Rocket Ride Spaceships

Image Credit: John Frassanito & Associates, Inc This low-thrust spaceship (an artist's concept) is propelled by an ion engine and powered by solar electricity. Eventually the craft will pick up speed - a result of relentless acceleration - and race along at many miles per second.

"A rocket is anything that throws something overboard to propel itself forward," Johnson pointed out. (Don't believe that definition? Sit on a skateboard with a high-pressure hose pointed one way, and you will be propelled in the opposite way).

Leading candidates for the advanced rocket are variants of ion engines. In current ion engines, the propellant is a colourless, tasteless, odourless inert gas, such as xenon. The gas fills a magnet-ringed chamber through which runs an electron beam. The electrons strike the gaseous atoms, knocking away an outer electron and turn neutral atoms into positively-charged ions. Electrified grids with many holes (15,000 in today's versions) focus the ions toward the spaceship's exhaust. The ions shoot past the grids at speeds of up to more than 100,000 miles per hour (compare that to an Indianapolis 500 racecar at 225 mph) - accelerating out the engine into space, so producing thrust.

Where does the electricity come from to ionize the gas and charge the engine? Either from solar panels (so-called solar electric propulsion) or from fission or fusion (so-called nuclear electric propulsion). Solar electric propulsion engines would be most effective for robotic missions between the sun and Mars, and nuclear electric propulsion for robotic missions beyond Mars where sunlight is weak or for human missions where speed is of the essence.

Credit: JPL's Space Place. The inner workings of an ion engine.

Ion drives work. They've proven their mettle not only in tests on Earth, but in working spacecraft - the best-known being Deep Space 1, a small technology-testing mission powered by solar electric propulsion that flew by and took pictures of Comet Borrelly in September, 2001. Ion drives like the one that propelled Deep Space 1 are about 10 times as efficient as chemical rockets.