Speaker
Description
The OSIRIS-APEX spacecraft will characterize asteroid (99942) Apophis over 18 months in 2029 and 2030 [1-3]. The mission is split into phases designed to address specific scientific objectives [3]. Because of the long period and non-principal axis rotation of Apophis, APEX will observe at regular intervals every few hours as it moves through multiple observing geometries to build up coverage while Apophis rotates and precesses. The initial observations are designed to be agnostic to Apophis’ physical state, so that later observations can be adjusted based on what is discovered upon arrival. The OSIRIS-APEX team is currently refining the concept of operations and mission phase designs.
Imaging with OSIRIS-APEX instruments will begin in late March 2029, with acquisition of Apophis as a disk-integrated point source no later than April 2, 2029. The spacecraft will make a close approach to Earth on April 13, 2029, only 1 hour after the Apophis-Earth encounter. During the approach phase, we will acquire observations to develop a global shape model, determine Apophis’ rotation state after the Earth encounter, and search for natural satellites and particles.
The proximity operations phases begin in June 2029 with global mapping to obtain datasets at the lighting conditions and viewing geometries necessary to build global topographic maps for precise navigation and to improve knowledge of the rotation state. We will also collect imagery for a global basemap and measure the asteroid’s mass.
Detailed mapping of Apophis begins in August 2029 with insertion into a terminator orbit at ~1 km altitude. This phase involves collecting scanning lidar topographic data and initiating the Yarkovsky measurement. In the subsequent detailed mapping phase, the spacecraft traverses a wide range of phase angles to collect global photometric and spectral datasets from 5–7.5 km. The final detailed mapping phase uses a resonant terminator orbit to acquire higher-resolution imagery for a global basemap and thermal observations of the night side of Apophis.
In April 2030, we transition into regional mapping of Apophis from altitudes of 1 km down to several hundred meters. One of the regional mapping locations will be used for the Spacecraft Thruster Investigation of Regolith (STIR) sortie, during which the spacecraft descends to a few meters above the target site, and thruster plumes from the back-away maneuver excavate and expose subsurface material. In November 2030, high-resolution observations will be collected during one final regional mapping pass to document the surface changes and newly exposed subsurface.
[1] DellaGiustina, D. N. et al. (2023) Planet. Sci. J. 4, 198. doi:10.3847/PSJ/acf75e
[2] Nolan, M.C. et al. (this meeting).
[3] Roberts, J. H. et al. (this meeting).