Atomic surfing: A pulse-propulsion craft would detonate small nuclear bombs behind it, and could surf the shockwaves all the way to Mars in as little as one month (artist's impression pictured).
Credit: NASA
SYDNEY: What does it take to boldly go where no man has gone before? Conventional rockets fire hot gas through a nozzle to get thrust, but that can't get us to deep space.
Rocket scientists have come up with a raft of solutions – some remain in the realm of science fiction, but others verge on reality. Here's a selection of those that might one day carry us across the final frontier.
NUCLEAR PULSE PROPULSION
Propelling your spaceship by setting off teeny atomic explosions isn't as crazy as it sounds, according to NASA. A pulse-propulsion craft would detonate small nuclear bombs behind it, and could surf the shockwaves all the way to Mars in as little as one month. Leaving radioactive debris as space junk in the vicinity of Earth (or other planets) probably isn't a good idea, though.
SOLAR THERMAL PROPULSION
For this you'll need some serious bling: NASA's prototype uses a sapphire concentrator to collect light from the Sun or other stars and create a powerful beam to heat hydrogen gas, which is ejected through a nozzle to provide thrust. But it's worth noting that this method would not work on the dark side of a planet or far away from a star.
VACUUM-POWERED SPACECRAFT
Arthur C. Clarke used "vacuum fluctuation" to send characters to deep space decades ago. But G. Jordan Maclay of research company Quantum Fields LLC in Wisconsin, USA, says vacuum-powered spacecraft are possible. His idea is to build a spacecraft that harnesses the Casimir effect: the attractive force between two uncharged metal plates set a few micrometres apart, caused by quantum vacuum fluctuation in the electromagnetic field. As the plates move closer together, the force gets stronger, and Macleay's engine would use energy generated by moving the plates closer before separating them again. The catch? Materials engineers are still light-years away from making this technique practical.
MAGNETIC SAILS
Unlike well-known solar sails, magnetic sails are completely invisible. Much like the Earth's protective magnetic field, an artificial magnetic field around a spacecraft would deflect the solar wind. This would be used to provide thrust; acceleration would start slowly, but NASA says that after three months a magnetic sail-powered spacecraft could be zipping along at more than 280,000 km/h.
ARTIFICIAL GRAVITATIONAL FIELDS
Anti-gravity engines might be possible according to the controversial Extended Heim Theory, which attempts to reconcile general relativity and quantum physics. Scientists have reported anti-gravitational effects, generated with a spinning, superconducting magnet. Jochem Häuser, a physicist at the University of Applied Sciences in Salzgitter, Germany, says that this should produce particles called 'gravitophotons', which have both electromagnetic and gravitational properties. They would produce a gravitational field that pushes against the engine itself, thus accelerating a spacecraft.
Get it right
1 gram of antimatter annihilated with 1 gram of matter produces 2*c^2 of energy. C^2 is 9E+16, thus 0.002*C^2 = 180 TJ (teraJoules). A Space Shuttle main propellant tank contains ~750 tons of hydrogen/oxygen propellant. 1 kiloMole (18.015 kg) of H2/O2 when combusted produces 241.83 MJ (STP) thus 750,000 kg of the stuff is 100 TJ. Just 1.8 Shuttle ETs full of H2/O2 would be the equivalent of 2 grams of energy.
Perhaps you meant kilograms?
Ships that self-lift by their own bootstraps much to be desired
but there seems to be no clue how they'll do that. "Vacuum-powered spacecraft" and those powered by "Artificial Gravitational Fields" and "Dark Energy Warp Drive" seem to be in this category.
Antimatter, nuclear explosives, and solar thermal all use on-board heat and share a common limit, that of how much low-grade heat they can get rid of. Only some of the heat can be converted into propulsion power, the rest having to be dumped through a radiator. Non-pulsed nuclear fission powering a VASIMR engine, an alternative that was not mentioned, would also have that limitation. The VASIMR is soon to be tested on the space station, I seem to recall.
--- G.R.L. Cowan
external detonation has advantages
One plus of nuclear pulse drives is that very little of the heat is retained by the pusher plate. Most of the plasma flies off into space taking the heat with it. Nuclear Salt-Water Rockets also dump heat too rapidly for it to be a major issue because of the high venting rate of propellant. External fusion-pulse drives, like the system recently described by Winterberg, would also vent most of the heatload directly into the void.
Alternatively one can leave all the nasty mass/heat issues at home and ride a beam of light/ions/pellets to relativistic speeds. Slowing down becomes problematic without a "starbase" at the other end, but advances in superconductors might allow very high efficiency magnetic sails by the time we're pushing off to the stars. Or rather, being pushed off...