as great as at Earth's distance) to both accelerate a spacecraft to the Centauri system and slow it down when it got there. To slow down, a smaller lightsail detached itself from the main one and was slowed by light reflected off the main one.

Sadly, manned space flight beyond the solar system isn't even close to something in the cards in the next few decades and the sheer scale of any such undertaking makes any propulsion preference I might have irrelevant.

As to the relative danger, at these distances it is difficult even to get the laser beam as intense as sunlight on Earth. Even that requires enormous( state of Texas ) sized optical elements. Hence as I said that's another story.

Steve

 

[DarkenedOne]

Thanks for the thoughtful repsonse and yes I am aware of how large of a concentrator mirror was required. A few years back we had quite a discussion about this right here in this forum. Even in my post you'll see I stipulated mirrors in excess of 100ft. diameter.
In the early nineties an inflated antenna of 40 ft. dia. was deployed from the Shuttle. If it had been aimed at the Sun it would have essentially been a solar concentrator that weighed in at 40lbs. including the inflation system if I remember correctly. I mention this because it is of the general type I've been advocating for quite a few years now, with one important difference. I beleive I originated the idea of space based insitu-form with degradable elements in which following on-orbit inflation, exposure to UV light from the Sun alternately causes some parts to harden while others vaporize. Using this tech which was proposed for the cancelled "Starfire" program, but what I had and have been advocating is much more extensive involving even the mirror material itself. With this technique I believe very low mass and fairly accurate mirrors of considerable size can be formed.

BTW I believe that antennas of around 300 ft. in dia. are currently doing some spy work from GSO.

I checked out the mission. The inflatable antenna was 7 meters in radius and 60 kilograms that being the antenna itself, not its supporting elements. In order to match the nuclear reactors 300 kW the antenna would have to be 90 times bigger. Assuming that mass was directly proportional to surface area the antenna would then weigh around 5400kg not including supporting systems.

That is not bad, and it just might be feasible up to Jupiter's orbit. However if you take that out to Saturn's distance it would have to be 300 times as large as the one demonstrated with a weight of 18180 kg. You see it was like I said before you can come up with all of these clever ways to improve solar propulsion, but it will always be limited its access to sunlight. Nuclear power on the other hand does not require any external power source.

I should have mentioned that the alumina is heated in the presence of hydrogen and the resulting water has to be split back to H2 and O2 to complete the cycle. Aluminum - air batteries have a fantastic energy density as you noted and I appreciate you figuring up how much mass of battery is required. I should have made myself more clear -
The batteries are formed(perhaps entirely) from Lunar regolith so the mass is in no way a problem. Any nuclear system will need backup power and you'd probably still want to charge up some Al -O2 batteries.

First of all I am assuming that equipment will come from Earth. I agree that in the future if they are able to use ISRU that it may be cheaper to simply build and produce solar panels and other materials right there on the moon than it would be to bring a reactor from earth. However then again the same technology could be used to build reactors on the moon itself, so I cannot be sure.

As for a backup power supply nuclear power is known for its reliability. Many reactors we have today have be run continuously for decades. The navy uses nuclear reactors in the bigger ships and submarines with little to no backup.

I will concede that the JIMO power system was probably not the lowest mass example of the general type - it was after all designed by submarine builders, but its 9 billion dollar cost was probably more representative of what to expect. My projections of concentrator mass may be a little rosy - or not, but they'd have to be off by an order of magnitude before nuclear electric systems even compete - at 100's of times the cost! Also, near the Sun solar thermal and/or electric can't be beat and many trips to Mars and beyond can use Sun approaching trajectories to great benefit.

JIMO was projected to cost around $400 million according to the sites I visited, but in actuality it would probably cost more than that I agree.

As far as nuclear competing with solar it is likely that solar will continue to dominate the inner solar system and nuclear power will continue to dominate the outer solar system. For the reasons I gave you.

The entire point of my post, or at least a main one was that large low mass solar concentrators are a game changer. You can argue about the highest practical specific power they can have, but I do not believe deployment issues are a signifigant problem. One of the first sattelites Echo-1 was an inflated sphere over a hundred feet in diameter. The sizes get large but the forces on the concentrator can be kept small. I've suggested actuator based active control to assist this. I agree its difficult to picture such large delicate structures, but you'll need big antennas to have decent communication from Neptune anyway.

