April 18, 2008

Ion Thrusters To Receive Debut In Space

Researchers at Hampshire defense and security firm Qinetiq are currently testing ion thrusters, which they hope will one day bring spacecraft to the planets through solar energy.

The ion engines create thrust by the acceleration if ions by electromagnetic forces. They make use of the fact that a current flowing across a magnetic field creates an electric field directed sideways to the current.

This is used to accelerate a beam of ions of xenon away from the spacecraft, thereby providing thrust.

Xenon pumps "are cooled down by the helium compressors to approximately 20 degrees Kelvin," explains Neil Wallace, technical lead of the electrical propulsion team at Qinetiq.

"So any gas atoms that strike those panels, they freeze. After you've been running the engines for a number of hours you can see a frost - it looks like snow - which is actually frozen air and xenon."

"The ions are traveling very fast, at approximately 50km a second," he says.

"When they strike the other end of the chamber, they actually knock atoms off the surfaces they strike; it's analogous to sand-blasting on an atomic level."

The T5, an ion engine developed by Qinetiq, will get its first flight on ESA's Goce spacecraft, which will fly only 200-300km above the Earth.

In space, ion engines will draw electric power from solar panels, generating a thrust equivalent to the weight of a postcard.

This incredibly gentle thrust could, in theory, take a spacecraft beyond our Solar System, if sustained for long enough.

"This spacecraft is [traveling] at a speed of about eight and a half kilometers per second," says Neil Wallace.

"As it travels around the Earth, it's going through the upper atmosphere and it experiences a buffeting.

"They need to compensate that buffeting very accurately and that's what we're doing, so we're actually providing cruise control for that spacecraft."

The craft will be able to map out the variations in the Earth's gravity field.

Smart-1, the European mission to the Moon, and NASA's Deep Space 1, which flew by a comet, have both used ion thrusters, and they will also be used in future ESA missions such as BepiColombo, which will go to Mercury.

Goce is slated to launch from the Russian space port of Plesetsk this year. Neil Wallace said watching the event may be nerve racking for those involved with T5's development.

"You spend 10 years working on a mission, treating the components and equipment like a newborn baby. You never take it out of the clean room, and then you put in on the top of 100 tons of high explosive and set light to it," he said.

"But no, the most exciting time for us will be when that spacecraft comes over the horizon and the ground station picks it up, and you can see the engines are doing what we've always said they will do."


On the Net:

QinetiQ Ltd T5 Ion Thruster