39 days to Mars possible now with nuclear-powered VASIMR.

[Exoscientist]

A criticism of the VASIMR plasma drive was that space nuclear power did not

have sufficient power at the needed lightweight. However, it turns out that

this is due to the heavy electrical generating equipment, not the nuclear

reactors themselves.

Then note that recent research has produced electrical generators at the

needed lightweight, thus making nuclear-powered VASIMR viable:

Nuclear powered VASIMR and plasma propulsion doable now.

http://exoscientist.blogspot.com/2015/08/nuclear-powered-vasimr-and-plasma.html

Bob Clark

[Elthy]

Afaik the problem isnt mechanical energy -> electrical energy conversion, but heat -> mechanical energy.

[peadar1987]

The best thermal power plants on earth run at about 40% thermal efficiency. This is approaching a hard limit imposed by the Carnot efficiency of the cycle. The other 60% of the energy needs to be dumped into the environment. If you're dumping multiple megawatts of heat into space, there's no way around it, you need heavy radiators.

It's also worth noting that the source you cited is only for the engine. It doesn't include any shielding at all. What it also doesn't include is some sort of working fluid for the cycle. No pump, no heat exchangers, no expander.

A power plant for electricity generation is a significantly more heavy and complex machine than something that just heats up fuel and spits it out the back.

[Thomassino]

Nuclear-powered VASIMR won't be tested in space anytime soon IMHO, because some people are not comfortable with putting nuclear devices into space (they can hardly stand RTGs).

[Streetwind]

doable now.

...with a VASIMR drive several years away from being flight ready, and a nuclear reactor which does not exist, not even in engineering blueprints - because it is physically impossible to achieve your numbers. I'm sorry Mr. Clark, but your article is pure clickbait with no substance. Please try to be more thorough in your research, and less sensational. If your math turns out an unbelievable result, it's usually best to actually disbelieve it and look for your error instead of taking it for truth.

The idea of using nuclear reactors for space applications isn't new. And it's not as simple as you think it is. For example, you conveniently ignore the mass of the radiators required to cool the reactor, which is not trivial - in fact, the majority of the reactor's output is going to be waste heat. The NTR does not require radiators, because the fuel carries the heat away. If you're producing power, the heat needs to go somewhere. You did not notice this because you went straight from "the reactor produces heat" to "I am converting mechanical into electrical energy". But where does that mechanical energy come from? You forgot the heat engine, the part that converts thermal energy into mechanical energy. And that part is massively inefficient, which causes the huge amount of waste heat.

Some 15 years ago, NASA construted a test reactor called the SAFE-400 ("Safe Affordable Fission Engine"). It produced just 400 kW of thermal power, and it had a built-in dynamo driven by an equally built-in brayton cycle turbine - the best heat engine that physics knows how to build today. It's rated electrical output was 100 kW. In other words, 25% of the reactor's output was usable, and 75% was waste heat. At 520 kg weight, the reactor had a specific power of 192 W/kg... and that is presumably measured without the mass of the radiators required to deal with the 300 kW waste heat, since such a thing was not part of the experiment setup according to photos.

Upscaling the reactor would yield better mass ratios and increase the specific power. Perhaps a fancy cryocooled generator could further improve things, but probably not by a lot, since a.) that is not where the major losses are in the first place and b.) cryocoolers are heavy and require even more radiators. However, to get anywhere close to your dream of 10 kW/kg, the reactor would need to become 52 times as efficient as it was in NASA's lab... and then it would need to become even more efficient, because that still ignores the weight of the radiators. Unfortunately I need to tell you: this is not going to happen. Even if the SAFE-400 had absolutely zero losses, it would still only have posted ~770 W/kg. And you are never going to get a lossless conversion. 300 W/kg? Sure, may work on a large-scale reactor. Maybe even 500 W/kg in the future, if such reactors were being actively developed, which they are not. 10-100 kW/kg? Not today, not ever, not with nuclear fission.

Edited August 29, 2015 by Streetwind

[theend3r]

Nuclear-powered VASIMR won't be tested in space anytime soon IMHO, because some people are not comfortable with putting nuclear devices into space (they can hardly stand RTGs).

