I love a long journey by car or rail, but not by airplane. Back in my flight instructing days, I used to love to take a Cessna 182 on a long jaunt, but these days the flying I do means sitting in the cheap seats in the back of a gigantic jet and suffering the various indignities of security checks, long lines and tightly packed quarters. Hence my 1000 mile rule: If the trip is less than that distance, I’ll drive it or look for a rail connection. My recent trip back to the Midwest reminded me how much I enjoy seeing the scenery at my own pace and having plenty of time to think.

One of the things I thought about was how to extract maximum value from spacecraft. A decade or so ago, JPL’s James Lesh explained to me how the signal from a distant probe passing behind a planet would be affected by that planet’s atmosphere. An elementary way to do atmospheric science! I’ve mused ever since about how to do complicated things with existing resources and how to put technology in the right place for bonus information returns. All that led to thoughts about our prime astrobiology targets in the outer system: Europa and Enceladus.

Earlier this month I wrote about Lee Billings’ Aeon Magazine essay Onward to Europa, in which he speculated about the the possibility of exploring what is beneath the Europan crust. A mission like this could be done without actually descending to the surface and penetrating the ice. Billings noted that the Hubble Space Telescope has detected water vapor, estimated at about 7000 kg of water per second, being blown into space from the surface. Europa’s high-radiation environment is challenging even for a robotic lander, but maybe we could fly through the Europan plume to sample the moon’s chemistry and possibly even detect signs of biological activity. The essay Ship of Dreams in Astrobiology Magazine speculates on the proposed Europa Clipper mission flying through the plumes, but budget issues could make the $2.1 billion Clipper too expensive.


Image: A prime target for astrobiology, Europa (as imaged here by the Galileo spacecraft) is the subject of multiple mission concepts. Credit: NASA/JPL/Ted Stryk.

Similar ideas have surfaced about Enceladus, with an eye toward flying a complicated mission on a tight budget indeed. Consider the Life Investigation for Enceladus mission concept, championed by Peter Tsou (Sample Exploration Systems). I read more about this one in an essay by Andrew LePage on his Drew ex machina website. LePage, a physicist and writer who serves as senior project scientist for Visidyne Inc. in Boston, notes that the LIFE mission would use an aerogel collector like the one NASA used in the Stardust sample return mission to return cometary dust in 2006. Some concepts also call for sample return from Saturn’s E-ring, thought to be made up of particles originally from Enceladus’ geysers.

All this came into the public eye last summer at the Low-Cost Planetary Missions Conference (LCPM-10) at Caltech, where Tsou laid out a 15-year mission that would launch in the early 2020s, reaching Saturn in May of 2030 after a series of gravity assists past Venus and the Earth. LIFE would use close passes by Titan to alter its orbit, allowing multiple low-speed approaches through the Enceladus geyser region above the moon’s south pole. At speeds slower than Stardust’s encounter with Comet Wild 2, the Enceladan material should be better preserved when captured. LIFE would then use Titan for further gravity assists followed by a return to Earth in 2036.

I love the concept as much as I love extracting atmospheric science from communications signals. The cost excluding launch might be kept as low as $425 million. The potential gain is high. LePage likes it, too, and goes on to suggest not just improvements to the Enceladus idea, but a different sample return mission that would bring back materials from both Europa and Io. The mission could launch as early as 2021, with rendezvous with Jupiter in October of 2025. LePage lays out the basics: An elongated orbit to avoid the worst of Jupiter’s radiation belts, gravity assists from Europa, Ganymede and Callisto, multiple low-velocity encounters with the Europan polar plumes and gathering of plume materials with the aerogel collector.

Then figure several months of observation to scope out a target on Io, then a close pass by the moon to sample one of its volcanic plumes, a scary swing through the most intense regions of Jupiter’s radiation belts, but one of only two passes through the worst of them (the other being at insertion into orbit around Jupiter). Re-entry to Earth’s atmosphere would occur in 2030. It’s a mission concept with intriguing resonance with the LIFE mission and builds on the same technologies. Says LePage:

While a lot more work is required to flesh out the details of a Europa-Io sample return mission (especially more information on the nature of Europa’s purported plumes), at first blush it does appear to be feasible using the same hardware proposed for the LIFE mission to Enceladus employing readily available launch vehicles. This proposed mission also nicely complements the investigations of the LIFE mission by returning samples from yet another set of plumes on a potentially life-bearing moon with the added bonus of sampling volcanic material from a second target of keen interest to planetary scientists – Io, the solar system’s most volcanically active world.

The nine-year mission LePage envisions is substantially shorter than the 15-year LIFE mission, and could be completed about the time that LIFE arrived at Saturn. This would have been a great concept to mull over on my trip, and I wish I could have read about it before I left. I’d love to see follow-up work, particularly on that white-knuckle pass by Io. The essay continues:

For minimal additional costs (i.e. a second spacecraft and launch vehicle along with the incremental cost increase of running two missions in parallel), this scientifically interesting mission could be flown in parallel with LIFE and greatly increase its total science return. And it could probably do so within the Administration’s proposed billion dollar price cap for a Europa mission.

Given that we’re now dealing with budget proposals that confine a NASA Europa mission to under a billion dollars, the sample return mission to Europa even without the Io component offers a profoundly interesting science return, and I like the synergies with the more fully developed LIFE concept. In any case, we have two highly intriguing astrobiology targets that are conveniently venting material into nearby space, making landing on the surface — much less trying to penetrate fissures or drill through thick ice — unnecessary at this stage of our investigations. What we learn from such missions could well determine how we press ahead with later, more complex missions that would demand operations on or below the ice.