Author Topic: Antarctic NTR  (Read 1811 times)

Offline bradjensen3

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Antarctic NTR
« on: 08/17/2017 05:32 PM »
The Nuclear Thermal Rocket is an exciting technology that promises specific impulses of 2 to 4 times what is achievable with chemical rockets.

The NTR functons by heating a reaction mass, which might be H2 or h2O, to a very high pressure which provides thrust.

The difference between NTR and conventional rockets, is that conventional rockets provide the energy by exothermic reactions within the reaction mass itself - basically by burning or oxidizing a fuel.

In an NTR, the nuclear reactor provides the heat energy to accelerate the reaction mass.

The reluctance towards using NTRs to launch from earth is that they can be radiologically 'dirty'.

In order to advance space exploration from its current status as a hobby for the human race, we need vastly cheaper launch systems.

The NTR could help get us there if we could figure out how to launch it.

How about launching NTRs from within the Antarctic? 

We could find the areas that are the most ecologically isolated on the continent, and launch NTRs from there.

The rocket pad would be surrounded by heaps of fluffy white reaction mass. Of course, you would use ice and not snow.

The rocket is already designed for the cold of space, which makes Antarctic temperature like a tropical day.

There are no animals or plants in the interior of the continent.

Of course you would lose the small launching advantage of the earth's rotational velocity. The increase in isp far outweighs this.

I would think the rockets would be simpler mechanically, and you could build a bunch of them to support a launch per day or more.

Obviously this is a big project that would need lots of engineering. You would probably want staging areas in Argentina or South Africa or New Zealand.

Offline Ictogan

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Re: Antarctic NTR
« Reply #1 on: 08/17/2017 06:05 PM »
Ok, ignoring the facts that it would be insanely expensive to build all the needed infrastructure there or that cold can indeed be very dangerous to rockets(read up on Challenger) or that you could only launch to Polar orbits, am I understanding correctly that you want to use NTRs on the launch vehicle itself?
If so, it's a terrible idea because while NTRs are able to achieve a great Isp, their TWRs are very bad. They may sometimes be useful for upper stages, but you would never want an NTR as a lower stage rocket engine.
« Last Edit: 08/17/2017 06:06 PM by Ictogan »

Offline bradjensen3

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Re: Antarctic NTR
« Reply #2 on: 08/17/2017 07:04 PM »
Ok, ignoring the facts that it would be insanely expensive to build all the needed infrastructure there or that cold can indeed be very dangerous to rockets(read up on Challenger) or that you could only launch to Polar orbits, am I understanding correctly that you want to use NTRs on the launch vehicle itself?
If so, it's a terrible idea because while NTRs are able to achieve a great Isp, their TWRs are very bad. They may sometimes be useful for upper stages, but you would never want an NTR as a lower stage rocket engine.

Thank you for the quick reply.

I think I suggested that much of the  infrastructure would not need to be at the site.  I think it is going to take less infrastructure at the pad for water based rockets than chemical reaction rockets with temperamental fuels.

I've spent over a week at temperatures of up to 20 below zero. It isn't as bad as you think. Polyethylene long underwear seems to be the key. Harbin China is a place where it gets like this every year, and they are doing fine.

I am not thinking we should use giant rubber washers on the engine.

Yes I mean as the launch vehicle.

The thrust to weight TWR figure I see for an NTR is under 2.  An Airbus is 1/4 of that. So launch the NTR horizontally with wings on a ten or 20 kilometer runway.  Think of it as a giant JATO unit for the upper stages.

Or design future NTRs with better TWRs. Or both.

Or a special NTR for the lower stage that might have better TWR but less attractive other characteristics.

So the lower TWR makes it take longer and use more fuel to get out of the draggy atmosphere? Or makes the vehicle more unstable and less controllable?

I'll have to read up on the polar orbit problem. Obviously it would take more fuel to take off from near the south pole and end up in an equatorial orbit.

I agree it would take quite an investment to get this going.

Offline Jim

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Re: Antarctic NTR
« Reply #3 on: 08/17/2017 07:09 PM »
1.  I think I suggested that much of the  infrastructure would not need to be at the site.  I think it is going to take less infrastructure at the pad for water based rockets than chemical reaction rockets with temperamental fuels.

