[PPS07-17] Overcoming the Challenges of Sample Collection at Nightingale
★Invited Papers
キーワード：small bodies, asteroid sample return, Bennu, OSIRIS-REx
The OSIRIS-REx mission will collect a sample of near-Earth asteroid (101955) Bennu and return it to Earth. The returned sample will provide valuable constraints on the earliest stage of rocky planet formation and the origin of life. The data collected at the asteroid, combined with the analysis of the returned sample, will also improve our understanding of hazardous asteroids. In preparation for retrieving a sample, the OSIRIS-REx spacecraft has been flying in close proximity to Bennu since December of 2018, conducting a campaign of challenging maneuvers and scientific observations.
The sample will be acquired using a technique called Touch and Go, or TAG. The spacecraft will contact the surface of Bennu with with its Touch-and-Go Sample Acquisition Mechanism (TAGSAM), mounted on the end of a 3-m-long robotic arm. Contact with the surface is for a few seconds before the spacecraft backs away. When contact is detected, pressurized gas will mobilize fine-grained material, some of which will be captured with TAGSAM. TAG begins from a safe home orbit with the spacecraft approximately 1 km from the surface. The spacecraft will depart from this orbit and descend over the sunward side of Bennu towards the location of the TAG site. During a four-hour transit, the spacecraft will take images of Bennu’s surface with a navigation camera and process these images to update navigation information onboard. As OSIRIS-REx nears the surface, the spacecraft will perform two maneuvers to precisely target the TAG location.
Earth based observations of Bennu, combined with the experience of the Hayabusa mission at (25143) Itokawa, suggested that Bennu would have large flat areas containing fine-grained regolith, ideal for our collection technique. However, the earliest global observations of Bennu revealed a dramatic, rocky world with no obvious hazard-free regions. Subsequent high-resolution imaging of candidate TAG sites revealed that even the best candidates have very few areas containing clearly resolvable particle sizes of 2 cm or smaller, as required for collection. In response to these challenges, the Site Selection and Sample Acquisition campaigns changed. The project switched the TAG autonomous guideance technique from an originally planned lidar-based navigation update to an image-based navigation method called Natural Feature Tracking (NFT). A new observation campaign, Reconnaissance A, was added during October 2019 that collected high-resolution imagery of the top four candidate TAG sites to search for sampleable material and provide data needed to build onboard feature maps. Finally, an onboard hazard avoidance capability was developed to keep the spacecraft safe from large hazards in close proximity to the targeted TAG location. The highest-resolution (8 cm/pixel) images collected of the primary sample site, Nightingale, provide direct evidence of abundant sampleable material.
This talk will describe the challenges of asteroid Bennu, the factors that went into selection of the Nightingale site for TAG, and the preparations for the TAG event planned for summer 2020. The latest images of Nightingale and the backup TAG site, Osprey, will be shown.
The sample will be acquired using a technique called Touch and Go, or TAG. The spacecraft will contact the surface of Bennu with with its Touch-and-Go Sample Acquisition Mechanism (TAGSAM), mounted on the end of a 3-m-long robotic arm. Contact with the surface is for a few seconds before the spacecraft backs away. When contact is detected, pressurized gas will mobilize fine-grained material, some of which will be captured with TAGSAM. TAG begins from a safe home orbit with the spacecraft approximately 1 km from the surface. The spacecraft will depart from this orbit and descend over the sunward side of Bennu towards the location of the TAG site. During a four-hour transit, the spacecraft will take images of Bennu’s surface with a navigation camera and process these images to update navigation information onboard. As OSIRIS-REx nears the surface, the spacecraft will perform two maneuvers to precisely target the TAG location.
Earth based observations of Bennu, combined with the experience of the Hayabusa mission at (25143) Itokawa, suggested that Bennu would have large flat areas containing fine-grained regolith, ideal for our collection technique. However, the earliest global observations of Bennu revealed a dramatic, rocky world with no obvious hazard-free regions. Subsequent high-resolution imaging of candidate TAG sites revealed that even the best candidates have very few areas containing clearly resolvable particle sizes of 2 cm or smaller, as required for collection. In response to these challenges, the Site Selection and Sample Acquisition campaigns changed. The project switched the TAG autonomous guideance technique from an originally planned lidar-based navigation update to an image-based navigation method called Natural Feature Tracking (NFT). A new observation campaign, Reconnaissance A, was added during October 2019 that collected high-resolution imagery of the top four candidate TAG sites to search for sampleable material and provide data needed to build onboard feature maps. Finally, an onboard hazard avoidance capability was developed to keep the spacecraft safe from large hazards in close proximity to the targeted TAG location. The highest-resolution (8 cm/pixel) images collected of the primary sample site, Nightingale, provide direct evidence of abundant sampleable material.
This talk will describe the challenges of asteroid Bennu, the factors that went into selection of the Nightingale site for TAG, and the preparations for the TAG event planned for summer 2020. The latest images of Nightingale and the backup TAG site, Osprey, will be shown.