Asteroid-bound spacecraft slingshots past Earth

Gravity assist will alter its trajectory while saving fuel.

Laurel Kornfeld | Oct 29, 2019

Traveling through space at 19,000 miles (30,000 km) per hour, NASA's Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft is flying by Earth on Friday, September 22, using the planet's gravity to redirect its path to the asteroid Bennu.

Launched a year ago from Cape Canaveral on an Atlas V rocket, the spacecraft will arrive at Bennu in November 2018. It will orbit the asteroid, identify ideal surface locations for collecting samples, then use a robotic arm to reach into the surface to take the samples and store them inside a special collection device.

In 2021, OSIRIS-REx will head back toward Earth where, two years later, it will return the samples by parachuting a canister containing them into Utah.

From there, they will be taken to NASA's Johnson Space Center in Houston, where scientists will analyze them for organic molecules and materials that make up the building blocks of life.

An Earth flyby is necessary to propel OSIRIS-REx to its target because a direct flight would have required additional fuel that would have mandated it launch on a larger rocket.

"It was a way to substantially save on resources, either on the spacecraft or on the launch vehicle, or both," said mission principal investigator Dante Lauretta of the University of Arizona.

The flyby, which takes the probe within about 11,000 miles (17,000 km) of Earth's surface, will increase its velocity by 8,400 miles per hour.

NASA will be out of contact with the probe for about an hour during closest approach while it flies over Antarctica.

"OSIRIS-REx uses the Deep Space Network to communicate with Earth, and the spacecraft will be too low relative to the southern horizon to be in view with either the Deep Space tracking station at Canberra, Australia, or Goldstone, California," explained Mike Moreau, NASA Goddard Space Flight Center flight dynamics system lead.

The spacecraft will photograph the Earth and Moon with its three imaging cameras for as long as 10 days after the flyby.

Earth data will be collected by its thermal emission spectrometer and visible and infrared spectrometer for instrument calibration purposes.

Members of the mission team plan to release photographs collected by the probe on Tuesday, September 26.