T.I.E. Fighter developement proceeds according to schedule

Powering the Future: Soup-Can Spacecraft and Postage-Stamp Engines

Inside a sprawling, crowded building at NASA's Jet Propulsion Laboratory is a small window to the future of space exploration. Busting out of one end of the building, a vacuum chamber the size of a motor home houses an engine that has been running for nearly three years.

It is months beyond its life expectancy. Its power source is unlimited. Its fuel is plucked from the air we breathe. And it is 10 times more efficient than a chemically powered engine.

This is rocket science for a new millennium.

It is called an ion thruster. No pipe-dream technology, this test engine in a JPL vacuum chamber is a twin of the one powering the Deep Space 1 spacecraft, which has logged more than 167 million miles (269 million kilometers) in space since its launch on Oct. 24, 1998.

John Brophy, an engineer who has worked on the ion engine since 1984, heads up a hill on the JPL campus toward Building 148 where he works in every day. As he walks he explains that he and his colleagues are working to develop tiny versions of the ion engine, thrusters no larger than a postage stamp that could power spacecraft the size of soup cans.

[...] Small world

Ion technology is one of a handful of "electrical propulsion" systems that might one day power such tiny probes.

Colleen Marrese works in the same lab as Brophy, but she spends her day working on things too small to see.

Using "field emission cathode" technology similar to what lights up a flat-panel computer screen, Marrese is helping to develop efficient microscale cathodes for very small propulsion systems. Some of these systems would fit into a square the size of a postage stamp -- to give a small but adequate impetus to a miniature spacecraft.

Some 50,000 tiny cones are deposited on one square millimeter of a silicon wafer. Each cone is about one micron tall (a human hair is about 50 microns thick) and pokes out through a small aperture, leaving a gap all around the cone of about half a micron.

A voltage of 50 volts is applied across the gap, from the cone to the aperture. In such a small distance, this voltage creates a strong electrical field compared to the surrounding space. The high electric field allows electrons to tunnel out of the tips into the vacuum.

Other researchers at JPL are working on ways to harness these electrons to produce a small thrusters.

This overall micro-propulsion effort at JPL is headed up by Juergen Mueller, and in addition to Marrese's work, there are several thrusters and propulsion system components under development. Marrese anticipates that microscale electric thrusters will be developed enough to qualify for a mission in about two years.


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