The threat of near-Earth asteroid (NEA) impacts is a long-term challenge facing humanity and has drawn the attention of the international community. To address this threat, the Chinese government plans to conduct verification work on the defense system to enhance the planet defense capabilities such as monitoring, cataloging, early warning, response, and disposal of NEAs, and promote the building of a global community with a shared future for mankind in the outer space sector. Therefore, comprehensively monitoring and cataloging the orbits of NEAs, and characterizing their physical properties are crucial steps for subsequent in-orbit disposal verification missions and the development of planet defense capabilities. How to obtain high-precision, long-term continuous multi-band observation data is the core of improving the monitoring and cataloging capabilities of equipment. Space-based and lunar-based observation equipment can avoid the influence of the Earth’s atmosphere, conduct more extensive continuous monitoring and in-depth research, and provide new opportunities for revealing the characteristics of NEAs. This work analyzes the real-time sky coverage and NEAs monitoring capabilities of three types of observation platforms deployed in near-Earth space, Earth?Moon space, and on the lunar surface for NEAs within one Earth’s revolution period. This analysis is crucial for obtaining the orbital characteristics (such as the orbit distribution of NEAs and the spatial distribution of relative station positions) and photometric characteristics (such as the temporal variation of the apparent magnitude) of NEAs.

This work first analyzes the position and diameter distributions of nearly 40000 cataloged NEAs in the heliocentric ecliptic coordinate system, regarding these as the general distribution laws of NEAs. Combining the environmental advantages of space-based and lunar-based observation platforms and the space-based NEA exploration missions that are on-orbit or being planned at home and abroad, three types of observation platforms for simulation in this work are finally selected: the Sun-synchronous orbit, the L4/5 dynamical substitutes orbit of the Earth?Moon Lagrange points (EML4/5 DSs orbit), and the lunar surface. Based on the technical parameters of commonly used optical observation equipment for space-based and ground-based observations, the detection limits of telescopes with apertures of 1 m, 2 m, 3 m, and 5 m are calculated. The orbits of the observation platforms and all cataloged NEAs are converted to the heliocentric ecliptic coordinate system using a Python program. Considering the avoidance angles of the Sun, the Earth, and the Moon, the real-time positions of the cataloged NEAs in the ecliptic coordinate system in the topocentric ecliptic coordinate system are calculated from January 1, 2030, to January 1, 2031, using the topocentric place-asteroid vector. On this basis, we calculate the ratio of NEAs that can be detected by different aperture telescopes at the positions of each observation platform within one Earth’s revolution period (a NEA is defined as being able to be monitored if the cumulative time in the visible sky area exceeds 75% of one Earth’s revolution period).

The real-time visible sky coverage of the three types of observation platforms within one Earth’s revolution period is approximately 40%, 50%, and 30% of the entire sky respectively. Each platform/site uses optical devices with apertures of 1 m, 2 m, 3 m, and 5 m. When the signal-to-noise ratio (SNR) is greater than 3, the detectable ratio of NEAs is approximately 4.5%, 11.7%, 18.8%, and 29.4% respectively. In addition, when different observation platforms are equipped with telescopes with the same aperture, the difference in the detectable ratio of NEAs is less than 2%. This means that the difference in the locations of the three observation platforms has little impact on the apparent magnitude of the same NEA. Based on the method of this work, the observation conditions of four key targets of the planetary defense project—Apophis, 2015 XF261, 2024 YR4, and Kamo’oalewa—within one Earth’s revolution period are analyzed. Without considering the detection limits of telescopes, the EML4/5 DSs orbit platforms have the longest total visible time for Apophis and Kamo’oalewa, which are 41.7% and 86.1% respectively. The lunar south pole site has the longest total visible time for 2015 XF261 and 2024 YR4, which are 65.0% and 66.8% respectively. Apophis can be monitored using a 1 m aperture optical telescope, Kamo’oalewa can be monitored using a 5 m aperture optical telescope, but 2015 XF261 and 2024 YR4 can only be monitored using telescopes with larger apertures.

The research results of this paper indicate that the observation platform at the EML4/5 DSs orbit has a significant advantage over the two types of observation platforms at Sun-synchronous orbit and lunar surface in terms of the real-time visible sky coverage; while when each observation platform is equipped with the same aperture device, the number of NEAs that can be detected within the visible sky area shows negligible differences, and the aperture of optical device is the core factor determining the NEA detection capability. Meanwhile, the simulation results of this work verify the NEA monitoring capabilities at the Sun-synchronous orbit, the EML4/5 DSs orbit, and several observation positions on the lunar surface. Results of this work provide theoretical support and decision-making basis for China’s subsequent development of NEA defense, monitoring and early warning capabilities based on the cooperative observation resources of space-based and lunar-based monitoring equipment.