The splashdown of a robot explorer in an extraterrestrial sea may recall the age of discovery involving wooden sailing ships. But the proposed expedition to a moon of Saturn also evokes some good old-fashioned spacecraft heritage and relies upon a powerful new nuclear battery.
The Titan Mare Explorer (TiME) mission being proposed to NASA would land in one of the largest seas of Titan, a moon where liquid ethane and methane rain onto a surface dotted by lakes and small seas. That may sound wildly different from NASA's moon or Mars landings, yet it would draw upon many past space missions, said Ralph Lorenz, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.
"It's actually not as crazy as it sounds," Lorenz told InnovationNewsDaily. "We'll land somewhere in the sea and we will drift, and in all probability we will probably drift to the edge of the sea."
Lorenz presented updates on the proposed Titan mission to a crowd of planetary scientists and engineers at the International Academy of Astronautics' ninth Low-Cost Planetary Missions Conference, held in Laurel last week.
Landing in liquid
Most landers target hard surfaces, not bodies of liquid. Yet Lorenz pointed out that NASA's Apollo capsules returning from lunar orbit would splash down in the ocean and float until pickup.
The Cassini mission to Saturn also deployed a Huygens probe that previously landed in the desert on Titan, even if it survived only a few hours because of its short battery life.
The Titan mission would last almost 80 days (five Titan days). It would depend on power and heat drawn from the nuclear decay of plutonium fuel in a Stirling radioisotope generator recently developed by NASA.
"We could not do a mission that studies the diurnal [day-night] cycles without radioisotope power; it's that simple," Lorenz said. "Even if you had big enough batteries to supply electricity, it would get too cold. In that way, the Stirling radioisotope generator is perfect for this very cold environment."
A matter of survival
A long survival would allow the Titan Mare Lander to study the interactions of Titan's atmosphere and the surface during both night and day on Ligeia Mare — an alien sea bigger than any one of the U.S. Great Lakes. The mission also plans to sample the many chemical compounds in the lake besides ethane and methane, and to see how certain chemical cycles work.
"All these kinds of questions we can't address with Cassini data, and so there's only one thing to do, and that is to get in there and sip the stuff and taste it," Lorenz said.
But first the mission must survive NASA's selection process. It is one of three candidates up for approval as a Discovery-class mission with a budget cap of $425 million. Fitting the long list of science objectives for Titan under a tight budget required much planning discipline.
"It's no secret that this mission is not going to be at the cheap end of the missions proposed under Discovery," Lorenz said. "But clearly we're pushing the limits of what has been done before. We think we have innovative approaches and heritages to build on to achieve it."
You can follow InnovationNewsDaily senior writer Jeremy Hsu on Twitter @ScienceHsu. Follow InnovationNewsDaily on Twitter @News_Innovation, or on Facebook. This story has been corrected to reflect the fact that the Huygens probe landed on Titan's desert surface, rather than in a liquid body.
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