NASA’s First Asteroid-Sampling Mission, the OSIRIS-REx Probe, Arrives at Bennu

Yesterday (Dec. 3) NASA’s first asteroid-sampling mission, the OSIRIS-REx probe, arrived at its destination. However, there is still lots of prep work to do before the spacecraft can dig into the diamond-shaped asteroid known as Bennu.

This event marked the end of a deep-space chase that lasted 27 months and covered over 1.25 billion miles (2 billion kilometres).

The primary objective of the $800 million OSIRIS-REx mission involves sending a sizeable sample of asteroid material back to Earth in 2023. However, the spacecraft is far from ready to gather any space-rock debris. First, OSIRIS-REx isn’t even in orbit around the 1,650-foot-wide (500 meters) Bennu yet; it’s presently flying alongside the asteroid, just beginning to take its measure in detail.

OSIRIS-REx will continue to do so over the next four weeks, during close flybys over Bennu’s north pole, equator and south pole that will bring the probe as close as 4.4 miles (7.1 kilometres) to the asteroid’s surface.

Mission team members want to make sure they pinpoint Bennu’s mass and precise shape before slipping into orbit around the asteroid on Dec. 31.


Well, even though Bennu has been adequately characterized by ground-based instruments over the years, maneuvering around a small body that has no gravity is a very challenging feat, said OSIRIS-REx Deputy Principal Investigator Heather Enos, of the University of Arizona. She added that they do have to get a little more information to proceed every step of the way.

On New Year’s Eve, OSIRIS-REx will be moving only 4 inches (10 centimetres) per second relative to the asteroid Bennu when it achieves orbit around the rock, as permission team members.

What’s more, Enos explained that OSIRIS-REx will set a record for the closest distance that a spacecraft has ever orbited a small body. The probe will get within just 1 mile (1.6 km) of Bennu’s surface on Dec. 31st.

Even after orbital insertion things won’t move any faster. OSIRIS-REx will spend another 18 months ardently seeking the best place to collect its sample. The mission team expects to narrow the possibilities to two sites by July 2020, which is when the gathering of this sample is scheduled to occur.

On that day, OSIRIS-REx will spiral down and tap Bennu with its Touch-And-Go-Sample Acquisition Mechanism (TAGSAM), sucking up at least 2 ounces (60 grams) of material. The maneuver will be more of a kiss than a landing, with a duration of only 5 seconds or so.

OSIRIS-REx, which is short for “Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer,” will depart Bennu in March 2021, when it heads back toward Earth. The asteroid sample will touch down in Utah, tucked inside a special return capsule, in September 2023.

Researchers from all over the world will begin to examine the space stuff with a variety of high-tech tools in the form of big and expensive equipment that could never have fit aboard OSIRIS-REx. Although the spacecraft is equipped with five science instruments of its own. This analyses will focus on the primary mission goal, which is helping researchers learn more about the solar system’s early days and the role that carbon-rich asteroids like Bennu may have played in life’s emergence on Earth.

The data gathered by OSIRIS-REx will be useful in many ways, however. For instance, the probe’s measurements, and those of researchers examining the sample should shed a lot of light on the resource potential of asteroids like Bennu.

Furthermore, OSIRIS-REx’s precise tracking of Bennu through space will aid researchers in learning more about the non-gravitational forces (notably, the Yarkovsky effect) that form asteroids’ trajectories. This work could improve asteroid-impact forecasts, said NASA officials.

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Jessica Zeitz