Large Ship Atomic Propulsion

tahanson43206 · 2022-02-21 08:34:38

Large Ship Prime is: Large scale colonization ship by RobertDyck

This topic is offered to collect knowledge, insights and best practices for an all-nuclear propulsion system for Large Ship.

"Large Ship" is (arbitrarily) defined as 5,000 metric tons, for the purposes of calculations to be posted in this topic.

It is clearly possible to deliver a 5000 ton vessel to Mars and return it safely to Earth using chemicals.
The challenge for contributors to ** this ** topic is to show how a nuclear propulsion system can perform the task.

It is also (clearly) a massive undertaking.

Fortunately, humans are good at doing large projects.

This one is on the larger size, but certainly not anywhere near the top of the chart.

This topic is intended to provide a resource for future readers/students/professionals who need to plan a flight for one of the versions of Large Ship that are in the early conceptual phases, and the customer insists upon using all-nuclear propulsion.

Mission plans should include:

1) Supply of all materials needed (from Earth as default but other locations as they become available)
2) Launch from LEO (I'd like to see the Space Tug concept fleshed out for this) (Include "finish to Escape" by Large Ship)
3) "Docking" into orbit at Mars using nuclear propulsion by the Large Ship itself
4) Launch from Mars orbit to an Earth grazing trajectory
5) Space Tug deceleration service to achieve "Docking" in LEO (no propulsion by Large Ship is needed)

Over time, and with any luck at all, this topic can become a valuable resource for space mission planners.

(th)

SpaceNut · 2022-02-21 10:29:13

This trades fuel volume for electrical power to move the ship depending on the acceleration rate means an ever increasing power level required. The use of the same system works for deceleration at a high power and larger fuel use initially but can throttle back as the ship does slow but only if you are reaching your insertion velocity to gain orbit on the first try without any aero-breaking in the atmosphere which requires heat shield to perform.

tahanson43206 · 2022-02-21 10:54:13

For SpaceNut re #2

Thanks for giving this new topic a running start!

My impression of Post #2 is that you are thinking (?) of a VASIMR type system?

That certainly seems to be a possible approach to use of nuclear fission to propel a space ship.

This topic is intended to include all possible modes of nuclear propulsion, including (at least):

1) nuclear thermal
2) mini-bomb putt-putt (See Freeman Dyson, et al)
3) micro-bomb putt-putt (See Calliban in this forum)
4) nuclear electric - several varieties

+ the ones I've missed ... other members... please add the options I'm forgetting

(th)

SpaceNut · 2022-02-21 11:06:48

VASIMR, ION,Thermal are all produced by the nuclear reactors power supplying system on a fuel type that exits the nozzle.

These only gain acceleration to the fuel.

Bombs as in the Orion topic as that is a different concept for nuclear use.

tahanson43206 · 2022-02-23 06:36:09

GW Johnson wrote:

Tom:
What I found and documented in the stuff you stored in the drop box was that chemical at half the Isp of NERVA (but comparable thrust) could not make the round trip single stage. Both the plain chemical propulsion stage and the tug-assisted chemical stage required significant propellant launched into LMO as well as to LEO, at around 20,000 tons each, unless reduced a bit by tug assist at both ends of the trip. The only difference was the strength of the gravity wells on how much propellant got consumed while launching those propellants. NERVA needed nothing launched at Mars, but about the same ridiculous quantity (20,000 tons) launched at Earth. It could make the round trip single stage, without tugs.
Electric could reduce the quantity of propellant required in LEO to something less ridiculous at 6-7000 tons for the round trip without tugs, because of its far-higher high Isp, despite the penalties for being very non-impulsive in thrust levels. The travel time is longer, due to the spiraling required for escape and capture. Travel time is bad enough for Hohmann transfer. Faster trajectories require significantly more propellant. The spiraling trajectories rule out the use of tugs.
Gas core nuclear Isp varies considerably with the exact cycle. I figured 8000 tons of propellant for the round trip with the nuclear light bulb at 1300 s, less for a regenerative open cycle at 2500 s, and less still for a radiator-cooled open cycle at 6000 s, all without tugs. These get you down near or under 1 ton of propellant per ton of dead-head payload. None of these are currently deployable technologies. All require considerable development with no guarantee of success. The nuclear light bulb has the most experimentation behind it, but still a whole lot less than will be needed.
The nuclear explosion drive shows the highest potential at well under 0.2 tons "propellant" per ton of dead-head payload (around 650 tons propellant to push 5000 tons of dead-head). In this case "propellant tonnage" is the mass of fission devices that are both shaped charges and have significant reaction mass that is to be vaporized and flung against the blast plate on the shock absorbers. This is 1957-vintage fission technology. We know it would work, but after the Starfish Prime space nuclear explosion test of 1962, we know EMP is a big risk.
Actually, I have known for many decades that the nuclear explosion drive is by far the highest propulsive potential that we humans know, in a technology that we know we could make work. In 10,000+ ton vessel masses, it is near 10,000 s Isp, and you have to work hard to hold the vessel acceleration levels down to 2-4 gees. Isp suffers if you try to use it for small vessels (down under 5000 s at under 5000 tons). I don't understand why that it true, but that is what Freeman Dyson and the rest found while working on it for General Atomics in the mid to late 1950's. I read his son's book about those efforts. The data is in there. That was USAF's old Project Orion.
You build ships like that of 2 inch steel plate, similar to how ocean-going vessels are built. The forces are horrendous. So is the radiation.
GW

