Skip to content
 
If you can read this, either the style sheet didn't load or you have an older browser that doesn't support style sheets. Try clearing your browser cache and refreshing the page.

(Space News)   Pentagon wants nuclear rockets for faster travel beyond Earth orbit. They are offering contracts if you can help. This makes me very angry, very angry indeed   (spacenews.com) divider line
    More: Scary, Spacecraft propulsion, fuel efficiency, electrical power, Defense Innovation Unit, mature commercial technologies, long-duration power sources, new solicitation, propulsion systems  
•       •       •

869 clicks; posted to STEM » on 19 Sep 2021 at 11:38 AM (5 weeks ago)   |   Favorite    |   share:  Share on Twitter share via Email Share on Facebook



51 Comments     (+0 »)
View Voting Results: Smartest and Funniest


Oldest | « | 1 | 2 | » | Newest | Show all

 
2021-09-19 9:01:15 AM  
Not much mention of plans for decommissioning these nuclear devices when usefulness expires.
 
2021-09-19 9:17:41 AM  
Why does this make you angry?
 
2021-09-19 9:27:17 AM  
Heard of the inverse square law, Subby? This is probably the safest and most logical use for nuclear power ever. Because: https://m.xkcd.com/1162/
 
2021-09-19 9:31:30 AM  
This will be a cost plus contract, which means the only thing it will generate is costs.  So everything will be fine, except for our taxes, of course.
 
2021-09-19 9:48:48 AM  
Daft Punk - Harder Better Faster (Official Video)
Youtube gAjR4_CbPpQ
 
2021-09-19 9:50:59 AM  

snocone: Not much mention of plans for decommissioning these nuclear devices when usefulness expires.


If they are too be used in space why decommission? Park them in a solar orbit and walk away, who knows they may be useful later.

We need to go beyond chemical propulsion. Ion is great for small probes but look at starship fuel requirements. It's insane what is needed to go anywhere with a large vessel and until new technology comes along we should be using the best we have to offer. Nuclear. It will go faster, further and cheaper.
 
2021-09-19 9:56:49 AM  

sithon: Why does this make you angry?


i.pinimg.comView Full Size
 
2021-09-19 10:55:23 AM  

SnowPeas: snocone: Not much mention of plans for decommissioning these nuclear devices when usefulness expires.

If they are too be used in space why decommission? Park them in a solar orbit and walk away, who knows they may be useful later.

We need to go beyond chemical propulsion. Ion is great for small probes but look at starship fuel requirements. It's insane what is needed to go anywhere with a large vessel and until new technology comes along we should be using the best we have to offer. Nuclear. It will go faster, further and cheaper.


Plus the heat from the decaying isotopes is useful and can provide warmth for the crew and keep instruments from freezing. NASA already uses radioactive isotopes this way, in RTGs (radioisotope thermoelectric generators) which is what NASA uses as a power source when solar appears to be unfeasable.
 
2021-09-19 11:04:38 AM  

greentea1985: SnowPeas: snocone: Not much mention of plans for decommissioning these nuclear devices when usefulness expires.

If they are too be used in space why decommission? Park them in a solar orbit and walk away, who knows they may be useful later.

We need to go beyond chemical propulsion. Ion is great for small probes but look at starship fuel requirements. It's insane what is needed to go anywhere with a large vessel and until new technology comes along we should be using the best we have to offer. Nuclear. It will go faster, further and cheaper.

Plus the heat from the decaying isotopes is useful and can provide warmth for the crew and keep instruments from freezing. NASA already uses radioactive isotopes this way, in RTGs (radioisotope thermoelectric generators) which is what NASA uses as a power source when solar appears to be unfeasable.


Exactly. And once in orbit these things can be as dirty as needed as long as the crew are shielded. Solar wind will push it all out of the system. Thus allowing for similar, more reliable reactors, when long term containment isn't a factor the designs are limitless. Things like a pebble bed reactor would become ideal instead of insane.
 
