By Eric Hand of Nature magazine

The potential cost of NASA's flagship mission to Jupiter's icy moon Europa was recently put at $4.7 billion. In an era of austerity, that's likely to be a show-stopper. But John Sommerer thinks that his laboratory can send a probe to Saturn's moon Titan for less than one-tenth of that.

Sommerer, head of the space department at the Applied Physics Laboratory (APL) in Laurel, Md., made his case to planetary scientists this week during a conference at the APL on low-cost space missions.

The APL, the research and development arm of the Baltimore-based Johns Hopkins University, is proposing to send a probe to Titan under NASA's Discovery Program, which caps budgets at $425 million, excluding launch vehicle.

"How many flagships are we going to get this next decade? Maybe none," says Sommerer. "That's why it's so important to preserve these low-cost, scientifically interesting and potentially paradigm-changing missions."

Cost cutting

There are many ways to keep costs down. For instance, MESSENGER, a Discovery Program mission to Mercury, did one fly-by of Earth, two of Venus, and three of Mercury before settling into orbit in March. By using the planets' gravity to get into position, the probe saved fuel for the difficult orbital insertion.

MESSENGER's instrument-management software, called SciBox, also saves money, by choreographing the probe's instruments itself, rather than leaving the job to researchers. This lowers personnel costs, says SciBox's inventor, APL software engineer Teck Choo, who adds that other mission proposals are adopting the software.

There are savings to be made on hardware, too. Maria Zuber, principal investigator for GRAIL, a mission to measure the Moon's gravitational field, used instrument designs from GRACE, an Earth-science mission with similar gravity-measuring goals, and adapted the spacecraft's design from that of a classified military satellite.

GRAIL, also a Discovery Program mission, is expected to launch in September well within its $468-million budget, which includes the cost of its launch vehicle. It will enter the Moon's orbit in January 2012 and get its science done rapidly -- another way of keeping costs down. "It's a three-month mapping mission, and then that's that," says Zuber, of the Massachusetts Institute of Technology in Cambridge.

Zuber saved money by looking to the past; other missions are looking to trailblazing technology that comes with risks but could also keep costs down. Many have high hopes for a new power source called the Advanced Stirling Radioisotope Generator (ASRG), which uses a smaller amount of plutonium-238 and is more efficient than previous radioisotope power sources.

Power players

Two of the three finalists for the latest round of Discovery Program missions, which were announced in May, include an ASRG. One is the APL's Titan Mare Explorer proposal, which would send a floating capsule to seas of methane and ethane in Titan's northern hemisphere to sample the liquids for any sign of organized chemistry.

An ASRG would be lighter than batteries and could power the probe for five or six of Titan's days--equivalent to nearly 100 Earth days. By contrast, the Huygens probe, which the Cassini orbiter dropped onto Titan in 2005, lasted for only about 90 minutes on the moon's frigid surface.

The Titan Mare Explorer would arrive in 2023, when it will be summer in Titan's northern hemisphere and that part of the moon will be facing Earth. That would allow the capsule to beam data back directly, without the aid of an expensive orbiter.

Since the Discovery Program began in 1992, seven stand-alone missions have launched successfully. Another three are under way, including GRAIL. One might think that the obvious targets have already been taken, but Sommerer says that his lab's proposal shows that's not the case.

"We're doing an outer-planets moon lander--and it's a boat by the way--on a Discovery budget," says Sommerer. "I don't think all the low-hanging fruit are gone."

This article is reproduced with permission from the magazine Nature. The article was first published on June 23, 2011.