Project Bifrost: (Fission) Rockets of the Future?

astroengine writes "Researchers from Icarus Interstellar Inc. and General Propulsion Science have announced their intention to pursue the development of Nuclear Thermal Rockets and other fission-based space technologies. The aim? To revolutionize space travel, ultimately paving the way to the goal of sending a probe to another star."

Comments

Good luck

[jonwil]

Anytime anyone even thinks about mixing "nuclear" and outer-space (even radioisotope generators as used on many space probes) all the anti-nuclear groups kick up a huge fuss.

Unless this mob has something different they can use to convince the anti-nuclear mob that its safe, they will have a hard time actually launching anything without massive protest.

Re:Good luck

[donscarletti]

My opinion is if this thing blows up, it will kill the crew and pollute an area of space millions of kilometres from anything I personally give a shit about. This is pretty much the same end result as if a chemical rocket blows up. Sounds like a fantastic application for nuclear, makes good use of what nuclear is good at (fuel energy density) while minimising what it is bad at.

I figure, presumably after the engine actually works and has been tested etc. we put this thing in orbit without any fuel, make sure it's an orbit that will stay stable for at least 20 years if something screws up. We then send up the fuel in small amounts, so if anything goes wrong, the amount of poisonous uranium or plutonium or whatever released is not going to kill whatever forest or reef or city etc it lands on.

Then if something goes like really bad, we fire up the partially fueled engine and fly it into the sun. If not, we complete the mission.

Re:Good luck

[symbolset]

Indirect Toynbee tile reference. +1 for the reference, +1 for subtlety. I don't get mod points any more for some obsure reason, so this is what I can do.

Re:Good luck

[Bill Currie]

Then if something goes like really bad, we fire up the partially fueled engine and fly it into the sun. If not, we complete the mission.

Flying something into the sun is rediculously difficult (compared to Earth's orbit, the sun is pretty small). Much easier to just send the thing on its way and forget about it. If it's got enough delta-V to get it out of the solar system, we need not worry about it ever again.

Re:Good luck

[dkf]

Anytime anyone even thinks about mixing "nuclear" and outer-space (even radioisotope generators as used on many space probes) all the anti-nuclear groups kick up a huge fuss.

Sucks to be them, then. Any time you push beyond the inner solar system, you need some sort of nuclear power to get electricity, as you can't burn things or use hydroelectric or wind-power. You can use solar panels in the inner solar system, but the further out you go the less practical that becomes. IIRC, solar is a no-go much beyond about the orbit of Mars, even for relatively low-power applications. High thrust engines are not low-power!

What's more, as long as you're outside the Earth's magnetosphere, any nuclear explosion is exceptionally unlikely to contaminate Earth (or the Moon) as the solar wind will push all of the small particles out to interstellar space. Yes, you could be hit by a large piece even so, but that would be amazing bad luck; space is damn big.

Re:Good luck

[sourcerror]

"My opinion is if this thing blows up, it will kill the crew and pollute an area of space millions of kilometres from anything I personally give a shit about. This is pretty much the same end result as if a chemical rocket blows up. "

You mean like the Challenger and Columbia? Except with nuclear fallout. I know the reactors in spaceships are usually much smaller than a nuclear plant, but this is definitely bigger risk than a chemical rocket.

Re:Good luck

[donscarletti]

From Wikipedia:

Earth orbital speed: 29.78 km/s

Sun's escape velocity at Earth (42.1 km/s)

Thus, the delta V to completely de-orbit from Earth's orbit is far lower than to escape the solar system. After de-orbiting, hitting the sun is quite easy, it just will tend to fall in.

Re:Good luck

[Bill Currie]

Yes, the escape velocity is 42.1km/s. But anything in Earth's orbit already has a velocity of 29.78km/s (+/- a bit if in orbit around the Earth). This means that the delta-V required to escape the solar system from Earth's orbit is 12.32km/s. Less than half that required to de-orbit and fall into the sun.

This is actually a mistake that I make quite often (forgetting to factor in the current orbital velocity).

Re:Good luck

[Anonymous Coward]

From Wikipedia:

Earth orbital speed: 29.78 km/s

Sun's escape velocity at Earth (42.1 km/s)

Thus, the delta V to completely de-orbit from Earth's orbit is far lower than to escape the solar system. After de-orbiting, hitting the sun is quite easy, it just will tend to fall in.

Hogwash. You do not know your stuff. Think before quoting Wikipedia.

As you have Earth's velocity of 29+ km/s already for free when departing from Earth in its orbit around the Sun, you are virtually "halfway to anywhere" (Robert A. Heinlein) when making it into Low Earth Orbit (LEO). Thus, the delta v needed for going from Earth surface to escape velocity out of the solar system is *much less* (~12.9 km/s) than for going to the Sun. In order to do the latter, you first need to get into LEO and then you need to decelerate from Earth's orbital velocity of 29.8 km/s to 0. So, your total delta v is around 40 km/s (!!!). More than three times than for going to infinity (and beyond ...). Good luck.

Hitting the Sun is anything but being "quite easy" (your words). That is the reason why it has never been done before.

Re:Good luck

[expatriot]

You are right. It's very hard to hit the sun. You could do it with less energy than the 40km/s delta implies by doing multiple slingshots, starting with the moon.

Re:Good luck

[donscarletti]

So, I mention de-orbiting (WRT the Sun) something already IN earth orbit, then you add in the delta V to get into LEO _again_, clearly distorting the number to prove your point. Also, you suggest needing to go to zero, which is untrue, if something enters the corona it will be decelerated, the corona takes about 2 degrees of arc in the sky meaning an elliptical orbit will be just as good, which does not require zero orbital velocity.

Re:Good luck

[BlueStrat]

You mean like the Challenger and Columbia? Except with nuclear fallout.

What, are you a Flash Gordon fan!?

Nobody designs even a chemical-powered interplanetary spaceship to land it's main mass (including it's main propulsion system) on a planet surface. That's what landers are for. Even Apollo used a Lunar Module to land on the moon and a small Command Module for Earth re-entry.

This thing would be assembled in orbit and would never land on a planet. For something like a nuclear-powered interstellar spaceship, I imagine most of the construction would be done in low Earth orbit and then moved to a parking orbit at a La Grange point for final departure preparations, including loading the nuclear fuel.

I think you understand this, but are allowing your nuclear fears to cause you to post ridiculous and unrealistic scenarios in an effort to fight the idea of nuclear-powered space propulsion systems.

Strat

Re:Good luck

[DerekLyons]

Anytime anyone even thinks about mixing "nuclear" and outer-space (even radioisotope generators as used on many space probes) all the anti-nuclear groups kick up a huge fuss.

Yes, look at the fuss kicked up over New Horizons and Curiosity... Oh, wait there wasn't any.
 
Seriously, this myth (about anti-nuclear activists) needs to die in a fire. Over time, the protests have gotten quieter and quieter and come from ever further out on the lunatic fringe - until, over the last few years, they've become essentially silent. (Cynics among the space community think this is because the Usual Suspects in such protests became busy with Anti-Bush/Iraq protests and have moved on to the Occupy movement.)

Re:Good luck

[CrimsonAvenger]

Also, you suggest needing to go to zero, which is untrue, if something enters the corona it will be decelerated, the corona takes about 2 degrees of arc in the sky meaning an elliptical orbit will be just as good, which does not require zero orbital velocity.

Dropping something into the corona of the sun from LEO....

Okay, assume that that requires us to get down to ~3,000,000 km (about four times the radius of the sun).

orbital speed up at this end of the hohmann ellipse is ~5900 m/s.