2021-09-19 11:19:52 AM  
If one of these nuclear rockets blows up on the pad, there will be an earth-shattering ka-boom.
 
2021-09-19 11:46:21 AM  

snocone: Not much mention of plans for decommissioning these nuclear devices when usefulness expires.


Better to make war with my dear.

Perpetual war for perpetual stock owner profits
 
2021-09-19 11:47:08 AM  

sithon: Why does this make you angry?


Probably bec hes paying for it.

So am i and so are you
 
2021-09-19 11:48:01 AM  

Marcus Aurelius: This will be a cost plus contract, which means the only thing it will generate is costs.  So everything will be fine, except for our taxes, of course.


Spending public money is easy.

And fun!!
 
2021-09-19 11:49:21 AM  

dstanley: If one of these nuclear rockets blows up on the pad, there will be an earth-shattering ka-boom.


An actual reactor on that pad is a bad idea. RTGs are likely to stay intact.
 
2021-09-19 11:57:26 AM  

snocone: Not much mention of plans for decommissioning these nuclear devices when usefulness expires.


Maybe they expect to just let the thing drift away into space? Or use the floating wreck as some kind of space buoy? They could presumably be repurposed in some kind of Flash Gordon, atomic age Rocketpunk fashion.
 
2021-09-19 12:00:11 PM  
The thing that I'm confused about is why the military wants to go beyond Earth orbit? There are no enemies there not named Marvin.  This seems to be more appropriate for NASA.

I think that any reactors in space should be constructed in space and be left in orbits high enough to avoid orbital decay. Use of RTGs make sense as they are easy to use and can be launched safely.
 
2021-09-19 12:01:50 PM  

sithon: Why does this make you angry?


The ruin my view of Venus.
 
2021-09-19 12:10:04 PM  

Bennie Crabtree: snocone: Not much mention of plans for decommissioning these nuclear devices when usefulness expires.

Maybe they expect to just let the thing drift away into space? Or use the floating wreck as some kind of space buoy? They could presumably be repurposed in some kind of Flash Gordon, atomic age Rocketpunk fashion.


IF you are disposing them, an orbit that never comes to Earth is easy enough. Solar orbit completely inside of Earth's should do the trick though I'd run an orbital simulation to be sure. In any event, how to dispose of a spacecraft is stand procedure these days. No plan means no launch approval.
 
2021-09-19 12:13:29 PM  

snocone: Not much mention of plans for decommissioning these nuclear devices when usefulness expires.


Not sure how that's a problem.

You probably won't refuel these ships. It wouldn't be cost effective and by the time it is cost effective to refuel this type of engine, the early spacecraft will be technically obsolete. You'd decommission the whole ship.

Except maybe for ferrying people and materials between Low Earth Orbit and the Moon, these will most likely be unmanned ships that operate outside of Earth orbit, so the likelihood of a decommissioned ship crashing back into Earth accidentally is extraordinarily low.

But, if you're still worried about it, when you decommission the ship it would probably be very easy to point it at the Sun or Jupiter and give it a nudge so it burns up harmlessly.

Even better - if there's still enough power left (and I bet there will be), turn it into a pure research vessel. Fire the engines and send it out of the solar system, using whatever sensors it has to gather as much data as possible and relay it back to us. As Voyager has proven, even "obsolete" tech can be a valuable research tool in the right place.
 
2021-09-19 12:22:17 PM  

Marcus Aurelius: This will be a cost plus contract, which means the only thing it will generate is costs.  So everything will be fine, except for our taxes, of course.


We need to spend many more trillions on military bullshiat like this, otherwise we'll be forced to feed the hungry, house the homeless, help the indigent, and create a single-payer health policy.

Not to mention help rebuild the cities devastated by natural disasters.
 
2021-09-19 12:23:52 PM  
"Bidders have to show 'credible manufacturing, regulatory, and licensing paths toward prototype development within three to five years and a follow-on path to flight based testing.'"

Well, at least this part cuts out the major power companies. Georgia's been building ONE nuke plant for thirty years.
 
