As someone who has had a longtime interest in Europa, I was devastated when they cancelled the Europa Orbiter mission, though for what it's worth I still think Pluto is a worthy target for a future mission. However, I have to admit that a Europa Orbiter would present a number of challenges.<br /><br />1.) Getting into orbit around the planet. This would require a relatively slow trajectory to reduce the necessary fuel to brake into orbit; in any event, the requirements would be considerable, and we'd probably be looking at several years of travel time, like Galileo.<br /><br />2.) Matching orbits with Europa. This would require yet more onboard fuel to reduce the eccentricity of the orbit, as well as a number of Galilean flybys to match orbits with Europa.<br /><br />3.) Orbiting Europa itself, which would require more fuel still to brake into orbit.<br /><br />4.) Radiation concerns. Though Europa is no Io when it comes to radiation, it's still a very harsh place for any spacecraft, and this would automatically limit the lifetime of any orbiter. In fact, IIRC, the Europa Orbiter mission itself was calculated to last no longer than a month or so before it was done it. <br /><br />I think these difficulties were part of the reason that some people balked at the concept, and why it was always going to be difficult to pull off a mission like this on the cheap, in the vaunted "Faster, Cheaper, Better" paradigm. The mission costs exceeded expectations quickly, and in tight budgetary times sounded the death knell for the mission.<br /><br />That said, I'd have to agree that I believe a Europa orbiter should be an exceedingly high priority. In fact, I favor Europa over Mars, even without the flashy volcanoes and ruddy deserts. Galileo's data, though not conclusive, was highly suggestive, and if there's *any* possibility of liquid water existing under the surface, then we should go for it. Something as simple as measuring its tidal flexing and thickness of its ice could b