There are many ways to decide on what would be a compelling mission. One would be on the vicarious thrill of exploration. On this basis, I would favor missions such as the Venus SAGE lander, the AVIATR Titan plane, and the Argo Neptune-Triton-KBO mission. (All would also provide great science.) However, nations chose to fund these expensive mission primarily on their scientific return. So I have taken that as my criteria. Which set of missions would most fundamentally advance our understanding of the solar system?
A recent paper in the scientific journal Astrobiology, New Priorities in the Robotic Exploration of Mars: The Case for In Situ Search for Extant Life (subscription or purchase required), has got me rethinking the priority for a Mars sample return. Mars has been the major focus of NASA's planetary program for the last 15 years. With the recent cooperative agreement, it has also become a major focus for ESA. Review board after review board for the last 30 years have concluded that the highest priority for Mars exploration is to return samples to Earth (see, for example, the 2003 Decadal Survey report). The mission has been recommended for flight at the earliest opportunity, but NASA's budgets have never permitted the mission to begin development.
There have been scientists who recommend a slower approach. Mars is highly diverse and we have explored its surface in only six places, and landing safety concerns limited our choice of places to explore. Samples of past or present life are likely to be hard to find. Instead of rushing to a sample return, these scientists argue, fly a number of landed missions, probably most of them rovers, to find the best place to return a sample. This, in a nutshell, is the argument the authors make in the New Priorities in the Robotic Exploration of Mars paper.
At least based on presentations at meetings and the roadmap adopted by the Mars science community (principally through MEPAG), this appears to be a minority view. Most of the community apparently has decided that we know enough about Mars to pick a very interesting site. The samples returned from that site when analyzed with Earth-based instruments (most of which would be larger than the rover collecting the sample and some of which would be larger than the launch vehicle -- size and power counts for sophisticated study at the scale of individual rock grains) would greatly deepen our understanding of the early history of terrestrial planets. Only Mars preserves that early history on a body that had both a significant atmosphere and liquid water.
Long term readers of this blog know that I am a skeptic on Mars sample return. Not because I don't think the science is absolutely compelling -- it is -- but rather because I doubt that Congress will fund a $6B+ program for robotic exploration. I've come to reevaluate that position, though. Congress has funded the James Webb Space Telescope to the tune of over $5B (but at the cost of the astronomy program foregoing many other missions). Also, events seem to make this the time to move forward:
- Fifteen years of missions by NASA and ESA to Mars have revolutionized our understanding of the Red Planet. We may not be able to pick THE most compelling site on Mars, but we can pick A (and actually several) very compelling sites.
- JPL has developed for the Mars Science Laboratory the entry, landing, and roving technology essential to carry out this type of mission. (Of course, it also hasn't been flight tested...) If NASA does not continue a program to use this technology, the key engineers will move on to other projects. As it is, waiting seven years between the launch of MSL and the proposed Max-C sample caching rover is stretching the period over which teams can be kept together.
- The opportunity to fly the caching rover with the ExoMars in 2018 rover is unique. ExoMars can allow samples to be collected from up to two meters below the surface while Max-C collects samples at the surface. This could greatly enhance the value of the returned samples.
- ESA has agreed to partner with NASA on a sample return (exact roles and funding levels to be determined). This offers an opportunity to share costs that may not come again.
So, I have come to decide that moving towards a Mars sample return with the 2018 Max-C rover/ExoMars mission is the most compelling mission to me on the list of missions under consideration by the Decadal Survey. This mission depends on an orbiter being launched by 2016 to act as a communications relay; the Mars Trace Gas Orbiter is currently slotted for this role. Together, the two missions would cost NASA probably $3B, perhaps as much as $4B with inflation and cost overruns (ESA would also make a substantial contribution for the orbiter and the ExoMars rover). This would represent a quarter to a third the expected NASA planetary mission funding for the next decade.
There is the risk that the current estimates for cost will turn out to be wildly optimistic and the true costs will eat up a large portion of the planetary science budget. After approval, politicians could cancel the mission to save money. It happened with the Venus Orbiting Imaging Radar mission in 1981 (the eventual Magellan mission was less capable), the Comet Rendezvous and Asteroid Flyby mission (ESA's Rosetta eventually filled this slot), and almost happened to the Galileo mission.
