Nuclear powered SABRE engines

[Clockwork_werewolf]

On 18/03/2016 at 8:55 PM, fredinno said:

Well, using 2 different fuels increases complexity, but ok, I see where you are coming from. How about using a air-breathing NTR that switches to O2 once it needs it (H2 has higher isp, but lower TWR.)

The TWR is realy the killer, but air-breathing might mitigate it enough to make nuclear SSTOs more practical

This is exactly what I said over a week ago.

"First is build it a bit like a plane so that it can take of and get into the upper atmo without needing a TWR of more than 1.

Second have the first stage heats air not fuel. https://en.wikipedia.org/wiki/Nuclear-powered_aircraft The idea was tested a bit for bombers and ICBM's with the idea that without fuel they could stay up for weeks or years."

I found the air thrusting Pluto design. NOTE it doesn't use ANY FUEL just the air. Make the wings larger so that they can produce lift and you don't need to worry about the low (but still usable) TWR. You now only need to use hydrogen for the last stage out of atmo.

[fredinno]

On 3/18/2016 at 2:46 PM, GDJ said:

 

Depending on the internal pressure of the tank. Lower pressures take longer (months), but if it's a high pressure tank (2000 + PSI) and the titanium isn't very thick, you're talking hours. It's a exponential increase based on pressure, amount of Hydrogen in the tank, and how thick the tank is.

 Basically, you pump it in, use it, throw it out. Even getting the hydrogen out of the Titanium alloy is a real PITA.

 

Then why did things like DC-X and X-33 use hydrogen if it was so bad for reuse?

[GDJ]

5 hours ago, fredinno said:

Then why did things like DC-X and X-33 use hydrogen if it was so bad for reuse?

Compact and powerful as a fuel. Function over form. It did the job needed, and Titanium was the magic metal needed for these kind of research aircraft.
Since they were part of government run programs, changing out tanks was a minor inconvenience in their eyes, and lets be honest: At that time money wasn't a real issue at all, especially with the political atmosphere.

As far as metallurgy is concerned, I have no idea if they did anything different, or just went to thick walls on the pressure vessels (which would make sense to do this on relatively small aircraft like these), so it's possible they just built very beefy tanks with a very strict schedule for replacement, which makes sense as well.

If there was a different alloy used in the tanks, I doubt if they would tell us. I think certain aspects of the program are still classified, AFAIK.
 

Edited March 25, 2016 by GDJ

[Nothalogh]

On 3/17/2016 at 5:40 PM, fredinno said:

Oh yeah, BTW, pad and VAB processes would need to be changed enormously to make 100% sure everyone stays away from the buiness end of the engine- which also means it'd have to run without extensive maintenance.

Not entirely true, it would just require robotics 

On 3/24/2016 at 3:39 AM, Clockwork_werewolf said:

This is exactly what I said over a week ago.

"First is build it a bit like a plane so that it can take of and get into the upper atmo without needing a TWR of more than 1.

Second have the first stage heats air not fuel. https://en.wikipedia.org/wiki/Nuclear-powered_aircraft The idea was tested a bit for bombers and ICBM's with the idea that without fuel they could stay up for weeks or years."

I found the air thrusting Pluto design. NOTE it doesn't use ANY FUEL just the air. Make the wings larger so that they can produce lift and you don't need to worry about the low (but still usable) TWR. You now only need to use hydrogen for the last stage out of atmo.

Pluto makes me giggle every time I look at it, just for the fact that it would have worked

[fredinno]

26 minutes ago, Nothalogh said:

Not entirely true, it would just require robotics 

Yes, and the VAB/Pad/Processing facilities would have to be redesigned to support robotics, and offer enough shielding that noone dies.

And even then, environmentalist and regulations in general make a non-nuclear solution far more viable. I would say so far that if your spacecraft uses nuclear, and does not need it, using nuclear will almost certainly be higher than the cost of a few more launches, so don't use it unless absolutely essential.