tahanson43206 · 2022-02-23 06:54:18

For GW Johnson re atomic powered space vessels...

It is impractical (and may be impossible) for NewMars members to read every post by everyone else.

Thus, it is not at all surprising that one of us might have missed work by Calliban that is in progress to invent a mini-atomic-putt-putt system.

The Project Orion system you've described may well come into play at some point.

However, long before then, if Calliban is successful in his quest, humans will have learned how to enlist atomic power at a much smaller scale.

However, I want to emphasize that the ** principles ** of operation of the equipment sound quite similar.

Therefore, assuming you read this post (which I recognize is not guaranteed) here is what I understand of Calliban's initiative, and where your insights from your study of Project Orion may be helpful.

Background:
The US National Lab at Lawrence Livermore is working on laser ignition of pure fusion pellets. These pellets are (working from memory) made of a combination of tritium and deuterium. The pellets are heated by a bank of more than 100 powerful lasers, and the lab has reported some success in achieving fusion.

That work will continue, I am sure.

However, let us consider merging that flow with the Project Orion concept.

As I understand Project Orion, the nuclear devices were very small, on the order of size of artillery shells developed on Earth to carry nuclear explosives.

The ignition was to be carried out by the "traditional" use of chemical explosives to put the nuclear material into proximity.

Calliban's proposal, which you can find in his "Nuclear is Safe" topic, is to package a small amount of fission material with a small amount of fusion material and to ignite the combination with laser input.

Such a system would operate at the level of a common BB shot. For those not familiar with this concept, Wikipedia has articles on "air rifle", "BB gun" and "Pellet

The system (if it can be made to work) would operate at a much smaller scale than the Project Orion idea.

Calliban has already expressed (what I interpreted as) dismay at the quantity of radioactive material that would be generated by this propulsion system.

Be that as it may, the concept would provide reliable, controllable thrust for as long as the supply of pellets holds out.

Some of the energy produced needs to be captured by magnetic fields in the "combustion chamber" of this vessel to provide the power to operate the system.

It would follow that some of the captured power would be diverted to support systems on the space vessel itself, but the space vessel needs it's own small reactor on board to sustain the vessel when it is not accelerating.

I hope this post is helpful, and that it reaches you (which I recognize is not guaranteed).

(th)

Oldfart1939 · 2022-02-23 09:54:10

Everyone seems to have overlooked my thread "Nuclear Thermal Propulsion Module," which was suggested for Starship, but would be even more applicable to the larger ships.

It's simply a deep space Nuclear Thermal propulsion module and is simply a matter of scale-up.

tahanson43206 · 2022-02-23 10:39:55

For OF1939 #7

You are preaching to the choir here, and in the forum. Your post on Nuclear Thermal Propulsion deserves to grow on it's own, although it is a duplicate of a pre-existing topic with a very similar title.

If you would like to contribute to ** this ** topic, please DO! This topic is about planning for propulsion of a space vessel of 5000 tons mass.

