Orion (the spacecraft, not the constellation)
Published on Nov 28, 2005 at 7:57 pm.
2 Comments.
Filed under books, rockets, space exploration.
I have been reading a very interesting Dyson’s Project Orion Book
Now, for those who don’t know about the Orion Project, let me explain. I first heard about this while growing up (late elementary school, early junior high, something like that). I read about it in a book about space travel. For the life of me, I can’t remember who wrote the book. I am thinking Asimov, but if it wasn’t by Asimov, then I am sure that he did write something along those lines. The book had a section on interstellar spacecraft, and it explained that ordinary chemical rockets simply could not gain the speed needed. Nuclear propulsion was the answer. Two types of nuclear spacecraft were described. One, the Daedalus, was expected to scoop up hydrogen from the interstellar medium along the way and fuse it to provide power for propulsion — a sort of interstellar ramjet. The other, Orion, was propelled by dropping atomic bombs out of its back end, and the resulting explosions would propel the craft. At the time, it seemed preposterous to me, and the Daedalus seemed the be the way to go.
Well, years passed. I went to college, then graduate school. I learned a lot of physics, and I also learned a lot more about the technology that needed to be developed for these ideas to work. I also learned about a third form of nuclear propulsion: the nuclear ion drive. In this third system, a nuclear reactor would provide power to operate an ion drive engine. An ion drive generates thrust by accelerating ions to exceedingly high velocities with electric fields and shooting them out the back of the spacecraft. Any rocket thrust is proportionate to the rate of mass expelled and to the relative velocity with which it is expelled. There is a formula called the “first rocket equation” that is used to compute this. Chemical rockets can accelerate a lot of propellant to fairly high velocities. This gives massive thrust, but you run out of propellant very quickly. Ion drive shoots ions out one at a time, but at much higher velocities. The rate of mass expelled is very low, so despite the much higher velocity, the thrust is rather low. However, each ion has far higher momentum than the corresponding atoms of a chemical rocket, so ultimately the corresponding final speed of the rocket is much higher, according to what we call the “second rocket equation,” which says that the final velocity is proportionate to the exhaust velocity times the logarythm of the ratio of the initial and final masses of the rocket. We now have constructed ion drives, but they get their energy from solar power rather than nuclear reactors.
So, back to the Orion spacecraft. I had always been under the impression that both the Orion and Daedalus craft were simply concepts. I presumed that some sort of feasibility study had been done to see if such things could one day be be built. With my physics background, I realized that the Orion would be much easier to build, and that it would require far less technological development. After all, we know how to make fission bombs, but we have a hard time with controlled nuclear fusion. Also, I also learned that atomic bombs don’t really just vaporize everything nearby as most people think. So, a “pusher plate” with an ablative coating that would vaporize and shoot off of the pusher plate with VERY high velocity would provide an extremely large thrust. The Orion was merely an engineering problem, not a technological one. You just needed to toss a nuke out the back, let it explode, toss out another one, etc. Keep it up, and the successive pushes would accelerate the spacecraft to very high velocities. Still, these are just wild ideas, right? Wrong. This book has opened my eyes quite a bit.
Apparently, the US Department of Defense had seriously studied the Orion concept, and had even built a small working model powered by chemical explosions!!!! They even had talked with the same people who designed nuclear submarines to design prototypes of the crew compartment of the spacecraft. I was completely shocked by how far work had progressed. I never knew! Because nuclear explosions are pretty large, nuclear pulse propulsion (the official designation) has a huge thrust, and so the Orion could be a VERY large and heavy spacecraft — much heavier than any spacecraft propelled by chemical rockets. This means that an Orion could carry more crew in comfortable quarters, along with sufficient air, water, and food, for an extended mission. The living conditions and duration of mission would be similar to that of a small nuclear submarine. There was talk of sending manned spacecraft to Mars, Jupiter, and even Saturn by 1980. This spacecraft would have opened up the solar system to human exploration! What happened?
Well, first of all, there was the issue of national security. Most of the work was classified. Why? Well, it wasn’t because the military was afraid of some other nation building an interplanetary spacecraft. Obviously, if one was to be built, we’d want to do it first for the sake of national pride. But, there were far more practical reasons. First of all, nuclear pulse propulsion permitted VERY large craft. It was possible to launch a flying warship using the technology. At the time, we were in the midst of the cold war. Even without a flying warship, a single Orion could launch and deliver enough thermonuclear warheads to wipe out an entire nation. A second, though no less important reason to keep the technology classified, was that some things survive nuclear explosions, and quite a lot of research went on to explore these materials and the conditions under which they survived in the hope of using them to construct the pusher plate. Naturally, we didn’t want anyone to know how to build tanks and bunkers capable of surviving nuclear explosions. Thirdly, the Orion needed rather small controlled explosions. Too big of an explosion would simply damage or destroy the craft. It turns out that it is rather tough to build a bomb that explodes with a small nuclear blast. The technology that was needed to build the bombs that would power the Orion is the same technology that it takes to build suitcase nuclear devices. Obviously, we didn’t want to tell the Soviets how to build such devices, nor did we want them to figure out the properties of such devices from backwards engineering from the specifics of the bomb deployment system or the pusher plate itself. So the whole project was kept under wraps. Even today, many of the propulsion details are classified, since the technology for the nuclear pulses is exactly the technology that terrorists would dearly love to acquire (not for space travel, though, but to blow things up).
At any rate, I was surprised to find how far along the project got. It finally died, though, perhaps because chemical rockets seemed to be getting the job done for less money. Security would always be an issue with Orion technology. And finally, nuclear pulse propusion, created by setting off atomic bombs, is simply not terribly environmentally friendly. An Orion would not be something that you’d want to launch from Earth’s surface. Now, if we had a permanent space base, such as in Earth or lunar orbit or even on the lunar surface, then that would be another matter. I’m not through reading the book, so I don’t know the end of the story yet (if it says). Still, I thought that this would be an interesting thing to blog about.
-Astroprof
Astroprof on August 25, 2006 at 2:50 pm: 1
Note: Since I wrote this, NASA has decided to name the new crew vehicle Orion. I wrote about that here:
http://astroprofspage.com/archives/202
Chris Berman on March 9, 2009 at 12:16 pm: 2
I love the concept of the Orion Spacecraft. I used both it and the alternative NERVA, nuclear rocket engine in my novel THE HIVE, just released.
Look at my site under “science in THE HIVE and Nuclear Power and Space.
http://www.freewebs.com/chisbfla