Finding ET life (Interstellar Travel)

Last updated: 30/01/01 - entire text

Aside from the more conventional methods of looking for extra-terrestrial life by SETI and interplanetary craft, visionary scientists such as Freeman Dyson and Michio Kaku believe that we may be able to contact other civilizations by sending probes to them.

	The British Interplanetary Society's Daedalus
	The Daedalus is probably one of the most well-known concepts for an interstellar spacecraft, having been worked out to the finest detail by the British Interplanetary Society. Powered by nuclear fusion, Daedalus would have weighed 49,000 metric tonnes and required 27,000 tonnes of helium-3 for fuel (which is not available on Earth, but luckily is available elsewhere - in Jupiter's atmosphere). Daedalus is an unmanned spacecraft which was intended for a one-way trip to Barnard's Star (if you wanted to slow it down and turn it around again, the amount of extra fuel required would unfeasible). Barnard's Star is 5.98 light years away, and travelling at an average speed of 0.15c (15% of the speed of light), Daedalus would have taken 50 years to get there. Original image courtesy British Interplanetary Society.

These probes would be accelerated to vast speeds, far greater than that of the Voyager or Pioneer probes (which are, as yet, the only spacecraft to have ventured outside the orbit of Pluto) - speeds that would be an appreciable fraction of the speed of light, nature's 'top speed'. This would be done in any number of ways; craft could be accelerated to such speeds by using nuclear fission or fusion powered rockets, huge laser-powered solar sails or anti-matter/matter reactions.

	An interstellar solar sail
	This is an artist's rendering of a multi-stage interstellar solar sail. Laser light from Earth (or a transmitter in Earth orbit) would be beamed at the sail. The first (white) stage would focus and redirect this light onto the second (yellow) stage. This second stage would then in turn focus and redirect the light onto the final (brown, top middle of image) stage. The main advantage of solar sails is that they don't need to take any fuel with them - instead, energy, in the form of light, is beamed to them from a 'home' system. Image courtesy NASA/JPL.

		Technical diagram of Project Orion. Project Orion was devised during the 1960's by General Dynamics, and is a 'nuclear pulse rocket'. Essentially, it would work by dropping a nuclear bomb out of its rear and detonating it, thus being pushed forward by the force of the explosion. 250,000 nuclear bombs would be required to propel its 400,000 metric tonnes to 1.6% the speed of light. Unsurprisingly, Project Orion is now widely derided as being astoundingly inefficient and incredibly unsafe. Courtesy General Dynamics.

Such interstellar craft have been planned in detail by many space enthusiasts although national space agencies still see them as being very far in to the future. However, NASA have launched a Breakthrough Propulsion Physics (BPP) research group aimed at investigating 'alternative' methods of travel that could go faster than the speed of light through scientifically controversial methods such as 'superluminal quantum tunnelling' and the use of zero-point energy.

Discounting the frankly long-term projects proposed by the BPP, we won't be able to go faster than the speed of light to reach other stars - in fact, we probably won't be able to reach more than 10% of the speed of light without great difficultly.

So, travelling to the star closest to Earth, Proxima Centauri, would take 4.22 years at the speed of light, and consequently much longer if we went any slower. Several decades (which is how long it is likely to take us to get there) is a long time and any humans on board would have to be kept healthy and happy for that time. This would test our present food and water recycling systems to the limit. And even then, Proxima Centauri isn't even a particularly interesting star - as a binary system with Alpha Centauri, even if it does have a solar system with planets, we can be fairly sure there isn't any life. To visit 'interesting' stars would mean going further than 4 light years - which could take up to 100 years for any travellers on board.

	The NASA/JPL Thousand AU Probe (TAU)
	Strictly speaking, the NASA TAU is not an interstellar craft - it was termed an 'interstellar precursor mission'. Powered by a nuclear reactor and accelerated using a stream of xenon particles, the TAU would travel at 95 kilometers per second (roughly 3.3% the speed of light). On its way out of the Solar System, the TAU would drop off the Pluto Orbiter. This is of course only a conceptual mission design made many years ago; NASA has no plans for any interstellar precursor missions in the near future. Original image courtesy NASA/JPL.

It's extremely doubtful as to whether we'd be able to sustain a human population for 100 years without them dying from lack of food/oxygen/essentials or going completely crazy - after all, the people who actually arrived at the destination star would be the children or grandchildren of those who first set off. These types of ships where multiple generations of explorers are involved are called Generation Ships.

However, with recent breakthroughs in genetic engineering and our understanding of human biology, it may be possible to put humans in a state of suspended animation (a kind of human hibernation). This does not necessarily mean 'freezing' them, although that is a possibility. It merely means slowing down the metabolic rate of humans so they do not require so much food, oxygen or energy (the metabolic rate of a human is the rate at which is uses up energy). If we did this, then the problem of 100 year flights would be lessened - keep in mind though that this still does not lessen the other problems of such a flight, including what happens when something on the ship breaks down, as it inevitably will do after 100 years.

Of course, this is assuming that we want to send humans in the first place - why not just send unmanned probes? Unmanned probes would be able to accelerate much faster than manned ships (since humans cannot withstand high G forces during acceleration) and they would be able to travel faster since they would be lighter. Moreover, you wouldn't have the problems of sustaining a human population.

Naturally, all these ideas are simply that - ideas. For the moment. NASA scientists freely admit that interstellar travel is entirely possible using some of the ship designs outlined above, even if they would require a huge engineering effort to produce. There's no doubt that someday in the future, the SETI project will not be the only way to contact alien intelligences around other stars.