2021-09-19 12:32:21 PM  

snocone: Not much mention of plans for decommissioning these nuclear devices when usefulness expires.


Are you going to travel to Alpha Centauri to decommision them?  Good luck then...
 
2021-09-19 12:34:32 PM  

p89tech: But, if you're still worried about it, when you decommission the ship it would probably be very easy to point it at the Sun or Jupiter and give it a nudge so it burns up harmlessly.


It is actually very difficult to send things to the Sun. Just to reach Mercury's orbit requires a big rocket and multiple gravitational slingshots. Jupiter is easier but will still require a nontrivial rocket.
 
2021-09-19 12:44:53 PM  

dstanley: If one of these nuclear rockets blows up on the pad, there will be an earth-shattering ka-boom.


Nuclear power doesn't work that way. Sure it would contaminate the area, but you won't get a nuclear explosion. That only happens when you shove a lot of nuclear material into a tiny space. It doesn't happen accidently.
 
2021-09-19 12:59:39 PM  

Linux_Yes: snocone: Not much mention of plans for decommissioning these nuclear devices when usefulness expires.

Better to make war with my dear.

Perpetual war for perpetual stock owner profits


Most likely they'll have the wrong type of plutonium in them.  Melt them down and make RTGs, but you'd have the same issues making a bomb out of that plutonium that you would making one out of raw uranium.

TheMysteriousStranger: p89tech: But, if you're still worried about it, when you decommission the ship it would probably be very easy to point it at the Sun or Jupiter and give it a nudge so it burns up harmlessly.

It is actually very difficult to send things to the Sun. Just to reach Mercury's orbit requires a big rocket and multiple gravitational slingshots. Jupiter is easier but will still require a nontrivial rocket.


If you can get to Jupiter, you can reverse slingshot around and get to the Sun.  Well, that's assuming you are starting from Earth and with most of your burn starting from Earth.  If you are further away you can try a bi-elliptical transfer, and even if you are nearby Jupiter, you could probably try some sort of reverse flyby to lower your periapse, do some trickery in between and do it again to drop yourself all the way into the sun.

There are a lot of ways to change your orbit, especially if you only want a collision course and not an actual landing.  There are plenty of ways of getting to the Sun but the obvious ones (burning straight at it is a non-starter, and trying to kill your velocity takes more work than leaving the solar system) aren't the ones to use.
 
2021-09-19 1:03:57 PM  
Asking for something with a high delta vee means you need to haul a lot of reaction mass around for the reactor to heat up and spit out. The rocket equation doesn't change because you switched from chemical to nuclear. So, you can make a reactor that heats a reaction mass to a ridiculous amount and expels it, but that's still a finite amount of propellant, with its own weight, and, lots more system weight to "throw" it. Further complicating matters is, they want a two-fer: the same power-plant for the engine has to also provide onboard spacecraft electricity. This adds further weight and complication. You might be able to make one of those two things happen efficiently, but I am skeptical it's practical to get both. I suppose thermocouples all around the reaction/thrust chamber to leech electricity from the latent heat, but thermocouples are not very efficient. More likely a sterling engine tapping the heat, but that's more mechanically complex, moving parts that can break.  TANSTAAFL.
 
2021-09-19 1:06:21 PM  
Build an O'Neill cylinder in lunar orbit using as much lunar material as possible, put an Orion drive on the back.  Now you can have manned missions around the entire solar system with a reasonable time frame.
 
2021-09-19 1:07:11 PM  
Am I the only one curious what kind of missions the DoD has "beyond Earth orbit?"
Exploration beyond Earth orbit makes sense. 
DoD long duration missions in Earth orbit makes sense.
I'm wondering what "new DoD missions [sets] in space" refers to.
 
2021-09-19 1:24:59 PM  

TheMysteriousStranger: p89tech: But, if you're still worried about it, when you decommission the ship it would probably be very easy to point it at the Sun or Jupiter and give it a nudge so it burns up harmlessly.

