The capsule looks a little bit like a miniature UFO from a 1960s sci-fi flick. Resting on the ground, slightly tilted, its white heat shield flaked off in places, it looks how one would expect it to after speeding in from outer space and streaking across the sky like a shooting star. But looks can be deceiving, and the mini-fridge-sized object has, in fact, never left the surface of Earth.

Instead, it is a replica of the sample capsule mounted on NASA's OSIRIS-REx spacecraft, which has been cruising through space since it departed asteroid Bennu in May 2021 with an estimated half-pound of pristine asteroid material onboard. For training purposes, engineers placed the replica capsule on a field on June 27 at the Lockheed Martin campus near Littleton, Colorado, where the spacecraft was built.

The sun burns hot on this June day, and gusty winds stroke meadows chirping with unseen crickets as a dozen or so scientists and engineers read measurements off screens, hammer sampling cores into the ground and scribble notes into field journals. Somewhere up in a tree, a bird makes a noise that sounds startlingly similar to the iconic beeps and trills of R2D2, the famous little droid from "Star Wars."

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OSIRIS-REx team members from NASA, Lockheed Martin and the University of Arizona have gathered for two days to rehearse procedures for the next critical milestone of the mission: recovering the real capsule after it lands and extracting the sample canister in a clean room that will be set up at the Utah Test and Training Range for the actual landing on Sept. 24.

"We're literally on a playground here," says OSIRIS-REx principal investigator Dante Lauretta, a professor of planetary sciences at the UArizona Lunar and Planetary Laboratory, who took part in the rehearsal June 27-28. "We have room to mess up and practice for the real thing."

Lauretta has swapped his usual jeans for trail pants, a ball cap and hiking boots. Today is very special, he says, because it is the first time all members of the sample recovery team are working together. For the exercise, the recovery team members have taken their positions, divided into four groups – each group next to a wooden stake that acts as a stand-in for one of four helicopters that will take the team to the landing site once the capsule is on the ground.

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Picking up a container on the ground may not seem like a big deal. But when that container has just dropped from the sky via parachute, bearing 4.5-billion-year-old material collected from an asteroid, it is. A major goal of the OSIRIS-REx mission is understanding the organic molecular evolution of the early solar system, Lauretta explains. Bennu was chosen as the target asteroid because it contains what planetary scientists call primitive carbonaceous material, left over from when the first planets were born in the swirling cloud of gas and dust that would eventually become the solar system.

Unlike meteorites that have fallen to Earth unprotected, the Bennu sample has been shielded in its capsule from terrestrial elements – air, water, weather, soil and microbes. Researchers covet such pristine asteroid material because of its promise to help them find answers about how the solar system and, ultimately, life itself came to be.

"Even though we'll be landing in a desert, and even if it is a nominal landing and the capsule looks great, there are still organisms around," Lauretta says. "The risk of any of that material contacting the sample is really low, but it is not zero."

To address this concern, the team practices taking samples from the environment around the capsule to create a library of all the things that it could potentially have been exposed to – soil, air, organic matter and so on. At this point in the rehearsal, Lauretta's science team isn't allowed to go anywhere near the capsule, which is sitting in the grass next to a knee-high pile of dirt and rocks.

Before anyone can approach the capsule, Vicki Thiem, a safety engineer with Lockheed Martin, rehearses taking its temperature – which will be an important step during the actual sample return to ensure it has cooled down sufficiently from its violent atmospheric entry. Next, the safety team practices inspecting the area around the capsule for potential hazards and taking measurements to rule out any hazards from gases that might be emanating from it, plugging its pressure vents and capping off electric wires exposed during the descent. Once the capsule has been secured, Lauretta and his team walk around, inspect the terrain, point out observations and plant little red flags in the ground to demarcate a "keep-out zone" where they don't want other team members to step.

"In the real event, we'll be particularly interested in documenting the tracks the capsule left as it landed, because most likely it's going to bounce or roll for a bit before it comes to rest," Lauretta says. "We need to document the environmental conditions that the sample capsule sees when it comes in, in as much detail as possible." 

Since its inception by the late Michael J. Drake, Lauretta's mentor and former director of the UArizona Lunar and Planetary Laboratory, the OSIRIS-REx mission has been designed around the idea of keeping a record of the capsule's history while keeping the mission's procedures as robust and simple as possible, according to mission experts.

"Even before we began building the spacecraft, as the clean rooms were set up, we documented every environment that this capsule has seen, even in space," he says.

So-called witness coupons inside the capsule record exposure to gases or particles shaved from moving parts, such as motors, and document the entire history of the capsule.

"That way, if you find something that looks really fundamental to the origin of life, you have no doubt, and you should be able to rule it out as a contaminant because of that documented history," Lauretta says.

Because the capsule will reach atmospheric pressure during its descent from space, it is outfitted with several layers of filters to remove particles and certain gases, preventing them from coming into contact with the sample. One of the first actions the recovery team will perform is to attach a hose that will bathe the sample in a continuous supply of ultra-pure nitrogen gas, says Richard Witherspoon, who leads ground recovery operations at Lockheed Martin.

"We have a significant amount of time to do our recovery operations, so we don't need to hurry," Witherspoon says. "We allotted about two hours for the recovery, which gives us a good balance of having enough time in the field to assess, take soil and air samples and get the capsule back without rushing the team. In the unlikely event anything doesn't go quite as planned, the team is prepared to move faster than that."

Once it has been secured, two people lift the capsule replica, which weighs about 100 pounds, into a metal crate and wrap it in multiple sheets of Teflon and a tarp. Next, they attach a harness to the crate so it can be attached to a cable, which would be attached to a helicopter. This is where the exercise ends.

The next round of sample recovery rehearsals will take place in Utah, where activities will get more realistic – or "flight-like" as Lauretta puts it – involving helicopters and training at the actual landing site. During the actual return event, after recovering the capsule and getting it ready for transport, the capsule will be taken to a clean room set up at a hangar, where crews will open it and extract the sample canister. The next day, it will be flown to NASA's Johnson Space Center in Houston, Texas, for disassembly and extraction of the sample for immediate analysis and preservation for the future.

Lauretta says the June rehearsal is just a "faint shadow" of what he expects to be experiencing on landing day.

"Just like today, I'll be working next to the capsule, but for the real thing, I will know there's an asteroid sample sitting inside," he says. "I'll know I'm supposed to be digging soil and collecting water samples, but all I'll really want to do is open that thing and see what's inside."