In a historic achievement, NASA’s OSIRIS-REx mission has accomplished a remarkable return journey from the asteroid Bennu. This pioneering robotic spacecraft made a groundbreaking attempt, unique to an American space agency, by briefly descending to the celestial body to collect pristine rock samples. It then embarked on a three-year roundtrip journey back to Earth, culminating in the safe landing of the samples in the Utah desert at the DoD’s Utah Test and Training Range and Dugway Proving Grounds.
Autonomous Touch-and-Go Sample Acquisition
A standout feature of the OSIRIS-REx mission was the spacecraft’s ability to autonomously execute the Touch-and-Go Sample Acquisition Mechanism (TAGSAM) maneuver. This groundbreaking autonomous operation was made possible by the onboard Natural Feature Tracking (NFT) visual navigation system, marking a significant milestone in space exploration.
Challenges of Asteroid Landing
The OSIRIS-REx mission faced a unique set of challenges due to the complexity of landing on an asteroid. Bennu, located approximately 70 million miles from Earth at the time of the mission, presented a daunting target with its intricate orbital dynamics. Precision in matching velocities and trajectories was paramount for the successful execution of the landing maneuver.
Detailed Surface Analysis
To ensure a successful landing, the spacecraft spent over 500 days meticulously circling Bennu, capturing high-resolution images of its surface. These images were crucial in generating digital terrain models, allowing for an accurate understanding of the asteroid’s topography.
Switch to Natural Feature Tracking
Initially, the mission planned to rely on LiDAR (Light Detection and Ranging) technology for navigation. However, the surface of Bennu surprised the team with an abundance of boulders, rendering LiDAR’s precision insufficient. The team swiftly transitioned to using the NFT system, which provided three-dimensional orbital state estimation capabilities. This enabled the spacecraft to identify potential hazards, such as boulders, during its descent.
The Four-Part Landing Maneuver
The TAGSAM maneuver was a complex four-part process. Starting at the “safe-home terminator orbit” of Bennu, the spacecraft moved to the daylight side of the asteroid at a position known as Checkpoint. It then shifted to Matchpoint, a mere 55 meters above the surface, ensuring a slow descent rate of 10 cm/s upon contact with the asteroid. During this phase, the spacecraft relied on onboard accelerometers and the delta-v update (DVU) algorithm to accurately estimate its relative position. The final maneuver involved gently backing away from Bennu, securing the collected samples.
Continuing Exploration
The success of the OSIRIS-REx mission opens the door to further exploration. An updated and enhanced version of the NFT navigation system is expected to be incorporated into future missions, such as OSIRIS-APEX. This improved system will enhance autonomy and reduce the involvement of ground crews, making future missions even more efficient.
