Osiris-Rex, NASA’s first-ever asteroid sample-return mission, is poised to execute its second dress rehearsal June 23 in preparation for a touchdown in August.
Preliminary data shows that Osiris, a $1 billion component of NASA’s New Frontiers effort to explore the Solar System, successfully carried out a 4-hr. series of spacecraft maneuvers and deployments on April 14. The run-through was executed to practice the critical early stages of operations planned for late August, when Osiris-Rex is to land briefly on the asteroid Bennu to gather up to 4.4 lb. of surface material. Bennu is a carbon-rich, boulder-strewn primitive Solar System body 140 million mi. from Earth.
- The spacecraft completed a successful test on April 14
- Asteroid landing is planned for Aug. 26
Responding to preprogrammed commands, Osiris-Rex autonomously departed its 0.6-mi.-high orbit around the 500-m-wide (1,640-ft.) asteroid, descending to its closest point near the surface since arriving at Bennu on Dec. 3, 2018. Confirmation that the “Checkpoint” exercise was a success concluded with the spacecraft ascending back to its orbital perch.
The mission was launched on Sept. 8, 2016, with Osiris-Rex outfitted to attempt up to three brief sample-collection attempts before departing for Earth in March 2021.
It is designed for the spacecraft to drop off its sample-return container as Osiris-Rex passes close to Earth. That container is set to reenter Earth’s atmosphere for recovery on Sept. 24, 2023, in a parachute-assisted descent onto the U.S. Army’s Utah Test and Training Range. The science team, led by University of Arizona Principal Investigator Dante Lauretta, is hopeful that laboratory analysis of the pristine asteroid material will help to further explain the Solar System’s 4.6 billion-year-old planet-forming era—including the role that asteroids played in the distribution of water ice and organics, the building blocks of life.
Also designated a near-Earth object, Bennu is of interest because of a one-in-800 chance it could collide with the Earth in 2182, possibly causing damage on a regional scale.
The April 14 Checkpoint exercise was the first of two planned rehearsals prior to the actual touchdown, now scheduled for Aug. 26 at a predesignated landing zone around Nightingale, a 66-ft.-wide impact crater near Bennu’s north pole.
Osiris-Rex departed its “safe home” orbit around Bennu with an attitude control system maneuver. It took 13 min. for data confirming the start of the drill to reach Earth, adding to the suspense.
“This is a bit of a nail-biter,” Lauretta wrote on Twitter. His comment was made during a temporary loss of signal lock between Osiris-Rex and NASA’s Deep Space Network (DSN) as Osiris-Rex began its slow descent. NASA’s DSN is the global network of ground stations used by NASA for two-way communications with planetary science mission spacecraft.
Next, the probe extended its 11-ft.-long robotic arm, the Touch-and-Go Sample Acquisition Mechanism (Tagsam). The device is to release a blast of nitrogen at the landing site in late August to kick up pieces of Bennu into a sample container.
The spacecraft then slewed into position to begin gathering images of the surface for autonomous navigation. The probe’s Natural Feature Tracking technology draws on software guidance systems and compares the real-time descent imagery with images stored in an onboard catalog of previously imaged landmarks. During its descent to the 410-ft.-altitude Checkpoint maneuver level, the probe’s solar arrays were positioned into a “Y-wing” configuration intended to prevent their contact with Bennu’s surface during the actual landing. The reconfiguration also extended the Tagsam along the spacecraft’s center of gravity so that it could make only brief direct contact with the surface.
After the 3-sec. Checkpoint thruster maneuver, Osiris-Rex continued its descent toward Bennu’s surface for another 9 min., reaching an altitude of about 243 ft., the closest the spacecraft has come to the asteroid yet.
That was followed by a back-away maneuver to begin the ascent toward the probe’s initial orbital position, including reconfiguration of the solar arrays to their original orientation and the issuance of commands for the Tagsam to reassume its stowed position.
Throughout much of the trial, spacecraft sensors also gathered thermal and mineral composition data from Bennu’s surface.
A second rehearsal is planned for June 23. It will take Osiris-Rex through the same Checkpoint deployments and maneuvers to a third critical descent milestone, the “Matchpoint” maneuver. Matchpoint is to occur at about 164 ft. over Bennu’s terrain, synchronizing the spacecraft’s descent with the rotation of the asteroid so it can navigate accurately to its constrained landing zone at Nightingale.
After a lengthy global reconnaissance of Bennu’s surprisingly rocky surface, the Osiris-Rex mission team announced the selection of Nightingale as the primary sample-collection site on Dec. 12, 2019.
At the same time as the NASA announcement, the Japan Aerospace Exploration Agency’s (JAXA) Hayabusa2 sample-return mission (launched on Dec. 3, 2014) to the larger asteroid Ryugu was starting to make its way back to Earth after gathering surface and subsurface samples in 2019. The Japanese spacecraft is to drop off a sample container as it passes by Earth in December 2020 during a parachute-assisted decent into remote Australia for recovery.
Scientists involved in Osiris-Rex and Hayabusa2 plan to exchange sample materials for scientific analysis.
Much of the Checkpoint rehearsal was carried out in telework fashion due to the coronavirus pandemic. The work was led by personnel from NASA’s Goddard Space Flight Center, Lockheed Martin Space Systems’ control center in Denver and the University of Arizona. Only a limited number of essential personnel—all taking safety precautions due to COVID-19—were at each of the sites during the drill.
