Study on Near Circular Orbits around Asteroids for Optical Observation.

This paper presents a study on near circular orbits around asteroids, whose purpose is to make optical observations of asteroids globally with high resolution. All the asteroids, whose sizes are below 100km, are objects. At first, the feasible region of the frozen orbit was studied. There exist two kinds of the frozen orbits. One is the orbit in the orbital plane of the asteroid and was found not to be adequate for observation with high resolution because of the large altitude. The other is the solar plane-of-sky orbit whose orbit normal corresponds to the solar or anti-solar direction, and was found to be adequate for asteroids whose radii are below 2 or 3km. Maintenance of polar orbits, which are adequate for global observations of asteroids and have the merit that effects of the oblateness disappear, was studied by numerical integrations. It turned out Cp/(Cs*ellmlt) can be used to roughly judge the necessity of maintenance maneuvers.