NASA’s robotic Mars exploration program is in crisis. A recent review of the plan of its flagship Mars Sample Return (MSR) mission pegged its cost at $10 billion, a price tag that threatens to preclude funding any other exploration missions to the Red Planet for the next decade and a half.
While the decadal plan issued by a National Academy of Science committee identifies the MSR mission as the top priority for NASA’s Mars exploration program, given the cost and schedule numbers now available, it is time for the rest of us to question whether the program of record still makes sense.
Let us consider the alternative. For the same $10 billion now projected to be spent on the MSR mission over the next 15 years, we could send 20 missions averaging $500 million each in cost. These could include landers, rovers, orbiters, drillers, highly capable helicopters, and possibly balloons or other more novel exploration vehicles as well. Instead of being limited to one exploration site, these could be targeted to 20 sites and carry a vast array of new instruments provided by hundreds of teams of investigators from around the world.
NASA claims that its Mars exploration program aims to search for life. However, the agency last flew a life detection experiment to Mars in 1976. With a robust program of this type, we could fly a dozen life detection missions to various locations and not only test the surface soil in various new ways for life but drill down to search much more life-favorable strata beneath the surface.
With a robust program of this type, we could do many other things. Helicopters of other aircraft could carry sniffers to search for methane vents, and study thousands of surface locations each time they land. Such craft could also scan the subsurface of the planet for caverns and hydrothermal systems using ground penetrating radars (GPR). The power of a radar return signal goes as the inverse fourth power of the distance from the transmitter to the target, providing an eight-order of magnitude advantage to aircraft over orbiters for this type of exploration. Most of Mars is underground. We should see what’s there.
These are just a couple of examples. For every instrument flown on Curiosity or Perseverance, there were 10 other good ones proposed that had to be excluded for lack of payload capacity. With a robust program of this type, many more instruments would get a chance to be flown. Not only that, but with plentiful missions in the queue, it would be possible to use the information provided by early missions to improve the engineering design of the exploration vehicles and identify the best instruments and target locations for follow-up investigations.
The science return from such a rich and varied program of this type would vastly exceed that offered by returning a few samples from one location on Mars. The authors of the National Academies of Science committee report apparently disagree. But there is another issue: Mission risk.
To be remotely competitive with the varied program, the MSR needs to actually return the samples it collects to Earth. What is the chance that will occur?
Let’s look at the numbers. In its history, NASA has flown 25 spacecraft to Mars, of which (if we include the Ingenuity helicopter in the count) 20 have been successful. That is a mission success probability of 0.8. The European Space Agency’s Mars spacecraft track record is two out of four, for a mission success probability of 0.5. The MSR mission, as currently conceived, includes two new NASA spacecraft (the sample return lander and the ascent vehicle), and one ESA spacecraft (the orbiter that will collect the sample in Mars orbit and return it to Earth.) If any of those three spacecraft fails, the mission fails. That means that to calculate the probability of mission success, one must put the success probability of each into series, and multiply them together. That means that, based on the individual risk presented by each of the principal flight elements alone, the overall probability of mission would be 0.8 x 0.8 x 0.5 = 0.32 or about one in three.
That estimate, however, does not include the additional risk associated with the interface between the flight elements, most importantly the success of the autonomous rendezvous and dock and sample transfer in Mars orbit between the Mars ascent vehicle and the sample return orbiter, which has never been done. Furthermore, the 0.32 estimate for the probability of MSR mission success only includes technical risk. It ignores programmatic risk, which in the case of the ESA orbiter is extremely high, as that program could easily be canceled should any one of a dozen governments have a change of heart about funding it any time over the next decade. Indeed, even if the ESA orbiter is funded, the probability is extremely high that it won’t arrive on time, as witnessed by the ongoing travails of ESA’s Rosalind Franklin Mars rover, which, while originally planned for 2018 launch, is now scheduled for flight in 2028.
In short, the MSR program of record is extremely high risk. It could very well not produce any science at all.
In contrast, the success of the varied program is virtually guaranteed. With 20 independent missions, each with a success probability of 0.8, the odds are that at least 16 of the 20 will succeed – most probably more, since later missions can take advantage of lessons learned on earlier flights.
Given these realities, it would be irresponsible for NASA to unquestioningly accept the National Academies of Science recommendations and put all its Mars exploration program eggs in the single high-risk basket of the sample return mission. At the very least, a study should be done comparing both the scientific return and risk of the MSR program of record against that of the varied program, assuming both are funded at the same level.
What is the best Mars exploration program that the American people can buy for their $10 billion? All options should be on the table. Congress should insist that NASA provide the numbers.
Robert Zubrin is an aerospace engineer and president of the Mars Society (www.marssociety.org). His next book, “The New World on Mars: What Can We Create on the Red Planet,” will be published in February by Diversion Books.
This article first appeared in the December 2023 issue of SpaceNews magazine.