Mars Sample Deferred
The early successes of the Mars lander Curiosity — including the apparent discovery of long-lived, fast-running streams in Gale Crater — are astonishing. Mars scientists are rightly upset about NASA’s decision to indefinitely defer their next flagship-class mission: a several-billion-dollar effort to retrieve samples from Mars and return them safely to Earth.
Another key NASA decision was to better coordinate management and funding of automated missions with long-term preparations for a scientific outpost on or near Mars. That has rightly been humanity’s goal since the earliest beginnings of spaceflight.
These decisions, while correct, do not go far enough. Having two separate efforts to explore the same destination wastes money and time on dual development of similar technologies. It unnecessarily duplicates missions and even data analysis. NASA should fully combine management of Mars exploration under one organization with a fully integrated plan: assigning orbital and surface reconnaissance to automated spacecraft, and geological field work and sample retrieval to human expeditions.
A Mars rover, even a large and sophisticated one like Curiosity, can deploy only a severely limited set of miniaturized instruments for a relatively short period of time. A Mars sample retrieval, especially if combined with one or more rovers, could bring samples of Mars, documented in their scientific context, to Earthly laboratories for long-term study throughout the world. Terrestrial scientists have access to state-of-the-art instrumentation that does not need to be compromised through miniaturization. They could rapidly change their research approach based on analysis of prior results. Properly stored samples would be available on Earth for generations of scientists to study with constantly improving techniques and equipment.
Much of Mars’ geological record was created at about the same time that life on Earth was getting its start. Mars is smaller than Earth and therefore cooled more rapidly, freezing that early geology and chemistry in place.
The larger Earth kept the residual heat of formation longer. Earth’s greater volume also generated more thermal energy from radioactive decay, and these two sources keep Earth’s mantle in constant convection. The heat ultimately escapes to the surface, generating rapid geologic change. Almost all evidence of what the planet was like during life’s origins has been destroyed. Samples from Mars could provide some of the missing data.
If a Mars sample retrieval could help answer fundamental questions like these, why put the project on the back burner? In a nutshell, trying to automate the sampling of Mars in a way that could answer questions such as, “Could or did life evolve on Mars?” is probably impossible. It certainly would cost too much and take too long.
Even though Mars is smaller than Earth, it is still a very big place. The surface area is about the same as all of Earth’s dry land. The landscape is vast, often very rugged, and highly diverse.
Most automated Mars sample retrieval architectures are complex and technologically challenging. They are also likely to be extraordinarily risky. Creating a Mars ascent vehicle represents a difficult and expensive development and technical risk all by itself. It must be small enough to deliver to Mars’ surface in a relatively small spacecraft, yet powerful enough to launch from the surface of a major planet with a significant suite of samples. Serious engineering analyses of ways to achieve that have barely begun.
Any likely automated mission would not be able to gather samples from more than a few hundred kilometers from the landing site, with lesser distances being more likely. Where on Earth would you land to find a chemical fossil from life’s origins if you could only explore an area with that radius? If the objects of your search were rare or widely separated, what would your chances be of finding one with a single automated retrieval? How much can we afford to pay for a few samples from one tiny area lost in the vast and majestic deserts of Mars?
Automated solutions that would reduce program risk and cover larger areas — such as a larger number of retrieval missions or greater numbers of better rovers per mission — would rapidly drive up costs with only small improvements in the prospects of success.
The Mars Program Planning Group was chartered to decide how to proceed after the administration of President Barack Obama cut Mars funding by some 40 percent and withdrew from a European project to help prepare for retrieval of martian samples. According to the final report released Sept. 25, “Preservation of biological signatures is rare on Earth, and investigations at multiple sites on Mars dramatically improve the probability of identifying biologically relevant samples.”
Such signatures will almost certainly be even more rare on Mars. Realistically, finding them, even with a large number of multibillion-dollar flagship-class missions, is probably not possible and will never be affordable.
Successfully collecting scientifically useful samples with reasonable efficiency requires a sustained presence on Mars, one capable of reaching many sites and doing detailed field work over wide areas. Geologists must be able to quickly replan on the fly based on new results, rapidly sending fully equipped expeditions to entirely new and unplanned destinations. At each site, they must carefully sift through great volumes of carefully selected rocks and fines, and examine promising specimens in the lab to decide which to send to Earth for more detailed study. While this sounds simple, in practice these procedures are extraordinarily difficult to automate, especially on the large scale required to succeed.
To have any realistic chance of finding life or life’s remains on Mars, permanent scientific bases like those in Antarctica are not options. They are absolute requirements.
Even so, we should continue the automated reconnaissance of Mars. The good news is that the near cancellation of sample retrieval schemes and NASA’s call for cheaper alternatives have led to a number of new and innovative ideas, and to reconsideration of old ones. At the low-cost end of the range are ongoing projects like Mars Atmosphere and Volatile Evolution, to determine where Mars’ surface water and other volatiles went, and InSight, to understand Mars’ interior structure. Data from both of these missions will help geologists on Mars locate resources and minerals useful for “living off the land.”
