The spacecraft OSIRIS-REx has been orbiting the asteroid Bennu since the end of 2018. The mission – stands for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer – was started in September 2016.
Since arriving in Bennu, the spaceship and its cameras have been collecting and sending back data and images to help the team learn more about the composition of the asteroid and map the best potential landing sites for sampling.
The mission’s main event, known as the TAG (Touch-and-Go Sample Collection Event), is scheduled for October 20 at 5 p.m. ET.
The asteroid and spaceship are currently about 207 million miles from Earth, which will result in a communication delay of about 18.5 minutes. The NASA team will create livestream animations that show what is happening based on the commands already sent to OSIRIS-REx for the sample collection sequence.
The spaceship performs the entire sequence in which it approaches the asteroid and collects the sample autonomously, as live commands from Earth are not possible.
Based on the data returned by the spaceship, the mission team should be able to confirm whether the touchdown on Tuesday was successful.
The starship conducted two rehearsals without actually touching the asteroid, and its team is prepared for this highly anticipated event.
Bennu is not what scientists expected, however. The nightingale’s landing site is surrounded by danger, so the mission must be carried out with the utmost precision.
The OSIRIS-REx spacecraft must recognize dangers and delay its own mission if obstacles stand in the way of sampling. However, if everything goes smoothly, the spaceship and its valuable sample will make the long journey back to Earth next year and the sample will land on Earth in 2023.
Avoid building-sized boulders
Imagine a van that seats 15 passengers as they fly through space and approach a rock that is the height of the Empire State Building and spinning rapidly. This is the OSIRIS REx mission for Bennu.
Bennu has an orbit that brings it close to Earth, which is why it is considered a near-Earth asteroid. One of his future approaches could bring it dangerously close to Earth in the next century; It has a one in 2,700 chance of affecting our planet.
Bennu’s samples could help scientists understand more not only about asteroids that could affect Earth, but also about how planets formed and how life began. In total, the spaceship collects about 2 ounces or 30 sugar sachets of material from the asteroid.
While this sounds small, according to NASA, it’s the biggest return on sample from space since the Apollo program.
But first OSIRIS-REx has to drive a small, narrow path to the landing site of the nightingale in a crater in the northern hemisphere of the asteroid.
The touchdown area has been reduced to about a tenth of the original plan, so accuracy is key. At the eastern edge of the crater is a building-sized boulder that could threaten the spaceship if it retreats from the asteroid after sampling.
Bennu “is nowhere near the sandy beach we hoped for and expected,” said Thomas Zurbuchen, deputy administrator of the Science Mission Directorate at NASA, during a press conference in September.
Instead, the scientists discovered that the asteroid was covered with boulders the size of a house. The team used the spaceship to map the entire asteroid and determine four possible landing sites. Nightingale was ultimately chosen as the best.
“We selected Nightingale because it contains by far the finest grain of any four candidates for the sample site,” said Dante Lauretta, the mission’s principal researcher and professor at the University of Arizona, Lunar and Planetary Laboratory, in September.
“We did low-altitude reconnaissance passes over this location in early 2020 and ended up mapping it with an image of about an eighth of an inch per pixel. We basically have incredibly detailed images covering the entire crater and we’ve counted all of those rocks.”
Do a touchdown
The nightingale’s landing pad is 52 feet in diameter and roughly the size of some parking lot where the van-sized spacecraft touches down for seconds. There is no room for failure; Boulders the size of buildings are just a few steps away.
The event will last approximately 4.5 hours and the spaceship will perform three maneuvers to collect the sample.
The spacecraft will fire engines first to exit its safe orbit around the asteroid, which is about 2,500 feet from the surface, and travel for four hours before reaching just 410 feet away. Then the spaceship adapts to position and speed in order to descend further.
Next, OSIRIS-REx slows its descent to aim at a path so that it matches the rotation of the asteroid during contact. The solar panels are folded over the spaceship in a Y-wing configuration to protect them.
Finally OSIRIS-REx takes less than 16 seconds. The spaceship fires a pressurized nitrogen bottle into the asteroid and uses the gas to lift material from Bennu’s surface.
The spacecraft’s collecting head captures the agitated material. This head, perched on the 11 foot long robotic sampling arm, is the only part of the spacecraft that Bennu will touch. The team compares it to an air filter in an older model car, which is perfect for collecting fine material.
Small disks that can collect dust like sticky pads are also on the head in case part of the sampling maneuver does not go according to plan.
A camera on the spaceship takes pictures of the collection event.
“We will be able to determine if we were overturned, if gas was blown aside, if the material was sufficiently agitated,” said Lauretta. “We will also have a very good indication of the exact location in Nightingale where we contacted and we can compare that to our sampling map to see if we ended up in an area where sample material is abundant , or one of the rockier places. “
The spacecraft’s engines then fire, helping it move away from Bennu’s surface and regain a safe distance.
The OSIRIS-REx spaceship will go through these maneuvers independently and must ultimately decide whether it is safe or not. The spaceship will rely on its natural feature tracking navigation system, which will actively capture images during the descent and compare them to images stored in an onboard catalog to ensure they’re on the right track. This affects every step of the descent and approach.
If it deviates from course, the spaceship stops the attempt.
The navigation system also contains a hazard map of the landing site. If it senses that the spacecraft is approaching danger, it will stop 16 feet above the asteroid and not continue the attempt.
This means that OSIRIS-REx can stay safe and try another sample collection in the future.
Check in to earth
During each step, the spaceship sends data back to NASA researchers on Earth, which they can use to determine whether the touchdown was successful or not. While only a limited number of the team will be in the Lockheed Martin Space Mission Support Area due to the pandemic, others will be in various locations to monitor the event.
To ensure that the spaceship has actually collected a sample, one of the OSIRIS-REx cameras takes pictures of the collecting head on October 22nd. On October 24th, the spaceship made a turn to determine the mass of the collected material.
Although 2 ounces is the goal, OSIRIS-REx can hold up to 4 pounds.
If sampling goes as planned, the head and sample will be placed in the sample recovery capsule and sealed to be returned to Earth.
However, if the collection fails or there is not enough material, there will be two more nitrogen charges in January 2021 for future trials at a second site called Osprey.
In total, team members will spend about a week evaluating what they have collected and ensuring that the spaceship and its instruments survived the encounter unscathed.
“By far the most likely result we’ll have on October 20th is that we contact the surface and get a large sample that exceeds our requirements. But Bennu has already thrown us a number of cornering balls, so we’re fully ready to tag at Osprey (the backup location) if necessary, “Mike Moreau, assistant project manager at NASA’s Goddard Space Flight Center in Maryland, said in a statement.
Recently, scientists discovered that the fine material at the Nightingale site was only recently exposed to the space environment. This means that the material collected by OSIRIS-REx is one of the most pristine materials on the asteroid.
And the sample from Bennu that is being brought back to Earth will not match the meteorites we have on Earth, NASA scientists say, because so much of what they have learned about Bennu is unexpected.