Author Topic: John Bucknell's Air Enhanced Nuclear Thermal Rocket  (Read 14211 times)

Offline Elmar Moelzer

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This looks interesting. I had thought about something similar before:
https://www.nextbigfuture.com/2017/07/air-enhanced-nuclear-thermal-rocket-by-x-spacex-engineer.html

Offline Asteroza

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #1 on: 07/13/2017 02:35 AM »
Gotta show some love for nuclear SERJ

Adding the presentation PDF here for posterity.

Offline Elmar Moelzer

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Offline sanman

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #3 on: 07/14/2017 06:23 AM »
What fraction of a G could this thing give while continuously accelerating/decelerating on a trip towards Mars?

Offline Asteroza

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #4 on: 07/14/2017 08:08 AM »
What fraction of a G could this thing give while continuously accelerating/decelerating on a trip towards Mars?

Considering this is intended to use atmospheric gases as additional reaction mass via pumping/compression/entrainment, it won't help you in deep space, in particular there may be some expectations on secondary combustion in the lower atmosphere. Unless you wanted to pull off a TMI direct launch...

For a reusable mars lander, the problem there is use/sourcing of LH2 propellant/fuel. Secondary problem is this is effectively a fan rocket (fanket?), but mars atmosphere is already so thin that the advantages aren't great for high thrust at launch/landing (the fan isn't augmenting your thrust much). Frankly you would be better off with a mars specific NTR lander, something like Zubrin's liquid CO2 NTR SSTO/hopper (maybe cheat with slush CO2)

Offline sanman

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #5 on: 07/14/2017 06:59 PM »
Gee, so this thing is restricted to being a SSTO shuttle between Earth Surface and Orbit?

Maybe it could also be used for high-speed point-to-point transport around the globe. But that would then expand the nuclear contamination risk to a wider swathe of the globe.

What role would it serve best? Orbital depot tanker?

Offline Elmar Moelzer

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #6 on: 07/15/2017 12:50 AM »
Gee, so this thing is restricted to being a SSTO shuttle between Earth Surface and Orbit?
You are acting like this is a bad thing? Considering that getting from earth to orbit is the toughest part, I am excited about a solution. Once you can cheaply "throw" lots of mass into orbit, everything else is much easier.
« Last Edit: 07/15/2017 12:50 AM by Elmar Moelzer »

Offline sanman

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #7 on: 07/15/2017 02:50 AM »
Gee, so this thing is restricted to being a SSTO shuttle between Earth Surface and Orbit?
You are acting like this is a bad thing? Considering that getting from earth to orbit is the toughest part, I am excited about a solution. Once you can cheaply "throw" lots of mass into orbit, everything else is much easier.

LOL, fair enough - getting to orbit is the hardest part. Maybe it could be used as part of a combined cycle nuclear propulsion?

Perhaps a rocket like this could be pitched to the American military, since according to Bucknell its nuclear fuel would allow it to make hundreds of trips to orbit and beyond before requiring a nuclear fuel change. That kind of long operational life could be very useful and offer considerable autonomy.

But if it's mainly useful in the atmosphere, why not re-work this idea as an aerospace plane, rather than as a VTVL rocket? After all, isn't its flight trajectory more similar to the former than the latter?


Offline KelvinZero

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #8 on: 07/16/2017 01:33 AM »
I don't see this happening on earth any time soon, but it could be great for somewhere like Saturn.

There is a great scene in that "Wanderers" short film showing people on some sort of floating platform on Saturn, needing only thermal protection. Roughly Earth gravity and earth pressure. I don't know what they are doing there. Could be He3 mining, could be just for the hell of it. Lets not get into that. :-)

Offline sanman

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #9 on: 07/16/2017 03:05 AM »
I was imagining a fusion-powered version of this maybe skimming through the upper atmosphere on Jupiter/Saturn and maybe harvesting Helium-3 which would then be used as its nuclear fuel.

Would Titan's atmosphere be thick enough for this kind of "turborocket" to take off from?
Or could it maybe be used for soft-landing heavy payloads on Mars?

