Ken Tapping, June 4, 2004

None of us can fail to be impressed at the sight of a large rocket being launched. If you are lucky enough to be at Cape Canaveral, you will see the spurt of flame and smoke as the engines ignite, followed by the slow rise of tonnes of spacecraft on a pillar of fire. Then a few seconds later, when you have almost forgotten to expect it, the sound arrives, unbelievably loud, and hitting your chest like a physical blow. The experience inside the spacecraft is even more dramatic. During launch, shuttle astronauts are subjected to such extreme vibration that they cannot focus their eyes. At the moment we get to where we are going by sitting on top of hundreds of tonnes of explosive and burning it all in minutes to give the spacecraft a big, but extremely precise shove. It then coasts to its destination. The problems of launching spacecraft cost-effectively are what make many countries, like Canada, prefer to spend the money on developing the spacecraft itself and pay someone else to launch.

Fortunately, we are beginning to see solutions. There are now spacecrafts wandering around the Solar System that are using ion engines. Instead of chemicals, these spacecraft carry a tank of inert gas, usually xenon. Using high voltages, some of the electrons are stripped from the xenon atoms, and the resulting xenon ions are accelerated electrically to almost the speed of light and expelled from the spacecraft in a beam. These engines do not produce the millions of kilograms of thrust produced by chemical rockets; they are more in the kilogram range, or less. Their big advantage is that you can leave them running for years. Fuel consumption is small, and even if the acceleration is slow, after a while you will be really moving! Such a gentle thrust provides more control. The problem is that ion drives don't work in an atmosphere, and even if they did, the thrust would be too small to lift the spacecraft off the ground.

However, the big plus is that we now only need to lift the spacecraft into orbit, and leave the rest of the trip to the ion engines. This makes the launcher smaller and cheaper, and less polluting, and opens the door to new kinds of launcher, such as combinations of air breathing ramjets and rockets, now under development. Over the next decade or so, expect to see more ion-powered robots exploring the Solar System, perhaps even dipping into the top of a planet's atmosphere to refuel, making it possible to continue their missions almost indefinitely.

This will be great for the Solar System. However, getting to the stars is another issue altogether. After the Sun, the next nearest star is Proxima Centauri. The light from this star takes 4.3 years to get here, travelling at 300 thousand kilometers a second. We won't hit speeds like that for a while, if ever, so using current technologies we can expect trips to even the nearest stars to take decades or centuries. Unfortunately, "Warp Drive" is still in the realm of Science Fiction. However, not long ago, ion drive was too.

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Ken Tapping is an astronomer at the National Research Council Herzberg Institute of Astrophysics (NRC-HIA), and is based at the Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9 Tel (250) 493-2277, Fax (250) 493-7767,
E-mail: ken.tapping@nrc-cnrc.gc.ca