If we assume our orbital speed in LEO is about 7100 m/s (corresponding to an escape speed of about 10 km/s), then a single burn of about 18800 m/s is required to reach the corona of the sun.

Note, for reference, that from the same LEO, solar escape speed requires ab out 8800 m/s deltaV.

No matter how you slice it, it's easier to just toss something out of the solar system than it is to toss it into the sun...

Re:Good luck

[CrimsonAvenger]

Yes, look at the fuss kicked up over New Horizons and Curiosity... Oh, wait there wasn't any.

Probably because noone told them there were RTG's on those spacecraft. It's not like they glow from radiation, after all (and I suspect that many of the anti-nuke whackjobs really do believe that "nuclear" power plants/etc GLOW)....

Re:Good luck

[BoRegardless]

Nearest Star = 4.2 light years. At the moderate speeds we would be able to generate to accelerate, but then an equal amount of fuel to decelerate to enter orbit around such a star in time measured in something larger than 10s of thousands of years at survivable speeds that don't erode the probe down from "plasma erosion" like you have with a plasma jet cutting machine.

Helium, Hydrogen and Protons and electrons hitting any metal or ceramic surface at huge speeds eventually cut through, even if only in thousands or tens of thousands of years.

A signal back from the probe would then take 4.2 light years to reach back to earth......if it didn't hit the smallest little rock or ice chunk along the way, which is a real undetectable possibility, and at the high speeds it takes, those would be fatal.

I understand the thrill of the thought process and the income if you are on the program and getting paid.

As a taxpayer, it leaves me as cold as intersteller space.

Re:Good luck

[donscarletti]

OK, that all checks out, in truth I _had_ forgotten that I could subtract the earth's orbital velocity from the sun's escape velocity (also the spacecraft's orbital velocity, but that would work for both escape and de-orbit). So, I would like to change my position ever so slightly to say: "throwing something hazardous into the sun is awesome and _worth_ the extra deltaV".

Re:Good luck

[ColdWetDog]

As a taxpayer, it leaves me as cold as intersteller space.

It leaves me with a warmer feeling than most of the things we spend our money on. Er, excuse me, we spend our kid's and grand kid's money on.

Your cold hearted appraisal of the issues certainly has validity, but stuff like that hasn't stopped us in the past.

Re:Good luck

[donscarletti]

I like your style.

I'd be like the half-qualified director of NASA and would make this rousing as hell speech "do you want to be remembered as just some ordinary guy, or as the hero who flew a nuclear powered spaceship into the sun" and all of these cynical know it all guys would be like "you dumbass, you forgot to subtract Earth's orbital velocity from the Sun's escape velocity". And you'd be the promising young mathematician would would run to the front of mission control with a stack of paper and diagrams and be like "no, we need to launch this deadly broken nuclear spaceship at the moon first", then I'd smile and puff my cigar, knowing that everything would be awesome in the end.

I'd pay my $8 to see that movie, I really would.

Re:Good luck

[petes_PoV]

pollute an area of space millions of kilometres from anything I personally give a shit about.

Though in space things don't stay where you put them - they have an annoying habit of forming closed orbits (unless they're going fast enough). So the area of space that you personally don't give a shit about could soon find itself on an intersecting path with a person, place or planet that you do have some small gravitational attachment to.

Added to which, if the engine does go <bang> then it's hard to say which pieces will go in which directions, and at what speed - so making any predictions about where they'll end up a little bit impossible.

The only safe way to do it is to stash the rocket at a Lagrange point and fire it from there, in a direction that will never let its orbit (powered or unpowered) intersect with Earth's.

And as for flying it into the sun - make sure there are no pesky inner planets anywhere near. One small orbital perturbation and that whole radioactive mess could miss the Sun and come swinging back to make a meteor shower you really wouldn't want to get too close to.

Re:Good luck

[WindBourne]

You have to be kidding. Far easier to point it at the sun and go in, or simply point it retrograde, slow down speed relative to earth and allow the sun to pull it in to either venus, mercury or itself.

Re:Good luck

[0111 1110]

What attempts were made exactly? Citation desperately needed. IIRC, Orion was canceled for political, not scientific, reasons. Nuclear propulsion is the only means we have of traveling interstellar distances in any kind of reasonable time frame. In what way are the concepts flawed?

Re:Good luck

[WindBourne]

who says that you have to hit the sun? Just let it fall slowly to the sun. Ideally, it can transmit information for a LONG LONG TIME as it heads there. Nothing better than allowing it to be a long life sat while on its way to oblivion.

Re:Good luck

[WindBourne]

Derek,
Sending up small amounts is now accepted. Sending up the amount needed for NERVA would drive the same group that objected to the IFR batty. ANd yes, they would protest.

But there is a simple solution. Send up a small processing/breeder unit to space, and then send up safe uranium. At that point, it gets bred to plutonium and allowed to be used.

I wonder if a NERVA can be used to land on the moon? If so, that would become a truck. I noticed that Japan found Uranium on the surface, though quantity was unknown.

Re:Good luck

[0111 1110]

Where are you getting your data from? The hydrogen in interstellar space is very sparse and what little there is might be scooped up and used for fuel with a magnetic scoop. A super-Orion sized craft could reach speeds of up to about 0.1c. At that speed Alpha Centauri is only 44 years away. The chances of hitting a macro sized object in interstellar space are low. The vast majority of matter in the galaxy has already clumped into solar systems.

Re:Good luck

[jeffb (2.718)]

I don't think you understand how "falling" works.

Earth is moving at about 30 km/s relative to the Sun. That happens to be just the right velocity to keep it in an orbit at a distance of about 150 M km.

Apply thrust along that same vector, and you go into a higher orbit. Apply thrust against that same vector, and you go into a lower orbit. Apply enough thrust against your vector long enough -- long enough to change your velocity by about 30 km/s, which is a heck of a lot -- and you eventually intersect the Sun's surface.

"Let it fall slowly to the sun" is a bit like saying "just pick up both feet at the same time, and until you put them down, you're flying!"

Re:Good luck

[jeffb (2.718)]

And by "failing" or "not working" I presume you mean "running for nearly two hours straight, including nearly half an hour at full design power".

NERVA worked. It could've put humans on Mars in the time that it took us to send the Shuttle program limping into LEO. The main "flawed concept" was the notion that the US had the political will to see it through.

My college roomate's father worked on the NERVA project back in the 60's. I don't know how he ever got over its ignominious cancellation. I'm not sure I ever would have managed it. I hope he's still alive to witness its rebirth.

Re:Good luck

[BlueStrat]

Well, what about using Biofuels? And also, if the crew was vegan, it would save a lot of energy on food! Meat take a lot of energy to produce, each time you eat at KFC it's the same thing as drinking half a barrel of petrol!

GAIA!

Biofuels!?

But...but...

We'd have to wait until we find aliens to give carbon credits to!

I'm surprised at your irresponsible environmental attitude. It's reckless plans like yours that will result in an AUW catastrophe (Anthropomorphic Universe Warming) and completely destroy the natural course of entropy! [shudder]

You make baby stars cry.

Strat

Re:Good luck

[athe!st]

By way of counter example, the Juno Jupiter mission uses solar panels for it's power rather than RTGs. They would generate 12-14Kw at earth but due to the distance to will only produce 486W at Jupiter.

Re:Good luck

[kelarius]

Yes, you could be hit by a large piece even so, but that would be amazing bad luck; space is damn big.

