NASA’s first asteroid-sampling spacecraft has had another close encounter with asteroid Bennu. Yesterday, NASA’s OSIRIS-REx spacecraft executed its lowest pass yet over sample site Osprey, taking observations from an altitude of 820 feet (250 m). Osprey, OSIRIS-REx’s backup sample collection site, is located within a crater just north of Bennu’s equator.

To perform the five-hour flyover, the spacecraft left its 0.6-mile (1-km) counterclockwise orbit (as viewed from the Sun) and aimed its science instruments toward the 52-ft (16-m) wide site. The science observations from this pass are the closest taken of Osprey to date. In March, the spacecraft executed a similar pass over primary sample site Nightingale.

A primary goal of the low flyover was to collect high-resolution imagery of the site’s surface material. The spacecraft’s sample collection mechanism is designed to pick up rocks smaller than 0.8 inches (2 cm), and the detailed PolyCam images from yesterday’s low pass will allow the team to identify rocks of this size.

The flyover also provided the opportunity to capture images for the Natural Feature Tracking (NFT) image catalog for site Osprey – documenting the site’s surface features. If the mission decides to collect a sample from backup site Osprey, the spacecraft will use this NFT image catalog to autonomously navigate down to Bennu’s surface. The mission originally planned to collect this imagery during a 0.4-mile (620-m) flyover in February, but the images from that pass are out of focus due to an anomaly in the low energy laser transmitter (LELT) subsystem with the OSIRIS-REx Laser Altimeter (OLA), which was providing range measurements to focus PolyCam. OLA’s high energy laser transmitter (HELT) was used in this most recent Osprey flyover, as was done in a similar flyover of the Nightingale site.

Several of the spacecraft’s other instruments also took observations of the Osprey site during the flyover event, including the OSIRIS-REx Thermal Emissions Spectrometer (OTES), the OSIRIS-REx Visual and InfraRed Spectrometer (OVIRS), and the OSIRIS-REx Laser Altimeter (OLA).

After completing the pass, OSIRIS-REx returned to its safe-home orbit and is now circling Bennu clockwise. The spacecraft normally orbits Bennu counterclockwise, but this shift in orbital direction was necessary to position the spacecraft for its next close encounter with the asteroid – the second rehearsal for the sample collection event.

The mission successfully executed the first sample-collection rehearsal on Apr. 14, completing a practice run of some of the activities leading up to the sampling event and bringing the spacecraft 213 ft (65 m) from the asteroid’s surface. The second rehearsal, scheduled for Aug. 11, will bring the spacecraft through the first three maneuvers of the sample collection sequence to an approximate altitude of 131 ft (40 m) over the surface of Bennu.

The spacecraft will attempt to venture all the way to the asteroid’s surface on Oct. 20, for its first attempt to collect a sample from site Nightingale. During this event, OSIRIS-REx’s sampling mechanism will touch Bennu and fire a charge of pressurized nitrogen to disturb the surface and collect its sample before the spacecraft backs away.

NASA’s Goddard Space Flight Center in Greenbelt, Maryland, provides overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and provides flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.

NASA’s first asteroid sample return mission is officially prepared for its long-awaited touchdown on asteroid Bennu’s surface. The Origins, Spectral Interpretation, Resource Identification and Security – Regolith Explorer (OSIRIS-REx) mission has targeted Oct. 20 for its first sample collection attempt.

“The OSIRIS-REx mission has been demonstrating the very essence of exploration by persevering through unexpected challenges,” said Thomas Zurbuchen, NASA’s associate administrator for science. “That spirit has led them to the cusp of the prize we all are waiting for – securing a sample of an asteroid to bring home to Earth, and I’m very excited to follow them through the home stretch.”

From discovering Bennu’s surprisingly rugged and active surface, to entering the closest-ever orbit around a planetary body, OSIRIS-REx has overcome several challenges since arriving at the asteroid in December 2018. Last month, the mission brought the spacecraft 213 ft (65 m) from the asteroid’s surface during its first sample collection rehearsal — successfully completing a practice run of the activities leading up to the sampling event.

Now that the mission is ready to collect a sample, the team is facing a different kind of challenge here on Earth. In response to COVID-19 constraints and after the intense preparation for the first rehearsal, the OSIRIS-REx mission has decided to provide its team with additional preparation time for both the final rehearsal and the sample collection event. Spacecraft activities require significant lead time for the development and testing of operations, and given the current requirements that limit in-person participation at the mission support area, the mission would benefit from giving the team additional time to complete these preparations in the new environment. As a result, both the second rehearsal and first sample collection attempt will have two extra months for planning.

“In planning the mission, we included robust schedule margin while at Bennu to provide the flexibility to address unexpected challenges,” said Rich Burns, OSIRIS-REx project manager at NASA’s Goddard Space Flight Center. “This flexibility has allowed us to adapt to the surprises that Bennu has thrown at us. It’s now time to prioritize the health and safety of both team members and the spacecraft.”

The mission had originally planned to perform the first Touch-and-Go (TAG) sample collection event on Aug. 25 after completing a second rehearsal in June. This rehearsal, now scheduled for Aug. 11, will bring the spacecraft through the first three maneuvers of the sample collection sequence to an approximate altitude of 131 ft (40 m) over the surface of Bennu. The first sample collection attempt is now scheduled for Oct. 20, during which the spacecraft will descend to Bennu’s surface and collect material from sample site Nightingale.

“This mission’s incredible performance so far is a testament to the extraordinary skill and dedication of the OSIRIS-REx team,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson. “I am confident that even in the face of the current challenge, this team will be successful in collecting our sample from Bennu.”

During the TAG event, OSIRIS-REx’s sampling mechanism will touch Bennu’s surface for approximately five seconds, fire a charge of pressurized nitrogen to disturb the surface, and collect a sample before the spacecraft backs away. The mission has resources onboard for three sample collection opportunities. If the spacecraft successfully collects a sufficient sample on Oct. 20, no additional sampling attempts will be made. The spacecraft is scheduled to depart Bennu in mid-2021, and will return the sample to Earth on Sept. 24, 2023.

NASA’s Goddard Space Flight Center in Greenbelt, Maryland, provides overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and provides flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.