Chang Díaz’s invention will do little to reduce the dangers of liftoff. Plasma engines depend on the vacuum of space and still require “venerable chemical rockets,” as Chang Díaz calls them, to reach Earth orbit. But outer space is where his work stands to vastly improve the safety of a crew. As he points out, a lot can go wrong en route to another planet. The limitation of space travel with a conventional rocket is that the rocket must use its entire fuel supply at once in a single, controlled explosion to reach Earth orbit. It then coasts along at a mostly uniform speed until it enters Mars’s gravity. NASA estimates that such a trip would take about seven months. During that time, Chang Díaz explains, there is no abort procedure. The ship cannot change course. If an accident occurs, Earth would be watching, in a 10-minute communications delay, the slow death of the crew. “Chemical rockets are not going to get us to Mars,” he says flatly. “It’s just too long a trip.”A plasma rocket like Vasimr, on the other hand, sustains propulsion over the entire journey. It accelerates gradually, reaching a maximum speed of 34 miles per second over 23 days. That’s at least four times as fast as any chemical rocket could travel, shaving at least six months off a trip to Mars and minimize the risk of mechanical dangers, exposure to solar radiation (Chang Díaz’s design shields the crew behind hydrogen
But human spaceflight programs are currently built around old-fashioned rocketry. NASA has invested mostly in propulsion systems powered by chemical fuel, and for sensible reasons. Chang Díaz’s rocket presents many challenges. For one thing, a Vasimr-powered Mars craft would need several nuclear reactors on board to generate the large amount of electricity required to heat the plasma. NASA set to work on a nuclear reactor for space travel in 2003 but scrapped the project after only two years—the risk of radiation from an explosion or crash was likely too great— and redirected its resources to more conventional propulsion programs. For another, no one has yet determined how to make certain that plasma gas can be safely channeled through a magnetic field. Or just how the human body might respond to traveling at speeds of up to 34 miles per second. “The reality is, rockets don’t always work,” says Elon Musk, the driving force behind the rocket company SpaceX, one of the key players in the emerging private space industry. For Musk, who struggled for years to get his Falcon 1 rocket into orbit, the stakes seem particularly high in the case of rockets carrying nuclear material. “If something goes wrong, you have radioactive debris falling to Earth—you have a disaster,” he says.
It’s true that conventional rockets would be required to put a Mars-bound plasma ship into orbit, but Chang Díaz disputes the notion that launching Vasimr would pose extra risks. The reactors would remain inactivate until the ship was out of the danger zone for spreading radiation back to Earth, he notes. And NASA has already successfully launched several nuclear-electric probes. Nothing is impossible. “We can do this safely,” he says. “Our understanding is evolving all the time, but we know that in order to go far, we have to go fast. That’s what Vasimr is all about.”single page
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