A Microsatellite Mission to Sample LEO and Lower MEO Environment

An accurate knowledge of the orbital environment is extremely important to correctly design space systems and, even more relevant, to better investigate the link with geophysics, which is now understood to be quite strong. Suitable models for quantities of interest, as the amount of radiations or the magnetic field, already exist, of course. However, and especially for radiations, the gained knowledge is not enough, because the scenario is far from being a steady one. As a result, studies on the terrestrial orbital environment are clearly an ongoing activity, and in situ measurements are important to validate and correctly tune existing or novel theoretical models. This paper intends to detail the orbital design of a mission aimed to provide an effective sampling of the Low Earth Orbits (LEO) and of the lower altitude portion of the Medium Earth Orbits (MEO), up to about 5000 km above the surface of the Earth, at different latitudes. The main characteristic of the proposed design is that it fully exploits the J2 (Earth flattening) effect, and the precession it induces on both the line of nodes and the line of apsides. In such a way, a high inclination, eccentric orbit can sweep in time a spherical shell, allowing for the collection of a significant set of measurements to characterize the radiation environment (and, additionally, the magnetic field). The strong advantage of the proposed design stays in the passive strategy, i.e. it does not require any thrust after orbit injection to explore a very large volume. It makes such a mission a suitable opportunity for microsatellite or cubesats, that cannot support significant propulsion capabilities. In addition to the orbital design, the expected radiation environment in the sampled regions is discussed, to allow for a preliminary sizing of the instruments – dosimeters - to be accommodated onboard.