It's not up to luck if there is an explosion in LEO, if something in orbit dies it WILL eventually make it to the surface one way or another, that's just the nature f orbit. The concern is that those large pieces of the spacecraft would be radioactive and an explosion in orbit would undoubtedly send them back into our atmosphere. While the actual fallout from an explosion wouldn't likely cause any damage (the Earth's magnetic field protects us from far worse than nuclear fallout on a daily basis)) any debris left over from the probe and especially the reactor sections would likely be very irradiated and would poison wherever they landed/flew over, and since re-entry can cover a distance of thousands of miles I think you can imagine what kind of damage that could cause.

As has been discussed before fueling and launching the probe from a La Grange point or Lunar Orbit would be the safest way to do this, using chemical rockets to provide the initial thrust to fire it out of our immediate orbit will help to minimize this risk. Now getting the fuel into orbit is a bit trickier, you would need to send small amounts of fuel multiple times and I believe it could be performed safely, we already have casks used to transport nuclear material and these are already proven to be capable of withstanding large forces so I'm not too terribly concerned about that as long as most of it's launch transit occurs over ocean)

Re:Good luck

[Patch86]

Citation needed, on the travel time aspect.

Project Orion (the 1970's attempt at a thermonuclear rocket) would have take 44 years to reach Alpha Centauri (assuming a fly-by with no deceleration time, and excluding 36 days worth of acceleration to it's top speed). A long time by human standards, but a very very long way short of "10s of thousands of years". If you launched one today, you could get your first pictures back in almost the same amount of time as between Apollo 11 and today. That's travelling about 10% the speed of light.

There was also Project Daedalus, which was a similar concept using fusion rather than fission. That could go 12% the speed of light, and was not really that much less practical than Orion.

Re:Good luck

[Patch86]

I won't answer it again (siblings posts have done a far better job of it than I could), but to sum up- no. That isn't how space works.

Re:Good luck

[newcastlejon]

What attempts were made exactly? Citation desperately needed.

They did some testing with scale models and conventional explosives. I'm very sorry but I can't seem to find the Youtube link, but if you want a citation and you have a large library try this:
Freeman Dyson, Disturbing the Universe (New York: Harper and Row, 1979)

Re:Good luck

[newcastlejon]

Just to clarify, I'm saying that they did some tests, not that those tests showed the concept to be impractical (though they may have).

Re:Good luck

[Truekaiser]

it wasn't because we lost the will. it's because our leaders chose immediate gratification due to our biology and political structure rather then a long term plan that for them at the time, 52~ years ago, which may or may not of payed off at LEAST 20 or 30 years later and in a minimal fashion without a more of a pay-of until now or at most 2020.

they chose to scramble for the remaining earth bound resources and a nonsensical fight against a ideal(communism then, then replaced with terrorism now so the same people can profit). rather then spend the same money, effort, and natural resources to set up the basic earth-moon & possibly martian infrastructure so for at least some natural resources we would have a bigger supply. that in turn has closed the window for this species to be be anything other then one which stays on it's own planet or planet with a occasional mission maned or not to their moon/moons and neighboring planets. even a colony ship is out of grasp as we do not have the resources to spare to build the infrastructure to make one in orbit.

i think, the best one can hope for is that the next intelligent species that evolves on this planet after about 250 million years(wither it be our decedents or some creature that is alive now) from now if their timing is as fortunate. will use their natural resources which resulted from our activity(oil and nat gas since they are renewable on a 'geological time scale' the massive plankton blooms we are causing due to our influence on climate will become their oil under the same processes that the Carboniferous era gave us ours.) and the earths plate tectonics bringing more to the surface within reach of any species more wisely and use this one time natural gift to propel them to the stars. Ironically our situation is rather like a bird in a egg, to the bird they have a lot of food in that embryonic sack, it's normally just enough to fuel them more or less to break through their egg. it's just that we are a bird who has seen this large natural resource and chose, foolishly, to stay with it. because we did not have the will nor the long term thinking to use it to get out of the egg after we stuck our beak out of the shell and did not find any more.

Re:Good luck

[khallow]

Nearest Star = 4.2 light years. At the moderate speeds we would be able to generate to accelerate, but then an equal amount of fuel to decelerate to enter orbit around such a star in time measured in something larger than 10s of thousands of years at survivable speeds that don't erode the probe down from "plasma erosion" like you have with a plasma jet cutting machine.

[...]

As a taxpayer, it leaves me as cold as intersteller space.

Well, it's a good thing then that you aren't paying for it. I imagine people who live much longer than we do, would have a different take on the value and cost of such things. But they'll get to use their own money for that. Nuclear-powered propulsion has more practical uses within the Solar System than without.

Re:Good luck

[the gnat]

Project Orion (the 1970's attempt at a thermonuclear rocket) would have take 44 years to reach Alpha Centauri (assuming a fly-by with no deceleration time, and excluding 36 days worth of acceleration to it's top speed).

That was Freeman Dyson's calculation of what sort of extreme the technology could be pushed to; it's by no means a sure thing. However, the Orion drive was vastly more complicated (and expensive) than the nuclear thermal rockets they're talking about in the article, which would never be able to get to anywhere close to 1% of light speed. The big difference is that an NTR engine was actually built and worked at one point, whereas Orion was never more than blueprints. Also, an NTR is something that a private company could theoretically build, whereas Orion requires setting off repeated fission explosions, which only a handful of governments know how to do - and which in any case genuinely would cause an uproar.

Re:Good luck

[jeffb (2.718)]

You're talking about Orion, not NERVA. This fission-rocket proposal is the same approach as NERVA.

Re:Good luck

[camperdave]

And what, exactly, can blow up on a nuclear rocket?

Re:Good luck

[Anonymous Coward]

Could it also be ridiculously difficult? I don't know what "rediculously " means.

Re:Good luck

[cavreader]

Not to mention we have been using nuclear reactors on subs and carriers for quite a few years and these vehicles were built for exclusively for the battlefield.

Re:Good luck

[jamstar7]

I'm thinkin the mission director will tell them to land at night when it's not so hot.

Re:Good luck

[jamstar7]

Profit!

Re:Good luck

[jamstar7]

Also, an NTR is something that a private company could theoretically build,

Yeah, they can build it, they just won't be able to fuel the reactor. Governments get nervous at the thought of plutonium in private hands that can leave an easily monitored site.

I'm thinking recalculate for http://www.thorium.tv/en/thorium_reactor/thorium_reactor_1.phpthorium reactors. Thorium reactors don't go 'boom'.

Re:Good luck

[newcastlejon]

You're talking about Orion, not NERVA.

Yes I was, as was the post I was replying to.

Re:Good luck

[Mateorabi]

Forward is up. Up is backwards. Backwards is down. Down is forward.

Re:Good luck

[jeffb (2.718)]

My bad, I dropped a stack frame somewhere.

Re:Good luck

[thermopile]

I call BS.

To the uninitiated, I agree it sounds bad. "OMGWTFBBQ we're putting NUKES in SPACE!!1!"

But it's not actually that bad. The fact is, uranium is not that radioactive before it has been in a nuclear reactor. I have held kilogram-quantities of uranium in my hands -- and still have all 10 fingers to show for it. Plutonium is more radioactive -- half a kilogram is warm to the touch -- but it's not deadly as long as it stays external to your system.

The nastiness starts coming in after the reactor goes critical and fission products have a chance to build up. But you'd only let the reactor go critical AFTER the thing has left LEO.

Having designed a space reactor before, I know that it's quite possible to even to criticality measurements on the reactor (i.e., zero power measurements) before you launch it and still call the reactor "clean."

