Hard Science: It's Not Necessarily a Limitation

Science fiction, or 'speculative fiction,' to use a more current term, would seem to be easier for a writer to handle if he or she doesn't bother with 'hard science' - that is, what we know today about how the universe works.

In a way, that's true. The Andre Norton stories, for example, often had science-fictionish accouterments like starships and blasters - but the author didn't bother with serious science: apart from generally seeing to it that things fell down, rather than sideways, for example.

Quite engaging stories can be written with a blithe indifference to quarks, specific heat, or tensile strength.

But, I think sometimes knowing a little science can help.

Take interstellar spaceships, for example.

Just Make it Look Cool

We're pretty familiar with the Star Trek or Star Wars approach: make a model that looks cool, and go with that. No problem: it works in the movies, and in written fiction.

But, there's something to be said with sticking with science as we have it.

Although there are some really promising theoretical possibilities on the horizon, involving aggressive warping of space-time, we probably won't be seeing 'warp drives' any time soon. In another blog, I opined that, depending on how you looked at current knowledge and technology compared to milestones in rocket technology and orbital mechanics, we might be anywhere from fifty to two thousand years away from having a practical 'warp drive.' (May 7, 2009)

But, that's wild guesswork at best.

Take Current Science and Technology, Add Imagination

There are quite a few might-work ideas out there, including light sails pushed by titanic laser arrays. Many of these have the advantage of both being something that might, plausibly, work - and having specific requirements that restrict what a vehicle would look like, and how it would perform.

That's not necessarily a bad thing. While it might be cool to imagine a spaceship shaped like, say, a teddy bear or a tennis racket, I think the appeal might fade a bit after a few chapters.

I went digging in my notes today, and found a design that isn't all that different from the rockets we use for space travel today.

Steam-Powered Space Ships?!

A philosopher in ancient Greece, Archytas of Tarentum, made what may be the first rocket-propelled vehicle about twenty three centuries back. It was a model bird, suspended from a ceiling, with a container of water and a heat source inside. The water turned to steam, shot out the back of the bird, and made the thing swing around, 'flying.'

Don't knock it: the gadget may have been a blast at parties. But it wasn't of much practical use.

Fast-forward a few centuries, and you get to Hero of Alexandria's aeolipile. It shot steam out of two nozzles , rotating a sphere. Quite an accomplishment: but there wasn't an effective method for getting work done with steam until the 1700s.

Gunpowder was developed in China, maybe as early as 850, and possibly as a spin-off from other research.

It would be possible to have a steam-powered space ship, provided there was a way to get the steam hot enough. Steam rocket engines have been built: one was used in the 1960s as the engine of a drag racer.

The idea of an atomic rocket - a vehicle using a nuclear reactor to heat water or some other liquid and squirt the resulting gas out a nozzle to produce thrust - is decades old, and will probably be done some day.

But, since there are limits on how fast the gas can be pushed out, even an 'atomic rocket' probably wouldn't be practical for an interstellar space ship. The problem is that a rocket's performance is linked to how fast it can push stuff off the vehicle - how fast its exhaust is.

And no, it's not that 'a rocket can't go faster than its exhaust.'

On the other hand, in the case of rockets: Faster is generally better when it comes to exhaust.

Beamed Core Antimatter Drive: Better Than a Steam-Powered Space Ship

The fastest that matter or energy can travel is the speed of light. Actually, there may be some work-arounds for that - but that's the sort of 'warp technology' that we aren't even close to having. Probably.

For rockets, the ideal would be to have an exhaust velocity around speed-of-light.

There are a few ways to do that. One is to get duct tape and attach an ordinary flashlight to your ship. Turn on the flashlight, and photons shooting out at speed-of-light will produce thrust. Not enough to measure, let alone move anything significant: but it does produce thrust.

Another is to use a beamed core antimatter drive.

We don't, quite, have the technology to build one: but we're very close. The beamed core antimatter drive is described on a website associated with the University of Alaska-Fairbanks, along with some other rather theoretical ways of getting to the stars.

This particular 'star drive' uses protons and anti-protons for fuel. They're brought together, annihilate each other, and then things get interesting:

"...Protons and Antiprotons are injected into the magnetic nozzle, where they collide and annihilate producing a collection of pions. The uncharged pions are unaffected by the magnetic field and fly off, almost immediately decaying into gamma rays. These gamma rays would have to be stopped by some sort of high-density shielding. The charged pions shoot down the magnetic nozzle at what is essentially light speed, after traveling a distance of 21 meters in 70 nanoseconds, they decay into muons and neutrinos. The muons are longer lived, they travel 1.85 kilometers in 6.2 microseconds (99.5% light speed) before decaying into electrons and positrons (and more neutrinos). As you may be aware, the performance of a rocket is mainly limited by its exhaust velocity. The Beamed core drive would have an exhaust velocity of near light-speed. Allowing (with sufficient amounts of antimatter) acceleration up to almost any arbitrary percentage of the speed of light...."
(Beamed Core Antimatter Drive)

There are some huge engineering issues to be resolved before anything like this can be done. A few particle accelerators have been set up to sort out protons and anti-protons, and store the things in very tiny quantities: but something like this would need tons of both. And this is a case where you definitely do not want to be anywhere near a fuel spill.

Also, we don't have the magnetic containment devices that would be needed. Superconducting magnets may be the route to go on this and (somewhat) high-temperature superconductors are around now.

So: What Would a Starship With a Beamed Core Antimatter Drive Look Like?

The drive itself would be huge. Besides whatever is used to contain the protons and anti-protons, there's the reaction chamber, then a 21-meter-long section to contain and direct positive and negative pions, and finally a 1.85-kilometer-long section that contains and directs positive and negative muons. After that, a stream of electrons and positrons, plus neutrinos, shoots off into space, pushing the ship in the opposite direction.

The engine, because of how fast the exhaust particles travel and how rapidly they break down, would have to be 1.871 kilometers long, plus the reaction chamber - or, in English units, a tad under a mile and a quarter long.

If built, it might be mostly an open framework holding coils, rings, or whatever geometry is required to generate the magnetic fields.

Impressive, I think. Add a plausible-looking set of containment vessels for the fuel, habitats for the crew, cargo modules, and you've got a whacking great starship: based on a bit of science and a bit of imagination.

Related posts:

• "A Serious Search for Other Worlds, Life, and - Maybe - Extra-Terrestrial Intelligence "
  Apathetic Lemming of the North (last updated July 15, 2009)
• "Warp Drive Might Not Be Stable: Physcisists Take Another look at Alcubierre's Work"
  Apathetic Lemming of the North (June 12, 2009)
• "Warp Drive: Yes, it May Be Possible; But Don't Hold Your Breath"
  Apathetic Lemming of the North (May 7, 2009)
• "Serious Discussions of Warp Drive"
  Apathetic Lemming of the North (May 24, 2008)
• "Interstellar Travel: Difficult, yes; Impossible; No - NASA"
  Apathetic Lemming of the North (April 30, 2008)

Background:

• "Beamed Core Antimatter Drive"
  The Physics of Starship Design, Physics Department, University of Alaska-Fairbanks
• "High Temperature Superconductors"
  Georgia State University