Which is quite sad as according to published papers, nuclear energy is by far the safest source of energy, even more so than hydro or solar.

[Nibb31]

Which is quite sad as according to published papers, nuclear energy is by far the safest source of energy, even more so than hydro or solar.

We are talking about space applications here. How would you put hydro power on a spacecraft?

[Robotengineer]

We are talking about space applications here. How would you put hydro power on a spacecraft?

You wouldn't.

[vger]

Which is quite sad as according to published papers, nuclear energy is by far the safest source of energy, even more so than hydro or solar.

Sooner or later people are going to have to get over it. And not just for the sake of space travel, but for Earth as well.

[Kinglet]

We are talking about space applications here. How would you put hydro power on a spacecraft?

Dam > Turbines > microwave transmitter > spacecraft

[Hcube]

Which is quite sad as according to published papers, nuclear energy is by far the safest source of energy, even more so than hydro or solar.

How is a nuclear fission plant safer than a solar cell array ?

[peadar1987]

How is a nuclear fission plant safer than a solar cell array ?

It's not, but you need a lot of solar cells to produce the same amount of power as a nuclear plant. The number of people killed during the mining and production of the materials to build the arrays is generally found to be higher per MW for solar power than for nuclear.

[PB666]

It's not, but you need a lot of solar cells to produce the same amount of power as a nuclear plant. The number of people killed during the mining and production of the materials to build the arrays is generally found to be higher per MW for solar power than for nuclear.

Is this before or after SpaceX blows up the first full uranium fission reactir payload?

Solar is safe, the mining is an issue because US does not protect against unfair trade practices and because this is the standard workplace safety issue on any Chinese based industry. Sinply close your eyes and don't let it happen in your country. If the US subsidized rare earth mining more we could bring Solar manufactoring back to the U S. Otherwise buy panels and know that some farners son has a job and can mostly support his family before work related breathing disorders take him down. We could also build hybrid engines and put our auto industry at the technological forefront of manufactoring.

The real issue here is not safety, if is a safety issue we could launch form american Samoa or the bikini Atoll. Better on DV anyway. Solar needs to get the watt/mass ratio up several fold to compete with nuclear engine, BUT with solar you do not have to protect the passengers from gamma and Xrays radiation. I dont know if they have done this but you can't taken a concrete contaiment facility, its got to be dense lead. You don't have the luxury of boyancy such as iin a sub.

[peadar1987]

Is this before or after SpaceX blows up the first full uranium fission reactir payload?

Solar is safe, the mining is an issue because US does not protect against unfair trade practices and because this is the standard workplace safety issue on any Chinese based industry. Sinply close your eyes and don't let it happen in your country. If the US subsidized rare earth mining more we could bring Solar manufactoring back to the U S. Otherwise buy panels and know that some farners son has a job and can mostly support his family before work related breathing disorders take him down. We could also build hybrid engines and put our auto industry at the technological forefront of manufactoring.

The real issue here is not safety, if is a safety issue we could launch form american Samoa or the bikini Atoll. Better on DV anyway. Solar needs to get the watt/mass ratio up several fold to compete with nuclear engine, BUT with solar you do not have to protect the passengers from gamma and Xrays radiation. I dont know if they have done this but you can't taken a concrete contaiment facility, its got to be dense lead. You don't have the luxury of boyancy such as iin a sub.

If SpaceX blow up a uranium-fuelled reactor on launch, there is zero problem. None. Uranium is toxic, but if the reactor hasn't been turned on, its radioactivity is in no way harmful unless you ingest a huge amount of it, in which case you'll get regular poisoning long before you get radiation poisoning. The lead shielding will kill you quicker than the uranium.

Edited August 29, 2015 by peadar1987

[tater]

Nuclear is incredibly safe in deaths per unit power produced. Safer than wind or solar. Solar is often placed on roofs, and one fall can kill their average. The nuke mortality includes Chernobyl. Being worried about nuclear power is like being worried about flying while driving to the airport (more dangerous than the flight by a wide margin).

