This is part of IEEE Spectrum's Special Report: Why Mars? Why Now?
From his corner office at Ad Astra Rocket headquarters near Houston, Franklin R. Chang Díaz hatches big plans. He’s tucked away behind a strip mall on a bland suburban street, but his mind is wandering the cosmos. He envisions multibillion-dollar mining operations extracting iron, cobalt, and platinum from asteroids for use in cities on the moon and Mars. He dreams of space infrastructures so evolved that astronauts freely roam the moons of Jupiter and Saturn. He sees parallel societies grown teeming and rich, and Earth gradually transformed into a grand nature preserve.
But first, he confides, he hopes to trade his comfy landing pad in Houston for an office on the moon.
If anyone can help launch a spacefaring society, it’ll be Chang Díaz. The former astronaut has spent more than two months in space during seven space-shuttle missions. Three times he has gazed down through his helmet’s mirrored faceplate at his white-swirled, blue-green ball of a home. Now he’s building the rocket engine that might make some of those galactic fantasies come true.
Decades ago, Chang Díaz, who holds a Ph.D. in applied plasma physics, concluded that chemical rockets were a dead end, owing to their modest performance specs and huge appetite for fuel. Voyaging in a chemical rocket is the celestial analogue of drifting around the world on a yacht that got its one burst of speed by charging out of port like an angry elephant. It’s heavy, it’s inflexible, and it breaks all the rules of sensible travel. So in the late 1970s he began developing an alternative technology he calls VASIMR, for ”variable specific impulse magnetoplasma rocket.” In its most ambitious form, VASIMR would be a nuclear-electric rocket engine—a fission reactor with a plasma thruster that could potentially push people to Mars and back using a fraction of the propellant and time needed for a chemical rocket.
With a power plant similar to the ones on nuclear submarines, the plasma rocket could carry several people from Earth to Mars in 39 days, as opposed to what would be at least a 180-day journey on a chemical rocket, Chang Díaz says. The savings in food, water, air, tedium, and cosmic-ray exposure would be immense. In 2012, Ad Astra plans to test a prototype—using solar power rather than nuclear—on the International Space Station. An astronaut will spacewalk out to attach the 200-kilowatt engine, and if all goes well, it will bump the ISS into a more attractive orbit with about 5 newtons of thrust. The tests will begin to indicate whether VASIMR can figure in NASA’s grand plan to shuttle people and cargo to the moon and perhaps Mars over the next couple of decades. In particular, engineers will analyze two things: how efficiently the engine uses its electricity to produce plasma and how fast its radiator can siphon away excess heat.
On a hot, cloudless February day in Costa Rica, that radiator is undergoing intense scrutiny. Its home is a sleek white warehouse that hulks in a meadow of feathery grasses, an awkward edifice that looks like it dropped from the sky in a space-age remake of The Wizard of Oz . Next to the building, six cars are parked with sun shields propped against their front windshields.
A bumpy dirt road links the warehouse, with its zippy Ad Astra logo, to an unnamed highway, one of two thoroughfares that connect the city of Liberia to the rest of Costa Rica. Rental-car agencies hawking rugged vehicles line the highway. In the window of one agency, a poster advertises a ”Race to Space.” Silhouetted runners glide across the surface of some space orb, with Earth hovering behind them on a field of luminous blue. In the foreground, Chang Díaz, who was born in Costa Rica, smiles benevolently in a bright orange space suit. The footrace is to raise money to build roads, but Chang Díaz’s engine may reach Mars before Liberia gets good roads.
Ad Astra’s warehouse lab in this Central American burg is the world’s foremost—and only—dedicated center for heat management in plasma rockets. With an average age of 28, the engineers make up a team as remarkable as it is improbable. The story begins in 2004, when Chang Díaz tapped his younger brother, Ronald, then running a construction company in the city of San José, to start up an Ad Astra office in Liberia. At age 42, Ronald embarked on a real-life Costa Rican version of Rocket Boys . He skimmed the best and brightest from local tech companies and Costa Rica’s universities. He added others as people showed up whose drive and aptitude appealed to him.
One electrical engineering grad appeared at the facility’s ribbon-cutting ceremony and refused to leave. Ronald hired him. The 21-year-old master of the machine shop, an immigrant from Nicaragua, was plucked from a local gas station, where he was an attendant. He’s now also the electrical technician, and he dabbles in computer-aided design.
On this sunny February day, the dozen engineers in the warehouse are scattered around a 50-kW version of the engine. They must design a lightweight thermal jacket for the thruster. The challenge lies in choosing a material that conducts heat well but electricity poorly, perhaps a ceramic made from silicon nitride.
The jacket would collect the heat between the magnetic fields and the thruster’s walls, radiating some of it back to the plasma and some of it into space. The engineers’ task is formidable: Many experts suspect that the combined weight of VASIMR’s power plant and radiator will bog it down too much.
To test their radiator, the engineers prepare to fire the thruster. They settle into chairs at a row of desks facing a vacuum chamber the size of a school bus. Attached to one side is the business end of the apparatus: permanent magnets, a radio-frequency generator, a tank of argon gas, and the tube where they will generate the plasma before venting it into the vacuum chamber. The argon is flowing, and the magnets are powered up.
”Cinco, cuatro, tres,” Jorge Oguilve-Araya, a lead engineer, chants into a walkie-talkie. ”Dos, uno. Pulso!” The RF generator switches on and releases a torrent of RF waves into the argon stream. The gas heats up and ionizes, turning into a plasma of about 50 000 kelvin. Magnetic fields generated by the permanent magnets hold and channel the viciously hot material, protecting the thruster walls from melting on contact. A purplish light fills the vacuum chamber before fading to black.
There’s a similar setup in Houston, but with one more stage. Another antenna generates an electric field to heat the plasma to a million kelvin. When the ions’ rotation frequency matches the frequency of the field, the potential energy in the electric field changes into kinetic energy for the ions, accelerating them in a direction perpendicular to the magnetic field lines. This configuration forms a magnetic beach—waves on which the particles then surf their way out of the rocket.