2.  The thrust to weight TWR figure I see for an NTR is under 2.  An Airbus is 1/4 of that. So launch the NTR horizontally with wings on a ten or 20 kilometer runway.  Think of it as a giant JATO unit for the upper stages.


3.  Or design future NTRs with better TWRs. Or both.

Or a special NTR for the lower stage that might have better TWR but less attractive other characteristics.

4.  So the lower TWR makes it take longer and use more fuel to get out of the draggy atmosphere? Or makes the vehicle more unstable and less controllable?

1.  That would be wrong.  Propellants equipment is not the bulk of the launch site equipment.  Anyways, the vehicle is still going to need other propellant for maneuvering.

2.  Not feasible.  Too large of an aircraft.

3.  No.  The future isn't going to change NTRs.  It is basic physics that limits them just like chemical rockets.

4.  No, it makes it so it can't lift itself
« Last Edit: 08/17/2017 07:11 PM by Jim »

Offline Asteroza

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Re: Antarctic NTR
« Reply #4 on: 08/18/2017 01:07 AM »
You can look at John Bucknell's recent conceptual design for a NTTR (basically a fanket NTR that is somewhat SERJ-like) for an actual NTR design operating in atmosphere. That uses the basic property of aerodynamic lift being several times more efficient than raw vertical rocket nozzle propulsion in the lower atmosphere via a tip driven fan, as well as ejector nozzle properties to entrain atmospheric air for more massflow to get higher thrust than the raw hot hydrogen output from an NTR implies.

https://forum.nasaspaceflight.com/index.php?topic=43344.msg1701830#msg1701830

Contaminating antarctica doesn't strike me as viable unless you had enough positive control to limit the contamination to only antarctica, even assuming you were already willing to sacrifice antarctica.

Online hop

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Re: Antarctic NTR
« Reply #5 on: 08/18/2017 05:37 AM »
even assuming you were already willing to sacrifice antarctica.
Which would require agreement or coercion of all the countries involved in current Antarctic treaty structure (http://www.ats.aq/index_e.htm)

Building re-usable chemical rockets is probably easier ;)

Offline john smith 19

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Re: Antarctic NTR
« Reply #6 on: 08/18/2017 07:01 AM »
How about launching NTRs from within the Antarctic? 
How about launching it from Alaska?

It's US territory and the exhaust plume can stay can blanket the US. It's closer to the equator, so it's likely to have a greater range of orbital inclinations to access easily. BTW The US has not claimed any part of Antarctica for itsefl.

We get it. You've just discovered the NTR concept and thinks it's a brilliant idea.   :)

NTR is attractive because it's about the only other system, apart from Orion, that's high thrust, and therefor offers the possibility of shorter transit times to other planets without needing any breakthroughs in science to make it viable.

However it comes with a shedload of issues and the need for a shedload of cash to deal with them. BTW outside of the works of AC Clarke or RA Heinlein no one AFAIK has tested an NTR with anything but LH2.

You really need to do more reading before posting. You are under prepared for any discussion.  :(
« Last Edit: 08/18/2017 08:40 AM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.
So you're going to Mars to seek a better life. What does that mean to you? Always spot a fanbois by how they react to their idols failures.

Online hkultala

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Re: Antarctic NTR
« Reply #7 on: 08/18/2017 08:55 AM »

3.  Or design future NTRs with better TWRs. Or both.

Or a special NTR for the lower stage that might have better TWR but less attractive other characteristics.

3.  No.  The future isn't going to change NTRs.  It is basic physics that limits them just like chemical rockets.

Could you elaborate on these physics?

Timberwind NTR's  were supposed to have T/W of 30.

It had numerious engineering problems, and the project did not get very far, but AFAIK those were engineering problems, not physics problems.
« Last Edit: 08/18/2017 08:56 AM by hkultala »

Offline john smith 19

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Re: Antarctic NTR
« Reply #8 on: 08/18/2017 07:02 PM »

3.  Or design future NTRs with better TWRs. Or both.

Or a special NTR for the lower stage that might have better TWR but less attractive other characteristics.

