It will drop off a sample return container in the Utah desert in a highly choreographed operation, while the spacecraft itself speeds off to another destination in space. 

OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) left asteroid Bennu after surveying the asteroid in 2018 and collecting the samples in 2020. 

Dante Lauretta, OSIRIS-REx principal investigator, called the spacecraft a “daredevil” because of how close it came to Bennu during its orbit and its audacious but brief “touch and go” sample acquisition. It used a special collector that reached out and plunged its arm into the asteroid’s loose surface, grabbing rocks and pebbles before quickly moving away, like a cunning jewel thief.   

Dropping off the sample return capsule from space so that it lands in a precise location on Earth — a remote area measuring 36 by 8.5 miles (58 by 14 km) — is daring as well. 

"It's the equivalent of throwing a dart across the length of a basketball court and hitting the bulls-eye," said Rich Burns, the mission’s project manager, during a media briefing last week.

When it approaches Earth, OSIRIS-REx won’t slow down to release its cargo. If all parameters are met, when the spacecraft is 63,000 miles (102,000 kilometers) from Earth — or about one-third the distance from Earth to the Moon — ground controllers will trigger the capsule’s release. The capsule will hurtle unpowered toward our planet for four hours, then at 10:42 AM EDT, begin plummeting through the atmosphere at about 27,650 mph (44,500 kph). 

Atmospheric drag will slow the capsule enough for parachutes to deploy, with the main chute unfurling about a mile above the Department of Defense’s Utah Test and Training Range. If all goes well, the capsule will touch down gently at just 11 mph (17 km/h), in a large unpopulated area. From entering the atmosphere to reaching the ground will take just 13 minutes, and a recovery team will be waiting to retrieve the capsule. 

NASA will provide a live stream of the sample being delivered to Earth beginning at 10 AM ET on its website and Youtube channel. 

Of course, all the safety parameters must fully align before the capsule is released. Most important is OSIRIS-REx’s trajectory, which determines the capsule’s ability to survive the angle and temperatures of entry. It also must be precisely on target for an accurate landing, ensuring the safety of the ground crew on hand within the landing zone. 

Controllers have been monitoring the spacecraft’s flight path, and performed a thruster burn on September 10th, putting it on course to release the sample capsule.

On September 17th, NASA’s engineers slightly shifted the OSIRIS-REx’s trajectory to refine the landing location. The spacecraft briefly fired its thrusters to change its velocity by 7 inches per minute (3 millimeters per second) relative to Earth. This final correction maneuver altered the sample capsule’s landing location east by nearly 8 miles (12.5 kilometers) to the center of its predetermined landing zone.

“We do have a ‘go no-go’ decision point,” said Sandra Freund, OSIRIS-REx program manager at Lockheed Martin, the company that built the spacecraft. “We fully expect that decision to be a ‘go’ at two o'clock in the morning local time on September 24th so at that point the mission operations team located at Lockheed Martin in Littleton, Colorado will be sending the commands to the spacecraft to start the sequence.” 

If for some reason the landing needs to be aborted, the spacecraft will be diverted to an orbit that brings it back for another try, but not until 2025. 

But if all goes well, about 20 minutes after releasing the sample capsule, the spacecraft will fire its engines to divert past Earth and head onto its extended mission to study asteroid Apophis. The spacecraft will then be christened with a new name, OSIRIS-APEX (OSIRIS-Apophis Explorer), and reach the asteroid in 2029. After its discovery in 2004, asteroid 99942 Apophis was thought to be one of the most hazardous asteroids that could potentially impact Earth. But that assessment changed as astronomers tracked Apophis, and now there is no risk of this asteroid impacting our planet for at least a century. 

The OSIRIS-REx sample return container will be sent to NASA's Johnson Space Center in Houston to be studied in a new state-of-the-art curation facility and laboratory, which replaced the original Lunar Receiving Lab which housed the samples of Moon rocks brought back by the Apollo astronauts. After the initial study, Lauretta said a briefing is already scheduled for October 11th to share the first findings. Portions of the asteroid samples will also be shared with researchers around the world. 

While Japan's space agency, JAXA, has retrieved asteroid samples twice, from Itokawa and Ryugu, this is the first asteroid sample return mission for NASA. But OSIRIS-REx’s sample is the largest sample collected from beyond the orbit of the Moon. Mission scientists estimate there is about a cup of rocky material on board — about 8.8 ounces, or 250 grams — collected from the surface of Bennu. This ancient space rock — or "grandfather rock," as the team has been calling it — could provide clues about how the entire solar system evolved over 4.6 billion years. 

“There’s a story these samples are going to tell us,” Lauretta explained. “We're going back to the dawn of the solar system and looking for clues as to why Earth is a habitable world, a rare jewel in outer space that has oceans and a protective atmosphere. We think all those materials were brought by these carbon-rich asteroids very early in our planetary system formation. Of course, the biggest question — the one that drives my scientific investigations — is the origin of life. How did it originate and why was the Earth the place where it occurred?”

Studying the Bennu sample could also aid in planetary defense. Astronomers estimate the 1,614-feet-(490-meter)-wide asteroid has roughly 1-in-1,800 chance of hitting Earth in the next 300 years.

The return of OSIRIS-REx’s samples is the beginning of what NASA is calling “Asteroid Autumn.” After the sample return in September, SpaceX is targeting early October for NASA's Psyche mission to a never-before-seen metal-rich asteroid. November brings the Lucy mission’s flyby of the small main belt asteroid Dinkinesh, and then it will go on to explore seven Trojan asteroids, a population of primitive asteroids orbiting in tandem with Jupiter. These asteroids are thought to be relics of the early solar system and fossils of planet formation.