Direct solar radiation pressure on the orbits of small near-Earth asteroids: observable effects?

We consider the perturbations of Near-Earth Asteroid orbits due to direct s olar radiation pressure (both the absorption and the reflection components) . When the body is spherical and the surface albedo homogeneous the effect is small (and only short-periodic). However, when at least one of these res trictive and unrealistic assumptions is relaxed,long-term orbital effects a ppear and they may potentially lead to observable displacement of the orbit . We illustrate this conclusion by computing the orbital perturbations due to radiation pressure for objects with an odd-zonal distribution of albedo and for objects with ellipsoidal shape. Especially in the first case the ef fects are large, due to the long-term perturbations of the semimajor axis. For high-eccentricity orbits observed over a long interval of time, the (v/ c)-correction of the direct radiation pressure, known as Poynting-Robertson effect, should be also considered. As an example we demonstrate that for t he asteroid 1566 Icarus, during its next close approach to the Earth, the o rbit displacement due to the direct solar radiation forces might be, under reasonable assumptions. comparable to the orbit determination uncertainty, thus potentially observable.