A sample retrieval that is cheaper, simpler and in some ways better than NASA’s flagship Mars sample return project has been proposed as a Mars Scout mission. This inexpensive spacecraft would fly through Mars’ upper atmosphere at approximately 40 kilometers altitude, preferably during one of Mars’ semi-predictable global dust storms. It would collect dust and atmospheric gas in a gel-like substance indirectly exposed to the spacecraft’s slip stream, and bring both to Earth. No expensive landing is required, yet because martian dust is distributed globally, the mission would provide a far more representative sample than any targeted mission to one location. It could obtain significant results without attempting to duplicate the geological field work that only geologists can do well.
A 100-square-centimeter collection grid, similar to that successfully flown on the Stardust mission that retrieved samples of Comet Wild 2, might capture as many as 11 million particles, every one of them from a different location on Mars. The scientists who proposed this low-cost alternative argued it could determine the extent of weathering by water on Mars, provide isotope ratios that could greatly constrain possible surface processes, and unambiguously prove whether the meteorites found in Earth’s Antarctic ice fields are from Mars.
It is worth recalling that, most likely, we already have samples of martian rocks. These were splashed from the martian surface during ancient meteor impacts, eventually fell to Earth and were preserved in Antarctic ice. The samples are weathered and contaminated by Earth’s environment, and do not come from known geologic contexts on Mars. Their scientific utility is limited, but they have the great advantages of being numerous, diverse and relatively cheap and easy to obtain.
Other proposals use Mars rover designs derived from Spirit and Opportunity to achieve low-cost targeted science and to prospect for useful resources like methane and water ice.
Meanwhile, human spaceflight is experiencing dramatic change. The advent of the international space station as a fully functional laboratory allows routine space testing of exploration technologies and survival skills. NASA and Russia are planning a yearlong mission in 2015 to help prepare for deep-space expeditions. Space Exploration Technologies and other companies promise to slash the cost of delivering cargo to orbit, and the MPPG report repeatedly suggested the use of the Falcon 9 rocket to reduce costs. These developments potentially create conditions for rapid improvements in the capabilities and economics of human deep spaceflight.
A well-planned effort aimed at answering fundamental questions about the history of the most Earth-like of accessible worlds would start by flying a regular series of small Mars Scout and Discovery-class missions, getting the most reconnaissance and science for the least cost. The primary goal should be to locate resources, making it easier for geologists to live off the land and reducing the costs and fragility of supply lines from Earth. Landers should practice ways to convert the resources into useful fuel, oxidizer, and air and water. They could get a head start characterizing Mars’ toxic dust, developing ways to mitigate the affects of the highly oxidizing particles on humans and robots alike.
Rather than develop a specialized lander and a small and expensive Mars-to-orbit rocket that could retrieve only a few kilograms of rocks, NASA should start early development of the techniques and larger equipment required to deliver geologists to Mars and return them and their samples to orbit.
Even astrophysics and solar science missions should emphasize knowledge of the sun, solar wind and galactic particles needed to keep scientists alive on the way to Mars and other destinations.
Both MPPG and the National Research Council are wrong, however, to reject a “pathway” emphasizing increased knowledge of Mars with low-cost missions before committing to a sample retrieval. In the long term, avoiding the billions of dollars that flagship-class spacecraft would cost, and preparing for human exploration instead, would get better results, and likely would be cheaper, than sending the large numbers of robots needed to try to do what only human geologists can do well.
More than saving money, combining the resources of NASA’s human and automated bureaucracies might get scientists carefully collected samples earlier than would a fully automated strategy. Any human architecture for exploring Mars is likely to require one or more sub-scale test flights before risking human geologists.
Retrieving samples during a 10 percent scale test of a human mission, according to the MPPG summary report, could also provide flight demonstrations of hypersonic inflatable or rigid aeroshells for aerocapture, supersonic retro propulsion, and local oxygen and fuel production for the return flight. Human crews in Mars orbit or at the international space station could allow scientists to inspect the samples while still separate from Earth’s fragile biosphere. Having a human crew in the loop, especially one located in Mars orbit, could reduce the complexity, risk and cost of the robotic part of the mission, according to the MPPG, while also achieving early human deep spaceflight.
Scaling up already flight-proven spacecraft would be much easier than developing a human architecture from scratch. The first geologists to explore Mars in detail would put the retrieved samples into context. The world could get both a sample of Mars and the human exploration that might successfully find evidence of life, for only a little more time and money than doing either separately.
Best of all, such a strategy could lay the groundwork for a transportation system that could provide regular deliveries of large volumes of carefully selected samples to scientists on Earth.
Donald F. Robertson is a freelance space industry journalist based in San Francisco. For further examples of his work, see www.DonaldFRobertson.com.