text: Under Chesley’s plan, the impact would occur while the OSIRIS-REx spacecraft lingers (at a safe distance) near Bennu following its initial study and the collection of the samples. At the time of the impact, the OSIRIS-REx cameras would watch the cloud of ejected material for clues to the composition and size of the blocks of material making up the surface. Once the ejecta had safely dissipated, OSIRIS-REx would move in for a close look at the ISIS impact crater to examine the composition of Bennu a few meters below the surface. The spacecraft would also remap the asteroid surface to see what changes occurred as the result of the seismic shock created by the impact, which will help us understand the role impacts have in shaping the surface of small bodies. (There is no plan to risk the OSIRIS-REx spacecraft by having it sample within the newly created crater.)
  While the impact would further our scientific exploration of asteroids, the ISIS mission also would contribute to other goals. If astronomers discover an asteroid on a collision course with Earth, one idea would be to send an spacecraft to change the asteroid’s trajectory through a high speed impact. Small asteroids like Bennu are believed to be rubble piles, and it’s difficult to model how an impact would affect an asteroid’s trajectory. The OSIRIS-REx mission team would measure Bennu’s trajectory before and after the impact to determine the resulting minuscule change in Bennu’s orbit about the sun. This would help us better understand whether future impactors could divert asteroids from collision courses with the Earth. (Bennu is among the known asteroids with the largest (but still small) probability of hitting the Earth in the future.)
  NASA also has goals to send humans to explore small near Earth asteroids like Bennu. Before astronauts arrive, the space agency would like to better understand these bodies’ surface mechanical properties, their local and global stability, and the environment of small particles likely to surround them. The ISIS impact experiment would further our understanding in all three areas.
  For those who don’t remember their ancient Egyptian mythology, Osiris was a god ruler of Egypt. Following his murder and dismemberment, his wife and queen Isis gathered together his scattered body parts and resurrected him. While there’s no murder in this story, the proposed ISIS mission would be enabled by taking advantage of various existing components.
  First, the OSIRIS-REx spacecraft will be at Bennu and will have several months available in its schedule to watch the impact and study the aftermath. The 2016 InSight Mars mission provides an option to launch ISIS at negligible additional cost on an orbit would take it twice past Mars and then to Bennu. The ISIS spacecraft itself would be built around an adapter ring designed to mate a main spacecraft to its launch vehicle and also provide attach points for small secondary spacecraft. The components needed to turn the adapter ring into a spacecraft – electronics, solar panels, propulsion, and a camera that would be used to track Bennu – would take the place of the secondary spacecraft. The final collision would be enabled by a JPL-developed AutoNav system, has been used for five previous NASA comet encounters, that would image Bennu in the final hours and steer the spacecraft to an impact.