The Osiris Rex spacecraft has been orbiting the asteroid Bennu since late 2018. The mission – which represents assets, spectral interpretation, resource identification and the Security-Regolith Explorer – was launched in September 2016.
Since its arrival at Bennu, the spacecraft and its cameras have collected and sent back data and images to help the team learn more about the asteroid formation and map the best possible landing sites for sample collection.
The mission’s main event, called the Touch-and-Go Sampling event, or TAG, is scheduled for October 20 at 5 PM ET.
The asteroid and spacecraft are currently located about 207 million miles from Earth, which would result in a delay of about 18.5 minutes in contact. The team at NASA will broadcast live animation depicting what is happening based on commands already sent to OSIRIS-REx for sample collection sequences.
The spacecraft will perform the entire sequence of approaching the asteroid and collecting the sample independently because live commands from Earth will not be possible.
Based on the data returned by the spacecraft, the mission team should be able to confirm whether the landing was successful on Tuesday.
The spacecraft performed two experiments without actually touching the asteroid, so its team is ready for this highly anticipated event.
However, Bennu is not what scholars expected it to be. The Nightingale landing site is surrounded by dangers, so the mission must be executed with utmost precision.
The OSIRIS-REx spacecraft will have to detect the risks and delay its mission if there are any obstacles in the way of sample collection. But if everything goes smoothly, the spacecraft and its precious specimen will begin the long journey to Earth next year and land the sample on Earth in 2023.
Avoid building-sized rocks
Imagine a truck with capacity of 15 passengers flying through space, approaching a rock the height of the Empire State Building, and spinning fast. This is Osiris Rex’s mission to Bennu.
Bennu has an orbit that brings it close to Earth, which is why it is considered a near-Earth asteroid. One of his futuristic approaches could bring him dangerously close to Earth in the next century; It has one chance in 2,700 to affect our planet.
Samples from Bennu can help scientists not only understand more about asteroids that could affect Earth but also about how planets formed and life began. In total, the spacecraft will collect approximately 2 ounces, or 30 sugar cans, of material from the asteroid.
Although this appears small, it is the largest sample returning from space since the Apollo program, according to NASA.
But first, OSIRIS-REx has to navigate a small, narrow path to the Nightingale landing site inside a volcano’s crater in the asteroid’s northern hemisphere.
Landing area reduced to about one-tenth of the original plan, so accuracy is key. On the eastern edge of the crater is a building-sized rock that could threaten the spacecraft as it retracts from the asteroid once the sample is collected.
Thomas Zurbuchen, associate director for NASA’s Science Mission Directorate, said during a press conference in September that Benno “is not near the sandy beach that we were hoping for and expecting.”
Instead, scientists discovered that the asteroid was covered in rocks the size of a house. The team used the spacecraft to map the entire asteroid and identify four possible landing sites. The Nightingale was finally chosen as the best one.
“We chose Nightingale because it contains, by far, the most accurate material out of all four candidate specimens,” said Dante Loretta, the mission’s principal investigator and professor at the University of Arizona’s Lunar and Planetary Laboratory.
“We spent early 2020 doing low altitude sweeping passes over this site, and in the end we photographed about an eighth of an inch per pixel. We basically have incredibly detailed images covering the entire crater, and we counted all those rocks.”
Going for the drop
The Nightingale Landing Site is 52 feet in diameter, about the size of a handful of parking spaces where the spacecraft will briefly land the size of a truck in just seconds. There is no room for error; Rocks the size of the building is just steps away.
The event will take about 4.5 hours to unfold and the spacecraft will perform three maneuvers to collect the sample.
The spacecraft will first launch propulsion engines to leave its safe orbit around the asteroid, which is about 2,500 feet from the surface, and travel for four hours before reaching a distance of only 410 feet. After that, the spacecraft will be adjusted to position and speed to continue the descent.
Next, Osiris Rex will slow its descent to target a trajectory that matches the asteroid’s rotation during contact. Its solar panels will be folded into a Y-wing configuration over the spacecraft to protect it.
Finally, the Osiris Rex will land for less than 16 seconds. The spacecraft will launch a compressed nitrogen bottle into the asteroid, using the gas as a way to lift material off the surface of Bennu.
The spacecraft collector head will pick up the flipped material. This head, located on the 11-foot robotic sampling arm, is the only part of the spacecraft that will touch Benno. The team compares it to an air filter in an older model car, making it ideal for collecting fine materials.
There are also small discs, which can collect dust like adhesive pads, on the head if part of the sampling maneuver is not carried out according to plan.
A camera on the spacecraft will capture footage of the group event.
“We will be able to see if we are tilted, if the gas explodes on the side, and whether the materials have been stirred enough,” Loretta said. “We would also have a very good indication of the exact location in Nightingale that we had contact and could compare that to our sampling potential, to assess whether we had arrived in an area with abundant material to sample or a rocky site.”
Then, it will fire the spacecraft’s defenses and help it retreat from the Bennu surface and reach a safe distance again.
The Osiris Rex spacecraft will go through these maneuvers alone and ultimately has to decide whether or not it is safe. The spacecraft will rely on the Natural Characteristics Tracking Navigation System, which actively captures images during landing and compares them to images stored in an onboard catalog to ensure they are on the right track. This will affect each step of the lineage and approach.
If it’s derailed, the spacecraft will abort.
The navigation system also has a hazard map for the landing site, and if it detects that the spacecraft is approaching a danger, it will stop at 16 feet above the asteroid and will not keep trying.
This means OSIRIS-REx can stay safe and try to collect other samples in the future.
Check with the ground
During each step, the spacecraft will send data to NASA researchers on Earth, which will allow them to determine if the landing was successful or not. While only a limited number of the team will be on site in the Lockheed Martin Space Mission Support Area due to the pandemic, others will be on site at various locations to monitor the event.
To ensure that the spacecraft has indeed collected a sample, one of the OSIRIS-REx cameras will capture images of the group head on October 22. On October 24, the spacecraft will rotate to determine the mass of matter it has collected.
Although the target is 2 ounces, OSIRIS-REx can hold up to 4 pounds.
If sample collection goes as planned, the tip and specimen are placed and sealed in a sample return capsule for return to the ground.
But if collection fails or there is not enough material, there will be two additional shipments of nitrogen for future attempts at a second site called Osprey in January 2021.
In total, the team members will spend about a week evaluating what they have collected and making sure that the spacecraft and its tools survive the confrontation unscathed.
“By far, the most likely outcome that we’ll get on October 20 is that we’ll come to the surface and come up with a large sample that goes beyond our requirements. But Bennu threw a number of really curved balls at us, which is why we said Mike Morrow, deputy project manager at Goddard Travel Center. NASA’s Space in Maryland, in a statement: “Willing to place a mark in Osprey (backup location) if this becomes necessary.”
Scientists recently discovered that the microscopic materials found at Nightingale have only recently been exposed to the space environment. This means that the materials Osiris Rex collected will be some of the purest materials on the asteroid.
NASA scientists say the Bennu sample that will be returned to Earth will not look like the meteorites we have on Earth, because much of what they have learned about Bennu is unexpected.
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