[Nothalogh]

1 hour ago, fredinno said:

And even then, environmentalists and regulations 

Nothing ignoring them won't solve. 

 

My point being, if you want real, large-scale, human access to space, there's going to be a long list of people and groups that you're going to have to tell to on no uncertain terms, to attempt procreation with themselves. 

Edited March 25, 2016 by Nothalogh

[fredinno]

22 minutes ago, Nothalogh said:

Nothing ignoring them won't solve. 

 

My point being, if you want real, large-scale, human access to space, there's going to be a long list of people and groups that you're going to have to tell to on no uncertain terms, to attempt procreation with themselves. 

Yeah, and making people unhappy means less money from less investors, or people will start suing to try to stop the mission from launching. It happened on Cassini, despite the relatively benign RTG. You're never going to be able to get a full scale reactor up without a major political uphill battle, when you could have just saved the trouble and bought another SHLV...

[Nothalogh]

7 hours ago, fredinno said:

Yeah, and making people unhappy means less money from less investors, or people will start suing to try to stop the mission from launching. It happened on Cassini, despite the relatively benign RTG. You're never going to be able to get a full scale reactor up without a major political uphill battle, when you could have just saved the trouble and bought another SHLV...

If it's handled correctly, there's no grounds for suit, if they block the road or attempt sabotage,  do what the USAF would do if they tried that crap at a missile silo. 

 

Rule number one is that you cannot play nice with these kinds of people, give them an inch and they'll take a mile.

This is why we're where we're at today. 

Either it's your goal or it's not, but there is no half arsed solution, we may as well just launch trinkets and comsats until we rot.

 

If you'd let a protest hold it all hostage, you may as well walk away from it, just burn it all and forget you ever tried. 

Edited March 26, 2016 by Nothalogh

[fredinno]

56 minutes ago, Nothalogh said:

If it's handled correctly, there's no grounds for suit, if they block the road or attempt sabotage,  do what the USAF would do if they tried that crap at a missile silo. 

 

Rule number one is that you cannot play nice with these kinds of people, give them an inch and they'll take a mile.

This is why we're where we're at today. 

Either it's your goal or it's not, but there is no half arsed solution, we may as well just launch trinkets and comsats until we rot.

 

If you'd let a protest hold it all hostage, you may as well walk away from it, just burn it all and forget you ever tried. 

The thing is, you don't need nuclear reactors to send a manned mission to Mars and closer to the Sun. Solar panels are also improving in weight and efficiency every day, so the need for nuclear reactors is not really big for inner solar system missions. And that's pretty much as far as we are likely to go in this century (with the exception of the asteroid belt, which may or may not work with solar panels depending on power requirements.

The point is, it's better to hold off nuclear fission for as long as we can while still making economical missions while we wait for nuclear fusion.

Besides, if people don't like something, it's very difficult (sometimes impossible) to convince them otherwise.

Edited March 26, 2016 by fredinno

[Clockwork_werewolf]

While you may be able to physically build a very good nuclear SSTO, I have to agree about the difficulty of getting it authorised.

In reality I think you need to use a sabre engine or reusable rocket like space X if you want the ship built in the next 20 years. A space X rocket can be used with only 5 years development as they are already using it. Sabre or skylon COULD be up and running in ten.

Once you are up there you could have a nuclear tug IF it used lunar Helium 3 and or ice water fuel. As no nuclear fuel would ever need to enter the atmosphere this could get around the anti nuclear lobby. One shuttle with a small payload fraction using Sabre engines and just carrying crew or a small amount of cargo and one large nuclear craft in space. I could see this as possible with a lot of funding in twenty years. Especially if asteroid mining provides the economic funding or investment (leading to future profit) to develop the Tech.

[RocketSquid]

So, just as a clarification, would this work like project pluto in-atmo, or would it use atmospheric air to afterburn, like a LANTR?

[Clockwork_werewolf]

2 hours ago, RocketSquid said:

So, just as a clarification, would this work like project pluto in-atmo, or would it use atmospheric air to afterburn, like a LANTR?