The size of an antenna you need to communicate is dependent on both the size of the transmitter and the receiver. We can always simply make the radio dishes on our end larger so that antennas on space craft remain small. That is why we are still in touch with the Voyager 1 even though it is leaving the solar system.

I agree that beyond the solar system, solar doesn't work.... directly. Actually with the high efficiency of solar concentrator PV, lasers could send power to another concentrator at great distances, but that's another story.

Steve

Lasers cannot work over distances of a few AUs because they will refract.

 

[Ruri]

Fear of nuclear power most defiantly is holding back space exploration.
A tug based off JIMO can make pretty much allow an EELV class LV to have lunar payloads approaching that of a Saturn V.

An ion or VASIMR engine has 10x the ISP of the best comical engine.
This would reduce the cost of lunar cargo by five over an Apollo style mission.

In fact JIMO probably is more important for Mars then all of Constellation.

A BNTR Mars mission can visit Mars and return home in no more then 460 days.
This is not scifi but simply what you can do with an ISP of around 900 for the main engines and 3,500 for the cruise engines.
http://www.astronautix.com/craft/mars1994.htm

This mission has a propellant mass ratio of .5 which means half the mission or 400T is useful hardware.

800T sounds heavy but it can easily be built using the Jupiter 246 in fact it's a little overkill for lifting the parts.

Heck even the lightest and cheapest of all realistic Mars missions Mars Direct requires a surface nuclear reactor able to generate about 100KW of electrical power.
This reactor would be remarkably similar to that used on JIMO.
http://www.astronautix.com/craft/marirect.htm

I feel Mars Direct is probably actually more difficult then Mars 1994 due to it's 500 day surface stay but it does slowly build a Mars base.

 

[Polishguy]

Fear of nuclear power most defiantly is holding back space exploration.
A tug based off JIMO can make pretty much allow an EELV class LV to have lunar payloads approaching that of a Saturn V.

An ion or VASIMR engine has 10x the ISP of the best comical engine.
This would reduce the cost of lunar cargo by five over an Apollo style mission.

In fact JIMO probably is more important for Mars then all of Constellation.

A BNTR Mars mission can visit Mars and return home in no more then 460 days.
This is not scifi but simply what you can do with an ISP of around 900 for the main engines and 3,500 for the cruise engines.
http://www.astronautix.com/craft/mars1994.htm

This mission has a propellant mass ratio of .5 which means half the mission or 400T is useful hardware.

800T sounds heavy but it can easily be built using the Jupiter 246 in fact it's a little overkill for lifting the parts.

Heck even the lightest and cheapest of all realistic Mars missions Mars Direct requires a surface nuclear reactor able to generate about 100KW of electrical power.
This reactor would be remarkably similar to that used on JIMO.
http://www.astronautix.com/craft/marirect.htm

I feel Mars Direct is probably actually more difficult then Mars 1994 due to it's 500 day surface stay but it does slowly build a Mars base.

How is long stay time a bad thing? You need to stay there to do any real science work, otherwise it's a giant stunt, like the first 2 Apollo landings. In your Mars 1994 mission, 460 days are spent outside earth, of those 30 on or in orbit around Mars. Let's say 20 of those days are used on the Martian surface. That means 440 days in full view of solar and cosmic radiation. Mars Direct, with 180 day one-way transit, totals just 360 days in view of radiation, so less chance of cancer. Besides, Mars 1994 sends just 5 people to Mars (Mars Direct sends 4 anyway), on 9 launches per mission (compare to 2 for Mars Direct), using unproven technologies (Nuclear Thermal vs. Chemical) and less scientific accomplishment. Mars Direct is clearly far, far better, and it is utter nonsense to say that Mars 1994 can be easier. Mars Direct requires direct launch, no on-orbit assembly. The ISS shows us exactly how on-orbit construction can go wrong.

Don't get me wrong. I believe in nuclear space power, but only when used sensibly. VASIMR, to get a payload to Mars in 39 days of flight, needs 600 tonnes put in LEO first (three Ares V, or 4 Saturn V). VASIMR is well and good for Outer Solar System (where you're putting a lot of mass in orbit either way, so may as well go faster), but it's just inefficient for Mars. NERVA, on the other hand, is something that can be utilized short term for higher payload. Mars Direct on Nuclear Thermal can put 6 people on Mars for 500 days, at 6 month either way transit, and then just fuel on Mars using compressed CO2. NERVA is great! But Mars 1994 is just absurd, another variation of NASA's 90 Day Study.

