As compelling as the scientific case is for Europa, NASA has yet to send a dedicated mission there. Part of that is due to the technical challenges involved in launching a spacecraft to Jupiter and operating in the high radiation environment created by Jupiter’s powerful magnetic field. Those technical obstacles drive up the costs of those proposed, and reduce the chances they can be funded. NASA has studied Europa orbiter mission proposals since the late 1990s, but those efforts typically foundered on costs and shifting priorities.
In 2011, the latest planetary science decadal survey—the once-per-decade report outlining priorities for planetary science missions based on science and other factors—identified a Europa orbiter as the second-highest priority large, or “flagship” mission, behind a rover to collects samples on Mars for later return to Earth. That ranking, though, came with a caveat: an independent study of the mission concluded it would cost $4.7 billion, too high a price tag. For a Europa mission to remain highly ranked, NASA needed to bring down the cost significantly. (See “Tough decisions ahead for planetary exploration”, The Space Review, April 4, 2011).
NASA has been working on reducing a cost of a Europa orbiter mission, in large part by no longer making it an orbiter. The concept now favored within the space agency is something called “Europa Clipper.” Instead of going into orbit around Europa, the spacecraft would instead go into orbit around Jupiter and make repeated close flybys of the moon. The most recent mission designs involve 45 flybys of Europa over three and a half years, with the vast majority of them coming within 100 kilometers of the moon’s surface. That approach minimizes the spacecraft’s exposure to radiation as well as propellant needed for entering orbit around Europa.
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