It is actually very difficult to send things to the Sun. Just to reach Mercury's orbit requires a big rocket and multiple gravitational slingshots. Jupiter is easier but will still require a nontrivial rocket.


Ok, you're right and I admit I understated the difficulty, but...

These are nuclear engines we're talking about, so (at least theoretically) much more powerful than anything we have today. I don't think it would be too difficult to calculate a trajectory the took advantage of that and send the ship on a spiral orbit into the sun.
 
2021-09-19 1:30:19 PM  

Saturn5: Am I the only one curious what kind of missions the DoD has "beyond Earth orbit?"
Exploration beyond Earth orbit makes sense. 
DoD long duration missions in Earth orbit makes sense.
I'm wondering what "new DoD missions [sets] in space" refers to.


I posted a similar comment earlier. Unless they preparing for trouble with space colonists a few decades from now, the military has no real purpose beyond Earth space.
 
2021-09-19 2:01:15 PM  

sorceror: Heard of the inverse square law, Subby? This is probably the safest and most logical use for nuclear power ever. Because: https://m.xkcd.com/1162/


Most stupid use ever precisely because of that high energy.

Newtons law says a rocket works by throwing stuff out the back. (How much mass X its velocity)/ how much mass its pushing. Nuke has great energy but no mass to throw out the back. So to use that energy, the engine MUST heat some mass and use that to throw. This is called reaction mass and most nuke designs use water. The idea that nuke rockets don't use fuel is simply wrong.

Fundamentally the only difference between rocket types is how the reaction mass gets heated/accelerated. Hall thrusters use electric fields, Chemical uses explosive reactions and Steam rockets use heat. The three main nuke designs use electric fields, heat and nuclear explosive reactions to heat reaction mass.

The first problem is the mass being pushed. Anything that can contain a reaction is massive compared to the energy that can be extracted. Ten times the energy is not useful if the engine masses 100 times more.

The second and much more difficult problem is heat. Cooling in space is incredibly slow and takes a lot of radiating mass to achieve. Ordinary rockets solve this by throwing all of the hot stuff overboard. While the nuke engine is running, it can mostly do the same but what happens when it shuts down/ runs out of reaction mass? That still very hot reactor needs to be cooled and there are no convenient cooling towers. If a ball of molten metal is all you want to send to the destination then nukes make sense. If you want something useful, then you can send a tiny little payload and a vast amount of radiators to keep it unmelted.

TLDR: High energy offset by terrible mass efficiency and even worse thermal efficiency make nukes really bad reaction motors.
 
2021-09-19 2:04:31 PM  
Anybody remember project Orion? We had big dreams back then.
 
2021-09-19 2:13:38 PM  
Isn't this how we get reavers?
 
2021-09-19 2:28:41 PM  

oldfool: Anybody remember project Orion? We had big dreams back then.


We have bigger dreams now, like Nuclear Salt Water Engines.  Closest we might get to an Epstein Drive from The Expanse in terms of performance during our lifetimes.

As for what might be possible now, there is always a Dusty Plasma Fission Fragment Engine/Reactor.
 
2021-09-19 2:50:56 PM  
upload.wikimedia.orgView Full Size


2.bp.blogspot.comView Full Size


Dr. Ernst Queller likes this.
 
2021-09-19 3:23:00 PM  

greentea1985: SnowPeas: snocone: Not much mention of plans for decommissioning these nuclear devices when usefulness expires.

If they are too be used in space why decommission? Park them in a solar orbit and walk away, who knows they may be useful later.

We need to go beyond chemical propulsion. Ion is great for small probes but look at starship fuel requirements. It's insane what is needed to go anywhere with a large vessel and until new technology comes along we should be using the best we have to offer. Nuclear. It will go faster, further and cheaper.

Plus the heat from the decaying isotopes is useful and can provide warmth for the crew and keep instruments from freezing. NASA already uses radioactive isotopes this way, in RTGs (radioisotope thermoelectric generators) which is what NASA uses as a power source when solar appears to be unfeasable.


