From position and velocity coordinates for several given instants, it is possible to determine orbital elements for the preliminary orbit. This theoretical trajectory, also known as keplerian orbit, is defined taking only into account mutual gravitational attraction forces between both bodies, the Earth and the satellite. Nevertheless it should be refined with later observations from ground sta...

In this paper we address the deterministic, multi-satellite, multi-ground station communication scheduling problem. As the number of small satellites in space increases, so does the demand for downloading their large quantities of acquired data. Given the capacity-constrained ground station network, efficient scheduling plays a major role in the overall performance of missions. The small-satell...

Microsatellites in Low Earth Orbits (LEO) have been in use for the past two decades. Low Earth Orbit satellites are used for public communication and also for scientific purposes. Thus, it may be expected that such missions will be further developed in the near future especially in fields where similar experiments by purely Earth-based means are impracticable. Ground stations have to be establi...

A common challenge in developing small-satellite-based Earth-observation (EO) missions is getting the data to the ground. Typically, most satellites download data via space-to-ground radio-frequency (RF) links, communicating directly with fixed ground stations as the satellites fly within range. For many next-generation EO missions, such as hyperspectral imaging or SAR missions, the volume of d...

I will discuss how time and frequency information can be distributed using satellites. I will focus on using the signals transmitted by the US global positioning system satellites, but I will also discuss other satellite-based systems such as the Russian GLONASS system, the proposed European Galileo System and two-way satellite time transfer, which uses active ground stations that communicate w...