« Last Edit: 07/16/2017 03:07 AM by sanman »

Offline Elmar Moelzer

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #10 on: 07/17/2017 01:49 AM »
I don't see this happening on earth any time soon, but it could be great for somewhere like Saturn.
I certainly hope someone will do it. If not the US government or a US company, then maybe Russia or China will be clever enough to give it a go.

Offline sanman

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #11 on: 07/17/2017 07:12 AM »
And yet nobody would want to risk a nuclear accident. Can a nuclear reactor be designed to withstand the stresses of a catastrophic rocket failure, while also remaining safe from any runaway meltdown?

Offline ChrisWilson68

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #12 on: 07/17/2017 08:20 AM »
I don't see this happening on earth any time soon, but it could be great for somewhere like Saturn.
I certainly hope someone will do it. If not the US government or a US company, then maybe Russia or China will be clever enough to give it a go.

Something similar has already been done by the US government.  In 1964.

It was called Project Pluto.  And it worked.  They built a nuclear thermal ramjet engine, put it on a rail car, fired it up, and confirmed it did what it was supposed to do.

The details are different in Bucknell's design, but the fundamental concept is the same -- to use nuclear power and incoming air.  Bucknell's design is more of a hybrid that can operate in regimes the Project Pluto engine could not.

The government abandoned it because they decided that even though it worked, they really didn't have a use for it.

https://en.wikipedia.org/wiki/Project_Pluto

Offline Elmar Moelzer

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #13 on: 07/17/2017 06:00 PM »
And yet nobody would want to risk a nuclear accident. Can a nuclear reactor be designed to withstand the stresses of a catastrophic rocket failure, while also remaining safe from any runaway meltdown?
According to Bucknell, yes it can. I don't see any reason why it could not. This reactor design is different from normal commercial ones in many ways. Bucknell thinks it is going to be quite safe and I have little doubt about it. You would not want the thing to land on your head, but that is true for chemical rockets as well. Rockets launch over water, however. So it is not going to fall on anyone's head.
« Last Edit: 07/17/2017 06:01 PM by Elmar Moelzer »

Offline KelvinZero

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #14 on: 07/17/2017 11:38 PM »
How about Mars? Would people who worry about this on earth feel safe with it's use on Mars? Would it be good for that? Cruising around like a 747? shuttling to orbit?

Although it is just a limited application compared to all the rockets on earth, you have to multiply that by the mass savings in payload, and that cuts straight into into the amount of chemical booster on earth. I think the ratio was something like 20:1? And maybe that was just to orbit so maybe it is greater. Is my logic screwy? Does that mean that one use on mars gives you similar savings to 20 uses on earth? (assuming the mars colony exists, a big assumption naturally)

Building up a flight history would be a good step to opening discussion for use on earth.

Offline Asteroza

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #15 on: 07/17/2017 11:58 PM »
NTTR has the same basic faults as a NERVA derivative hydrogen heater NTR, the new addition is the ejector fan with associated turbine safety. There is some engineering base for that from various hot cycle tip propulsion setups for helicopters, but nothing terribly recent. The external burning aspect of the fan blade trailing edge linear aerospike to increase entrainment/mass flow (if that is actually occurring in this design) might be sticking point. The probably most well known being the deltoid pumpkin seed design, which used the mach shockwave from the body as a virtual nozzle wall, which if applied here would imply a very fancy supersonic fan blade which increases design difficulty at standing start (plus RPM issues unless the overall turbine is fairly small in radius)

The big difference of the NTTR being it can do a standing start from sea level, which most classic hydrogen propellant NERVA derivative NTR's can not do due to lack of T/W ratio. So it breaks the old rule of thumb of no earth SSTO NTR's in an approachable engineering package.