For some real fun-and-games, check out the re-entry of the Soviet TOPAZ reactor (Cosmos-954) over Northern Canada in the late 1970's.

Re:Good luck

[a_hanso]

I have held kilogram-quantities of uranium in my hands -- and still have all 10 fingers to show for it. Plutonium is more radioactive -- half a kilogram is warm to the touch

Just out of curiosity, have you ever tried to figure out what went down in between all those times when you got angry and those times you woke up somewhere in torn pants?

Re:Good luck

[ChrisMaple]

Does using a nuclear engine to power the vehicle through the atmosphere increase the risk of a nuclear spill, or will it inherently spew radioactive material into the air? If not, why not use a nuclear engine to get off the surface?

Re:Good luck

[bill_mcgonigle]

but this is definitely bigger risk than a chemical rocket.

You'd rather get showered in hydrazine than plutonium?

Re:Good luck

[sjames]

You don't have to apply the entire 29.78km/s, just enough that the thing passes through the corona at some point in it's orbit.

Re:Good luck

[BlueStrat]

If not, why not use a nuclear engine to get off the surface?

Short answer: Shit happens.

Longer answer:

Why tempt Murphy's Law and/or an unlucky turn of the odds? Seems to me to just be smart risk management if you choose NOT to have critical fission piles screaming through the atmosphere of an inhabited planet at thousands of miles per hour if it's not necessary, even if the tech itself is very mature.

Besides, the mass of shielding and armoring/hardening for the reactor core necessary to make it reasonably safe and resilient in a crash on the Earth's surface or in the atmosphere would likely render the thing unable to leave the ground, atomic engine or no.

That's the whole idea behind landers. Leave the heaviest parts like the main interplanetary/interstellar propulsion systems and fuel/tanks in orbit where you need it, and not waste energy hauling them up and down a gravity well for no reason.

I'm so disappointed in mankind. Back in the late '70s, I was certain we'd have a semi-permanent station/lab/etc at Earth's La Grange points and at least sent several manned missions to Mars by 2012.

Strat

Re:Good luck

[Mephistro]

This thing would be assembled in orbit and would never land on a planet.

How would you send the radioactive fuel to orbit? By FedEx?

Re:Good luck

[EdZ]

However, the Orion drive was vastly more complicated (and expensive) than the nuclear thermal rockets they're talking about in the article

Not really, no. Ol' put-put is a dirt simple device: a gun to fire bombs a short distance, and a big honking pusher-plate on heavy suspension. A NTR needs some pretty esoteric construction materials to maintain integrity at the very high operating temperatures used (and some rather creative layout of the fuel elements to allow good hypersonic flow), whereas the Orion drive just needs to be big and heavy. The bigger the better, in fact; it scales up better than it scales down.

Re:Good luck

[sourcerror]

I'm talking about accidents, obviously. Space rockets are more fragile and less reliable than our usual nuclear power plants. That's what I'm talking about. Assembling the thing in the orbit doesn't really change the fact that space rockets are prone to fail.

Re:Good luck

[BlueStrat]

This thing would be assembled in orbit and would never land on a planet.

How would you send the radioactive fuel to orbit? By FedEx?

[sarc]
Well, obviously, the fuel will be sent up in one huge and extremely dangerous near-critical-mass lump to maximize the possible danger rather than some other boring way, like over time in small quantities on multiple.Earth-to-LEO launches.
[/sarc]

C'mon, dude! Seriously!?!?

I know this is rocket science and nuclear science, but this is Slashdot!

Please turn in your geek card at the door on your way out for not being able to figure out that you don't send all the fissionable material into orbit on one launch vehicle!

Strat

Re:Good luck

[tempest69]

the speed of the earth has you moving fast enough that getting enough speed to retrograde to a lower orbit (venus) is substantially more than the fuel needed to crash into jupiter.
Really we just steer it into a comet, and let her take it into the sun for us ;)

Re:Good luck

[DerekLyons]

I don't believe NERVA can be throttled that deeply... if that's true, it can't be used as a lander engine.

Re:Good luck

[BlueStrat]

I'm talking about accidents, obviously. Space rockets are more fragile and less reliable than our usual nuclear power plants. That's what I'm talking about. Assembling the thing in the orbit doesn't really change the fact that space rockets are prone to fail.

What kind of "accidents" do you mean here? We're talking about an interstellar spaceship that stays in space and doesn't ever land. If you're worried about a meltdown or explosion in space, then I hate to break it to you, but there are a whole lot of extremely dangerous, deadly-radiation-emitting, and lethal things in space. One of the most dangerous is a titanic ongoing thermonuclear reaction millions of times the size of Earth only about 93 million miles away, which is practically in our laps.

Assuming the ship is finished and fueled at the closest Earth-Moon La Grange point (L2), that still puts the starship just 37,000 miles closer to the Earth than the moon. All the other La Grange points are either the same distance as the moon or further away from Earth. You could set off every nuclear/thermonuclear weapon that's ever existed on the planet up to this time at once at that distance and you'd never know it, unless you happened to be looking at that point at the right moment.

I just don't get the fear. It seems purely emotional and not based on logic at all.

Strat

Re:Good luck

[BlueStrat]

...closest Earth-Moon La Grange point (L2)...

Oops. Should read L1, not L2.

http://en.wikipedia.org/wiki/Lagrangian_point

Strat

Re:Good luck

[tragedy]

Usually because you won't get enough thrust out of the engine. At an unachievable optimum efficiency, you need a theoretical 48 watts of power per kilogram just for the thrust to counteract gravity at the surface of the earth. This is ignoring aerodynamic effects entirely, of course, but it's just illustrative. So, if you want to actually go up, you need more power than that. So, the absolute maximum that 1 MW could lift would be a bit more than 20 tons. With an imaginary efficiency of 25 % (still unrealistically high), that would be around 5 tons. Considering that you're still going to have to carry the craft itself, crew, cargo, engines and propellant (unless you come up with some neat air breathing design that refills its propellant tanks with air as it lifts off), it's unlikely that you're going to find a nuclear reactor that can provide you with that kind of power per kilogram in a practical weight range. That's ignoring whether or not the engines themselves can be made to weigh less at the earth's surface than the thrust they're capable of producing. Now, as nuclear reactors get bigger, it is possible that they could scale so that they provide the necessary power per unit of weight. That might mean a nuclear rocket that can take off from the surface of the earth. Until then, chemical rockets are the way to go. They don't have remotely near the energy density of nuclear, but for up to maybe 15 minutes, they can pour out massive amounts of power

Now, nuclear can certainly pour out power faster than chemical rockets too, but not usually in a safe, contained manner. There are some nuclear rocket designs that carry out fission externally that could take off from earth (either by a continuous reaction, or by throwing a bunch of small, low yield nuclear bombs out of the back), but people aren't too keen on massive use of open air fission reactions these days. Plus, you need a way to protect the cargo and crew from the radiation. Carrying enough shielding to do that with such an active nuclear reaction tends to re-introduce the weight problem. You can also use distance as a substitute for shielding, like the spacecraft from _2001_ which had the engines and the crew compartment separated by a very long thin section , but such a design is impractical to launch from earth. So, overall it looks like we're stuck with using reactors to make power to run some sort of electric drive or direct thermal exhaust options. Either way, the actual thrust to weight ratios of these systems looks like it's less than 1 on the surface.

In space, however, the nuclear rockets blow by chemical rockets by a huge margin. Out there, for most operations, you may be able to get 100 times the total thrust out of a nuclear rocket than you could ever get out of a chemical one, it just may take 1000 times as long to do so. Since chemical rocket burn times are measured in seconds, that's not much of a problem out there.

