| The increasing capabilities and low cost of microsatellites makes them ideal tools for new and advanced space science missions, including their possible use as interplanetary exploration probes. There are many issues that have to be resolved when it comes to employing microspacecraft on such missions. One problem is how to maintain a reliable communications link with the microspacecraft over long, interplanetary distances. When looking at the feasibility and costs of these alternatives, it is shown that a ground station array seems to be an ideal solution to the problem. Simulations are performed that demonstrated that it is possible to create such an array using small antennas employing low-cost equipment, including, though not limited to, the ground stations employed by amateur radio operators. Such an array would be an affordable alternative to arrays made up of large antenna assets, such as the Deep Space Network, which uses 34 m and 70 m antennas. An array must be capable of correcting for changing time and frequency offsets between the signals received at each antenna. Time correlation is a standard technique used by the DSN to solve the time-offset problem. The use of highly stable frequency oscillators at each antenna solves the frequency-offset problem. Such equipment would be too difficult and expensive to install on small antenna assets, so another solution was developed. By applying a technique known as Orthogonal Frequency Division Multiplexing to the microspacecraft transmission, a frequency correlation algorithm is developed that can be used to bring all the signals of the array into alignment. Simulations and hardware prototyping experiment were performed that confirm the functionality of these algorithms. The results of these experiments are discussed and the benefits of this new system of arraying are shown over current techniques. Finally, it is demonstrated how these new techniques can be applied to create a ground array that works in reverse, whereby an array is used to uplink a transmission to a spacecraft. |
