Why Is a NASA Spacecraft Currently Orbiting an Asteroid?

While much of planet Earth stays home to stop the spread of the coronavirus, the OSIRIS-REx spacecraft hovers 105 million miles away in the ultimate act of social distancing. The NASA spacecraft has been in orbit around the asteroid Bennu since 2018 with the goal of eventually grabbing a sample from its surface and returning that sample to Earth.

The sample grab is planned for August 2020, so in April, the team of scientists and engineers behind the OSIRIS-REx mission had a dress rehearsal of sorts. They practiced two of the four steps the spacecraft will have to perform to leave its orbit, approach the asteroid’s surface, and retrieve the sample before backing away.

First, they fired the spacecraft’s engines so that it left its safe orbit of 1 kilometer (or 0.6 miles) away. Then, while on its approach, they performed a checkpoint burn or a second engine firing. That's when the spacecraft checks its location and adjusts its position so that its trajectory heads toward the planned sample retrieval site. The spacecraft continued its approach, making it within about 75 meters (or 246 feet) of Bennu, but then backed away.

The whole smash-and-grab event will take only five seconds of actual contact between spacecraft and asteroid.

The team also practiced successfully deploying the spacecraft’s Touch-And-Go Sample Acquisition Mechanism—a fancy name for its arm, which will extend toward the asteroid’s surface to grab the sample. The whole rehearsal took about four hours and was performed mostly by a team of scientists operating from home. (Talk about working remotely!) During it's close approach, the spacecraft took pictures. You can check out the detailed images of the asteroid's surface on the mission website.

When the real sample grab happens in August, OSIRIS-REx will fire a charge of pressurized nitrogen. This blast is meant to stir up the surface so that the arm can collect a sample before the spacecraft backs off. The whole smash-and-grab event will take only five seconds of actual contact between spacecraft and asteroid. The spacecraft is planned to eventually begin its two-and-a-half-year journey back to Earth in March, 2021.

Why are we orbiting an asteroid?

Asteroid Bennu is one of a subset of elite asteroids classified as PHAs, or potentially hazardous asteroids. This means they cross Earth’s orbit and are large...

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