Designing a Near-Earth Asteroid Survey for a Telescope in Geosynchronous Orbit

The detection and characterization of Near-Earth Objects (NEOs) is important for both planetary defense against dangerous asteroids and for solar system science. In 2005, the US Congress directed NASA to detect and characterize 90% of NEOs greater than 140 meters in diameter by the end of 2020. By the beginning of 2024, it is estimated that only around 43% of these asteroids have been cataloged, and even fewer have been characterized. Upcoming surveys such as the future space-based infrared telescope NEO Surveyor and the ground-based Rubin Observatory's Legacy Survey of Space and Time (LSST) will dramatically increase the NEO discovery rate. However, existing resources that perform follow-up observations to characterize these asteroids do not have the capacity to keep up with all of the projected new discoveries. This paper discusses a new mission concept for an optical telescope in geosynchronous orbit dedicated to follow-up measurements and characterization of NEOs. Expanding resources for characterizing NEOs is important to improve orbital estimates and to measure the physical properties of potentially dangerous asteroids. Scheduling follow-up observations with large in-demand facilities can be challenging since many NEOs are only visible for a small fraction of their orbits and they need to be observed again quickly. A telescope in geosynchronous orbit would be able to rapidly characterize asteroids discovered by NEO Surveyor that may be out of reach for ground-based instruments which have a limited ability to observe the inner solar system due to daylight. These follow-ups would also have the benefit of complementing the NEO Surveyor's infrared data with visible spectrum measurements. We present simulations that use synthetic populations of Near-Earth Objects to analyze the potential capability of this proposed telescope. With a mirror diameter of 25 cm, we estimate a limiting visible apparent magnitude of 22.4 and assume a minimum solar viewing angle of 45 degrees. From this, we analyze what populations of NEOs this telescope would be sensitive to considering the observing geometry and magnitude thresholds. We then compare these results with the capabilities of NEO Surveyor and LSST in order to discuss how NEO observations with this telescope could complement these missions. We find that the proposed telescope could observe NEOs after they move outside of the viewing range of most ground based instruments and could observe NEOs interior to Earth's orbit which may never have solar viewing angles above 60 degrees.