Nuclear Propulsion - The best way for space travel

Bill White · 2003-05-12 14:47:33

This would mean permanent elimination of radioactive nuclear reactor waste, and careful monitoring of all spent fuel from all reactors in the world would mean greater safety from rogue nations producing nuclear weapons. Convincing the administration to do this would be a highly political matter.

At least for the politics portion of this.

Suppose we wanted to build a nuclear propelled spacecraft. Am I correct in finding three primary options:

(1) Nuclear ion - - nuclear electric power ionizes gas which then uses emitters more or less like Deep Space 1;

(2) Nuclear thermal - - nuclear reactions heat gas (preferably hydrogen, right?) which is ejected at high velocity; and

(3) Orion derived (including mini-mag Orion) - - nuclear bombs are detonated and "push" the spacecraft.

Both for category (1) & (2) propulsion and for power facilities for a Mars base, isn't a fast breeder reactor a "good idea" to delay the reactor running out of fuel? Refueling a nuclear reactor in zero gee or on Mars would require significant infrastructure, no?

With the reactor contemplated for Zubrin's MarsDirect, how long can the nuclear reactor operate before running out of fuel?

RobertDyck · 2003-05-13 01:23:20

Suppose we wanted to build a nuclear propelled spacecraft. Am I correct in finding three primary options:
(1) Nuclear ion - - nuclear electric power ionizes gas which then uses emitters more or less like Deep Space 1;
(2) Nuclear thermal - - nuclear reactions heat gas (preferably hydrogen, right?) which is ejected at high velocity; and
(3) Orion derived (including mini-mag Orion) - - nuclear bombs are detonated and "push" the spacecraft.
Both for category (1) & (2) propulsion and for power facilities for a Mars base, isn't a fast breeder reactor a "good idea" to delay the reactor running out of fuel? Refueling a nuclear reactor in zero gee or on Mars would require significant infrastructure, no?
With the reactor contemplated for Zubrin's MarsDirect, how long can the nuclear reactor operate before running out of fuel?

You've convinced me, now convince the politicians with the power to make policy.

Bill White · 2003-05-13 11:47:44

With the reactor contemplated for Zubrin's MarsDirect, how long can the nuclear reactor operate before running out of fuel?

I am serious about this question. Anyone know?

Any permanent settlement that relies on nuclear power must plan decades into the future. Perhaps many decades. Can we re-core a nuclear reactor on Mars? Can we re-core a reactor in LEO?

Easy? Difficult?

Thoughts?

RobS · 2003-05-13 16:21:26

Many proposals for nuclear thermal engines say that the engines be jettisoned after one or two uses, just like any other spent rocket stage. If the idea is to reuse the engine, it probably is to reuse the engine until the fuel runs out, then jettison it. Perhaps a spot on the back side of the moon would be chosen where it would be crashed, or it would be launched into a solar orbit that guarantees it doesn't come back to earth for over a million years.

I suspect the same would be true of reactors on the Martian surface because the equipment to refuel them, and the personnel to run the refueling, would not be available on Mars. You'd run a reactor until it dies, then bury it under a pile of dirt for a few decades until either (1) the land near base gets so valuable, you have to move it, or (2) the equipment and people to refuel it become available. In case (2) so much time might elapse, you might declare the thing obsolete junk.

The best situation on Mars would probably be eventually to mine natural uranium, collect local deuterium--it's more common in martian water than terrestrial water--and build your own CanDU reactor. As Robert says, it makes plutonium and thus lasts a long time. Since it uses natural uranium, you avoid the need to concentrate uranium isotopes. With a bit more equipment and people--perhaps half a dozen, if automation and other technologies continue to advance--you could extract the plutonium and use it to fuel nuclear thermal engines, and export the fueled engines to earth orbit (I suppose unfueled engines would be assembled on Earth and shipped to Mars). That way space nuclear power would not require lifting nuclear fuel through the Earth's atmosphere and triggering all sorts of protests. But Mars would have to reach a pretty sophisticated level to do this.

