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

[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

[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

[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

[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

[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]

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.

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:Painted red and whote in hommage to Hergé

[maxwell demon]

I think your title was damaged by a radioactive particle.

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?

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,