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NASA astronaut Franklin Chang-Diaz talked about interplanetary space travel during a talk at the Laboratory last week. The talk was sponsored by the International, Space and Response (ISR) Division. Photo by Brenna Moore, Public Affairs

Chang-Diaz takes Lab audience on travel through space

"I had been to Los Alamos a few times while earning my Ph.D. Those were exciting days when fusion was still 20 years away," said veteran astronaut Franklin Chang-Diaz.

Chang-Diaz spoke at Los Alamos' Physics Building Auditorium last week as part of a International, Space and Response (ISR) Division colloquium. The talk, "The Future of Plasma Thrusters," focused on the Variable Specific Impulse Magnetoplasma Rocket (VASIMR).

Chang-Diaz also is director of the Advanced Space Propulsion Laboratory at NASA's Johnson Space Center. The VASIMR engine design will provide a new method of propulsion that can reduce interplanetary flight time, according to Chang-Diaz. High frequency radio waves are used to ionize gas particles creating plasma in a magnetic field. Low frequency radio waves are then used to add rotational energy to the ions. A magnetic nozzle converts rotational energy of the ions into parallel energy, he added. The exhausted ionized gas provides thrust for the engine. The mass flow rate of the gas into the ionization chamber is controllable with a throttle, changing the specific impulse of the engine. In the future, VASIMR engines will be powered by multi megawatt nuclear power systems, Chang-Diaz said.

According to information on the Web, a VASIMR rocket system consists of three major magnetic cells: "forward," "central" and "aft." To get the rocket roaring, a neutral gas, typically hydrogen, is first injected at the forward-end cell of the motor and ionized. This electrically charged gas is then heated to create a desired density in the engine's central cell.

The gas is heated by the action of electromagnetic waves, similar to what happens in a microwave oven.

After heating, the plasma, which is essentially a superheated gas, enters a two-stage hybrid nozzle at the aft-end cell. The plasma detaches from the magnetic field and is exhausted to provide "modulated" thrust. This VASIMR configuration guides and controls the plasma over a wide range of temperatures and densities.

The VASIMR engine has the capability to reduce travel time to a few months, much shorter than today's chemical rockets, making manned missions to Mars a real possibility, said Chang-Diaz.

"The lifetime of an operational [VASIMR] engine will be more than one mission," said Diaz-Chang, explaining that in a two-flight, split sprint approach, the first launch will be an unmanned ship, which will carry furniture, food and supplies, but no people. "The cargo ship will take longer to get there, but the fuel that is used will be minimal with higher efficiency. The ship will remain in orbit ensuring that the crew has ample capability to return," said Chang-Diaz.

Chang-Diaz also said, that once the crew is finished with the cargo ship they would send it into the sun, rather than keeping old nuclear material and making for a clean disposal.

Chang-Diaz showed the audience a satellite map of the planet, pointing out that the United States, Europe and India are densely populated and that other parts of the world are largely desert or unusable real estate. "Look at our planet, we hardly have any room left," he said.

"The reason we fly in space is human survival, this is the ultimate reason," said Chang-Diaz.

The ISR Division colloquium series is a monthly forum for the presentation of cutting edge science and technology with relevance to the mission of the ISR Division and the Threat Reduction (TR) Directorate.

--Kathryn Ostic

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