Posted by Jason Callahan
08-04-2015 13:05 CDT
Last month teams of scientists from around the United States submitted proposals for the thirteenth mission in NASA’s Discovery program. Discovery is a class of small planetary science missions, with costs capped for this round of proposals at $450 million (not including the cost of a launch vehicle). There is no pre-specified target list for Discovery missions, but they must be based on the scientific questions highlighted in the National Research Council’s Planetary Science Decadal Survey in order to be competitive. Last week, I published an article in The Space Review discussing the latest round of proposals.
The strength of Discovery missions lies in their frequency. By flying more frequently than larger missions, Discovery projects allow scientists greater opportunities and shorter waiting periods to fly their instruments (a particularly important proposition for early-career scientists). And since Discovery missions are competitively selected, they provide increased opportunities for scientists outside of NASA centers to design missions.
Discovery is a fiercely competitive program. In this latest round NASA received twenty-eight proposals, which is the same number the agency received in 2010 during the twelfth Discovery mission competition. This round includes a number of new competitors, while some from the last round are not competing this time. The competition is particularly strong this round, in part due to the long wait for NASA’s solicitation for proposals. Discovery competitions are supposed to occur every two to three years.
NASA will now conduct reviews of all twenty-eight proposals, evaluating them in terms of science quality, technical maturity, and cost. Each of these factors is important. The proposed mission must answer scientific questions that the planetary science community is interested in; the spacecraft must not rely on technology that is insufficiently mature; and the mission must have a good chance of staying within the cost cap, as determined by an independent group hired by NASA to perform an evaluation.
NASA does not disclose which proposals it receives for Discovery competitions and mission proposers do not have to make any aspect of their participation public. Some principal investigators choose to keep their proposals secret so as not to tip off their competitors. Considering that it is common for teams to lose once or more before they eventually get selected, there is logic to this secrecy. Unusually (and somewhat surprisingly), two-thirds of the proposing teams during this thirteenth round have publicly revealed basic information about their proposals.
Because the principal investigators for so many of these missions have gone public, it is possible to discuss them, although generally not in much detail. There is considerable information available for some of them, such as IVO, but little more than a discussion of science goals for others. The list below is categorized by target or mission type and includes nineteen missions. In addition, the author is aware of another Venus mission and another comet mission, although their principal investigators have not publicly revealed them.
Moon Mission Proposals
Following the Apollo program, two decades passed before the United States returned a spacecraft to the Moon. The Department of Defense’s Clementine spacecraft orbited in the early 1990s, later followed by the third Discovery mission, Lunar Prospector, and the eleventh Discovery mission, GRAIL. NASA has also launched LADEE, LCROSS, and the Lunar Reconnaissance Orbiter (LRO) as part of other programs. LRO still operates around the Moon, although the president’s most recent budget proposes shutting it down. This would reduce NASA’s presence at the Moon to the ARTEMIS extension of the THEMIS mission, a heliophysics project from the Small Explorer program. The Moon still poses many scientific questions, but because previous missions have answered most of the basic questions, the remaining questions are more complicated and require more complex spacecraft to answer – and some of those spacecraft are too expensive to fit in the Discovery program. Nevertheless, some scientists continue to propose Discovery lunar missions. Two of them are publicly known for this Discovery round.
NanoSWARM is a CubeSat Discovery mission to study space weathering, lunar magnetism, lunar water, and small-scale magnetospheres. It would consist of several CubeSats in lunar orbit. NASA is currently undertaking a small CubeSat mission known as Lunar Flashlight, but so far no CubeSats have ventured beyond low Earth orbit so this would be a novel mission.
MARE (Moon Age and Regolith Explorer) is a proposed lunar lander mission that would provide more accurate dating of the lunar surface than can be achieved without bringing samples all the way back to Earth.