Project Pluto In-atmo, then Nerva out of atmo. The complex part would be changing from heating air to make thrust, to heating liquid hydrogen (or another fuel) using the same core. The Partial Nuclear Test Ban Treaty of 1963 bans nuclear bomb propulsion like Orion but not nuclear thrust but it could be considered close in design.

[fredinno]

9 hours ago, Clockwork_werewolf said:

While you may be able to physically build a very good nuclear SSTO, I have to agree about the difficulty of getting it authorised.

In reality I think you need to use a sabre engine or reusable rocket like space X if you want the ship built in the next 20 years. A space X rocket can be used with only 5 years development as they are already using it. Sabre or skylon COULD be up and running in ten.

Once you are up there you could have a nuclear tug IF it used lunar Helium 3 and or ice water fuel. As no nuclear fuel would ever need to enter the atmosphere this could get around the anti nuclear lobby. One shuttle with a small payload fraction using Sabre engines and just carrying crew or a small amount of cargo and one large nuclear craft in space. I could see this as possible with a lot of funding in twenty years. Especially if asteroid mining provides the economic funding or investment (leading to future profit) to develop the Tech.

...You do realize you can mine H2 from the moon, making He3 (which is even more croygenic than H2) kind of pointless? Either way, you would need to start by sending H2 (possibly in the form of water for better long-term storage) to your space tug.

Also, NERVA Space tugs are DANGEROUS. Come in from the side, or god forbid, the back, and your payload is toast. https://falsesteps.wordpress.com/2013/09/27/the-reusable-nuclear-shuttle-to-the-moon-again-and-again/

Also, there will still be fear that the tank/engine will explode and spread radiation all across the Earth, like the fears in the Cassini Earth Flybys.

You're 100% better off using VASMIR, possibly uprated to higher thrust/lower ISP, even if it means you can't use Lunar resources. (Though you can  modify the VASMIR system to use H2 (and probably also O2) http://spaceflight.nasa.gov/shuttle/support/researching/aspl/reference/develop.pdf)

[magnemoe]

On 24.3.2016 at 10:05 PM, fredinno said:

Yeah, and making people unhappy means less money from less investors, or people will start suing to try to stop the mission from launching. It happened on Cassini, despite the relatively benign RTG. You're never going to be able to get a full scale reactor up without a major political uphill battle, when you could have just saved the trouble and bought another SHLV...

Note that China pretty much ignore this issues, number of people in an protest rally in China will be low. 
They still don't go for something like this even if it would have both strategical and economical benefits. 

[Clockwork_werewolf]

12 hours ago, fredinno said:

...You do realize you can mine H2 from the moon, making He3 (which is even more croygenic than H2) kind of pointless? Either way, you would need to start by sending H2 (possibly in the form of water for better long-term storage) to your space tug.

 

21 hours ago, Clockwork_werewolf said:

IF it used lunar Helium 3 and or ice water fuel.

The Helium 3 was intended to be the nuclear fuel not the reaction fuel but after some investigation I found that my initial search criteria of fission had appeared but in articles about fusion. As no fusion reactors exist I retract my suggestion of H3 and submit the possibility of mining for uranium http://www.space.com/6904-uranium-moon.html. I can't find any clear evidence for the presence of the elements needed to enrich uranium on the moon but this would be a very small payload weight needed compared the to thrust produced.

The ice water would be for the reaction fuel with or without a nuclear reactor. Of course the tug would need some fuel to start with to at least maintain a lunar orbit if not land on the moon. this would depend in the ability's of the lunar mining vehicle.

12 hours ago, fredinno said:

Also, there will still be fear that the tank/engine will explode and spread radiation all across the Earth, like the fears in the Cassini Earth Flybys.

The likelihood of it exploding in earth orbit are very low but it would be a problem. While initially only a tiny proportion or parts would enter the atmosphere unless it exploded in a very high orbit the parts would eventually slow down and enter the atmo.
 

