Darren Baird

Mars Exploration Rovers orbit determination filter strategy.

§†† ‡‡ §§ §§ , The successful delivery of the Mars Exploration Rover (MER) landers to well within the boundaries of their surface target areas in January of 2004 was the culmination of years of orbit determination analysis. The process began with a careful consideration of the filter parameters used for pre-launch covariance studies, and continued with the refinement of the filter after launch based on operational experience. At the same time, tools were developed to run a plethora of variations around the nominal filter and analyze the results in ways that had never been previously attempted for an interplanetary mission. In addition to achieving sub-kilometer Mars-relative orbit determination knowledge, the filter strategy and process detected unexpected error sources, while at the same time proving robust by indicating the correct solution. Consequently, MER orbit determination set a new standard for interplanetary navigation. Nomenclature

Zonal Wind Calculations from Mars Global Surveyor Accelerometer and Rate Data

TheMars Global Surveyor spacecraft was initially placed into a high-eccentricity, nearly polar orbit about Mars with a 45-h period. To accomplish the science objectives of the mission, a 2-h circular orbit was required. Using a method known as aerobraking, numerous passes through the upper atmosphere slowed the spacecraft, thereby reducing the orbital period and eccentricity. To successfully perform aerobraking, the spacecraft was designed to be longitudinally, aerodynamically stable in pitch and yaw. Because the orbit was nearly polar, the yaw orientation of the spacecraft was sensitive to disturbances caused by the zonal components of wind (east to west or west to east) acting on the spacecraft at aerobraking altitudes. Zonal wind velocities were computed by equating the aerodynamic and inertia-related torques acting on the spacecraft. Comparisons of calculated zonal winds with those computed from the Mars thermospheric general-circulation model are discussed.

Mars Exploration Rover cruise orbit determination

The Mars Exploration Rover project consisted of two missions (MER-A: spirit rover and MER-B: opportunity rover) that launched spacecraft on June 10, 2003, and July 8, 2003, respectively. The spacecraft arrived at Mars approximately seven months later on January 4, 2004, and January 24, 2004. These spacecraft needed to be precisely navigated to a Mars atmospheric entry flight path angle of -11.5 deg +/-0.12 deg (3(sigma)) for MER-A and +/-0.14 deg (3(sigma)) for MER-B in order to satisfy the landing site delivery requirements. The orbit determination task of the navigation team needed to accurately determine the trajectory of the spacecraft, predict the trajectory to Mars atmospheric entry, and account for all possible errors sources so that the each spacecraft could be correctly targeted using five trajectory corrections along the way. This paper describes the orbit determination analysis which allowed MER-A to be targeted using only four trajectory correction maneuvers to an entry flight path angle of -11.49 deg +/-O.010 deg (3(sigma)) and MER-B to be targeted using only three trajectory correction maneuvers to an entry flight path angle of -11.47 +/-0.021 deg(3(sigma)).

Mars Exploration Rovers entry, descent, and landing navigation.

During the final approach and Entry, Descent and Landing (EDL) of both Mars Exploration Rovers (MER), one-way Doppler were monitored to detect, in real-time, the following events.

Calculation of Zonal Winds Using Accelerometer and Rate Data from Mars Global Surveyor

ठThe Mars Global Surveyor spacecraft was initially placed into a high eccentricity, nearly polar orbit about Mars with a 45-hour period. To accomplish the science objectives of the mission, a 2-hour, circular orbit was required. Using a method known as aerobraking, numerous passes through the upper atmosphere slowed the spacecraft, thereby reducing the orbital period and eccentricity. To successfully perform aerobraking, the spacecraft was designed to be longitudinally, aerodynamically stable in pitch and yaw. Since the orbit is nearly polar, the yaw orientation of the spacecraft was sensitive to disturbances caused by the zonal components of wind (east-to-west or west-to-east) acting on the spacecraft at aerobraking altitudes. Zonal wind velocities were computed by equating the aerodynamic and inertia-related torques acting on the spacecraft. Comparisons of calculated zonal winds with those computed from the Mars Thermospheric Global Circulation Model are discussed.