[AngelLestat]

Nuclear is incredibly safe in deaths per unit power produced. Safer than wind or solar. Solar is often placed on roofs, and one fall can kill their average. The nuke mortality includes Chernobyl. Being worried about nuclear power is like being worried about flying while driving to the airport (more dangerous than the flight by a wide margin).

please, dont come out with trash stadistics. This is not even the topic for that, this has nothing to do with normal nuclear thermal plants.

[Nibb31]

Nuclear is incredibly safe in deaths per unit power produced. Safer than wind or solar. Solar is often placed on roofs, and one fall can kill their average. The nuke mortality includes Chernobyl. Being worried about nuclear power is like being worried about flying while driving to the airport (more dangerous than the flight by a wide margin).

We're talking about space applications here. Comparisons with wind and hydro dams do not apply.

The problem with nuclear in space is that you need huge radiators. Those radiators are going to be heavier than solar panels that produce the same amount of power as your nuclear reactor.

[Bill Phil]

We're talking about space applications here. Comparisons with wind and hydro dams do not apply.

The problem with nuclear in space is that you need huge radiators. Those radiators are going to be heavier than solar panels that produce the same amount of power as your nuclear reactor.

But wouldn't you need a large amount of radiators either way?

[SargeRho]

But wouldn't you need a large amount of radiators either way?

No, because the solar panels, while they do heat up, produce energy from sunlight. They don't need to get rid of several megawatts of heat. You still need radiators, but not nearly as much as you'd need for megawatt-range nuclear reactors.

[vger]

please, dont come out with trash stadistics. This is not even the topic for that, this has nothing to do with normal nuclear thermal plants.

It's less of a concern than a nuclear plant. A meltdown anywhere beyond LEO isn't going to be much of a concern. Alright, so it's leaking radiation. Who on Earth has any reason to worry about it? Obviously it's bad for anyone riding the engine, but comeon. It's in deep space. Everyone needs to quit worrying about a repeat of Chernobyl.

[Gaarst]

About radiation in space, have you ever heard of solar wind ?

[Elthy]

Nuclear-powered VASIMR won't be tested in space anytime soon IMHO, because some people are not comfortable with putting nuclear devices into space (they can hardly stand RTGs).

Who are those people, ive never heard of them. Even in Germany i dont know anyone saying anything about nuclear power in space, even when Curiosity was launched in the aftermath of Fukushima...

[AngelLestat]

It's less of a concern than a nuclear plant. A meltdown anywhere beyond LEO isn't going to be much of a concern. Alright, so it's leaking radiation. Who on Earth has any reason to worry about it? Obviously it's bad for anyone riding the engine, but comeon. It's in deep space. Everyone needs to quit worrying about a repeat of Chernobyl.

I dint said nothing about space, I just disagree with tater´s stadistics and I comment than this topic was not about that, the same than Nibb31.

As many said, If you need to produce a lot of power in space, you need to take into account all the extra mass you need to radiate waste heat.

Then you need to keep your crew far from the reactor. And your rocket launch may have extra security measures because you need to launch a nuclear reactor (that of course will not be operative in the moment of launch, which reduce by a lot the damage that can made).

But then we need to think if the extra isp may be worth it against all cons.

[PB666]

If SpaceX blow up a uranium-fuelled reactor on launch, there is zero problem. None. Uranium is toxic, but if the reactor hasn't been turned on, its radioactivity is in no way harmful unless you ingest a huge amount of it, in which case you'll get regular poisoning long before you get radiation poisoning. The lead shielding will kill you quicker than the uranium.

Those Bluefin off the coast of Florida are just waiting to ingest any uranium pellets that fall from the heavens. Its psychological issue, people would be afraid at just the hint that there was a reactor breach. Lead shielding wont kill you, I have worked around it for 30 years, uh... uh-oh..... damn [ker-plonk].

[Bill Phil]

No, because the solar panels, while they do heat up, produce energy from sunlight. They don't need to get rid of several megawatts of heat. You still need radiators, but not nearly as much as you'd need for megawatt-range nuclear reactors.

For a given amount of useable power produced, what would the answer be?

You are still moving megawatts of something.

And why don't we use mirrors to foul us more solar energy onto the panels? At least for some applications...

Wait a minute, does heat have a power unit?