12 hours ago, fredinno said:

Also, NERVA Space tugs are DANGEROUS. Come in from the side, or god forbid, the back, and your payload is toast. https://falsesteps.wordpress.com/2013/09/27/the-reusable-nuclear-shuttle-to-the-moon-again-and-again/

The shielding was low due to two reasons. Heavy shielding reduces thrust to weight, which is still a problem but the tug was being launched on a Saturn rocket so the weight added the normal cost to weight problem for launching it up. If the shuttle has no nuclear fuel when launched, it doesn't need any shielding at that point. The shielding can be mined and added at the same time as the nuclear fuel. You can also use a lot more shielding if it never lands but stays in orbit and still have a better fuel to thrust ratio.


It should be noted I am mostly playing devils advocate. The dangers of nuclear contamination (while not as bad as most people think) would still stop any modern nuclear rocket program. The masses involved also mean that other tech like VASMIR engines and mass drivers on the moon would probably be better in reality even if not from a pure physics point of view.

[fredinno]

13 hours ago, Clockwork_werewolf said:

The Helium 3 was intended to be the nuclear fuel not the reaction fuel but after some investigation I found that my initial search criteria of fission had appeared but in articles about fusion. As no fusion reactors exist I retract my suggestion of H3 and submit the possibility of mining for uranium http://www.space.com/6904-uranium-moon.html. I can't find any clear evidence for the presence of the elements needed to enrich uranium on the moon but this would be a very small payload weight needed compared the to thrust produced.

You DO realize Uranium mining is no easy task, right? We'd see fusion before then, and thus null the point of building a fission reactor...

 

13 hours ago, Clockwork_werewolf said:

The shielding was low due to two reasons. Heavy shielding reduces thrust to weight, which is still a problem but the tug was being launched on a Saturn rocket so the weight added the normal cost to weight problem for launching it up. If the shuttle has no nuclear fuel when launched, it doesn't need any shielding at that point. The shielding can be mined and added at the same time as the nuclear fuel. You can also use a lot more shielding if it never lands but stays in orbit and still have a better fuel to thrust ratio.

Yeah, and good luck building reactors and engines in space. You're still going to have a bad TWR (especially if you add more shielding, which can actually mitigate the higher efficiency of NTR). It would be better to use boiled water or Lunar Lox to increase TWR.

[Clockwork_werewolf]

9 hours ago, fredinno said:

You DO realize Uranium mining is no easy task, right? We'd see fusion before then, and thus null the point of building a fission reactor...

Yeah, and good luck building reactors and engines in space. You're still going to have a bad TWR (especially if you add more shielding, which can actually mitigate the higher efficiency of NTR). It would be better to use boiled water or Lunar Lox to increase TWR.

 

23 hours ago, Clockwork_werewolf said:

It should be noted I am mostly playing devils advocate. The dangers of nuclear contamination (while not as bad as most people think) would still stop any modern nuclear rocket program. The masses involved also mean that other tech like VASMIR engines and mass drivers on the moon would probably be better in reality even if not from a pure physics point of view.

 

[sevenperforce]

I'm pretty sure an airbreathing LANTR pushing liquid hydrogen at launch would have enough T/W to take off vertically. Then you could slowly dial down the propellant flow as airflow took over, use that to get up as high as it will allow, then switch back to pure hydrogen. 

[Nothalogh]

1 hour ago, sevenperforce said:

I'm pretty sure an airbreathing LANTR pushing liquid hydrogen at launch would have enough T/W to take off vertically. Then you could slowly dial down the propellant flow as airflow took over, use that to get up as high as it will allow, then switch back to pure hydrogen. 

That would give me an instant 1950s coldwar insanity boner

[fredinno]

6 hours ago, Nothalogh said:

That would give me an instant 1950s coldwar insanity boner

And that's exactly why it would never happen.

[Nothalogh]

18 hours ago, fredinno said:

And that's exactly why it would never happen.

As a missionary of the church of Teller and Ulam, I will not be deterred