-- RobS

RobertDyck · 2003-05-14 10:08:30

The Nerva engine used a relatively slow nuclear reactor, and that would not run out of nuclear fuel. The stage would be discarded when propellant was expended, but the nuclear reactor could last a lot longer. I have seen a NASA document for a hybrid engine that could operate as a nuclear thermal rocket, or a fission reactor to produce power. I believe you could balance how much heat was used for propulsion vs. electric power generation. The reaction could be damped to reduce the total heat produced. However, one advantage to the Timberwind engine was that it was a fast reactor, so it consumed its nuclear fuel quickly. That permitted it to carry a much lower mass of nuclear fuel. Lower engine mass means more payload. Since the Timberwind was a pebble bed reactor, its nuclear fuel was basically a bunch of marbles held within the rocket reaction chamber. It should be easy to open the engine and replace the nuclear pebbles, but the spent fuel would be highly radioactive so it would require a robot, and a radiation hardened robot at that. I believe the pebble bed design also makes it hard to control the reaction rate; once the pebbles are inserted into the reaction chamber they continue to operate at maximum heat until they run out of nuclear fuel. Nerva could be throttled or turned off, but the fuel was finely machined hexagonal rods. In fact, the first version of Nerva had the problem of hypersonic propellant flow causing vibration that literally shook the engine apart. They solved that, but the result is a high precision metal machine with tightly fitting components, so refuelling would be a major job to dismantle/reassemble. That would be very difficult in zero-G.

Does anyone know how the reaction rate would be controlled for a pebble bed power plant?

Another advantage of the CanDU over other nuclear power plants is that fuel rods can be replaced while the reactor is operating. Opening the radiation shield door to the reactor core is done in a sealed room with radiation shielded walls, and only a robot in that room to replace fuel rods. Grabbing a fuel rod while the reactor is a full normal reaction rate is definitely not something to be done by a human. That means a robot is necessary. The robot is really just a stock picker; that is a rail along the floor with a vertical riser to lift a telescoping grappler arm. Today such a thing might be equated more to a remotely operated forklift rather than a robot, but you do need it to operate a CanDU reactor. Then you need the swimming pool size storage pool to hold spent fuel rods for 1 year while the radiation cools down. Fuel bundles themselves are steel tubes filled with uranium oxide powder. Since fuel bundles are washed in heavy water primary coolant, they have to be stainless steel to prevent rusting. Building and maintaining the reactor, and processing uranium ore into fuel, would require an industrial infrastructure. Then there is reprocessing spent fuel to extract plutonium, purify that and make NTR fuel elements from it. It may happen, but as RobS says it would be a pretty sophisticated level. I imagine a simpler reactor for the first Mars mission; a reactor designed to be used once then burried.

clark · 2003-05-15 08:39:42

http://www.spaceref.com/news/viewpr.html?pid=11536

NASA Awards Teledyne up to $10M in Contracts for Advanced Thermoelectric Power Generators

Teledyne Technologies Incorporated today announced that Teledyne Energy Systems, Inc. received an award for two contracts under NASA's Radioisotope Power Conversion Technology Program. The awards, collectively valued at $10 million, if funded fully over the three year multi-phase effort, will focus on the development and demonstration of advanced thermoelectric power generators that will deliver higher efficiency and greater reliability for use in the exploration of the solar system and its planets. First year funding, beginning in July 2003, is approximately $2.5 million.
Teledyne Energy Systems' two awards will pursue different paths to achieve the same goal - a doubling of conventional thermoelectric power generator efficiency. The first project will focus on segmenting different thermoelectric materials and unique heat management techniques to optimize the power generated from a given heat source. The second project will focus on processing and material options to produce a super-latticed thermoelectric material structure that will take better advantage of the heat energy provided by the fuel.

Project Prometheus is moving forward....

Bill White · 2003-05-15 09:46:52

http://www.spaceref.com/news/viewpr.html?pid=11536
NASA Awards Teledyne up to $10M in Contracts for Advanced Thermoelectric Power Generators
Teledyne Technologies Incorporated today announced that Teledyne Energy Systems, Inc. received an award for two contracts under NASA's Radioisotope Power Conversion Technology Program. The awards, collectively valued at $10 million, if funded fully over the three year multi-phase effort, will focus on the development and demonstration of advanced thermoelectric power generators that will deliver higher efficiency and greater reliability for use in the exploration of the solar system and its planets. First year funding, beginning in July 2003, is approximately $2.5 million.
Teledyne Energy Systems' two awards will pursue different paths to achieve the same goal - a doubling of conventional thermoelectric power generator efficiency. The first project will focus on segmenting different thermoelectric materials and unique heat management techniques to optimize the power generated from a given heat source. The second project will focus on processing and material options to produce a super-latticed thermoelectric material structure that will take better advantage of the heat energy provided by the fuel.
Project Prometheus is moving forward....

