In addition to the three Discovery mission proposals, a fourth mission concept was proposed, the LIFE Enceladus Sample Return. A previous incarnation of this mission was proposed for the last Discovery competition but wasn’t selected. Like the ELF mission, the LIFE mission would make multiple flybys through Enceladus’ plumes and would use a mass spectrometer to study their chemistry. Unlike ELF, the LIFE spacecraft would collect dust plumes in a fashion similar to that done by the Stardust spacecraft that collected comet dust samples in the mid-2000s. The samples would later be returned to Earth where far more sensitive measurements would be made than could ever be done by instruments on a spacecraft. The cost estimates presented by the LIFE team puts the mission outside the current scope of the Discovery program, and the team is building support to add an Enceladus sample return mission to the New Frontiers candidate mission list for the 2020s.

After 2017, there are no plans to have a spacecraft operating in the outer solar system until the late 2020s at the earliest. That decade gap will exist because outer planet missions in the past have had to be infrequent because of their costs. The four proposals presented at last month’s meeting represent the planetary community’s attempt to find a new class of much lower cost missions that could fly more frequently. The Kuiper telescope would be an entirely new approach to the problem that could begin providing data in the early 2020s. The missions to Io and Enceladus face a tougher challenge because they propose to do missions for half the cost of any previous outer planet mission orbiter.

Missions to both Enceladus and Io have been studied before, and the costs were two to four times that of the cost cap for Discovery missions ($450M). Teams that propose missions are generally fairly open about the great science their missions would do if they are selected to fly. These teams tend to be much more reluctant, however, to discuss the specifics of how they would accomplish their goals within the tight cost caps of a Discovery competition – that is their secret sauce. The teams proposing ELF and IVO are seasoned veterans and their credibility gives me hope that the outer solar system may open to low cost missions. We can assume that they have had a laser focus on finding ways to reduce costs to a fraction of what previous studies have assumed. Estimating development cost, however, is always part art. NASA will perform its own assessment of mission risks and costs, and its reviewers may be more risk adverse and conservative than the mission proposers in assessing likely costs and risks.

For this Discovery competition, NASA’s managers have changed the rules in a key way that will help outer planet proposals. In previous competitions, the costs of mission operations had to be included in the mission cap. A mission to Mars with an operations lifetime of two to three years had an inherent advantage over an outer planets mission that might take five to seven years to reach its target and then require another year or two of operations. Now NASA has excluded “reasonable” mission operations costs from the cost cap (which means it picks up those costs separately). This goes a long way to leveling the playing field between inner and outer solar system Discovery proposals.

In the last Discovery competition, a mission to land on a lake in the north polar region of Saturn’s moon Titan made it to the list of finalists. (The Mars InSight geophysical lander was the winner.) If either ELF or IVO is selected this time, then outer solar system will have been opened to exploration by a new, low cost class of missions. If neither mission is selected, then the experience learned from these proposals will become part of the community experience that is likely to sharpen future Discovery proposals for the outer solar system. I believe that eventually an outer planets Discovery proposal will find the right formula for selection; I hope that this happens sooner rather than later.