"As usual, says committee member Stephen Mackwell, director of the Lunar and Planetary Institute in Houston, Texas, there is too little money for too many ideas. 'We have to deal with a whole Solar System of possibilities,' he says.... 'I find it very hard to see doing them both in the decade,' says Fran Bagenal, former chairwoman of an external NASA planetary-science advisory committee... What's more, attempting a Europa mission and the Mars sample return at the same time could crowd out smaller missions to other parts of the Solar System, says Alfred McEwen, principal investigator for the HiRISE camera on the Mars Reconnaissance Orbiter, which is currently imaging Mars... "What Squyres has called 'sticker shock' for the biggest missions could bias the survey in favour of small- and medium-cost mission lines known as Discovery and New Frontiers. 'I could put together a spectacular programme without either one of those [flagship missions]. There are many ways to slice this,' says Squyres."
Editorial Thoughts: This crunch between desires and budgets isn't a surprise. In my analysis of NASA's budget for the last two years, I have not seen a way to fund all three programs within the probable budget for the coming decade. The increasing political focus on cutting federal budgets would seem to make it unlikely that the planetary program budgets will grow, and we may well see cuts. The Nature article points out that the proposed Precursor missions could add additional missions to the line up. However, the budget for these missions seems extremely uncertain as the administration and Congress argue over the nature and budget for the manned spaceflight program that would pay for the Precursor missions. If any of these missions survive, I suspect that the focus will be on near Earth asteroids, which would be the first focus of manned exploration.
What follows is my analysis of the pros and cons for a program that focuses on any of the three major program options.
Mars Sample Return
Pro: The analysis of carefully selected samples from Mars would revolutionize our understanding of Mars and, by extension, conditions on the early Earth. If those samples include signs of past or current life, then the mission will revolutionize our understanding of our place in the universe. The ability to tease out insights from samples with sophisticated instruments in terrestrial labs cannot be overstated. While instruments on planetary probes are engineering marvels, mass, volume, and power restrictions restrict their sensitivity.
Con: While Mars sample return missions have been studied for decades, detailed engineering analysis has rarely been done. The current concept for a three part mission is still fairly new, and the possibility of rapidly rising costs is real. Then there is the question of whether there is the political will to fund a mission this large. Political support would have to be sustained through 2-4 presidencies (depending on whether incumbents win re-election) and 8 Congresses. The complexity of the program with three major mission elements (a sample colleciton rover, a Mars lander with ascent vehicle, and a spacecraft to fetch the samples from Martian orbit and return them to Earth) means that many mission elements must go off without a failure to actually return the samples. There is also the question of where and how to sample. We know enough about Mars to pick a good location to sample, but will politicians fund this large a program without assurances that we already know that the chosen sampling location is optimal? And should samples be taken from near the surface (current plan), from the shallow subsurface (where ExoMars will sample), or from the deep subsurface?
Jupiter Europa Orbiter
Pro: This mission appears technically ready to enter development after a decade of technology development and analysis. Europa is one of the most likely spots in the solar system in which to find life, and the mission would also study the rest of the Jovian system. The proposed spacecraft will have the capability to study Europa in depth and to locate places on the surface where ocean material has recently been brought to the surface where future landers could study it.
Con: This mission is a bet that Europa (1) harbors an environment capable of supporting life and that (2) locations can be found near at the surface where future (expensive) landers could explore in more detail. Without the possibility of explorable life (life locked below a hundred kilometers ice would be unreachable with current technology and budgets), would the planetary community choose to spend $3.2B to explore this moon? This mission also requires a larger stockpile of Pu-238 to fly than NASA currently has on hand. Either the Russians would have to agree to resume sales of Pu-238 to the U.S., or the U.S. would have to restart Pu-238 production, which may not occur in time to fly this mission by the end of the decade.
Discovery and New Frontiers Missions
- 2 small flagship ($1.8B or 1.5 times the standard New Frontiers mission) missions that might fund a Mars rover, a network of Mars landers, a cryogenic comet sample return, or a Jovian or Saturn orbiter to continue the exploration of the moons of those worlds.
- 4 standard (~$1.2B) New Frontiers missions that might include a Ganymede orbiter with Europa and Callisto flybys; a near Earth asteroid sample return; and Venus lander; a lunar sample return; a mission to flyby Neptune, Triton, and Kuiper belt object; or a modest Enceladus mission.
- 4 Discovery (~$800M) missions that might fund the U.S. contribution to the Mars Trace Gas Orbiter, remapping Venus with radar at higher resolution, an Io volcano observer, a Titan lake lander, a Trojan asteroid mission, a Venus balloon mission, or a comet lander.
(Note: The missions listed above are possibilities. At least some of them probably would prove too expensive for the mission class suggested.)
One advantage of a program built on smaller missions is that if budgets are cut or one mission has to be cancelled because of cost overruns or technical difficulties, a robust program remains.
Con: None of these missions is likely to revolutionize our understanding of the solar system or to find an abode of past or present life. The Mars sample return and Jupiter Europa Orbiter missions have remained at the top of the priority list for solar system exploration because they offer the chance for a revolutionary discovery.
What's my take on the options? A program that focused on any of these elements can be justified in terms of scientific return for dollars spent. A Mars sample return mission is a high risk/high return proposition, because it could consume the budget for a decade only to fail because of eventual political cancellation or because one of the many critical mission stages ends in disaster. Combining the Jupiter Europa Orbiter with several New Frontier and Discovery missions would be a less risky approach, but would leave key questions about Mars -- the most Earth-like world -- unanswered.
It will be very interesting to see how the Decadal Survey resolves these problems. The Survey members could go for a compromise that funds the first element of the Mars sample return mission (the ~$1.9B sample acquisition rover), the Jupiter Europa orbiter, and a modest New Frontiers and Discovery program. Or they could decide to radically restructure the shape of the program and bet big on Mars or to go only with smaller missions. The Nature article suggests that we may see the first draft of the proposed plan this Fall.