Humans have sent several unmanned probes to Mars and plans are in the works to mount crewed missions to the Red Planet within the next couple of decades. But it’s extremely expensive and fuel-intensive to put a spacecraft in orbit around Mars—and voyages have to be scheduled for narrow “launch windows” anticipating an arrival date when Earth and its neighbor are at their closest to each other. That could all change if a new technique for reaching Mars called “ballistic capture” proves to be possible.
Getting spacecraft to Mars is quite a hassle. Transportation costs can soar into the hundreds of millions of dollars, even when blasting off during “launch windows”—the optimal orbital alignments of Earth and Mars that roll around only every 26 months. A huge contributor to that bottom line? The hair-raising arrivals at the Red Planet. Spacecraft screaming along at many thousands of kilometers per hour have to hit the brakes hard, firing retrorockets to swing into orbit. The burn can require hundreds of pounds of extra fuel, lugged expensively off Earth, and comes with some risk of failure that could send the craft careening past or even right into Mars. This brute force approach to attaining orbit, called a Hohmann transfer, has served historically deep-pocketed space agencies well enough. But in an era of shrinking science budgets the Hohmann transfer’s price tag and inherent riskiness look limiting.