Teledyne Technologies Incorporated today announced that Teledyne Energy Systems, Inc. received an award for two contracts under . . . NASA's Radioisotope Power Conversion Technology Program.

Isn't this low power stuff like that used on Cassini?

I had thought radioisotope power generation was great for small unmanned probes but pretty much useless for the propulsion or energy needs of crewed spacecraft.

If I am wrong I will gladly delete this question.

soph · 2003-05-15 16:00:48

RTGs are not reactors. You are right, they are used for very low power needs, and would not suffice for an interplanetary mission.

RobertDyck · 2003-05-16 00:15:42

The article Clark referenced sounds like the Peltier Effect. That uses dissimilar metals to convert heat flow into electricity. According to Microsoft Encarta,

The current can be increased by using semiconductors instead of metals, and a few watts of power can be produced at efficiencies of up to 6 percent (Transistor). Such thermoelectric converters, powered by kerosene lamps, are widely used in Russia and other republics of the Commonwealth of Independent States to provide power for radio receivers in remote areas.

It sounds like Teledyne is trying to find a way to use the Peltier Effect to generate enough power to supply a spacecraft while using the reliability of a solid state device. Lack of moving parts means very little can go wrong. Perhaps this is a growth out of the science fiction fear that a nuclear reactor will fail enroute to a remote planet. Science fiction is always looking for a drama so they introduce problems to make the story interesting; I fear this has contributed to the public's fear of nuclear power in space. Does anyone know the efficiency of power conversion using steam turbines?

soph · 2003-05-17 06:19:58

I believe that turbine power is limited to 33% efficiency by the laws of thermodynamics, but I need to find the source I remember that from. I can't give you an exact figure, though.

RobS · 2003-07-10 00:12:41

Somewhere on one of these forums I heard reference to something that perhaps could be referred to as a nuclear/chemical hybred rocket. The rocket would have a solid core nuclear engine cooled by hydrogen gas (and maybe part of it could be cooled by oxygen as well; I don't know). The heated hydrogen then would enter a combustion chamber and burn in a stream of oxygen gas.

I'm not sure what the resulting Isp would be. Maybe someone has seen a number somewhere. The Isp for hydrogen propellant run through a solid core nuclear engine is about 900 to 1,000, which is twice as good as a hydrogen-oxygen chemical rocket (which has an Isp of about 450). Since Isp is a function of temperature and the cube root of the molecular weight, and oxygen has sixteen times the molecular weight of hydrogen (cube root of which is 2.5), oxygen run through the same solid core nuclear engine and heated to the same temperature as the hydrogen should produce an Isp of about 400. If it then combines with hydrogen, perhaps that adds 450 to the Isp and gives a final Isp of 950.

This is the same as an all-hydrogen solid core nuclear engine, but there are advantages to consider. If water is very expensive to extract from permafrost at the lunar south pole or from the rocks of Phobos and Deimos--and all the studies indicate that the cost of creating equipment and hauling it to the moon does make for pretty expensive water--you don't want to throw away 8/9 of the water (the oxygen) and just use the hydrogen for propellant. This system allows one to use all the water for propellant.

Now, here are my questions:

1. Has anyone seen a website about this matter?

2. Does anyone know whether my calculations about Isp are correct?

3. Does anyone know whether such a rocket, with an Isp for water vapor of 950, wouldn't melt the combustion chamber? The water vapor would be pretty damn hot.

-- RobS

RobertDyck · 2003-08-30 16:09:22

In the thread "Columbia Loss Adds More Support to Hypothesis" under "Human missions" we started to discuss options to use existing Nuclear Thermal Engines on an X-33 style lifting body launch vehicle.