In the long run, we may get total package nuclear powered spacecraft that can take off from the ground and fly all the way to another planet, land, take off again and land back on earth without needing to refuel or use chemical stages, etc. There's nothing saying it's impossible. Our current tech can't manage that (safely) yet, however. We may get there some day, however.

Re:Good luck

[tragedy]

If you encapsulate the nuclear fuel (non-critical masses of it obviously) in a sufficient container, it will be able to survive re-entry and hitting just about anything without rupturing. Even it lands where it can't be retrieved, the container won't leak for a good few millenia and will contain the fuels radiation. Of course, you wouldn't want one of those containers to land on you.

Re:Good luck

[tragedy]

Depending on whether or not the plutonium were fine dust and what isotope it was, I personally would probably go for the hydrazine. Plutonium 238, for example, is really toxic (not due to its radioctivity, since it's hundreds of times more toxic by weight than plutonium-239, which has a similar radiation profile).

The GP posters fears are a bit wacky of course, since nuclear fuel sent into space would be a solid mass and encapsulated so that it wouldn't burn up or break up and be distributed in the atmosphere. Also, there would be a few kilograms of plutonium, but potentially hundreds of thousands of kilograms of hydrazine. Still, to answer your question again, if I had a choice between being showered in hydrazine or with an encapsulated lump of plutonium falling from space... I'd take the one that wouldn't blow me into a thousand pieces.

Re:Good luck

[tragedy]

Just so you know, the plutonium-238 plugs in those RTGs do actually glow. It doesn't make the whole rover glow of course (unless you can see in the infrared), but the actual plutonium does.

Re:Good luck

[sourcerror]

"What kind of "accidents" do you mean here? We're talking about an interstellar spaceship that stays in space and doesn't ever land."
1, Challenger blew up during takeoff, so all the bullshit about Langrangian points is perfectly irrelevant
2, http://en.wikipedia.org/wiki/Ariane_5_Flight_501#Launch_failure
http://en.wikipedia.org/wiki/Kosmos-3M#Accidents
4, http://en.wikipedia.org/wiki/Fobos-Grunt#Post-launch

These are accdents all launch related accidents, and the list is not complete.

Re:Good luck

[BlueStrat]

"What kind of "accidents" do you mean here? We're talking about an interstellar spaceship that stays in space and doesn't ever land."
1, Challenger blew up during takeoff, so all the bullshit about Langrangian points is perfectly irrelevant
2, http://en.wikipedia.org/wiki/Ariane_5_Flight_501#Launch_failure [wikipedia.org]
http://en.wikipedia.org/wiki/Kosmos-3M#Accidents [wikipedia.org]
4, http://en.wikipedia.org/wiki/Fobos-Grunt#Post-launch [wikipedia.org]

These are accdents all launch related accidents, and the list is not complete.

I don't know if you're being deliberately obtuse or trolling at this point.

Do you honestly not get that the ship is never launched from Earth? That it would be built in space?

You wouldn't even fuel the thing until you had it parked way out at a La Grange point ready for departure. The fuel would be sent in small quantities, a little at a time. Heck, the fuel may not even come from Earth at all. It might come from a lunar mining operation along with many of the raw materials for the structural components.

The electronics may be the only parts to climb the gravity well up from Earth. Depending on how far in the future this starship project would occur, even that may not be necessary. It may quite well be the case that the first starship may for all intents and purposes be entirely the product of materials and resources gathered from places other than Earth. Even if the first ship isn't built almost entirely from off-Earth materials, it's certain that if following ships are built, at some point that will become true.

There's really no reason why such a ship would ever come any closer to the Earth than lunar orbit or parked at a La Grange point.

You're in far, far, far more danger from existing terrestrial reactors than you would be from any nuclear accident regarding the fueling/operations of a nuclear-powered starship that may never come close enough to see from Earth without very sophisticated optics.

Strat

Re:Good luck

[rufty_tufty]

"Does using a nuclear engine to power the vehicle through the atmosphere increase the risk of a nuclear spill"
Yes.
Burnt Nuclear fuel is more dangerous than unburt, being assembled in a form of an engine means that in the case of a malfunction (which is almost certain to be in the engine) the nuclear material is going to be in a higher energy part of the craft than whatever is in the payload section..
Also assuming you were carrying this stuff up to orbit for assembly into the reactor there then you could pack it in a capsule that would survive de-orbit and therefore be recovered in the event of an accident (much as you would humans) it would be much harder to do the same for the engines.
Now while getting to orbit on a nuclear rocket would be awesome and potentially safer than chemical rockets (you could build in more safety margin with the excess power you would have) that's not the question you asked....
On a less serious note let's face it they use depleted uranium for shielding on tanks and re-entry shrouds on nuclear weapons, so it should survive re-entry ;-)

Re:Good luck

[careysub]

Derek, Sending up small amounts is now accepted. Sending up the amount needed for NERVA would drive the same group that objected to the IFR batty. ANd yes, they would protest. ...

A fission space propulsion system would be made using highly enriched uranium, and launched cold. By the methods used to measure radioactivity (decays per second), a HEU reactor core definitely qualifies as a "small amount" and in fact would be far, far less hazardous than the plutonium RTGs send up routinely today.

Re:Good luck

[shmlco]

"... could soon find itself on an intersecting path..." "One small orbital perturbation and that whole radioactive mess could miss the Sun and come swinging back to make a meteor shower you really wouldn't want to get too close to."

Why do people always conflate possibility with probability? I "could" win the state lottery while simultaneously getting struck by lightning, but the odds of that happening are (forgive me) astronomical.

Heck, it's hard enough to get close to Venus or Mercury when you're trying to do on purpose. Care to calculate the odds of getting close enough to a planet to affect the orbit to the point where it's going to miss the sun and then come back out to intersect a point on a circle 82 billion miles long, at the same exact instant in time we just happen to be there?

Car analogies

[Anonymous Coward]

Brad Appel of General Propulsion Sciences frames the situation in more familiar terms: "To look at it another way, imagine you are planning a road trip from New York to Los Angeles and back. Except, there are no gas stations along the way -- you need to pack all of the fuel along with you. Using a chemical rocket to send humans to Mars would be like making the road trip in a cement truck. You might barely make it, but it would be one enormous, inefficient, and expensive voyage. Using an NTR, however, would be more akin to taking a Prius. It'll make it there comfortably, and it can go a lot further too."

A terrible car analogy quite worthy of Slashdot. Bravo.

Painted red and whote in hommage to Hergé ?

[Hamsterdan]

http://en.wikipedia.org/wiki/Destination_Moon_(Tintin)#Representation_of_space_travel

legal?

[kaspar_silas]

Sounds exactly like 1955s project Orion. And similarily to it I don't think they can actually legally work on this idea due to international nuclear regulation. In particular the comprehensive test ban treaty. Because after all what you are designing is something very like an icbm with a "dirty" warhead. I god damn guarantee if Iran openly worked on this the US would bust itself to attack ASAP.

Re:legal?

[Anonymous Coward]

Nothing at all like Orion. This is using hydrogen as the reaction mass, heating it with a fission reactor. Orion uses nuclear bombs set off repeatedly behind a fscking huge steel plate.

You're right about there being international nuclear regulation that may stop it, though - if I recall correctly, there are legal hurdles to even test-flying nuclear reactors up to orbit and all kinds of international agreements following near-misses with both soviet and american test reactors in the 60s.

Re:legal?

