Foust Forward | The most expensive rocks in the solar system

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Can there be too much of a good thing? Perhaps, when it comes to asteroid samples. That’s what NASA discovered in October when its OSIRIS-REx spacecraft swooped down to collect material from the surface of the asteroid Bennu on a “touch-and-go” maneuver. The mission hoped to get at least 60 grams of rocks, but the sampling probe was so stuffed with material that it wedged a flap open, allowing some rocks to leak out. Mission controllers decided to accelerate the process of stowing those samples to avoid having the entire cache lost to space.

For many scientists, sample return is the apex of robotic planetary exploration. While there have been great strides in the development of instruments that can be sent to other worlds on spacecraft, they still pale in capabilities to those in laboratories on Earth. Bringing samples of those worlds to the lab, rather than trying to send the lab to those worlds, can offer better science, both now and for decades in the future as those samples are studied by ever-improving instruments.

The problem with sample return is that it is complex and expensive. The OSIRIS-REx mission cost NASA more than $1 billion, counting the spacecraft itself as well as launch and operations. If OSIRIS-REx returns in 2023 with around a kilogram of samples of Bennu, in line with project officials’ best guesses, that works out to $1 million per gram. The price of gold is about $60 a gram.

The challenges are even greater with Mars. NASA launched the Mars 2020 rover mission in July as the first phase of its effort to return samples from the red planet. But that $2.7 billion mission is just the beginning: it will simply gather several hundred grams of rocks, sealing them in tubes either kept on the rover or cached on the Martian surface.

Two more missions will follow. One will land and deploy a rover to pick up the Mars 2020 samples, put them into a small rocket and launch it into orbit. The other will pick up that sample container in orbit and return it to Earth. It’s a complex, risky chain of events, the failure of any one of which would prevent the samples from making it to Earth.

NASA, wisely, wants to understand the feasibility of those missions before spending several billion dollars on them. In August, the agency commissioned an independent review of its Mars sample return plans, and released the final report Nov. 10. The good news: “We unanimously believe that the Mars Sample Return program should proceed,” David Thompson, the chair of the panel, told reporters.

The bad news: NASA needs more time. NASA, working with ESA, is planning to launch the lander and orbiter missions in 2026, collecting the samples in 2028 for return to Earth in 2031. But, Thompson said, the schedule for doing so is not “compatible with recent NASA experience.” In other words, delays with other programs make it likely these missions will also slip.

The panel recommended delaying the orbiter and lander missions to 2028, and also increasing its budget to as high as $4.4 billion. NASA officials said they would consider that recommendation but won’t make a decision for about a year. The agency has dozens of other recommendations to analyze, such as splitting the rover and rocket onto separate landers.

That revised cost estimate could bring the total cost of Mars Sample Return, when including both Mars 2020 and ESA’s contributions, to nearly $9 billion, or about the same as the James Webb Space Telescope. If all goes well, it will provide about half a kilogram of samples, or nearly $20 million per gram of Martian rocks and soil.

Scientists, though, argue it’s worth it, giving them material that they can study in labs for years. “It’s all about the samples,” Thompson said. In that case, it may be wise to stuff those sample tubes as full as possible, and get the most for their money.


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Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. His Foust Forward column appears in every issue of the magazine. This column ran in the Nov. 16, 2020 issue.