Phobos/Deimos Mission Proposals
Mars’ moons Phobos and Deimos have always been bridesmaids and never brides when it comes to Discovery mission proposals. Scientists have proposed Phobos and Deimos missions at least a handful of times before, such as the Aladdin mission proposal which came very close to selection in 1999. Russia launched the Phobos-Grunt mission in 2011 to bring a sample of Phobos back to Earth only to have the spacecraft fail as soon as it reached Earth orbit. Future Russian Phobos plans appear to be on hold due to the country’s financial situation. The Martian moons pose a number of scientific questions, such as their origin—are they captured asteroids or parts of Mars itself?—and the nature of unusual features on Phobos’ surface. One question of possible interest to future human missions to Mars is whether the moons contain any volatiles. There are three proposals for missions to these moons during this Discovery round, two orbiters and a lander.
PANDORA (Phobos ANd Deimos ORigin Assessment) is a JPL Phobos/Deimos mission that would use a Boeing spacecraft equipped with solar-electric propulsion.
PADME (Phobos And Deimos & Mars Environment) is an Ames Research Center Phobos/Deimos mission that would use a spacecraft similar to the LADEE lunar orbiter launched in late 2013. Compared to PANDORA, PADME would carry fewer instruments and be less expensive.
MERLIN (Mars-Moons Exploration, Reconnaissance and Landed Investigation) is a Johns Hopkins Applied Physics Laboratory-led proposal for a Phobos lander. It would conduct in situ measurements of Phobos.
Venus Mission Proposals
The last NASA mission to Venus was Magellan launched in 1989, so one could argue that it is past time that NASA returned to Earth’s hellish twin. During the last Discovery competition, NASA received seven Venus mission proposals, including four radar missions. This time there are apparently four Venus missions, although only three of them have been publicly announced.
VASE (Venus Atmosphere and Surface Explorer) is a Venus atmospheric mission that would deploy balloons to Venus and drop an impactor to the surface that would take close-up images of the surface during its descent.
RAVEN (Radar At VENus) is a Venus radar mission that would map the surface at higher resolution than Magellan did before finally ending its mission in 1992. It is led by researchers from the Lunar and Planetary Institute with Boeing participation.
VERITAS (Venus Emissivity, Radio Science, InSAR Topography and Spectroscopy) is another radar mission led by JPL.
Outer Planets Mission Proposals
It can take five years or more for a spacecraft to reach Jupiter, and even longer to reach Saturn. Because of their distance from the Sun, the outer planets pose challenging power requirements. Only a few years ago it was inconceivable to use solar power at Jupiter distances, but NASA’s Juno mission is currently heading to Jupiter and will use large solar panels, and the Europa Clipper mission will also use solar power. Suddenly solar is viable for some outer planets missions, at least at the distance of Jupiter.
IVO, the Io Volcano Observer, is a mission to study the volcanic, ever-changing moon of Jupiter. During the last Discovery round IVO was a spacecraft proposal that would have used a plutonium-powered Advanced Stirling Radioisotopic Generator, but this time it will operate using what the scientists call “remote fusion power,” otherwise known as the Sun. IVO’s principal investigator, Alfred McEwen of the University of Arizona, has spoken in detail about this mission and provided extensive summaries of the mission design and instrumentation, in addition to the science his team will conduct.
Enceladus Life Finder is a mission that would send a solar-powered spacecraft to Enceladus, the geysering moon orbiting Saturn. ELF’s solar panels are over 43 meters in length, and the spacecraft would use various instruments to try to detect life at the tiny, but thermally active moon.
Planetary Telescope Proposals
Before the space age, the only way to study the planets was to use telescopes. Today telescopes are still important for many planetary observations, particularly of more distant objects such as the ice giants Uranus and Neptune and Kuiper Belt Objects beyond Pluto. Kepler was a Discovery mission that was later taken over by NASA’s astrophysics division and has gone on to fame and glory detecting planets around other stars, but planetary scientists have been talking about space-based telescopes for looking within our solar system.
Whipple was a telescope proposal that was selected for technology development funding in the last Discovery round in 2011. It would use a new technique called “blind occultation” to find objects in the outer solar system and determine the structure of our solar system beyond Pluto. Relatively little information is available about this mission.
