FIRE SAIL: MESSENGER'S USE OF SOLAR RADIATION PRESSURE FOR ACCURATE MERCURY FLYBYS

ENvironment, GEochemistry, and Ranging) has successfully completed its first four years of flight operations following launch on 3 August 2004. As part of NASA's Discovery Program, MESSENGER has executed the first two of three Mercury flybys, leading to an eventual orbit about Mercury in March 2011. Accuracy at these Mercury flybys is critical, as the flybys provide a significant portion of the AV required for the mission. Due to MESSENGER's proximity to the Sun, solar radiation pressure is the dominant perturbation on the spacecraft. With intelligent planning and management of the spacecraft attitude and solar array articulations, the solar radiation pressure can be used to improve the accuracy of these flybys. MESSENGER uses this disturbance to help control the growth of spacecraft angular momentum, minimizing the perturbations due to thruster momentum off-loads. The force due to solar radiation pressure is also used directly as a precision trajectory control for the Mercury flybys. This method reduced the amount of propellant required to navigate the first and second Mercury flybys.