Monday, July 27, 2009

Accidental Orion?

Of all seriously proposed space concepts, the Orion drive most lends itself to organ music and black capes with high collars. It invites the question, "You want to launch yourself into space by setting off hundreds of WHAT?" (For those of you not familiar with this remarkable concept, the answer is 'atomic bombs.') The chief potential advantage of Orion is that it combines enormous thrust with high specific impulse – the only space drive able to achieve 'torch' performance without invoking technomagic. The chief disadvantage is left as an exercise for my readers.

This idea was first proposed in 1947. Not, as I would have supposed, by Dr. Strangelove Edward Teller, but by his partner in inventing the US hydrogen bomb, Stanley Ulam. In 1958 a formal study was launched as Project Orion, hence the name still used for this drive. (NASA, perhaps seeking to rehabilitate the noble celestial hunter, has also dubbed its new manned spacecraft Orion, ensuring future confusion among space geeks.)

Even a launch site was proposed, with a colorful if awkward name: Jackass Flats, Nevada. But growing public doubts about atmospheric nuclear explosions doomed Orion, and the 1963 test ban treaty nailed shut the coffin. Of course it walks among the undead in the science fiction and space geek communities. Not the least of its appeals for its fans, I suspect, is its sheer political incorrectitude – no great surprise that Jerry Pournelle is a leading proponent.

Whether it would work in practice remains unanswered, and is likely to stay that way for some time to come. Building a spacecraft, even a massive one, to stand up to repeated self-nuking could be a significant engineering challenge; likewise smoothing out the bumpy ride. Concept sketches show Orion sitting above its pusher plate on what look like enormous automotive shocks, described by Wikipedia as 'one of the most difficult design features.' To solve the lesser problem of popping bombs out the back at regular intervals, the designers apparently consulted the Coca-Cola company, which knew something about dispensing machines.

What leads me to write all this, however, is something I only discovered yesterday – that the concept was inadvertently tested in 1957, a year before Project Orion formally commenced. It happened during Operation Plumbbob, a series of nuclear tests at the Nevada Test Site. Plumbbob later became notorious because after one test, 'Smoky,' more than 3000 GIs performed maneuvers near Ground Zero. People in the 1950s were cavalier about radiation. But our concern here is another test, 'Pascal-B,' set off a few days earlier.

Pascal-B was the second-ever deep underground detonation of a nuclear weapon. Like its predecessor, Pascal-A, it was a safety test intended to produce only a minuscule nuclear yield, about 1 kg TNT equivalent. Instead it delivered nearly a third of a kiloton. But what makes it noteworthy is the unknown fate of a steel plate that plugged the shaft.

Physicist Robert Brownlee, in charge of preparations, thoughtfully considered the possibility that Pascal-B would deliver more – lots more – than its intended yield. Among other things he calculated the shock wave that would move up the 500-foot shaft when instruments just above the test 'device' were vaporized. At the top of the shaft was a cap plate, reportedly four feet in diameter, four inches thick, and weighing about a ton.

According to Brownlee's calculations, the cap plate would be blown off at a modest 56 km/s.

A high speed camera was duly positioned to film the liftoff of the plate. It was not quite high speed enough, because the ascending plate was only caught in one frame of the film The speed and field of view of the camera are not reported, so the minimum speed cannot be determined, but Brownlee described it as 'going like a bat.' Well, yes. I imagine so.

But how far did it go? Did the US send an impromptu Orion mission into space more than a year (oops!) month before Sputnik? Alas, probably not. Even if it was still intact when filmed during its unscheduled launch, atmospheric deceleration would have its say. Meteors of that mass are fully decelerated by passing through the atmosphere and 'simply end up as a falling rock.' But wherever it went, what a spectacular way to go.

Related links: Naturally Orion is discussed in more detail at the Atomic Rockets site. And I previously blogged here about the broader significance of nuclear weapons.


Citizen Joe said...

Much of the inertial confinement fusion is essentially Orion drive concept. A small shell of fusion fuel gets suspended inside the combustion chamber (probably magnetically). Then a laser detonates the fusion pellet causing a nuclear explosion. The blast gets blown out the back. Additional thrust can be added by dumping extra mass 'behind' the fusion pellet (like a chunk of ice). This is very much an impulse drive and your delta-v's can pretty much be physically counted by the number of fusion pellets you have.

Nyrath the nearly wise said...

And a friend of mine used the idea to make a diorama for a lunar model contest.

Rick said...

Citizen Joe - IC fusion has features in common with Orion, but without the, ah, dramatic quality of individual bangs a significant fraction of a kiloton. :-)

Nyrath - Great diorama! One question not answered in the link is where the Moon was when the plate was ... launched. This should not be hard to figure out, given the known time of the Pascal-B test, for someone familiar with using ephemerides.

Going straight up from Nevada probably never intersects the lunar orbit, but if you assume the plate was partly decelerated it might have gone into an elliptical Earth orbit, or a closed solar orbit that would eventually encounter the Moon.

Also, thinks to your link I caught a stupid mistake I made - I was somehow thinking Sputnik was in 1958. (Yikes!)