The RS-2200 engine used on VentureStar has an oxidizer fuel ratio of 6.00 so that means 6kg of LOX for every 1kg of LH2. The XRS-2200 engine used on X-33 has an oxidizer fuel ratio of 5.50. The X-33 had a gross mass of 123,800kg and an empty mass of 28,600kg so the propellant mass is 95,200. That consists of 14,646kg liquid hydrogen and 80,554kg liquid oxygen. LOX has a density of 1,141kg/m^3 and LH2 is 70.973kg/m^3 so the volume is 70.60m^3 of LOX and 206.36m^3 LH2. The total volume is 276.96m^3. If all of that were LH2 the mass would be 19,657kg. Timberwind-45 engines have an Isp in vacuum of 1,000 seconds and at sea level of 890 seconds, but let's use the launch mass to propellant mass ratio that I calculated earlier for VentureStar with Timberwind-250 engines; that is 991,000kg / 393,648kg = 2.5174775. Therefore a propellant load of 19,657kg could lift a spacecraft with a launch mass of 49,486kg. Subtracting the propellant mass and empty mass of X-33, that leaves 1,229kg of cargo. I don't know the mass of the XRS-2200 engines but they were based on J-2S and had similar thrust, so let's say they had the same mass. Subtract 2 XRS-2200 engines at 1,400kg each and add 2 Timberwind-45 engines at 1,500kg each, that increases the spacecraft mass by 200kg so it reduces the cargo capacity that much leaving 1,029kg cargo. The thrust to launch mass ratio would be 14.7% greater than VentureStar so it would be slightly over powered, but not much. You might be able to reduce structural mass since it doesn't have to hold as much launch mass, but you still have to withstand re-entry stress, and I didn't include mass or volume for the cargo bay. This is what I meant by the propellant tank consuming your cargo capacity.

I just had a thought. Since the problem is the volume of LH2, could you use another propellant with a Nuclear Thermal Engine? The Isp may not be as high, but the propellant tank would be smaller. RP-1 has a chemical formula of C12H24, normal storage temperature of +25?C, density of 820kg/m^3, and boiling temperature of +175..+325?C. The boiling temperature is a range due to the fact that a petroleum distillate is mixture, not a pure compound. Kerosene is as easy to handle as gasoline so it would be very convenient. Chemical rockets that burn RP-1 often have a problem with soot build-up in the exhaust nozzle, this problem would be even more pronounced in an NTR using the same fuel. In fact, the heat of the reactor would crack the petroleum molecule causing soot build-up in the nuclear reactor. You could use liquid oxygen but that would be a cryogenic propellant again. Water is liquid from 0..100?C and has a density of 1,000kg/m^3. Water is ridiculously cheap and when it breaks down it leaves hydrogen and oxygen gas. Since the engine would have a steady rush of water flushing through it, you wouldn't need distilled water, just tap water filtered through a reverse osmosis filter. What would be the Isp of a NTR using water as propellant?

One reason a gas core NTR is a higher Isp than a solid core NTR is that the gas core engine is so hot it cracks the H2 molecule into mono-atomic hydrogen. That doubles the number of gas molecules. Water will dissociate into hydrogen and oxygen at temperatures above 1,800?K (1,527?C) into a mixture of H2, O2, H2O, O, H and OH. Above 3,500?K (3,227?C) it will dissociate completely into mono-atomic hydrogen and oxygen. Uranium dioxide melts at 3,075?K so attempting a complete dissociation would result in a liquid core, but a partial dissociation is possible with a solid core NTR. It would take more heat to use water than liquid hydrogen, but the mass of additional uranium would be small compared to the reduction of tank size, spacecraft structure and heat shield. I had argued elsewhere that LH2 was a more appropriate propellant for NTR spacecraft to tool around the solar system, but I think for a launch vehicle the reverse is true. I could calculate the expansion ratio from liquid water to partially dissociated steam, then calculate the pressure caused by gas expansion to get thrust force, then divide thrust per unit mass of propellant consumed per second to get specific impulse. However, the lady I've been dating wants me over at her place so I'll have to leave now.