Huh?  Usually, the engineering problem in spaceships is to *avoid drowning in your own waste heat*, not to keep the crew from freezing - manned ships, anyway.

Check out 'Saturn Run', by John Sandford and Ctein, for a fictionalized but detailed and interesting look at the issues of heat management for Nuclear Thermal Propulsion and VASIMR engines.
 
2021-09-19 3:46:42 PM  

ExYank: sorceror: Heard of the inverse square law, Subby? This is probably the safest and most logical use for nuclear power ever. Because: https://m.xkcd.com/1162/

Most stupid use ever precisely because of that high energy.

Newtons law says a rocket works by throwing stuff out the back. (How much mass X its velocity)/ how much mass its pushing. Nuke has great energy but no mass to throw out the back. So to use that energy, the engine MUST heat some mass and use that to throw. This is called reaction mass and most nuke designs use water. The idea that nuke rockets don't use fuel is simply wrong.


Nope.  Nuke rockets use hydrogen (at least the ones that heat the propellant and throw it out.  If they use nukes to make electricity they probably want something heavy like Xenon).  This is the entire key as you get vastly more momentum out of heating up hydrogen and throwing it out the back.

In the 1970s, NASA was getting something like an 800s Isp out of nuke rockets.  Convince the thing to not melt at higher temps, and you can get even higher.  This is hugely higher than anything else we have at that level of thrust.  Granted, that thrust is still low (you aren't lifting off with it) but it is vastly higher than ion/Hall/other electrics (which are even more mass efficient).

If you managed to resupply with water, it is entirely possible that you would crack the water, assuming your nuke can provide power without thrust, something I would be on, and your heating chamber and nozzle could survive superheated pure oxygen.  Run the oxygen through first then the hydrogen.  If you can't, you'll get slightly less efficiency than a hydrolox engine (which is still pretty good), but you will be limited by lower temperatures (with the water being cooler than the rest of the engine instead of the other way around) and lack of extra hydrogen.  Hydrolox engines run fuel-rich simply to gain the efficiency of having hot hydrogen in the output mix.
 
2021-09-19 4:04:07 PM  
Professor Cuthbert Calculus did it.

Fark user imageView Full Size
 
2021-09-19 4:10:40 PM  
Has there been a major breakthrough recently I haven't read about? Last time I looked, nuclear-powered spacecraft used reaction mass (Orion excepted) in the form of water, heated and expelled as steam. Probably useful amounts of thrust for maneuvering in microgravity, but not useful for getting out of a gravity well. Unless there's been some major engineering breakthrough recently, all they're doing is exchanging volatile chemical fuels for water.

Water as reaction mass has only one major advantage over volatile chemicals- water is more readily available from asteroids, comets, and other bodies in space. Note this is only relatively 'more available'. The distances between potential water sources are mind-blowingly large, and get larger the farther you get from the sun. Then there's the necessity of acquiring (or extracting) the water and rendering it into a useful form for reaction mass. All that requires a significant chunk of your spacecraft dedicated to storing and processing water.

Why is the US Department of Defense interested in anything outside cislunar space?
 
2021-09-19 4:22:14 PM  

dstanley: If one of these nuclear rockets blows up on the pad, there will be an earth-shattering ka-boom.


US government is actually fairly experienced with cleaning up after a rocket with nuclear material explodes.
 
2021-09-19 4:26:57 PM  
Nuclear Thermal Propulsion: Game Changing Technology for Deep Space Exploration
NTP yields exceptional efficiency, measured in space-speak as "specific impulse" - the change in momentum per unit mass of propellant. NTP offers enhanced energy density, far greater than that of customary chemical systems.

If chemical rockets are the Wright Flyer of space vehicles, NERVA is descirbed as more of a "DC-3" moment than Concorde moment, but it's a step in the right direction.  I'm guessing ion drives powered by onboard nuclear reactors will be the winning technology for the next century.  Both are already proven designs on small scales.
 
