From Centauri Dreams :
The launch of the Dawn mission to the asteroids makes me think about solar sails. I realize that Dawn uses ion propulsion, about which more in a moment, but watching ion methods as they mature makes an emphatic point: We need to bring solar sail technologies up to the same readiness level that ion propulsion currently enjoys. And we need to be shaking out sail ideas in space. The Russian Znamya attempts at a ’space mirror’ were attached to a Progress supply ship, and interesting mostly in terms of their deployment problems, leaving the 2004 Japanese test of reflective sails in space as the only free-flying experiments I know about.
Which is not to say I’m a skeptic about ion propulsion. It will be fascinating to follow the performance of Dawn’s engines as the mission progresses. 54 feet of solar array produce the needed power to ionize their onboard xenon gas, which is four times heavier than air. The ions are then electrically acccelerated and emitted as exhaust from the spacecraft. The result is an engine of great utility over time, as JPL’s Keyur Patel notes:
“Each of our three ion engines weighs in at 20 pounds and is about the size of a basketball. From such a little engine you can get this blue beam of rocket exhaust that shoots out at 89,000 miles per hour. The fuel efficiency of an ion engine is an order of a magnitude higher than chemical rockets and can reduce the mass of fuel onboard a spacecraft up to 90 percent. It is a remarkable system.”
Remarkable indeed. Dawn’s engines will accumulate 2,000 days of operation during the course of its eight-year investigations, pushing the vehicle with about the same amount of thrust as the weight of a piece of paper in your hand. Days and months of thrusting add up, giving the vehicle an effective change in speed of about 37,000 kph by the end of its mission.
The history of ion propulsion goes back to the 1950s at least. Light sails might go back further to Tsiolkovsky, the Grandfather of Russian Spaceflight.
These technologies have been a long time coming and light-sails should be developed along side of the ion drive. Recent advances in launching laser tech (space-based) should be coupled with light-sail development as a way to shorten the length of human-based trips in the Solar System. Moon based lasers would be the ticket. The trouble is, any suffiently powerful propulsion unit could also double as a weapon. (kzinti lesson)
Another reason for the Chinese to establish Moon bases?