Mankind's quest to better understand asteroids just went a step closer. Yesterday, on April 15, NASA's OSIRIS-REx space probe reached its closest yet approach to the asteroid Bennu, marking a final trial run of sorts ahead of its eventual landing and sample collection endeavour scheduled for later this year. Having successfully completed what NASA called a 'checkpoint rehearsal', the Origins-Spectral Interpretation Resource Identification Security Regolith Explorer, which is the official nomenclature of OSIRIS-REx, has also sent home photographs from Bennu.
These photographs have revealed in closer detail Nightingale, the northern hemisphere crater on Bennu's surface, in which OSIRIS-REx is set to land in. The probe's closest ever approach to Bennu brought to a mean altitude of 75 metres from the asteroid's surface. Since reaching Bennu, OSIRIS-REx has remained in a 'safe home' orbit, studying the asteroid from up close, yet afar. Its general orbit around Bennu is 1km above the surface. Yesterday's manoeuvre included two key steps of the landing process that will be followed by OSIRIS-REx in August 2020, which are the departure from its mean orbit and approach to Checkpoint (at 125 metres above surface), and a subsequent, nine-minute descent towards Bennu that brought the probe to its closest ever point to the asteroid.
In a statement shared by NASA, Erin Morton, the communications lead for the OSIRIS-REx mission, said, "During the rehearsal, the spacecraft successfully deployed its sampling arm, the Touch-And-Go Sample Acquisition Mechanism (TAGSAM), from its folded, parked position out to the sample collection configuration. Additionally, some of the spacecraft’s instruments collected science and navigation images and made spectrometry observations of the sample site, as will occur during the sample collection event.
"This first rehearsal provided the mission team with practice navigating the spacecraft through both the orbit departure and Checkpoint maneuvers and with an opportunity to verify that the spacecraft’s imaging, navigation and ranging systems operated as expected during the first part of the descent sequence. Checkpoint rehearsal also gave the team confirmation that OSIRIS-REx’s Natural Feature Tracking (NFT) guidance system accurately estimated the spacecraft’s position and speed relative to Bennu as it descended toward the surface."
The first asteroid rock sample collection procedure is scheduled for August 25, when OSIRIS-REx will reach Bennu's surface, deploy its sample collection arm for just five seconds, and collect a surface sample and safely return to its positino. This is believed to be the first attempt at capturing a piece of the asteroid, and it is likely that the probe may need a few more attempts, if results are unsatisfactory. OSIRIS-REx is expected to come back to Earth with a chunk of Bennu on September 24, 2023.