As to NTR acceptability, when NTR's were being seriously pursued, design constraints seemed to imply 2nd stage/upper stage use due to poor T/W ratio, so there was not much serious discussion of ground launch. Project Pluto was a ramjet, using solid rocket boosters to get up to start speed, so again launch was not an issue (though apparently the hot air exhaust was considered a radiological weapon in and of itself, though that may have more to do with chunks of the engine coming out due to oxidization). NERVA NTR's are traditionally pure LH2 propellant based (LANTRN aside), so besides unexpected spalling of the core, the exhaust itself shouldn't be terribly radioactive, just the raw radiation escaping from the reactor that isn't blocked by shadow shields and propellant.

Let's not forget that NERVA NTR's were tested in the open at Jackass Flats exhausting direct to atmosphere, though admittedly that was before we had good awareness of certain radioogical issues.

NTTR seems reasonable, compared to other nuclear SSTO's. LANTR SSTO doesn't use air mass so suffers from classic chemical rocket weight issues. Liberty Ship gas core "nuclear lightbulb" suffers from not having a demonstrated lightbulb gas core reactor first and foremost. Ice bore launch Orion is the least likely to gain any approval.

Offline Asteroza

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #16 on: 07/18/2017 12:02 AM »
How about Mars? Would people who worry about this on earth feel safe with it's use on Mars? Would it be good for that? Cruising around like a 747? shuttling to orbit?

Although it is just a limited application compared to all the rockets on earth, you have to multiply that by the mass savings in payload, and that cuts straight into into the amount of chemical booster on earth. I think the ratio was something like 20:1? And maybe that was just to orbit so maybe it is greater. Is my logic screwy? Does that mean that one use on mars gives you similar savings to 20 uses on earth? (assuming the mars colony exists, a big assumption naturally)

Building up a flight history would be a good step to opening discussion for use on earth.

A fanket (fan rocket) requires reasonably thick atmosphere to be useful. On mars, hydrogen is going to be a very dear commodity for water, so one would like to avoid using imports for ISRU export fuel where possible.

Offline aceshigh

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Offline speedevil

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #18 on: 07/12/2018 11:01 PM »
NextBigFuture has posted again a series of articles on this concept.
https://www.nextbigfuture.com/2018/07/turbo-rocket-economics-are-85-kg-to-leo-or-715-kg-to-luna.html

https://www.nextbigfuture.com/2018/07/us-government-should-dump-sls-and-make-turbo-rocket-instead.html

a 2018 presentation

The architecture in principle looks interesting. But - I have real questions about gigawatt scale reactors at flight weight ever being able to be produced cheaply in todays environment.

The flight averaged ISP of 1200 - assuming that this is considered as averaging so as to produce the same mass ratio as a chemical rocket, compared with an ISP of 380, takes you from needing 50% fuel, to 90% fuel or so.
This is valuable if fuel is expensive - but with cheap fuel in orbit, it's basically meaningless.
(cheap = $100/kg).

IMO this would work lots better as a Mars shuttle, with very large tanks or outer planets.

There are some significant inaccuracies on BFR at least.

For example, assuming that payload to the moon, refuelled in LEO, BFR can't get back to earth, hence assuming all the cost of the BFR as $/kg, because it's assumed as 150000kg/BFR cost.
Whereas in fact, with a couple more flights, and staging fuel in LLO, you can, fairly easily with relatively minimal penalty.
This leads him to conclude BFR has $12000/kg to lunar surface.
This seems to also assume that the refuelling BFRs are not in fact reused, and you're paying the whole cost of $360M or so per.

SpaceX alleged cost of launch would take this to $400/kg.

« Last Edit: 07/12/2018 11:22 PM by speedevil »

Offline aceshigh

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Re: John Bucknell's Air Enhanced Nuclear Thermal Rocket
« Reply #19 on: 07/13/2018 01:05 AM »
I donīt see how payload fraction is meaningless.

Yes, fuel may be inexpensive and you could refuel in orbit.

Still, wouldnīt that still mean that every single launch of a 1000 tons chemical rocket you would put only 40 tons in LEO, while a 1000 tons NTTR would be able to put 250 tons in LEO in every launch?


There ARE costs associated with each launch. Time, launch crew, inspection upon returning...

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