Perseverance to establish sample cache for later return to Earth

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WASHINGTON — NASA and the European Space Agency have selected a location on Mars to cache samples collected by the Perseverance rover, one step in the overall process of returning those samples to Earth.

NASA announced Oct. 28 that the agencies agreed to deposit some of the 14 samples collected by Perseverance to date at a location dubbed “Three Forks” in Jezero Crater, near the remnants of an ancient river delta that once flowed into the crater. Those samples, encased in metallic tubes, will be picked up for return to Earth by later missions.

“NASA and ESA have reviewed the proposed site and the Mars samples that will be deployed for this cache as soon as next month. When that first tube is positioned on the surface, it will be a historic moment in space exploration,” Thomas Zurbuchen, NASA associate administrator for science, said in a statement.

The sample cache is part of a revised strategy for the overall Mars Sample Return campaign announced in July. That strategy does away with a European “fetch” rover that was to pick up samples cached by Perseverance. Instead, it will rely on Perseverance as the primary means of returning samples to a future lander, which will then launch them into orbit to be picked up by an ESA orbiter for return to Earth.

This cache serves as a backup should Perseverance be unable to return to the lander. That lander will have two small helicopters, based on the Ingenuity helicopter accompanying Perseverance, that will fly to the cache, collect sample tubes, and return them to the lander.

“The depot is risk mitigation if the rover does not make the long journey” to the lander, said Francois Spoto, the Mars exploration group leader at ESA, during a presentation about Mars Sample Return at the International Astronautical Congress (IAC) in Paris Sept. 20.

Perseverance had been taking duplicate samples from each site so that one set can be kept on Perseverance and the other deposited in the cache. “Once we’ve done that, we’ll stop double sampling and continue to build the cache to be retained on Perseverance,” said Jeff Gramling, director of the Mars Sample Return program at NASA, at the IAC presentation.

In the announcement of the sample cache plans, NASA also said that on Oct. 1 the Mars Sample Return program entered Phase B, which covers preliminary design work and completion of key technologies needed for the future lander mission.

Both NASA and ESA officials have remained reticent to discuss the costs of the revised Mars Sample Return architecture, including any cost savings from deleting the fetch rover and a second lander that would have delivered it. NASA generally does not provide formal cost and schedule estimates for a mission until it is ready to enter Phase C, where the design is finalized and fabrication of components begins.

Asked about the costs of Mars Sample Return during their IAC presentation, neither Gramling nor Spoto would give a specific cost or range of costs. However, they did estimate that ESA’s share would be 15-20% of the overall cost.