[cbhacking]

Nuclear thermal rocket != nuclear pulse rocket. The latter is the classic "Project Orion" engine, utilizing super-critical explosions for propulsive force. The former is actually more akin to a traditional chemical rocket, in that it works by expelling reaction mass from thruster nozzles. However, the energy of the reaction mass is imparted by heat generated in critical or sub-critical (but not super-critical) nuclear reactions. You can use any number of materials for this reaction mass, though the popular ones are hydrogen and water. Neither is inherently harmful, nor is there any reason they would need to pick up radioactivity from the reactor (any more than the cooling water which cycles through the heat exchangers of nuclear electrical plants or naval vessels becomes radioactive).

The test ban treaty has nothing to do with this. Nuclear pulse rockets are certianly forbidden by the test ban treaty - after all, they are literally exploding nuclear bombs as part of the engine's normal operation - but there's no reason nuclear thermal rockets would be that I can see. The argument about a "dirty warhead" is potentially valid (in that some would claim it, not in that it would be a plausible danger when you consider we already have nuclear-tipped ICBMs). However, there's no law or treaty against launching radioactive material into space. In fact, quite a few of our space probes and planetary rovers use radioactive thermal generators.

Compared to chamical rockets, nuclear thermal rockets have a vastly higher specific impulse, which is to say that a given quantity of reaction mass (rocket fuel or hydrogen flowing past a reactor) can produce a greater thrust (simply put, higher efficiency). This is due to their (much) higher exhaust velocity. Remember, E (in Joules) = mass (in kg) * velocity (in meters/second) squared. If you divide both sides by kilos (fuel or reaction mass), your energy per unit of reaction mass becomes a function of v^2. In other words, doubling the speed of the reaction mass will get you four times as much energy for a given unit of reaction mass.

Since the amount of thrust you can get out of the quantity of reaction mass that can be placed on a spaceship is the current limit on spacecraft range, speed, and payload, increasing that efficiency has the potential to revolutionize space travel.

Re:legal?

[jamstar7]

Orion was the one you set off nuclear bombs under a heavy plate as a thrust mechanism. BiFrost is basically an upgraded NERVA system, from what little I can gleam from the article. Not a lot of hard science in it.

NERVA basically pumps liquid hydrogen through a fission reactor core. The core heats up the hydrogen, it expands, escapes through the bottom of the reactor and the nozzle providing thrust. Think 'tea kettle'. It'll help you visualise it.

The best reaction mass for this concept is stabilized monotomic hydrogen ('single-H', as Heinlein put it).

Re:legal?

[gatkinso]

Clearly you are either unfamiliar with Project Orion, or you didn't read the article.

Re:legal?

[Lord_Naikon]

I think you make some mistakes in your calculations. First, it's E = 1/2 * m * v^2. Secondly, the force the engine generates is proportional to m*v (impulse). The energy required to create an impulse of m*v is indeed 1/2mv^2. In other words, as the amount of thrust doubles, the required energy quadruples. Hence the need for a nuclear reactor. Basically energy efficiency is lower for high velocity rocket engines. In this case that is not a problem because this engine doesn't require much mass to operate resulting in high specific impulse (but low energy efficiency). Normally though, in chemical rockets, it is a tradeoff.

Re:legal?

[WindBourne]

nope. Not from a treaty POV. We send up reactors all the time. NERVA has ZERO issue going. Orion is a different matter. Those are technically bombs on there. The treaties prevent that from going to space, though I suspect that if we got ALL of the signatories to agree to it, we could do it. And I have serious doubt that we could get that, except when an asteroid or some other major threat were in-bound to earth (and in light of how America's CONgress is acting, I would guess that even with a massive alien invasion coming in, that we would get a number of nations or even extremists that would object to orion).

Re:legal?

[WindBourne]

oops. I should have read yours first. You are correct.

Re:legal?

[cbhacking]

The factor of 1/2 is irrelevant here - I'm not talking in absolute quantities (and arguably shouldn't have given actual units at all) but in ratios. E/m (energy per unit mass) is a function of v^2. Since energy is relatively cheap (especially with a fission reactor), but mass is hideously expensive, you want an engine with the highest possible exhaust velocity, as that will maximize the E/m ratio very quickly.

Impulse is another story entirely. Impulse mesures the strength of the engine, not its efficiency. For high impulse, you typically want a relatively low velocity and high mass - this applies to everything from modern chemical rocketry (which is powerful enough to lift itself off Earth directly, something only a few even theoretical high-efficiency rockets can do) to early cannons (which used a heavy shot to maximize the impluse transfer they could get out of the limited energy of low-grade gunpowder).

Specific impulse (Isp) is the impulse as a function of mass flow. High Isp does not neccessarily mean high impulse - ion drives have excellent Isp, but push so little mass that their actual impulse is very weak - but it is one of the most popular measurements of efficiency for a rocket. In essense, it addresses the question of "If we are unconcerned with energy cost, how much mass do we have to consume to get us there?" (although "get us there" is actually much more complex in a real-world system).

Of course, extremely high Isp engines do tend to be energy-limited; not necessarily in the ability to supply it, but in the ability to move and dissipate it. In the case of nuclear thermal rockets, the limit is quite literally the melting point of your reactor assembly (including its controls and containment). That's still enough energy to accelerate a good quantity of mass to a truly absurd velocity, though - giving enough impulse to allow (among other things) more than 1G of thrust while still having a sufficient Isp that distant destinations and round-trip journeys become practical.

Re:legal?

[Lord_Naikon]

I don't disagree with you, my comment was merely an attempt to clarify things, however I botched things up when I wrote "thrust" when I meant "velocity". The factor of 1/2 is not relevant in this case but when you wrote in a imho condescending way that E=mv^2 and explicitly stated the units I felt compelled to correct it, hence my reply :-)

Re:Painted red and whote in hommage to Hergé

[maxwell demon]

I think your title was damaged by a radioactive particle.

What is this, a Tom Swift book?

[Shag]

Paging the young inventor to the white courtesy phone, please.

Credibility

[Extremus]

It would be easier to believe in these guys if they provide more technical details in how they pretend to achieve fission propulsion. As it is mentioned in the article, this is not a new idea. Is there any new development that could cast new light on the problem of fission propulsion?

Re:Credibility

[Oidhche]

We should've been using NTR for the past 30 years or so: http://en.wikipedia.org/wiki/NERVA.

Re:Credibility

[IntoMars.com]

This group will have an extremely hard time launching anything without massive protest from the anti nuclear groups. Pampers Diapers

Re:Credibility

[0123456]

Is there any new development that could cast new light on the problem of fission propulsion?

What problem? We've built and tested fission rockets; the only problem is getting them into space when politicos would prefer to listen to the anti-nuclear luddites.

Nothing new

[tsotha]

There's nothing new here. It's another "study" rehashing technology that's been rehashed over and over for at least sixty years. And anyway nuclear thermal rockets don't address the biggest problem we have with space exploration, which is getting to orbit in the first place. Heinlein famously observed "Get to low-Earth orbit and you're halfway to anywhere in the solar system." But the converse is also true - no matter how good your deep space rocket is you're only half way to where you want to be.

Nuclear thermal rockets have a wonderful ISP, but they don't have as much thrust as chemical rockets, and they're heavy. Even assuming you wanted to use one for the first stage it probably wouldn't have enough thrust to do the job. And you wouldn't want to start one up on earth, either. They never did figure out how to keep bits of the radioactive core from breaking off and entering the exhaust stream,

Re:Nothing new

[Hentes]

You could build the ship in orbit thus circumventing those problems.