There is one other puzzle in Brownlee's description. He says the shock wave took 31 milliseconds to travel some 150 meters, which is only about 5 km/s. So how would the plate be popped off ten times faster than that?

Citizen Joe said...

The shockwave isn't what knocked off the plate, it was the heat and pressure build up after that. Likewise, if you swing a bat at a ball, the speed of the ball is is related to the transferred momentum, not the velocity of the bat.

Anonymous said...

Propulsion via nuclear explosions, an interesting rocket design that is featured in a few hard science fiction stories featuring interplanetary travel. As noted by the initial blog and other sources pertaining to the technology in question, the real hitch in the whole Orion Design is effectively how to keep the space craft, and specifically the pusher plate, in one piece from not one or a few, but a series of nuclear explosions directed at it. It wouldn't be impossible and rarely improbable, but I have a feeling that trying to find that little answer to the survival question is going to be hard. Very, very hard.

That notation about plumbbob is rather interesting in that whatever data that could have been salvaged might have been used to further refine the Orion Drive idea. However the idea that it could have sent that cap plate into orbit is something of a stretch. Correct me if I'm wrong, but if a single nuclear explosion is only able to fling out dust into the atmosphere, then the chances of a one metric tonne metal plate going into orbit are extremely low, if at all.

Though I have to admit, the idea of using the Orion Drive as a surface-to-orbit rocket gives me the knee-jerk response quite similar to what was quoted in the blog post. The earth's environment, in my humble opinion, is scarred and damaged enough as is. Pretty sure that regular nuclear launches aren't going to make the process of environmental recovery easier.

qwert said...

Well i have often thougth, that the orion pulse propulsion and the space elevator would complement each other nicely. You would use an elevator to asemble an Orion in orbit and the use it at a safe distance from Earth for interplanetary travel. You would have to move it away from geostationary orbit by conventional rockets, but still you would not need to blst off from earth surface.

It´s sad that such a concept was entirely abandoned, but I can not stop imagining Ahmadinejad saying that Iran´s nulear bombs are for peaceful space travel. Better have a clear distinction between peacefull and military use of nuclear energy.
That said I would be among the first to support new research into Pulse propulsiĆ³n.

Rick said...

Citizen Joe - Apparently I know less about momentum transfer than I thought. :-) Which is why Brownlee is a physicist and I am not.

Anon - When Project Orion was officially established in 1958, the people in charge surely knew about the Plumbbob episode. (Though Ulam had suggested the idea a decade before Plumbbob.

But I certainly agree that building a spacecraft to withstand some 800 nuclear bangs is ... challenging. And I agree that it is very unlikely, at the least, that the plate got into space, no matter what its initial velocity. Atmospheric deceleration would slow it down or vaporize it, whichever came first.

qwert - In a way they complement each other, but once you're in orbit Orion has no special advantage over gentler nuclear drives (and is extremely wasteful of nuclear fuel). Milligee acceleration is ample in deep space.

Orion would simplify landing on other planets, but it complicates ground operations. It can't safely land or take off anywhere near your bases, and you'd need a special shielded surface transporter just to exit the ship.

Fusion pulse propulsion, on the other hand, has a big future - if we can ever master controlled fusion.

Anonymous said...

A nuclear-propellant kinetic-kill weapon. That just seems... Backwards, somehow.


Rick said...

LOL ... But not the first time things in space turn out to be contrary to everyday terrestrial experience!

Anonymous said...

"Anon - When Project Orion was officially established in 1958, the people in charge surely knew about the Plumbbob episode. (Though Ulam had suggested the idea a decade before Plumbbob.

But I certainly agree that building a spacecraft to withstand some 800 nuclear bangs is ... challenging."

The son of one of the scientists wrote a book about Project Orion; I'm not sure about the name; that described it from the late 1950s until it's cancealation in 1963. They did several tests, in conjunction with nuclear bomb tests of the time; several of the scientists were on both Project Orion and the various nuclear test shots at the same time. (and that steel plate probably made a pretty good shooting star) An Orion landing and taking off from, say Mars, would be spectacular.


Calsir said...

"Going straight up from Nevada probably never intersects the lunar orbit, but if you assume the plate was partly decelerated it might have gone into an elliptical Earth orbit, or a closed solar orbit that would eventually encounter the Moon.

I agree that it is very likely that the plate intersecting the moon is impossible. I apologize for the convolution :). About the elliptical earth orbit: it would surely re-enter atmosphere, since its perigee would be below the earth surface. I also think that it is more likely that a closed sun orbit would bring it back to earth than to the moon, as earth is a bigger target :).

Of course, being shot at 6 times earth escape velocity in the lower (denser) atmosphere does not give you much chance to survive the initial phase of the flight.

Rick said...

Oops, you're right - an elliptical orbit would impact the surface. Not that it really matters, since the plate was probably vaporized in the first few km.

Eric said...

My father is an Atomic Veteran. He was in those maneuvers. BTW, they were Marines.

Rick said...

Eric - Did he have anything to say about the experience? I hope he had no ill effects.

My source just said 'servicemen' - at least I didn't say 'soldiers.' :-) I guess they aren't strictly GIs either, though I just read that (to my surprise) 'gyrenes' goes back a century. I'd assumed it originated in WW II.