This continues a series of posts inspired by a similar set of posts at Future Planetary Exploration blog selecting the 5 most compelling missions from the Planetary Science Decadal Survey list.
As should be no surprise, Mars is well represented in the Planetary Science Decadal Survey Mission and Technology Studies. My personal selection of the most compelling Planetary Science missions probably goes against the prevailing preference of the Planetary Science community, so I'm certainly not going to be so rash as to skip favored Mars in my list of compelling missions. The question then becomes which Mars mission should I select from the Decadal Survey's list?
The Survey includes 7 papers on Mars missions, but the choice isn't going to be as hard as that makes it sound. Two of the papers are on the same general topic - a Mars Geophysical Network mission. Three are on a 3-part series of missions to return Mars samples to Earth, and I'm simply going to rule out selection of the 2nd and 3rd of these missions in case the 1st fails or does not find samples that are interesting enough to deserve 2 additional missions to return. There is a study on Sky Crane capabilities for the 2018 Mars opportunity which really boils down to a potential augmentation of the first of the Mars sample return missions. Finally, there is an investigation on a variety Mars Polar Climate missions. In other words, there are 3 basic missions to choose from, possibly followed by additional choices on the details of the selected mission.
Out of the 3 basic mission choices, the first of 3 Mars Sample Return missions surely has the most backing within the Mars science community. That community has hungered for Mars Sample Return since, well, the Noachian period, it seems. Not only that, but the 2018 MAX-C Caching Rover, which is to perform this first phase of the sample return sequence, is part of a multi-component international collaboration between NASA and ESA. In 2016, NASA and ESA plan to launch the ExoMars Trace Gas Orbiter and an ESA Mars landing technology demonstration. The Mars Trace Gas Orbiter is intended to investigate methane and other trace gases on Mars. This will help select interesting destinations for the 2018 mission. The orbiter will also serve as a telecommunications relay for the 2018 lander elements.
The 2018 NASA-ESA collaboration uses the Sky Crane landing method of NASA's Mars Science Laboratory. However, instead of one larger rover, this time the payload is 2 smaller rovers. ESA will contribute the ExoMars Rover, which will be able to drill 2 meters and collect soil samples. The rover includes a variety of instruments to analyze the samples, drilled hole, and region around the rover.
NASA's 2018 contributions include the rocket, Sky Crane, and Mars Astrobiology Explorer-Cacher Rover. This rover would be able to rove 20 km over 500 sols, retrieve 19 ten-gram rock core samples, and store them in a cache that is easily fetched by the next phase of the sample return (with a backup cache that also holds 19 samples). The proposed rover instruments include a Panorama camera like the MER and Phoenix lander cameras to identify good sample sites and to give sample context, a NIR spectrometer for mineralogical mapping, an arm-mounted microscopic imager like the MER one, an Alpha-Particle X-Ray Spectrometer (APXS) similar to the MER and MSL ones to show what elements make up rocks the instrument is placed on, a Raman/fluorescence instrument to assess organics in rocks, and a sample caching system using an arm, drill, and caches.
All of this in-situ science and sample return preparation is compelling, but the decision becomes more difficult when costs are considered. The estimated FY15 cost (with the usual reserves) for NASA's contributions to the 2018 mission is about $2.2B. That's quite a lot. Now to be fair, the mission doesn't just do top quality in-situ science and take a big step towards the Mars sample return holy grail. It also delivers an entirely separate and capable rover from ESA that can do work that MAX-C can't, which probably makes the 2 rovers more valuable as a team than they would be as rovers at separate locations.
Still. $2.2B ...
The Sky Crane study raises an interesting possibility. Apparently, even with 2 rovers, there is plenty of room for additional payload for the mission. For an additional $150M, a basic geophysical Network Pathfinder could be delivered to the Martian surface with the 2 rovers. Mass delivery margin would be 29%, which is less than the 30% that is required, but this is close enough that a more detailed investigation might find ways to fit the additional payload comfortably within the mass margin like merging the Network Lander and landing pallet. The Network Pathfinder would include a seismometer and meteorological sensors. (More ambitious Network Pathfinder scenarios are also presented should the ESA rover not be assigned to the mission).
Still, it might be nice to see that Sky Crane actually work on Mars for MSL before developing the MAX-C plan.
The bottom line is that this is a compelling mission, but it's expensive. Is it compelling enough to be worth the expense (and therefore missed opportunities)? Will I let my emotional annoyance at the fact that the mission uses a whole new rover design after all the trouble we went to design and build MSL and the MER rovers before that, and even uses the Sky Crane in a different way (2 rovers instead of 1) get the best of me? Find out as I take a look at the Mars Geophysical Network and Mars Polar Climate mission concepts in the next 2 posts.