Performance evaluation of the fast-moving NEO detection mission

Abstract

Near-Earth Objects (NEOs) impact hazard has become of great concern among the space communities as our NEO detection capability has been drastically improved over the last decades and numerous NEOs discovered. As of today, our discovery efforts resulted in discovering over 90% of NEOs greater than one kilometer in diameter and none of them has imminent impact threats to the Earth in the foreseeable future. However, the majority of the NEOs with 100-meter diameter or smaller, including potentially hazardous objects, are yet to be discovered. These objects are more frequent impactors and can cause local-scale damage if they impact over a populated area on the Earth although they are statistically more likely to impact over the ocean. In any case, impact hazard warning is important but impossible if we cannot find them. Conventional discovery efforts on the smaller NEOs with telescopes are suffering the following issues. First of all, since these objects are very small, they have to be close enough to the Earth and bright enough to be detected by telescope. Even if they come across the field of view of a telescope at close approaches when their apparent magnitude increases, their images are so faint that they are often buried in noise. This is not only due to their size but also their line-of-sight change rates during the exposure time. Secondly, those who approach from the sun-direction cannot be detected with ground-based telescopes. These issues have driven the planetary defense community to develop new detection techniques and study new survey mission concepts. The Japan Aerospace Exploration Agency is currently studying a new NEO detection mission concept consisting of a cluster of ground-based telescopes and a constellation of space-based telescopes in sun synchronous orbit (SSO). A state-of-art synthetic detection technique based on time delay integration is used to detect the small and fast-moving NEOs. In this work, the mission performance evaluation is conducted in terms the number of NEO discoveries by the mission through one-year observation simulations with the Granvik model-based NEO population, where the number of telescopes and the detectable apparent magnitude limit as a function of line-of-sight change rate are given as design variable. NEO detection capabilities with synthetic and non-synthetic detection approaches are compared. Finally, opportunities for post-detection actions such as follow-up observations are discussed. The observation simulations resulted in 40 ground-based telescopes could achieve 2,080 detections annually whereas 4 space-based telescopes in SSO could achieve 1,280 detections annually with 20 cm telescopes. The detectability of the NEOs based on the synthetic detection technique could be 3–5 times better than that based on a conventional non-synthetic detection technique. The maximum line-of-sight change rate of the fastest-moving NEO with absolute magnitude 24.1 was 13,865 arcmin/day at the detectable condition. It is also presented that some of the NEOs detected and tracked by the ground part of the proposed mission could be further tracked by follow-up observations of the space part of it, and vice versa.