Europa mission concepts under study. Credit: JPL
At today's Outer Planet Analysis Group (OPAG) meeting, more details of NASA's study of cheaper Europa flagship missions were presented. The attendees also had a lively discussion of which of three mission concepts NASA should concentrate on for further analysis.
At the last OPAG meeting last Fall, the study team presented a flyby spacecraft that would focus on remote sensing studies requiring power and data hungry instruments and an orbiter that would conduct those studies that could only be done from Europan orbit. (See this post for a description of the orbiter and multiple-flyby concepts.) At that meeting, early ideas for a Europa lander were presented. (See this post for both background on the earlier concept and a description of a high priority location to land at.)
Members of the study team today presented a more mature concept for an Europan lander. The early ideas included a very simple carrier craft that would deliver two landers into orbit about that moon. Two landers provided redundancy in case one crashed. With further analysis, the study team members have concluded that high resolution imaging is needed to find a safe landing site. Europa is so rough that simple redundancy isn't a viable plan.
The new concept has a much more capable orbiter with a high resolution camera to image the surface at sub-meter resolution (which would put it in the class of the HiRISE camera currently in orbit about Mar). Images would quickly be acquired of a small number of preselected possible landing sites to find at least one area 100x100 meters that would be flat enough to enable a safe landing. Advanced precision landing technologies would be used to guide the lander to a landing location as small as a hectare (2.5 acres) and then further analyze that target location during descent to find the safest spot within that location. Once the lander was safely down, the orbiter would act as a communications relay (although the lander would have its own backup communications capability)
The lander would conduct three types of studies. It would image the local site to enable scientists to select sampling locations and to understand the processes that created the surface. A robot arm would drill into the surface to collect samples from as deep as 10 cm to get at ice that had not been altered by Jupiter's intense radiation field. A mass spectrometer and possibly a Raman spectrometer would be used to analyze the sample composition. Seismometers and a magnetometer would be used to study Europa's interior by measuring seismic activity and the induced magnetic field created by the subsurface ocean's interaction with Jupiter's magnetosphere.
After the lander concept was presented, the overall study's team leader, Bob Pappalardo of JPL, presented the wrap up. The two key slides were the estimated cost and risk of each concept and a checklist of questions that each of the concept missions could address about Europa.
The estimated costs of each mission, not including a launch vehicle that would add approximately $275M to the total, were:
Europa orbiter - $1.6B (low risk)
Europa multiple-flyby - $1.9B (low risk)
Europa lander - $2.8B-$3.5B (high risk)
The multiple flyby craft's higher cost compared to the orbiter results from both requiring more capable instruments and spacecraft systems and from the much longer mission duration creating higher operating costs. A group at Aerospace Corporation did independent costs analyses for the orbiter and multiple-flyby missions and came up with similar estimated costs.
They study team recognized that at best NASA will at some future time go forward with only one of these concepts. None would answer all the high priority questions by itself. For example, characterizing Europa's ocean and its interface with the overlying ice shell and underlying rocky core requires either the orbiter or the lander. Understanding the structure and composition of the ice shell would require either the heavy, data hungry instruments of the flyby craft for global studies or the lander to characterize conditions at one location.
The meeting attendees spent almost an hour discussing which of these missions they believe would provide the greatest advance in the study of Europa. No clear answer emerged, in part because OPAG is chartered by NASA to analyze plans and proposals but not to provide advice. (Note: It's not clear to me how you can cleanly separate the two.) Pappalardo stated that he felt that the multiple-flyby spacecraft would provide the most Europa science for the dollar. Most of the participants also seemed to lean towards the multiple-flyby option as their preference. (While it was not discussed, the multiple-flyby spacecraft with its highly capable remote sensing instruments also should be better able to study Jupiter and the other moons than the less capable instruments planned for the orbiter.)
Examples of a possible set of flyby ground tracks at Europa for the multiple-flyby spacecraft. Credit: JPL
Editorial Thoughts: The study team has shown that there are two small Flagship (<$2B) class missions that are low risk that could start development without additional technology development. This is in sharp contrast the previously planned Jupiter Europa Orbiter with its >$4B estimate. Various strategies such as using solar panels instead of plutonium power supplies or international collaboration might reduce the cost to NASA for either the orbiter or multiple-flyby missions.
The studies also show that viable mission concepts are outside the $1B budget cap of the New Frontiers program. This isn't surprising. The Juno New Frontiers mission that is en route to orbit Jupiter has a cost of $1.1B. The proposed European JUICE Ganymede orbiter (which would also flyby Europa and Callisto) would have a cost of at least $1.3B. (I've read that ESA increased the cost caps for its Large mission proposals, but don't know by how much.) Other studies have found similar costs for minimal Titan and Europan missions. The outer planets are expensive to reach and study.
Unfortunately, NASA's projected budgets do not include beginning funding for any planetary flagship missions until at least the end of this decade. We remain dependent on the selection of the Discovery Titan TiME lake probe and/or the European JUICE proposals to continue the exploration of the outer solar system once the Cassini and Juno missions end in 2017.
In the meantime, I hope that NASA will select one of the Europa mission options for continued low level study so that when the budget situation eventually improves, it can be ready to begin development.