Title: A method for classifying orbits near asteroids Author: Xianyu Wang, Shengping Gong, Junfeng Li

A method for classifying orbits near asteroids under a polyhedral gravitational field is presented, and may serve as a valuable reference for spacecraft orbit design for asteroid exploration. The orbital dynamics near asteroids are very complex. According to the variation in orbit characteristics after being affected by gravitational perturbation during the periapsis passage, orbits near an asteroid can be classified into 9 categories: (1) surroundingto-surrounding, (2) surrounding-to-surface, (3) surroundingto-infinity, (4) infinity-to-infinity, (5) infinity-to-surface, (6) infinity-to-surrounding, (7) surface-to-surface, (8) surfaceto-surrounding, and (9) surface-to- infinity. Assume that the orbital elements are constant near the periapsis, the gravitation potential is expanded into a harmonic series. Then, the influence of the gravitational perturbation on the orbit is studied analytically. The styles of orbits are dependent on the argument of periapsis, the periapsis radius, and the periapsis velocity. Given the argument of periapsis, the orbital energy before and after perturbation can be derived according to the periapsis radius and the periapsis velocity. Simulations have been performed for orbits in the gravitational field of 216 Kleopatra. The numerical results are well consistent with analytic predictions.

(216) Kleopatra / TYC 5738-02638-1 event on 2017 Apr 10, 08:03 UT

On 2017 Apr 10 UT, the 138 km diameter asteroid (216) Kleopatra will occult a 11.2 mag star in the constellation Aquila for observers along a path across Brazil, Bolivia, Peru. Read more

In the case of an occultation, the combined light of the asteroid and the star will drop by 3.9 mag to 11.9 mag (the magnitude of the asteroid) for at most 8.0 seconds. Read more

Like the ancient Egyptian queen it was named for, the asteroid Kleopatra has birthed twins - a pair of moons that have helped scientists learn that the huge space rock is a rubble pile rather than a chunk of solid rock. These two moons, named Alexhelios and Cleoselene after the twin children of the queen, were discovered in 2008. Now, astronomers studying their orbits have deduced that their parent asteroid is a jumble of loosely held rocks. Read more