Shaun Barrett · 2003-09-05 07:30:47

Hi Robert!
You back from that lady's place yet? :;):

These little exercises in drawing-board rocketry are very absorbing. I suppose if engineers juggled with figures like this often enough, they'd eventually come up with the ideal configuration and fuel for a nuclear Single-Stage-To-Orbit vehicle.
The proportions of LOX to LH2 you mention, 5.5- or 6-to-one, aren't what I found when I looked them up. I think I was in Encyclopedia Astronautica at the time .. not quite sure .. but they said 4-to-one (unless I'm hallucinating). Perhaps that was a theoretical best ratio while yours are based on practical performance data (?).

The idea of using water as fuel (or reaction mass) in an NTR sounds appealing. I suppose the average exhaust velocity must be lower than with LH2 but how would the ISp be affected?
And the fuel density would be greater than the average for the cryo-chemical fuels originally planned for VentureStar, so presumably we would need to carry a lesser volume in the tanks. And, if the nuclear engines are more compact, does this mean we could create a more streamlined, more robust, but lighter craft than VentureStar? Or is the straight-across-the-back linear aerospike still the way to go with the new propulsion system?
This all sounds very promising!

Water-fuelled nuclear-thermal VentureStar, here we come!!

All we have to do now is convince the greenies they like it!

RobertDyck · 2003-09-05 11:30:40

The oxidizer to fuel ratio I got from Encyclopedia Astronautica. Just look up the specifications for the engines. RS-2200 and XRS-2200

When I got back last Tuesday, I tried to look up development work already done rather than trying to calculate from first principles. The result was a NTR that did use water, but had a relatively low temperature and very low performance. They kept the temperature down below 1,000?K and the engine produced an Isp of 100 seconds. If NTR performance is that low we are better off with chemical rockets. I'll try calculating Isp myself based on an exhaust temperature of a little over 3,000?K. I think that was the exhaust temperature of a pellet bed fast nuclear reactor (PeBR), or was it the temperature for a particle bed reactor (PBR)? I'll have to look it up again. One source claimed Timberwind development was never completed, and they had a problem with pebbles burning through the engine casing. Encyclopedia Astronautica lists it as developed. The article that claimed Timberwind wasn't completed stated the development was halted due to protests from the greenies. Timberwind was a military project, so did they really cancel it?

One concern I had was how to control a PBR or PeBR. You can't move the pellets away from each other, or insert a control rod into the bed. They did it by encircling the reactor with control rods that rotate: one way it absorbs neutrons, the other way it reflects. Quite ingenious.

Shaun Barrett · 2003-09-05 18:48:59

An ISp of 100 seconds?!!

We may as well hitch up a donkey and force feed it baked beans with chilli relish!!
:laugh:

RobertDyck · 2003-09-21 16:29:30

I promised to give an update on water/nuclear VentureStar. I could give complex formulas for rocket engine design, but the bottom line is combustion chamber temperature. The Space Shuttle Main Engine burns LH2 with LOX to produce steam, so the exhaust of a water NTR can be directly compared to SSME. Actually, SSME has a slightly rich mixture of more hydrogen than would burn with oxygen to produce water. Combustion dynamics dictate that the maximum temperature produces maximum thrust, so that can't be just unburned hydrogen. The exhaust must contain some hydroxyl (OH) and peroxide (H2O2). Encyclopaedia Astronautica does not give combustion chamber pressure or temperature statistics, but the Rocketdyne web site does. The combustion chamber reaches +6,000?F (+3,588?K). That is hotter than the temperature to dissociate water back into monoatomic hydrogen and oxygen. No wonder the SSME has such high performance. An NTR could not do better. I guess the way Nerva or Timberwind produced such high specific impulse was using a light propellant, one that didn't require oxygen. I must complement whoever designed the SSME.

So we need a propellant that has lower molecular mass than water, yet is easier to store than liquid hydrogen. Methane is liquid at -161.6?C and liquid methane's density is 422.62kg/m^3. That's not as dense as water or LOX, but a lot better than LH2. That's a cryogenic propellant again, but easier to handle than LH2. The molecular weight is 16.043 grams per mole (g/mol), the molecular weight of water is 18.01528g/mol so at the same temperature the specific impulse would theoretically be 1.1229 times as great. A 12.29% increase in Isp over the SSME would not justify switching to nuclear technology. Does anyone else have a suggestion?