If we were really serious about colonizing space, we'd dust off the blueprints at General Atomic, build up in Jackass Flats, and launch Project Orion.

 

[SteveMick]

DarkenedOne, I found your post to be most disappointing. As I said, the point of my mentioning the inflatable antenna was to illustrate type and nothing else. I apologize for getting the mass of this particular antenna wrong, but its not particularly relevant. The question to be asked is "What is the minimum practical mass required to concentrate sunlight?" and "Can inflation insituform with degradable elements or some similar technique produce something close to the highest theoretical specific power?". A Diamond film simple lens can be perforated with spaces smaller in dia. than visible light wavelengths and have an overall thickness averaging perhaps a few atoms or so. I don't pretend to know if this is practical, but please do not think for a minute that the inflated antenna was even close to what is possible. The JIMO probe had a mass in excess of 50,000 lb. if my frequently foggy memory is randomly correct and it was guessed in the old discussion that the electric powerplant with its enormous radiators. Stirling engine(moving parts unlike solar but I guess it will be more reliable because it has the magic nuclear pixie dust : ) ), etc. made up about half that. It was so massive that it was to take 2 years just to get to escape velocity. I could have acted as if this was a reasonable example of the best nuclear could do but I didn't. This would be a specific power for nuclear electric in the range of 250 lb./KW elec. compared with a solar concentrator which would have to intercept about 50 sq. meters at Jupiter or about 200 at Saturn for 1 KW with 40% efficient PV. Concentrator cells currently weigh a little over a kg/ KW(Spectrolab) I think, but I don't know if a little work could improve this or not. Anyway,I don't think 200 m^2 of thin aluminized mylar(as an example) with a lightweight support structure( part of which doubles as radiator ) would weigh anything like 250 lbs. - do you? - and that's hardly the best possible.
As for the JIMO probe cost you mentioned - did that include the development cost of the reactor and power system?

As far as Al-O2 batteries; imagining for one minute that ISRU won't be central to any sustained activities on the Moon is borderline crazy to me. O2 production figures heavily in every such scenario at the very least. If you can make O2 out of Lunar regolith, you will have aluminum and iron and silicon etc. as by-products and so materials for making a battery would be readily available. Stereolithography and other tech can make production of even complex parts on the Moon feasible. By producing the solar concentrators needed out of aluminum, the total power available can increase at a exponentialish rate, particularly if thermodissocation of the water vapor is used instead of electrolysis( which requires electricity and hence PV which is a little harder to produce in-situ), to recycle the hydrogen. Only materials and parts that absolutely cannot be made on the Moon if any need be imported as the total power, O2, and metal production on the Moon grow rapidly.
Contrast this with the "trashcan" nuke that NASA is currently studying. It will produce heat to run a Stirling engine to produce a given amount of power in one location with no portable power unless batteries are brought from Earth I suppose. If it breaks, the cost of replacing or repairing it could be massive. The Lunar GDP would be in a nuclear choke hold even if no malfunctions occurred. The cost of bringing up a new reactor to double power production would be extreme.

When you have a reactor you have a very expensive and heavy heat source that requires a Stirling engine or other mechanism to make electricity that you must carry with you everywhere you go or have batteries. There is no possibility that in-situ reactor production is gonna happen any time soon on the Moon. Solar mirrors are quite easy to make in-situ by contrast.

BTW with all that Al and O2 around perhaps Al -O2 rockets need a closer look.

As for dust refraction at distance with lasers in space, the power lost would increase with distance and so a more powerful laser is required for a given amount of power transmission, but we're talking terawatts here. Anyway, you can take it up with astronomers: Seems they're able to see MASERS at great distances and it seems like I saw something about a kind of laser being seen from a supernova recently.

As for antennas at Neptune, surely you agree that bigger results in higher rates of data transmission regardless of the receiving antenna. Time on really large terrestrial antennas is limited anyway. BTW the radiators required for JIMO were enormous and they could have been shaped to double as antenna support with little mass penalty.

Steve



I take it from the fact that you didn't challenge

 

[neutrino78x]

As for a backup power supply nuclear power is known for its reliability. Many reactors we have today have be run continuously for decades. The navy uses nuclear reactors in the bigger ships and submarines with little to no backup.