Your design for a nuclear power system should provide for:

1) Push Large Ship out of LEO to escape velocity
2) Adjust course during flight to insure optimum placement ahead of Mars at destination
3) Accelerate to allow Mars to catch up gently, so that Large Ship falls into a clean LMO
4) Accelerate out of Mars gravity well to begin descent to Earth
5) Adjust course during flight to insure optimum placement with respect to Earth at destination
6) Decelerate to enter a clean LEO

Your plan should include:

1) Design of engine (or engines if multiple due to 5000 ton mass of vessel)
2) Quantity and types of radioactive material
3) Quantity and type(s?) of propulsion material
4) Management issues ... control electronics, radiation spewing from stern
5) Legal issues ... securing releases to operate vehicle near Earth
6) Insurance issues ... securing insurance for your design in case(when) something fails and people or property are damaged

There may be more items for your contribution here, but this will give you a running start.

PS ... your 17 person expedition plan awaits your attention.

From my point of view, that is important work that deserves to be brought forward.

We have a Companion topic set up so you can work on your Expedition topic without interference

Your energy (at this point in your advanced life) is likely to increase as you receive feedback from supporters.

(th)

Calliban · 2022-03-16 06:05:53

I have made some limited progress researching this topic. One important realisation is that inertial confinement fusion has important scale effects that are introduced by the need to maintain confinement time. The Lawson criterion for an imploding fuel pellet can be reduced to the product of pellet radius (which scales with confinement time) and compressed pellet density.

Radius x Density > 3g/cm2.

The central region of the pellet is where ignition is expected to occur. The goal is to create conditions for a stable thermonuclear burn wave to propagate through the pellet within the time allowed by confinement time. One way of increasing confinement time is to surround the pellet with a dense tamper material like lead or Uranium.

One clear conclusion for IC fusion is that from a technical view point, it becomes easier with increasing scale. As the pellets increase in size and energy content, confinement time naturally increases, because it takes longer for a hot ion to cross the radius of the pellet. This relaxes the requirement for achieving extreme density in the compressed pellet, because the whole assembly remains together for longer, allowing more time for reactions to take place.

More later.

Last edited by Calliban (2022-03-16 06:19:46)

tahanson43206 · 2022-03-16 06:57:49

For Calliban re #9

Thanks for your report of progress in this important work!

The news that pellets must be larger does have a favorable aspect ... It is known that small nuclear fission devices will work.

The implication is that as you increase size, eventually you will arrive at a size that works.

The disadvantage of increased size is lumpiness of the impulse production, so the smaller the pellets the better.

There is probably a sweet spot in that range.

I am reminded of the hit and miss designs for gas engines still operating at museums in the US and probably elsewhere in the world.

The flywheel of such engines is large to carry momentum for intervals between explosions of fuel.

For spacecraft the size of Large Ship (estimated 5000 tons) impulses occurring at intervals of 1 second might be tolerable, but passengers will probably sign with relief when the engines are turned off.

I'd been hoping for power impulses at a rate greater than one per second, but we'll have to live with whatever you find that works.

***
In an earlier post, you expressed concern about production of energetic particles as the design your are considering operates.

I've been thinking about that (and not for the first time) and would like to offer the suggestion that the spacecraft navigator find a way to apply power so that the ejecta from the engine is headed toward a gravity sink such as the Sun. As the particles travel toward the gravity sink, they present a risk for humans or equipment who might be in the path, so I can imagine the courtesy of notifying the space faring community when burns are planned, and where the ejecta is going to be.

The risk of human generated energetic particles combining with Solar and Galactic particle flows is more incentive for SpaceNut to continue working on design of dynamic radiation protection.

(th)

SpaceNut · 2022-03-16 20:17:15

With what we are seeing here on earth we might never see nuclear use in space....

Radius x Density > 3g/cm2.

concentrated mass

RobertDyck · 2022-03-21 14:31:37

Saw this meme on Facebook. Let's see if it works...

Calliban · 2022-03-25 19:01:06

Updated post on this topic:
http://newmars.com/forums/viewtopic.php?id=10192

The key enabling technologies for producing IC Fusion systems compact enough for spacecraft drive systems are:

1) The use of fissile elements to ignite compressed Fusion fuel pellets;
2) The use of electrostatic ion accelerators as the drivers for IC pellet compression. These have efficiency 90%, very high energy density, but ion energy is limited to low MeV. This is a tolerable situation if the driver is used to provide compression, without other energy sources (I.e fission) providing the temperature needed for pellet hot spot ignition.

Calliban · 2022-04-05 17:23:34

I have sent an e-mail to First Light Energy. This is the company that recently achieved advancement in kinetic impact induced Fusion.
https://newmars.com/forums/viewtopic.ph … 92#p193192

Hopefully, they will reply with some helpful feedback. There is an outside possibility that they had not previously considered this Fusion fission hybrid approach. If so, our work on the topic on this board may lead them in new directions.