Tyr · 2003-10-03 15:41:07

If you like external tanks and nuclear thermal rocket motors, here's more: http://groups.msn.com/DaveDietzler/newn … ckets.msnw

I got the ISP for methane from Zubrin's "Entering Space" and the ISP for ammonia from Mark Wade's astronautix.com It all depends on how hot your reactor is, does it not?

SpaceNut · 2005-03-29 11:38:41

Well as indicated in the title with RUSSIA TO HELP DEVELOP NUCLEAR-POWERED SPACECRAFT

Russia that has developed state-of-the-art rocket engines is ready to use them within the framework of the international space program. Consequently, Russia is quite eager to explore deep space with the rest of the world.
In Moscow's opinion, such is the gist of international accords that were approved by 21 countries and 15 international organizations in the United States late this March. The concerned parties discussed interplanetary space-flight plans that were suggested by national space agencies. A document would be expected to formalize the discussion's results by August 2005.
Russia suggests that those involved in the Martian program use its nuclear rocket engines and propulsion units, Academician Nikolai Ponomarev-Stepnoi, vice-president of the Kurchatov Institute national research center, noted in early March. He made this statement at an international conference in Moscow that discussed nuclear-powered spacecraft.

It should be mentioned in this connection that the Energomash science-and-production association (NPO) had developed the first Russian nuclear rocket engine back in 1981. However, its comprehensive tests never took place because of tougher nuclear environmental-safety requirements in space research. The United States also conducted similar experiments, failing to test even a prototype version.

Mars_B4_Moon · 2024-03-30 04:20:52

an older topic perhaps worth bumping

Nuclear fission reactor from NASA will provide electricity on the Moon and Mars
https://www.earth.com/news/nasa-designs … -and-mars/

DARPA tasks Northrop Grumman with drafting lunar train blueprints
https://www.theregister.com/AMP/2024/03 … oon_train/

All aboard the moon train: DARPA is trying to figure out how to build a lunar railroad
https://uk.news.yahoo.com/aboard-moon-t … 45494.html
and the famed US research agency

China Aerospace Science and Industry Corporation’s (CASIC) Flight Vehicle Technology Research Institute, which has reportedly built a two-kilometer (1.2-mile) test track in Datong, Shanxi Province.
https://newatlas.com/space/china-railgu … aft-orbit/

2023 article

Lockheed Nabs $500M to Build Nuclear Powered Rocket
https://payloadspace.com/lockheed-nabs- … ed-rocket/

orbital Spinlaunch concept seems like it could work on the Moon or Mars
https://www.spinlaunch.com/

The country of Angola became the 33rd country to sign up for Gateway Artemis
https://twitter.com/nasaartemis/status/ … 7910255882

Saudi and religion and space

Four key points regarding Saudi Arabia’s withdrawal from the Moon Agreement
https://thespacereview.com/article/4706/1

The Trump Administration ended the US silence on the Moon Agreement and halted the creep of customary international law when it issued Executive Order 13914 on April 6, 2020, which expressly denounced the Moon Agreement and reasserted the legitimacy of space resources. This executive order met with resistance from the Russian Federation in a statement from Roscosmos. However, the statement, which is distinctly a propaganda and lawfare maneuver intended for political effect, did not directly support the Moon Agreement, which means its impact on customary international law was negligible if existent at all.

Artemis Gateway
https://www.youtube.com/watch?v=vVLK0tgLHro

an environmental danger for Earth and radical approach that was considered unsafe

Project Orion: Detonating Nuclear Bombs For Thrust
https://hackaday.com/2018/08/13/project … or-thrust/

Mars_B4_Moon · 2024-04-13 14:56:33

Northrop Grumman hint at new radical Nuke power and lunar train concepts, the Europeans and British and French admit Nuclear power is needed in space, China says it will put more Nuclear power in space.

some other news

Could a self-sustaining starship carry humanity to distant worlds?
https://www.popsci.com/science/starship … nt-worlds/
Generation ships offer a tantalizing possibility: transporting humans on a permanent voyage

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#251 2003-05-12 14:47:33

Re: Nuclear Propulsion - The best way for space travel

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