Is there such a thing as too many asteroids?
Scientists and engineers at NASA's OSIRIS-REx decided to stow away the sample from asteroid Bennu collected by the spacecraft on October 20, as the collection container is overfilled and may block the collection head by locking.
Images returned by OSIRIS-REx on October 22nd showed an asteroid regolith slowly escaping from the spacecraft's collection head, called the Touch-and-Go Sample Acquisition Mechanism (TAGSAM).
This illustration shows NASA's OSIRIS-REx spacecraft stowing the sample collected from the asteroid Bennu on October 20, 2020. The spaceship uses its TAGSAM (Touch-and-Go Sample Acquisition Mechanism) arm to place the TAGSAM collection head in the sample return capsule (SRC). Credits: NASA / University of Arizona, Tucson
"The abundance of material we have gathered from Bennu made it possible to expedite our stowage decision," said Dante Lauretta, principal researcher for OSIRIS-REx at the University of Arizona, Tucson. "The team is now working around the clock to speed up traffic jams so we can protect as much of this material as possible for return to Earth."
The science team wants to collect at least 60 grams of regolith. The sample container can hold up to 2 kg.
NASA said a Mylar flap on the TAGSAM allows the material to easily enter the collection head and should seal once the particles pass through. However, larger stones that did not fully pass through the flap into the TAGSAM seem to have trapped this flap, allowing parts of the sample to escape.
The sample stowage was originally scheduled for November 2nd, 2020, but NASA has given the mission permission to stow it today, October 27th.
"We are working to keep up with our own success and my job is to safely return as large a sample of Bennu as possible," said Lauretta. "Mass loss is important to me, so I strongly encourage the team to stow this valuable sample as quickly as possible."
For the sample collection sequence on October 20, OSIRIS-REx performed the operations autonomously, with software on board to safely navigate the spacecraft to the surface, enable the extraction, and then perform a "return path" combustion to remove the spacecraft from Asteroids take away surface. Since Bennu is so far from Earth, there was a delay of 18.5 minutes before the signal from the spaceship reached Earth.
The entire event, from burning the deorbit to taking samples, lasted around four and a half hours.
However, for the stowing sequence, stowing the sample is gradual and requires control and input from the team. The team sends the preliminary commands to the spaceship to start the stowage sequence and then waits for the spaceship to send telemetry and images back to Earth for the team to confirm the success of the process. The process can take several days.
The mission has canceled tomorrow's sample mass measurement to protect the sample and is now well on its way to stowing the sample as quickly as possible. The spaceship remains in good health and the mission is confident that the spaceship has collected more than 60 grams of material. pic.twitter.com/hABL4n3JYN
– OSIRIS-REx (@OSIRISREx) from NASA on October 23, 2020
It may not be possible to determine exactly how much sample has been collected until the sample return container returns to Earth in September 2023. A spin maneuver called Sample Mass Measurement, in which the spaceship would turn with the sample arm extended, was aborted in order to preserve the remaining material in the probe head. This rotation would have allowed the team to determine the change in "angular moment of inertia" of the spacecraft and the change with the sample on board. This would allow them to deduce the weight of the sample being added.
"I am proud of the amazing work and success of the OSIRIS-REx team to this point," said Thomas Zurbuchen, NASA's Associate Administrator for Science. "This mission is well positioned to bring a historic and substantial sample of an asteroid back to Earth and they have done everything right on an accelerated schedule to protect this precious cargo."
This series of three images was captured by the spacecraft's SamCam camera on October 22, 2020 and shows that the probe head on NASA's OSIRIS-REx spacecraft is full of rocks and dust that has accumulated from the surface of the asteroid Bennu to have. They also show that some of these particles are slowly emerging from the probe head. Analysis by the OSIRIS-REx team suggests that pieces of material are getting through small gaps where the Mylar flap of the head is easily pinched. The Mylar flap (the black bulge on the left side of the ring) is used to keep the collected material locked inside. These unsealed areas appear to be caused by larger stones that did not fully pass through the valve. Based on the images available, the team suspects there is an abundance of samples in their head and is on their way to stow the sample as soon as possible. Photo credit: NASA
Please refer to the OSIRIS-REx website for more information and the latest information.