Re:Nothing new

[tsotha]

Well, yes, you could. But now you'll have to send up a bunch of extra kg into orbit, and the whole point of having an engine with high ISP is to get really good performance from your fuel because you didn't want to send a bunch of extra kg to orbit.

Re:Nothing new

[tsotha]

No, that's not the whole point of a high ISP engine

Sure it is. A high ISP engine is simply more efficient per kg of fuel. If you supply enough fuel to a high mass ratio chemical rocket you can overcome that efficiency advantage. We don't do that today because it's a whole lot cheaper to send a little rocket on a high efficiency trajectory. But since we're talking about sending many extra tons into orbit, including whatever infrastructure needed for construction activities, what we have to compare the NTR to is the best chemical rocket we could have in that mass budget.

Would you have to do a trade study to see if you'd rather do impulsive-ish chemical burns rather than have a fancy, probably much heavier nuclear engine with higher ISP that can do something more akin to a continuous thrust trajectory? Yes, of course, and you'd probably see that it's a huge win for an interplanetary manned craft or anything else with a lot of dry mass.

NASA was never able to do better than 800 seconds with an NTR, which is less than double what you get with a conventional hydrogen/LOX engine, and far less current electric engines. It's definitely not suited to the pie in the sky interstellar probe in the article. Hell, at 800 seconds NTR isn't a good fit for a mars mission. In theory they could get one up to 1000 seconds. So... worth the time and effort? I don't see it, particularly when Ad Astra has already demonstrated an ISP of 4900 seconds in a full-scale test of a VASIMR engine.

In any event, to do such a trade study you'd have to have a working design, something we don't have. Nobody knows exactly how heavy a working NTR would be beyond "pretty damn heavy". I don't see that changing, either, for the same reason Rover and NERVA were eventually abandoned. The concept is just too messy to test. It's unlikely you could ever keep uranium and/or plutonium out of the exhaust stream without physically separating the core from the working fluid. That's going to make it still heavier and probably less efficient. Assuming it could be made to work at all.

All this assumes, of course, a NERVA style solid core engine, which is I think what they're proposing, though it's hard to tell from the article. And the numbers don't pass the laugh test. A liquid or gas core engine would be a real game-changer from the performance perspective and probably a whole lot safer if we could actually build one, but from what I can see we're no closer than we were when the idea was first proposed more than half a century ago. And even the holy grail gas core "nuclear light bulb" engine will only produce an ISP of between 1500 and 2000 seconds (according to the wiki page). Good for an SSTO assuming you weren't worried about spreading nuclear fuel everywhere if it crashed.

Re:Nothing new

[careysub]

...

NASA was never able to do better than 800 seconds with an NTR, which is less than double what you get with a conventional hydrogen/LOX engine, and far less current electric engines. It's definitely not suited to the pie in the sky interstellar probe in the article. Hell, at 800 seconds NTR isn't a good fit for a mars mission. In theory they could get one up to 1000 seconds. So... worth the time and effort? I don't see it, particularly when Ad Astra has already demonstrated an ISP of 4900 seconds in a full-scale test of a VASIMR engine.

...

All this assumes, of course, a NERVA style solid core engine, which is I think what they're proposing, though it's hard to tell from the article. And the numbers don't pass the laugh test. A liquid or gas core engine would be a real game-changer from the performance perspective and probably a whole lot safer if we could actually build one, but from what I can see we're no closer than we were when the idea was first proposed more than half a century ago. And even the holy grail gas core "nuclear light bulb" engine will only produce an ISP of between 1500 and 2000 seconds (according to the wiki page). Good for an SSTO assuming you weren't worried about spreading nuclear fuel everywhere if it crashed.

A key problem with nuclear thermal rockets is that when you consider all technologies on the table they have a fairly small mission space where they are the engines of choice. They have higher thrust than electric rockets, and higher ISPs than chemical rockets, but if high ISP is needed they are poor choices, and if high thrust is needed, ditto. This is one key reason why these systems have never flown - there is no mission requiring them yet identified. Most candidates in the past have been military missions, but none have been compelling.

This is now antique technology

[drewsup]

I was under the impression that the new Vasimir or Ion drives were WAY more efficient than this old tech. The only limiting factor is the size we currently them at.
Imagine an ion drive with 8 or ten modules, all powered by a fission reactor, it would start slow, but by the time it got halfway through the solar system would be cooking along at good clip. How fast is the potential ? No one seems to know, but a constant acceleration sustained for years would get you to a nice portion of C.

Re:This is now antique technology

[bejiitas_wrath]

If we wanted to go to another star system far in the future would it be possible to build an electromagnetic ramscoop ship or is that still in the realms of fantasy? Such a ship could get to the centre of the Milky Way galaxy in 25 years ship time, although 50,000 years would have passed by on Earth. The only question is what would the Earth look like politics wise in 100,000 years?

Would they have forgotten about you? What sort of technology do you really need to construct a ship to constantly accelerate at 1g and reach the galactic core safely, not to mention coming back.

Re:This is now antique technology

[Oidhche]

Ion engines have wonderful Isp, but very low thrust. And it's not just that a journey with such an engine would be longer - low-thrust transfers are inherently less efficient than Hohmann transfers, negating some of the Isp advantage. Moreover, you couldn't reach a nice portion of c with current ion engines: their Isp is good, but not that good. Most of them only have at most a few hundred km/s of effective exhaust velocity, limiting the maximum delta-v to like 0.3%-0.5%c under any design with realistic mass ratio.

Re:This is now antique technology

[gatkinso]

I have read rebuttals to the ramscoop concept. Not sure if they are valid or not. One thing however that seems right: the amount of radiation produced by such a system is thought to be deadly to life. So such ships would have to be unmanned.

Re:This is now antique technology

[WindBourne]

Sigh.
Ok, a VASIMR (a type of an ion engine) can drive an ion out at high speeds. HOWEVER, where does it get the energy to accelerate the ion from? Obviously from a generator or a solar collector. The problem with the solar collector is that not only does it add drag, it does not work as you get further and further from the sun. So, that leaves a nuke reactor. How much does it weigh? A lot. The real problem is one of efficiency and the fact that it will break down. To get electricity, you had to convert an element to steam and then run an engine that turns a generator. All of that is not just a loss of efficiency, but something that WILL burn out down the road. 50 years is a LONG TIME TO LAST.

Instead, it is far far better to simply use the nuke reaction to heat hydrogen to use it as a propellant. This is not just simpler in terms of mechanics. It is also a great deal more efficient. In fact, comparing NERVA to Orion, I will take NERVA. Again, it is simpler design. Simple wins for long term issues.

Re:This is now antique technology

[WindBourne]

This was already shown that the drag from the magnetic scoop was more than the energy that was derived from the particles. IOW, no.

Re:This is now antique technology

[stevelinton]

Ramscoops, as described in the literature have basically two problems:

1. Getting protons (as opposed to deuterium or something heavier) to fuse at a decent rate requires conditions substantially hotter and denser than found in the cores of even quite large stars. Something more like the conditions met in shockwaves in exploding supernovae. Without this your ramscoop isn't much use.

2. The interstellar medium is very unevenly distributed. The sun is deep inside the bubble created by an ancient supernova, so there's not much to collect.

Something like monopole catalyzed proton decay might work to solve problem 1, if it happens, and if we can find or make some monopoles.

Re:This is now antique technology

[drinkypoo]

At the point where we can actually do it, perhaps we can create an inverse field to protect crew. But they're theoretically plenty useful for unmanned probes, anyway.