It is my hope that this approach will allow us to develop a propulsion system that combines high thrust and high ISP for the large ship. A propulsion system capable of achieving 1g> acceleration and ISP greater than 2000, would be revolutionary. Ships could take off from Earth surface, transit to Mars, land and return to Earth surface again on a single fuel load. This is the way to make Mars colonisation a truly affordable option for individuals on Earth. That would allow the really high population growth rates necessary to build up a population of millions by the middle of this century. It would also solve our energy problems here on Earth. We need prosperous economies here on Earth for any of our ambitions to stand a chance. That precondition really depends on our ability to replace fossil fuels with a cheap and power dense alternative at a rate that exceeds their depletion. Fission could do that. But Fusion would be better.

Last edited by Calliban (2022-04-05 17:38:14)

Calliban · 2022-04-11 09:27:04

A technically easier propulsion option for the large ship would be a low-pressure pebble bed NTR using hydrogen propellant. This NTR could use very low enriched or even natural Uranium as fuel. This would allow fuel to be sourced on Mars, without need for any fuel launches from Earth. The core would be two-pass, with an outer low temperature region and an inner chimney running at much higher temperature. As pebbles burn up, they would be shuffled from the inner core to the outer core. Spent pebbles would be discharged into a shielded store probably on or near Phobos. The high discharge rate and low burn up of LEU or NU pebbles isn't really a problem. Graphite will suffer erosion in hot hydrogen gas, so no graphite component is really suitable for long life. Sintered aluminium oxide could be used to provide core components.

Last edited by Calliban (2022-04-11 09:28:45)

Calliban · 2022-06-21 04:55:35

We will probably need to wait until Mars is populated before we can develop the technology. Much as Americans resist unjustified gun regulation, Martians will resist counterproductive nuclear regulation, because their lives and livlihood will depend absolutely on the unfettered expansion of the power supply and heat source.

One high ISP, moderate-thrust propulsion option, is a hybrid liquid-plasma nuclear thermal rocket. This would consist of an outer cylindrical liquid flouride uranium-thorium molten salt bed, which rotates, clinging the salt to the walls leaving a void at the core. Through the core, we pass a mixture of hydrogen and highly enriched uranium hexaflouride.

The outer liquid flouride blankets would provide neutrons which would fission the uranium in the central hydrogen stream. The neutron flux in this reactor follows a very steep parabolic curve, with much higher flux (and power) in the central gas column. The neutron spectrum would be relatively hard in the blankets, but softer in the central column, where hydrogen will provide moderation. This means there is much more reactivity in the central column, which is where the bulk of the fission will take place.

The hydrogen stream is directly heated by the fission products reaching temperatures of tens of thousands of kelvin. The salt blankets are kept cool by a combination of bleeding hydrogen through them and conduction through the outer casing. There would also be some evaporation of lower boiling point salts, principally berylium flouride. We could reduce this by separating the central core void from the blankets using a sintered aluminium oxide tube. The tube would allow a vapour pressure to be maintained above the salt beds. Pores running through the aluminium oxide tube would bleed hydrogen, keeping its surface cool.

Power could be generated during interplanetary coast by using decay heat generated in the salt beds to run an S-CO2 generator. Even 1 year after shutdown, decay heat will be 0.1% of blanket power at shutdown. If blankets generated 1GW of heat in operation, then 0.1% is 1MW of heat and 500kW of power generation in an S-CO2 generating loop.

PS. By adding a circumferential magnetic field to this concept, we suppress lateral transportation of plasma particles. This allows a temperature gradient to be sustained from the central core outwards. This potentially allows the central core to reach very high temperatures, sufficient for fusion within the hydrogen stream to generate a lot of high energy secondary neutrons. This allows an even sharper flux profile within the core with most fission events taking place within the plasma. The very hot plasma at the centre of the core will have a much shorter confinement time than colder plasma bleeding in from the edges. This boosts ISP as the higher energy plasma particles are more likely to escape.

Last edited by Calliban (2022-06-21 06:21:42)

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#1 2022-02-21 08:34:38

Large Ship Atomic Propulsion

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Re: Large Ship Atomic Propulsion

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Re: Large Ship Atomic Propulsion

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Re: Large Ship Atomic Propulsion

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