Actually we can power the boat from three sources. The primary source for power and propulsion is the nuclear reactor. It produces steam, which turns both a turbine for electric power, and the main propeller shaft (the new Virginia class uses electric power to run the propeller, instead of mechanically driving it with the steam). The secondary source is the diesel engine, though it can only run when the boat is at periscope depth (snorkeling) or on the surface. The tertiary source is the battery. We have a set of batteries, in a compartment under the torpedo room. With the battery, the boat is propelled by an electric outboard motor. I can't tell you the maximum speed in any of these modes, nor the location of machines in the engine room. Obviously the boat goes a lot slower when running on the battery.

So, the reactor is the primary power source, and the battery and diesel are backups.

I know this because I am Qualified in Submarines, I served on the USS Florida (SSBN-728) and USS Asheville (SSN-758), although I never went underway on the Asheville, she was in drydock the whole time. An interesting Too Much Information side note is that my doctor at the Department of Veterans Affairs suspects that the hemorrhoids I had earlier were caused by the radiation on the boat. :lol: actually I shouldn't say lol because it was extremely painful, luckily it seems to be greatly reduced now. I was a sonar tech, not a nuclear operator, but I did go back there for various reasons, it would be hard to spend a whole patrol and never go to the engine room.

As far as nuclear competing with solar it is likely that solar will continue to dominate the inner solar system and nuclear power will continue to dominate the outer solar system. For the reasons I gave you.

I would tend to agree with that, although I would add the idea that solar may be viable on a moon of Jupiter or Oort Cloud object, because that provides you with a solid platform to mount the solar thermal mirror. I would agree that for vehicles going far beyond the sun, you would want nuclear, because you don't want to have to stay pointed at the Sun.

Lasers cannot work over distances of a few AUs because they will refract.

Refract? Or just get weaker? I've seen a lot of stories about solar sails traveling between stars using powerful lasers in Solar orbit.

--Brian

 

[neutrino78x]

moving parts unlike solar

Well, solar thermal has moving parts, only PV has no moving parts (and that is assuming you don't track the sun with the PV).

As far as Al-O2 batteries; imagining for one minute that ISRU won't be central to any sustained activities on the Moon is borderline crazy to me. O2 production figures heavily in every such scenario at the very least. If you can make O2 out of Lunar regolith, you will have aluminum and iron and silicon etc. as by-products and so materials for making a battery would be readily available. Stereolithography and other tech can make production of even complex parts on the Moon feasible. By producing the solar concentrators needed out of aluminum, the total power available can increase at a exponentialish rate, particularly if thermodissocation of the water vapor is used instead of electrolysis( which requires electricity and hence PV which is a little harder to produce in-situ), to recycle the hydrogen. Only materials and parts that absolutely cannot be made on the Moon if any need be imported as the total power, O2, and metal production on the Moon grow rapidly.
Contrast this with the "trashcan" nuke that NASA is currently studying. It will produce heat to run a Stirling engine to produce a given amount of power in one location with no portable power unless batteries are brought from Earth I suppose. If it breaks, the cost of replacing or repairing it could be massive. The Lunar GDP would be in a nuclear choke hold even if no malfunctions occurred. The cost of bringing up a new reactor to double power production would be extreme.

I completely agree with this part. I strongly advocate solar for a lunar or Martian colony. However, I think for deep space vessels themselves, nuclear would be used.

--Brian

 

[DarkenedOne]

