NASA's OSIRIS-REx spacecraft, on a return mission to the far-off asteroid Bennu, will pass by Earth on Friday, and you're invited to wave as it goes by.

OSIRIS-REx — which has been orbiting the sun for a year — is on a seven-year mission to the asteroid. While the spacecraft is scheduled to arrive there in August 2018, it must undergo some manoeuvres to adjust its trajectory without using fuel, one of which is a gravity-assist.

The spacecraft will use Earth's gravity to slingshot toward the asteroid. This is fourth trajectory correction engineers have made to OSIRIS-REx.

On Friday, the spacecraft will fly just 17,000 kilometres above Earth at about 12:52 p.m. ET, between Antarctica and Cape Horn. OSIRIS-REx has already travelled 965 million kilometres.

To calibrate its instruments, four hours after its close pass by Earth, OSIRIS-REx will make scientific observations of Earth and the moon.

Look up and wave

NASA and the mission partners are asking the public to participate in the Wave to OSIRIS-REx social media event by taking photos of themselves waving. They can post the pictures on Twitter using the hashtag #HelloOSIRISREx.

Canada has contributed a vital piece of instrumentation to the mission, called the OSIRIS-REx Laser Altimeter, which will fire a laser and create a 3D map of the asteroid. It will be the most detailed map of an asteroid and provide scientists with information on the asteroid's shape, rocks and topography.

The flight unit of OLA, the Canadian Space Agency's contribution to NASA's OSIRIS-REx mission. OLA consists of two parts: an electronics box (left) and the sensor head (right) housing two lasers that fire short laser pulses and a receiver to capture the beam that will bounce back from the surface of the asteroid Bennu. (NASA/Goddard Space Flight Center/Debora McCallum)

This is a unique mission: aside from mapping Bennu, OSIRIS-REX will also collect samples from the asteroid and deliver them back to Earth, a first for NASA.

Bennu was chosen in part for its relative proximity to Earth. It is also known as a carbonaceous asteroid, one that is carbon-rich and that has changed very little since the birth of our solar system 4.5 billion years ago. It's believed that asteroids like it could contain organic molecules and amino acids, some of the building blocks of life.

OSIRIS-REx will return to Earth on Sept. 30, 2025.