OSIRIS-REx, the NASA asteroid mission being run by the University of Arizona’s Lunar and Planetary Lab, is ramping up its public outreach as it prepares to launch — in about three years.

Dante Lauretta, principal investigator for the mission, started the mission’s three-digit countdown clock at “999” Monday at a ceremony at the Michael J. Drake Building near campus.

The $1 billion mission, which will investigate a potentially dangerous near-Earth asteroid and return a pristine sample of it to Earth, already employees about 100 scientists, technicians and students in Arizona and will staff up to 400 worldwide at its peak.

It is set to launch during a 39-day window that begins Sept. 4, 2016.

It will rendezvous with a 500-meter-diameter asteroid named Bennu in October 2019 and spend up to 500 days mapping its features and analyzing its composition before grabbing a small sample and returning it to Earth.

The return date is planned for September 2023.

The mission is undergoing its critical design review. The team, with members at Arizona State University, the Canadian Space Agency, MIT and Lockheed Martin has built working models of the cameras and instruments.

The suite of three cameras is being built at the UA.

The instruments are being subjected to “shaking and baking” tests that mimic the stresses of launch, Lauretta said.

In an effort to build public enthusiasm for the mission, the team has revamped its website and blog and will be posting daily on its Twitter and Facebook feeds.