3.  No.  The future isn't going to change NTRs.  It is basic physics that limits them just like chemical rockets.

Could you elaborate on these physics?

Timberwind NTR's  were supposed to have T/W of 30.

It had numerious engineering problems, and the project did not get very far, but AFAIK those were engineering problems, not physics problems.
You have it backwards. :(

The hig T/W ratio was predicated on being able to mfg specific flow paths and they would give specific gas flows.

They could not make the flow paths with adequate consistency and the flow they got through them was not up to what they expected.  The kludges to try to fix this (making it a pebble bed design, then a spinning PB design) just kept adding complexity and reducing T/W, which remained poor relative to chemical engines (even the LH2 SSME has close to 2x that of Timberwind, and LH2 are notoriously bad for T/W to begin with.
« Last Edit: 08/18/2017 09:01 PM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.
So you're going to Mars to seek a better life. What does that mean to you? Always spot a fanbois by how they react to their idols failures.

Offline KelvinZero

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Re: Antarctic NTR
« Reply #9 on: 08/19/2017 12:03 AM »
Anyway, leave Antarctica alone. It is a perfectly good continent and we will all be living there shortly. It is the equator that will be uninhabitable.  :)

Offline bradjensen3

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Re: Antarctic NTR
« Reply #10 on: 08/19/2017 05:56 AM »
You can look at John Bucknell's recent conceptual design for a NTTR (basically a fanket NTR that is somewhat SERJ-like) for an actual NTR design operating in atmosphere. That uses the basic property of aerodynamic lift being several times more efficient than raw vertical rocket nozzle propulsion in the lower atmosphere via a tip driven fan, as well as ejector nozzle properties to entrain atmospheric air for more massflow to get higher thrust than the raw hot hydrogen output from an NTR implies.

https://forum.nasaspaceflight.com/index.php?topic=43344.msg1701830#msg1701830

Contaminating antarctica doesn't strike me as viable unless you had enough positive control to limit the contamination to only antarctica, even assuming you were already willing to sacrifice antarctica.

Yes I was wondering about adding a turbofan like a high bypass jet engine for the lower stage.  Sounds interesting.

You could probablly cleanup Antarctica much easier than any other place.

Offline tyrred

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Re: Antarctic NTR
« Reply #11 on: 08/19/2017 08:38 AM »
NTR in atmosphere is a non-starter, however interesting it sounds.  The engineering complexity is just not worth the risk, otherwise it would have become the modus operandi. Remember that modern rocketry is about the same age as nuclear engineering.  Nuclear turned out to have only two practical uses, weapons and power plants.  The first is a Pandora's box we can't seem to get closed.  The second boils water to turn a turbine, how quaint.
We as a species should leave to the graveyard of the past any notion that we can contaminate our environment for the sake of progress and leave future generations to clean up the mess.  To plagiarize a phrase once popular in my old home state,  "Don't mess with Antarctica."

Offline Nilof

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Re: Antarctic NTR
« Reply #12 on: 08/19/2017 12:43 PM »
Most of those high specific impulse NTR designs reach their targets with a low chamber pressure and a huge expansion nozzle. Don't expect anything other than negative thrust if you try to fire it in the atmosphere. And that's ignoring the issue of the low vaccum thrust to weight ratio of NTR engines, or the issue of LH2 tankage mass.

An NTR upper stage might be an okay design IF it separates fairly late and gets a lobbed trajectory. But it would make the Centaur look like a high thrust stage and still eat significant gravity losses. Nuclear thermal only really makes sense for Mars missions, not for anything closer or further away. For anything closer, chemical tends to just beat it easily in performance. For anything further away, electric propulsion blows it out of the water. SEP is also nearing the point where it'd beat NTR for Mars missions too in terms of travel time.
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Jim

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Re: Antarctic NTR
« Reply #13 on: 08/19/2017 01:51 PM »

You could probablly cleanup Antarctica much easier than any other place.

More unsupported claims.  It would be harder. 

Tags: NTR