The Mars sample return plan involves a large collection of challenges, but the central one is that the samples are currently on Perseverance, but eventually they must end up on a rocket that lifts off from the surface of Mars. This means that Perseverance will have to get close enough to the rocket’s landing spot—which we can’t choose precisely—to exchange the samples, potentially diverting it from science targets. It also cannot be too close when the rocket lands, as the landing of the rocket and related material could pose a hazard to the rover and its samples.
The original plan included a contingency. The persistence would approach after the rocket landed and the samples would be transferred directly. If that didn’t work for whatever reason, a second rover sent to Mars by ESA would act as a go-between, visiting a location where the samples were stored, retrieving them, and then delivering them to the rocket.
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In the new design, this second rover has been eliminated. In his place? Two helicopters. These will be delivered as part of the same payload as the rocket carrying the samples into orbit. As a result, the new plan includes only one land-based aircraft (beyond what Perseverance delivered) that will carry both the missile and the helicopters, greatly reducing the risk of the overall plan.
These helicopters, of course, will be based on the Ingenuity design, which was sent to Mars as a test vehicle and greatly exceeded expectations, completing 29 flights in a year. Given this experience, NASA is confident that the helicopters can be designed to carry small payloads and potentially complete multiple flights between the return rocket and wherever the samples are—either on Perseverance or at a cache location.
After that, the plan remains the same. The samples will be loaded into a container that will be placed on the NASA-designed Mars rover and carried into orbit. There, the container will be transferred to the Earth Return Orbiter, built by ESA, which will bring them back to Earth in 2033, when they will fall into the atmosphere for recovery and study.
The next step will be approval from ESA, after which both agencies will begin the preliminary design phase, which will handle all the details of the different vehicles that will be needed. Meanwhile, Perseverance has already collected a dozen samples from the red planet’s surface.