DarkenedOne, I found your post to be most disappointing. As I said, the point of my mentioning the inflatable antenna was to illustrate type and nothing else. I apologize for getting the mass of this particular antenna wrong, but its not particularly relevant. The question to be asked is "What is the minimum practical mass required to concentrate sunlight?" and "Can inflation insituform with degradable elements or some similar technique produce something close to the highest theoretical specific power?". A Diamond film simple lens can be perforated with spaces smaller in dia. than visible light wavelengths and have an overall thickness averaging perhaps a few atoms or so. I don't pretend to know if this is practical, but please do not think for a minute that the inflated antenna was even close to what is possible. The JIMO probe had a mass in excess of 50,000 lb. if my frequently foggy memory is randomly correct and it was guessed in the old discussion that the electric powerplant with its enormous radiators. Stirling engine(moving parts unlike solar but I guess it will be more reliable because it has the magic nuclear pixie dust : ) ), etc. made up about half that. It was so massive that it was to take 2 years just to get to escape velocity. I could have acted as if this was a reasonable example of the best nuclear could do but I didn't. This would be a specific power for nuclear electric in the range of 250 lb./KW elec. compared with a solar concentrator which would have to intercept about 50 sq. meters at Jupiter or about 200 at Saturn for 1 KW with 40% efficient PV. Concentrator cells currently weigh a little over a kg/ KW(Spectrolab) I think, but I don't know if a little work could improve this or not. Anyway,I don't think 200 m^2 of thin aluminized mylar(as an example) with a lightweight support structure( part of which doubles as radiator ) would weigh anything like 250 lbs. - do you? - and that's hardly the best possible.
As for the JIMO probe cost you mentioned - did that include the development cost of the reactor and power system?

As far as Al-O2 batteries; imagining for one minute that ISRU won't be central to any sustained activities on the Moon is borderline crazy to me. O2 production figures heavily in every such scenario at the very least. If you can make O2 out of Lunar regolith, you will have aluminum and iron and silicon etc. as by-products and so materials for making a battery would be readily available. Stereolithography and other tech can make production of even complex parts on the Moon feasible. By producing the solar concentrators needed out of aluminum, the total power available can increase at a exponentialish rate, particularly if thermodissocation of the water vapor is used instead of electrolysis( which requires electricity and hence PV which is a little harder to produce in-situ), to recycle the hydrogen. Only materials and parts that absolutely cannot be made on the Moon if any need be imported as the total power, O2, and metal production on the Moon grow rapidly.
Contrast this with the "trashcan" nuke that NASA is currently studying. It will produce heat to run a Stirling engine to produce a given amount of power in one location with no portable power unless batteries are brought from Earth I suppose. If it breaks, the cost of replacing or repairing it could be massive. The Lunar GDP would be in a nuclear choke hold even if no malfunctions occurred. The cost of bringing up a new reactor to double power production would be extreme.

When you have a reactor you have a very expensive and heavy heat source that requires a Stirling engine or other mechanism to make electricity that you must carry with you everywhere you go or have batteries. There is no possibility that in-situ reactor production is gonna happen any time soon on the Moon. Solar mirrors are quite easy to make in-situ by contrast.

BTW with all that Al and O2 around perhaps Al -O2 rockets need a closer look.

As for dust refraction at distance with lasers in space, the power lost would increase with distance and so a more powerful laser is required for a given amount of power transmission, but we're talking terawatts here. Anyway, you can take it up with astronomers: Seems they're able to see MASERS at great distances and it seems like I saw something about a kind of laser being seen from a supernova recently.

As for antennas at Neptune, surely you agree that bigger results in higher rates of data transmission regardless of the receiving antenna. Time on really large terrestrial antennas is limited anyway. BTW the radiators required for JIMO were enormous and they could have been shaped to double as antenna support with little mass penalty.

Steve



I take it from the fact that you didn't challenge

Ultimately Steve I do not understand your optimism for solar power. Personally I understand that solar power does have its uses and does have a great amount of potential in some applications. However it is as I said before it has its limits. It is and will always be limited by the amount of sunlight received. You have some hope that solar cells will be come more efficient and cheaper.

Nuclear power on the other hand has far greater potential. As a stored energy source it relies on nothing. It can work anywhere equally well. It can work on the moon. It can work on Mars. It can work deep under the ice in the oceans of Europa. It can work on Titan. It can work on Neptune's moon. It can work on Pluto. It can work on Eris. It can work on comets. It can work in the vast space between solar system. In the future we will have even more advance reactors with new fuels such as hydrogen, the most abundant element in universe. In addition future astronauts will not want the complex logistics solar power would require. If history has taught us anything it is power sources that are versatile that dominate.

Why spend so much money and effort on build these giant concentrator to harvest solar energy in locations that are increasingly distant from the Sun or masked from the Sun for other reasons. We can not even get solar power to provide power that economically here on earth on a large scale. In addition if humans are ever to achieve FTL travel and interstellar travel how can they do so relying on solar power.

Remember after all the Sun is a giant, natural nuclear reactor. Think about it as going directly to the source of the Sun's power itself.

Nucl