The OSIRIS-REx team decided to postpone the departure of the spacecraft from the asteroid Bennu by two months. The departure window will open in March 2021, and the original plan was for OSIRIS-REx to set course for Earth on March 3 to bring home the asteroid samples collected last October.
In a revised timeline, the spaceship leaves Bennu on May 10, 2021. This does not affect the target delivery dates of September 2023, but allows further observations of the asteroid.
“If we leave Bennu’s area in May, we will be at the ‘sweet spot’ when the departure maneuver consumes the least amount of the spacecraft’s on-board fuel,” said Michael Moreau in a press release. Moreau is the deputy project manager of OSIRIS-REx at NASA’s Goddard Space Flight Center. “With a speed change of over 595 miles per hour (265 meters per second), however, this is the largest propulsion maneuver carried out by OSIRIS-REx since the approach to Bennu in October 2018.”
This series of three images was captured by the spacecraft’s SamCam camera on October 22, 2020 and shows that the probe head of NASA’s OSIRIS-REx spacecraft is full of rocks and dust accumulated from the surface of the asteroid Bennu to have. Based on the images available, the team suspected there was an abundance of samples in their head and decided to stow the sample away early. Credits: NASA
During the October 20, 2020 sampling, OSIRIS-REx collected a significant amount of material from Bennu’s surface and likely exceeded the mission’s 2 ounce (60 grams) requirements. Images returned by OSIRIS-REx on October 22nd showed an asteroid regolith slowly escaping from the spacecraft’s collecting head known as TAGSAM (Touch-and-Go Sample Acquisition Mechanism), meaning the Collection container was overfilled.
NASA said the May departure will give the OSIRIS-REx team an opportunity to schedule a final flyby of Bennu, which was not part of the original mission plan. Of particular interest is a final observation to take a look at the sample site on Bennu – called Nightingale – and possibly learn how the spacecraft’s contact can alter the surface.
If the team determines that this is feasible, the flyby will take place in early April and observe Nightingale from a distance of approximately two miles. Based on the images the spacecraft collected during the rehearsal event, Bennu’s surface was severely disturbed as the TAGSAM collecting head sank 48.8 centimeters into the asteroid’s surface. The spacecraft’s engines also disrupted a significant amount of surface material during the burnback.
The nightingale crater on Bennu with the relative size of the OSIRIS-REx spacecraft. Image: NASA
The spaceship would take new images of Nightingale and compare them to the very detailed, high-resolution observations from 2019 in order to select the sample location and then plan the sampling event.
“OSIRIS-REx has already delivered incredible science,” said Lori Glaze, NASA director of planetary research at the agency’s Washington headquarters. “We are very pleased that the mission is planning another flyby of the asteroid Bennu to provide new information on how the asteroid responded to the TAG and to give a proper goodbye.”
Another advantage of the new observations is the evaluation of the current functionality of scientific instruments on board the spacecraft – in particular the OSIRIS-REx camera suite (OCAMS), the OSIRIS-REx thermal emission spectrometer (OTES), the OSIRIS-REx visual and infrared spectrometer (OVIRS)) and OSIRIS-REx laser altimeter (OLA). If possible expanded mission options are to be considered, the team needs to understand the state of the instruments. It is possible that the instruments are coated with dust during sampling and that the mission would like to assess the status of the individual instruments.
This mosaic image of the asteroid Bennu consists of 12 images taken on December 2, 2018 by the PolyCam instrument of the OSIRIS-REx spacecraft from a distance of 15 miles. Photo credit: NASA / Goddard / University of Arizona
The spacecraft will fly past Earth in 2023 to drop the Sample Return Capsule (SRC). As it nears Earth, OSIRIS-REx will drop the SRC, which will parachute to land on the Utah Test and Training Range.
Once restored, NASA will ship the capsule to the curation facility at the agency’s Johnson Space Center in Houston and distribute the sample to laboratories around the world. Scientists look forward to studying the ancient asteroid samples that provide information about how our solar system was formed.
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