This illustration shows Osiris-Rex touching asteroid Bennu during a sample collection operation.

NASA’s Goddard Space Flight Center

We know it can be done. Japan’s Hayabusa-2 spacecraft triumphantly scooped up a bit of asteroid Ryugu before heading home. NASA hopes it will soon have similar success with the Osiris-Rex mission currently in residence at asteroid Bennu. It’s going to be challenging.

NASA is days away from choosing a sample site for its intrepid spacecraft’s sample collection operation, the agency  announced on Wednesday. It hasn’t been an easy process. In July, NASA narrowed the options down to four sites with bird-themed names: Nightingale, Kingfisher, Osprey and Sandpiper. 

These are the four potential sample sites on asteroid Bennu.

NASA/Goddard/University of Arizona

Osiris-Rex has been performing reconnaissance flybys of the sites, snagging high-resolution images and giving its team plenty of food for thought. 

Bennu is a much messier, rockier place than NASA expected. It’s littered with boulders, some of which are as big as buildings. 

The agency had hoped to find a spacious sandy area free of obstacles. “In reality the potential sample sites are not large, clear areas, but rather small spaces surrounded by large boulders, so navigating the spacecraft in and out of the sites will require a bit more fine-tuning than originally planned,” said NASA in a release on Wednesday.

Osiris-Rex has a built-in safety system that will abort the sample collection run if the spacecraft detects a potential hazard. The trick will be navigating it down to Bennu’s surface in a spot that won’t trigger the system. 

“If the spacecraft executes a wave-off while attempting to collect a sample, that simply means that both the team and the spacecraft have done their jobs to ensure the spacecraft can fly another day. The success of the mission is our first priority,” said deputy project manager Mike Moreau.

We’ll soon know which bird will come out on top. NASA will name a primary and a backup site. Sample collection is scheduled for mid-2020. If all goes well, Osiris-Rex will bring a bit of Bennu back to Earth in late 2023.