Given these risks, I favor a go slow approach. Fly the Max-C and ExoMars rover in 2018. Wait until we know there is a compelling set of samples waiting on the surface for pickup before committing to the next mission in the sequence (see this blog entry for a description of the three missions needed to return a sample to Earth). If the 2018 mission fails or is skunked, launch another rover to find and cache a compelling set of samples. Under this approach, the earliest a sample could be returned would probably be 2028 (instead of the current strawman for 2026).
Going with a sample return mission isn't without its risks, both technically and politically. However, the return seems to me to be greater than any other mission on the list.
I hope to hear your opinion whether or not you agree or disagree.
I agree. This mission has the potential to become a complexity quagmire, a delay hell, a budget bottomless hole, a delay purgatory - and when it fails (and the chances are good), a blight on the chances of other unmanned program targets and aspirations for years and years.
ReplyDeleteMars sample return should wait for humans. If that means waiting a long time then so be it.
FWIW
P
Very interesting commentary. My most compelling mission would be the Jupiter-Europa Orbiter, JEO. It would scout Europa for an ocean and future landing sites. In addition, it would recover a lot of the Jupiter science lost when Galileo's high-gain antenna would not deploy. Especially intriguing would be long-term observations, including movies, of Jupiter's system of clouds.
ReplyDeleteHowever, I do find a Mars Sample Return to be fascinating. I posted a proposed sequence of Mars missions leading up to sample return in the comment section of the October 2, 2010 blog entry. The key to any proposed scenario is cost. Any way that NASA can cooperate with other nations, as well as its manned flight division, would be welcome.
One element that is always needed is orbital relay. One way or another, I think that NASA should try to convince the Indians or Japanese to provide this relay capability. That would take care of one ongoing expense. By 2020, either country should have gained enough experience with lunar and planetary orbiters to be a reliable partner. However, my betting is that Japan will be the most prepared.
As I mention in my earlier post of October 7, 2010, I think that NASA's manned spaceflight division should be ready to assist with Mars Sample Return in the 2020's. If an unmanned Orion capsule, on a dry run to Mars orbit, could be modified to capture the orbiting sample canister, and return it to Earth, we would have a win-win situation. The unmanned division would save a lot of money, and the manned flight division would gain experience.
Van, it was a bit eerie to read this because I have had some recent religious conversion myself on the topic of Mars Sample Return. I remain just as ignorant as I was about the crucial question of engineering challenges. Is it destined to become a quagmire of upcoming delays? I don't know.
ReplyDeleteBut the science interest is much more compelling as a new perspective arises, and this information was beneath my radar, and perhaps is for some who read this:
It now seems that Mars was, because of the patterns of volcanic activity, chemically more suitable for life in the first half billion years than it was in the next half billion years. MER has found us the sulfurous, salty remnants of the second time period; the compelling argument for MSR would be that the first time period is entirely more likely to be an era of past life. Moreover, the geology of candidate sites for future landers offers a bonanza: Sites which offer Noachian *and* Hesperian samples within the range of one rover, with multiple suitable sites that have exposed rock which formed in this earlier era.
In other words, MER's findings (jarosite and hematite at Meridiani) are an informative dead end. But some of these other sites might give us the holy grail: Fossil evidence of ancient life in an aqueous environment.
A large number of documents are available here:
http://mepag.jpl.nasa.gov/decadal/
Especially "Why Mars Remains a Compelling Target for Planetary Exploration".
And a tremendously interesting overview is here:
http://www.geochemsoc.org/publications/geochemicalnews/gn142jan10/diverseaqueousenvironments.htm
To get back to the question, I think an N-mission exploration of Mars culminating in MSR sounds to me like an excellent pathway with a relatively well-defined endgame; it ought to be pursued if the engineering makes sense. But it's not one mission, and it will take two decades to bring about.
I think mankind should dedicate itself to the Mars and Europa pathways. Titan is perhaps more interesting than either of those worlds, but the exploration pathway is going to be hard. I think the best path forward is, with a tragic delay of what is sure to be wonderful exploration at Titan, to get the "twenty questions" games underway at Europa and Mars. Then we might devote ourselves to Titan when the massive Mars campaigns yet to come are completely and totally brought to a (tentative, of course; everything is tentative) conclusion around 2028. Europa would continue as a pathway, but involving, always, a lower rate of launches than a Mars program allows.
Venus (and the non-Europa jovian system, besides observations of opportunity) will lose out or eke out intermittent missions. Because, unfortunately, we just can't do four targets right at the same time.