After 688 days around asteroid Bennu, OSIRIS-REx's big day is finally here. The NASA spacecraft will today perform the crucial objective of its mission – to fly down to the rubbly surface of the asteroid and grab a pristine sample of Bennu's soil.
In its 22 months orbiting the asteroid, OSIRIS-REx has collected fantastic data. This has led to several intriguing discoveries about the asteroid as well as allowing the team to select the best place for the sampling event, a spot they have nicknamed Nightingale. Now, the craft will at last fly down and scoop up at least 60 grams (2.1 ounces) of regolith, and if we're lucky up to 2 kilograms (4.5 pounds), to return to Earth in 2023.
“From a science standpoint and from a mission achievement standpoint, this is really the core moment,” Beau Bierhaus, OSIRIS-REx scientist at Lockheed Martin, told IFLScience. “This is where we accomplish what the mission set out to do.”
The spacecraft will not land actually on Bennu. Instead, it will get very close to the surface where it will extend its Touch-and-Go Sample Acquisition Mechanism, or TAGSAM, an articulated 3.35-meter-long (11 feet) arm, down to the soil. After making contact with the ground for around 10 seconds, it will shoot nitrogen gas at the ground, which will cause fine grain material to lift up and get trapped in the sample collector.
If the collection is successful – and it will be 10 days before we know for sure if it is – OSIRIS-REx will continue to study Bennu for several months before slowly journeying back to Earth in September 2023 with its precious cargo. It will take a few days for the spin of the spacecraft to indicate a change in its mass that shows it is carrying the sample material. So there's a lot of trepidation about what can and will happen today.
The collection is not without its challenges. The asteroid has a gravity many thousands of times weaker than Earth, so sunlight hitting the spacecraft actually alters its orbit. The lower gravity also means that forces that on Earth are negligible, such as the cohesion between material in the soil, is a lot more crucial. Flying down also requires extraordinary precision. Nightingale is only 16 meters (52 feet) wide, much smaller than the planned 25 meters (82 feet), which Bennu's rocky surface ruled out. This is where the natural feature tracking comes in.
The team has created extraordinary maps of the asteroid. In fact, Bennu is the best-mapped body in the Solar System, and its onboard AI will use these maps to know where it is with respect to the rocky surface at all times.
Bennu is currently 333 million kilometers (207 million miles) from Earth so it takes 18 minutes for communications to get there. Once the go signal is sent, OSIRIS-REx will have to carry out the mission all by itself without further human input.
“The spacecraft is far enough away that we can't do real-time communication. So we're not joy sticking the spacecraft. We've developed a whole sequence of commands that we've now uploaded to the spacecraft and so when the final command is sent to go do TAG, to go collect the sample, all of the work that happens from the time that the spacecraft leaves orbit is done autonomously,” Bierhaus told IFLScience.
“it's a very multi-layered set of challenges that we had to work through to make this successful!”
OSIRIS-REx will attempt its sample collecting at 6.12 pm EDT. A live stream using animation to show what the spacecraft is doing will begin on the mission website from 1.20 pm EDT. NASA TV will share a broadcast from 5pm to 6.30 pm.
You can also watch it here.