NEOCam is a JPL mission that was also selected for technology funding in the last Discovery round and is probably competing again. The tech funding went to support the development of the telescope sensor, which presumably would be integrated into any new spacecraft if NASA chooses to build it. NEOCam is a survey mission that would detect a large number of near-Earth objects that are too small or faint to be spotted with ground-based telescopes.
Kuiper is a planetary telescope proposal for looking at a number of different objects and phenomena in the solar system. The proposal team is led by Principal Investigator Jim Bell of Arizona State University, who also happens to be the President of The Planetary Society. Since it is expensive and time-consuming to send missions to the outer planets and to observe their atmospheres, magnetospheres, and moons, Kuiper would view them remotely. It would be able to monitor the complex weather on Jupiter, Saturn, and the ice giants and could also view their aurorae. And it would provide a powerful tool for finding and characterizing the mysterious objects in the Kuiper Belt, possibly finding other bodies larger than Pluto.
Asteroid Mission Proposals
Lucy is a mission that would journey to the Trojan asteroids. This class of asteroid occupies locations leading and trailing Jupiter’s orbit. They are essentially captured there by gravity and, as a result, could be left over from the early period of solar system formation. There is relatively little public information available about Lucy.
DARe (Dark Asteroid Rendezvous) is apparently a mission to visit up to nine asteroids using what the proposers refer to as a high heritage spacecraft equipped with ion propulsion, essentially a spacecraft similar to Dawn which is currently orbiting Ceres. Based upon the limited data available, it is unclear if the targets are near Earth asteroids or those farther out.
BASiX (Binary Asteroid in-situ Explorer) is a mission to visit an asteroid with a satellite of its own, something that is surprisingly common among asteroids. The goal would be to set off small explosions to see how they affect the movement of both objects.
Comet Mission Proposal
The European Space Agency’s Rosetta mission and the exploits of its wobbly lander Philae demonstrate that comets can fascinate the public and hold many scientific secrets. What particularly interests scientists is the possible presence of organic materials on comets. Although there are probably at least a couple of comet mission proposals this Discovery round, only one is publicly known.
CORE (COmet Radar Explorer) is a mission to put a spacecraft close enough to a comet to map its interior using ground/ice penetrating radar and also map its surface.
Mars Mission Proposals
Until 2010 NASA had a separate class of small mission proposals for Mars known as Mars Scout. Both the Phoenix lander and MAVEN were Mars Scout missions. But in 2010 Mars Scout was discontinued and Mars missions were then included in the Discovery program. The most recent Discovery mission selection, InSight, will head to Mars in March 2016.
Mars Icebreaker Life is an Ames Research Center mission based on the Phoenix lander. It would follow up on Phoenix’s discoveries but also use different sampling devices and instruments to try to overcome some of the frustrating problems that Phoenix encountered. The goal is to determine whether the ice fields near Mars’ poles are habitable and might contain complex organic chemistry.
A plethora of worlds to choose from
Judging from the number and variety of proposals, there is clearly a lot of scientific interest in the Discovery program. Putting together a proposal requires people who are interested in doing the work and institutions—NASA centers, universities, industry contractors—willing to spend the money on the proposals. According to insiders, these proposals can cost a quarter of a million dollars or more to assemble, so twenty-eight proposals, involving hundreds, if not thousands, of participants represent a substantial expenditure.
The last Discovery selection was nearly five years ago. The Planetary Science Decadal Survey recommended a higher cadence of Discovery missions, essentially one every two years. Certainly there are more possible missions than NASA is being given money to pursue.
Right now, NASA’s plan is to down-select by September. Although the last time around, NASA selected three proposals for further study and three technologies for further development, there is no hard and fast rule for what it has to do this time. If more missions are considered viable, NASA could select more for further study and technology development. But based upon current plans and funding profiles, NASA will probably select a single mission for full funding by fall of 2016, with a launch scheduled probably in 2020 or 2021. This Discovery destination currently unknown, but it is certainly somewhere out there in the dark.