Re:This is now antique technology

[jamstar7]

Ion drives are more efficient, but they don't have enough thrust to take off in a gravity field. You need something with high thrust like a NERVA or a conventional rocket to pull that off. Otherwise, all us space cadets would have built ion rockets and left already.

Re:This is now antique technology

[Electricity Likes Me]

This type of problem is why fusion is also considered an ideal propulsion system - because the fusion reaction itself is an electrically responsive plasma, so you can go more or less directly from energy generation -> propulsion.

Re:This is now antique technology

[drwho]

Regarding the weight of nuclear reactors - I don't know exactly what 'a lot' means, in terms of weight, to WindBourne. I can mention that newer designs of nuclear (fission) power plants are smaller. The steam turbine will be replaced by a helium turbine. One of the advantages of space (when away from stars) is that heat loss due to radiation is high, so cooling is easier, so the difference in gas pressure between helium heated by a fission reaction and that at the other end of the turbine, cool be radiation to space, is high, allowing a higher efficiency.

The problem is, this is still complex. Perhaps a better approach is to use advanced RTG (radioisotope thermal generator) concepts. These have been very inefficient so far, but new developments such as the Advanced Stirling Radioisotope Generator (http://en.wikipedia.org/wiki/Advanced_Stirling_Radioisotope_Generator) show promise. These, however, are still way too small and inefficient to replace the heated hydrogen which WindBourne suggests. So, I agree with WindBourne....as the technology currently exists. However, I wonder if it may be possible to not bother with the hydrogen at all, and simply use the high-energy neutrons (or Alpha, or Beta, particles) as the reaction mass. What I don't know is if the energy of the decay particles are high enough (in comparison to those from fission) to efficiently propel a spacecraft, especially at higher velocities. I recall that the exhaust velocity needs to be approximately equivalent to the velocity of the spacecraft in order to be efficiently utilized, however, I don't know what frame of reference this refers to. Also, because the spacecraft will have different velocities as it accelerates, the velocity of the exhaust would ideally be variable, and I don't see how that's possible when using decay particles.

Re:This is now antique technology

[careysub]

... However, I wonder if it may be possible to not bother with the hydrogen at all, and simply use the high-energy neutrons (or Alpha, or Beta, particles) as the reaction mass....

The mass of the these particles from fission and resulting decay processes are too low to provide much thrust - but you can do much, much better than that (in theory) by using the momentum of the fission fragments themselves. Those two massive atoms carry nearly all of the fission energy as kinetic energy on formation, if a significant fraction of those fission fragments can be used as reaction mass then a very high ISP engine would result - one of the few conceivable ones that really could power an interstellar probe. See: http://en.wikipedia.org/wiki/Fission-fragment_rocket

It isn't what we need.

[sgt scrub]

What we need is a reusable and reliable system to get objects out of earth's orbit. I would think the nuclear energy would be better utilized in a magnetic launch system. After that is established, then building an ORION/NERVA powered vehicle in space would be practicle. Using an ORION/NERVA powered launch rocket isn't my idea of a good start, so to speech.

Re:just bomb everything

[DerekLyons]

just go with the old project Orion (http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29) if you have to use fission, its still the most effective one.

To the extent that something that's never been tested can be said to be 'effective' sure.
 
Seriously, Orion has gained a reputation all out of proportion to reality. Few people seem to realize that not one single significant component has ever been built, let alone tested at even the most modest scale. None. Zero. Zip.
 
Yes, I know about the scale models they built - and they're roughly as relevant as an R/C car is to Formula One racing. The R/C vehicles 'proves' that a four wheeled vehicle can operate, but doesn't have an IC engine and the stresses on the suspension are orders of magnitude below those the Formula One racer experiences - not to mention the vast differences in aerodynamics. The same is true of the Orion scale models. They had no pusher plate or shock absorbers. They depended on the atmosphere to produce the propulsive shock waves. Etc., etc..
 
While it's true there are no obvious show stoppers, there are a lot of unanswered questions - particularly in the behavior of the pusher plate and the shock absorber system.
 
Also, few people realize the whole craft is designed around nuclear weapons of a type that don't exist - extremely small, extremely light, highly efficient, very clean (I.E. most of their yield was from fusion rather than fission) fusion weapons. Dyson and his team had very little access to nuclear weapons design details (something less than is publicly available today), and thus were relying on shaky assumptions about the direction of nuclear weapons research and the capabilities of nuclear weapons.

Icarus?

[Anonymous Coward]

Seriously?

Oh Please!

[rocker_wannabe]

"Mass ejection" propulsion is so last century. Where are the darn warp drives? I say: "Go FTL or go home."

Trivial to restart NERVA

[WindBourne]

The problem is that we have so many left wingers that are gaga over the idea of nukes being launched into space. Yet, we could easily put up a small processing plant on either the moon or even in space, and simply send a safe form of Uranium up there to be processed and bred.

Re:Space travel is nuclear!

[WindBourne]

Nope. Chernobyl is where you want to go. However, if doing something like NERVA, I will be happy to have it tested in my state. After all, it was designed here. The fact is, that NERVA is exceptionally safe.

It all comes down to exhaust velocity + mass ratio

[stevelinton]

Basic physics tells you that total delta-V for any kind of rocket comes down to just two things: how much of the ship you can throw away to get thrust (mass ratio) and how fast you can throw it (exhaust velocity). For mass ratios of less than say 1000 (ie ship at launch no more than 99.9% reaction mass at launch), and non-relativistic exhaust velocities, total delta-V is no more than 8-10 times the exhaust velocity. Exhaust velocity of chemical rockets tops out at about 3-5 km/s, nuclear thermal rockets get up to perhaps 10 km/s, ion and similar rockets at the moment do perhaps 40-50 km/s, although they could get much higher at huge cost in engine size and power and very low thrusts-- not so much a rocket as a particle accelerator!

Basically to get anywhere within spitting distance of relativistic speeds with a rocket you have to get MUCH, MUCH higher exhaust velocities which means some kind of direct nuclear propulsion (where the reaction mass is actually produced and heated in a nuclear explosion). Orion might manage one or two percent of lightspeed in principle, or better if you could replace the fission bombs with some kind of laser ignited fusion or matter-antimatter bombs.

Warp drive off a planetary surface?

[jeffb (2.718)]

Oh, sure. "Nukes are too scary, so let's just goatse a big hole in space itself right next to an effectively unlimited reservoir of condensed matter."

Re:Warp drive off a planetary surface?

[The Living Fractal]

Never stare directly into the ... wormhole.

Re:Warp drive off a planetary surface?

[Lanteran]

Goatse: now a verb!

Legal?

[nurb432]

I thought this was banned by international treaty.

Atomic rockets

[Patch86]

Reminds me of one of my favourite geek-out websites:

www.projectrho.com/rocket/

If only more writers of science fiction television trash would spend just one afternoon of their life skimming that website...

Project in DARPA's Starship Program

[newsfan]

if you do your research, you'll notice that Icarus is charged with DARPA's 100 year starship program, which means that effectively Bifrost is going to be doing all things nuclear for DARPA in space

Queller Drive

[smoothnorman]

Too bad they won't name it "The Queller Drive" (cf. http://en.wikipedia.org/wiki/Voyager_One_(Space:_1999) ) a fun scifi plot device being that there's this space drive system that gets you there really fast, but unfortunately kills everything that's in its wake.

Stories for grown-ups, please

[drwho]

Anyone who has any knowledge of space travel knows the issues raised in the referenced article. If you didn't care about space, you wouldn't read the article. Please, can we have reference to more scientific articles which advance the knowledge of geeks (that's what slashdot is for, remember)? I feel dumber just for having read that article.