2021-09-19 4:30:15 PM  

Wenchmaster: Has there been a major breakthrough recently I haven't read about? Last time I looked, nuclear-powered spacecraft used reaction mass (Orion excepted) in the form of water, heated and expelled as steam. Probably useful amounts of thrust for maneuvering in microgravity, but not useful for getting out of a gravity well.


What they're basically looking for is a replacement for the NERVA engine, which was designed to make vacuum propulsion way more efficient.  You could run even hydrogen over it and it would still produce significant improvements in delta-V, but having a cheap, safe, and even drinkable fuel available is better. Hell, many missions think of using the water for shielding against cosmic rays and solar radiation.  NASA considers the NERVA program a huge success and even had deliverable upper stages built, but Nixon axed the project because of anti-nuke sentiments at the time.
 
2021-09-19 7:48:33 PM  

TheMysteriousStranger: dstanley: If one of these nuclear rockets blows up on the pad, there will be an earth-shattering ka-boom.

An actual reactor on that pad is a bad idea. RTGs are likely to stay intact.


It's not the RTG in probes that cause the problem, it's the 100 or so pellets of plutonium that they spread around the spacecraft to act as 1W heaters to keep equipment from freezing.
 
2021-09-19 8:53:51 PM  

Saturn5: Am I the only one curious what kind of missions the DoD has "beyond Earth orbit?"
Exploration beyond Earth orbit makes sense. 
DoD long duration missions in Earth orbit makes sense.
I'm wondering what "new DoD missions [sets] in space" refers to.


To investigate those UAP sightings that got declassified, duh.
 
2021-09-20 1:05:54 AM  
Wonder if someone will try and resurrect Project Orion.
 
2021-09-20 1:10:28 AM  
Anyone who has played Kerbal Space Program knows the advantages of nuclear engines - it's high efficiency, not really high thrust.  It's for getting around for a long time on the fuel you have.

/Surprised I'm the first to mention Kerbal.
 
2021-09-20 3:27:27 AM  

snocone: Not much mention of plans for decommissioning these nuclear devices when usefulness expires.


It would be terrible if humanity managed to introduce radiation into the pristine environment of space.
 
2021-09-20 7:05:56 AM  

Trik: Wonder if someone will try and resurrect Project Orion.


It's kind of a sledgehammer approach, but it certainly looks like a viable way to move large masses between distant points quickly.

I think you'd have to have all the nuclear powers cooperating on it, though, otherwise you'd never convince the non-participants that you weren't using it as an excuse to get a nuclear weapons platform into orbit.  Which, given history, you almost certainly would be.
 
2021-09-20 2:52:56 PM  
DoD looking for commercially available nuclear propulsion for small spacecraft

Is anything nuclear commercially available?  As in, I could buy a half dozen or so?

As I have pointed out before, you could drive your Tesla 50 miles a day on RTGs if you could buy the really good ones (in terms of power/weight) they used for the Voyager probes.
 
2021-09-20 2:55:30 PM  

Unsung_Hero: Trik: Wonder if someone will try and resurrect Project Orion.

It's kind of a sledgehammer approach, but it certainly looks like a viable way to move large masses between distant points quickly.

I think you'd have to have all the nuclear powers cooperating on it, though, otherwise you'd never convince the non-participants that you weren't using it as an excuse to get a nuclear weapons platform into orbit.  Which, given history, you almost certainly would be.


You could never get away with using an Orion-type system for launch.  So, once in orbit, would Orion really be more efficient than a reactor powering an ion drive?
 
Displayed 50 of 51 comments


Oldest | « | 1 | 2 | » | Newest | Show all


View Voting Results: Smartest and Funniest

This thread is closed to new comments.

Continue Farking




On Twitter


  1. Links are submitted by members of the Fark community.

  2. When community members submit a link, they also write a custom headline for the story.

  3. Other Farkers comment on the links. This is the number of comments. Click here to read them.

  4. Click here to submit a link.