Adjusts Course

OSIRIS-REx Adjusts Course to Target Sample Capsule’s Landing Zone

Lonnie Shekhtman

On Sept. 10, NASA’s OSIRIS-REx spacecraft briefly fired its ACS (attitude control system) thrusters to point itself toward Earth, putting it on course to release its sample capsule, carrying rocks and dust from asteroid Bennu, from 63,000 miles (or 102,000 kilometers) above Earth’s surface on Sunday, Sept. 24.

Yesterday’s trajectory-correction maneuver changed the spacecraft’s velocity about a ½ mph (less than 1 kph) relative to Earth. Without this tiny but critical shift, the spacecraft and its asteroid cargo would have flown past Earth.

But now, the spacecraft is set up to release the capsule to enter the atmosphere just off the coast of California at 8:42 a.m. MDT / 10:42 a.m. EDT.

Traveling at a precise speed and angle, it will land approximately 13 minutes after release in a 36-mile by 8.5-mile (58-kilometer by 14-kilometer) predetermined area on the Department of Defense’s Utah Test and Training Range southwest of Salt Lake City.

Meanwhile, about 20 minutes after releasing the sample capsule, the spacecraft will fire its engines to divert past Earth and onto its next mission to asteroid Apophis: OSIRIS-APEX (OSIRIS-Apophis Explorer).

OSIRIS-REx may fire its thrusters again on Sept. 17 if engineers determine that one final adjustment to its trajectory is necessary before it releases its capsule a week later.

The spacecraft is currently 4 million miles, or 7 million kilometers, away, traveling at about 14,000 mph (about 23,000 kph) toward Earth.