The impacts of Mars Reconnaissance Orbiter roll steering on Phoenix relay link

The 2005 Mars Reconnaissance Orbiter (MRO) mission has the primary objective of placing a science orbiter into Mars orbit to perform remote sensing investigations that will study the surface, subsurface and atmosphere of Mars and will identify potential landing sites for future missions. Its relay service for a landing asset on the Martian surface will not begin until the arrival of the 2009 Phoenix Mars Lander. Among the many newly added features such as finer resolution camera, advanced instruments, and the second-generation communication radio Electra, MRO is capable of rolling the spacecraft at a fixed angle during its flight over a surface asset. This improves MRO´s link performance and thus, increases the overall data throughputs. In our study, we are interested in determining the optimum roll angle for each pass relative to nadir pointing and its impact in terms of data throughput gain. In this paper, we present a mathematical formulation, which is based on the constrained optimization framework, to determine the optimum roll angle. The model is designed to find the best roll angle for each pass, where the roll angle is bounded by plusmn30deg so that the resulting data throughput is largest. The data throughput is computed based on MRO´s and Phoenix´s geometry, the roll angle, and the telecom parameters and capabilities, including supportable data rates, antenna patterns, etc. Other important quantities include the statistics of the passes of different peak elevation angles, margins, day passes, duration and frequency of the passes, type of data rates, etc. These questions can provide a general guideline to facilitate the planning process between the science and the navigation teams. Long-term simulation and study have also been implemented. Statistical findings based on the simulation for several possible future landing sites will be presented