Michael A. Shoemaker

Trajectory Estimation of the Hayabusa Spacecraft During Atmospheric Disintegration

The Hayabusa spacecraft was intentionally destroyed in the atmosphere at superorbital velocity at the conclusion of its asteroid sample return mission in June 2010. This study uses single-station ground-based video observations of the reentry to analyze the breakup of the spacecraft and estimate the trajectory of 80 individual spacecraft fragments. An extended Kalman filter with batch initialization is used to estimate the position, velocity, and aerodynamic ballistic coefficients of the fragments. The breakup is characterized and compared with preflight predictions. A high area-to-mass object is seen early during the reentry, which matches closely with the predicted solar panel separation. Nearly all fragments have decreasing freestream dynamic pressure during their observed trajectories. Fragments with high drag ballistic coefficients are more likely to be observed early in the reentry. Assuming simple aluminum spheres, the estimated ballistic coefficients show that the fragments would have radius and m...

Modeling and Validation of Thermal Radiation Acceleration on Interplanetary Spacecraft

Precisemodeling of nonconservative forces is becoming increasingly important for deep-space and interplanetary missions, especially those with strict targeting requirements. Apparent errors in the solar radiation pressure model are often corrected with estimated scale factors in the orbit determination process. For example, several European Space Agency deep-space spacecraft have estimated solar radiation pressure scale factors between 1.05 and 1.15. This work shows that including separate thermal accelerationmodels can account formany of these apparent errors in the solar radiation pressure modeling. Using the Rosetta spacecraft as an example, a steady-state thermal model that is applicable to the cruise phases of interplanetary missions is described. The surface temperatures on the spacecraft body are solved in closed form,whereas those on the solar panel front and rear surfaces are solvedwith an iterative numerical procedure. The thermal model is validated by comparing the predicted thermal radiation acceleration with the remaining unmodeled acceleration extracted from the operational orbit estimates. The solar array temperatures from this model also agree with finite element method results and thermistor telemetry to within several degrees.

Comparison of Integrated and Nonintegrated Wide-Field Optic Flow for Vehicle Navigation

Recent studies of vision-based navigation and guidance for robotic vehicles have been inspired by the biological systems found in flying insects. The wide-field integration of optic flow is one pre-existing method, in which the sensed optic flow is integrated along with sensitivity functions to mimic the action of directionally sensitive cells observed in some insects’ visual systems. This study re-examines the wide-field integration method and reformulates the problem from a summation rather than an integral. This reformulation allows the wide-field integration measurement outputs to be directly compared with nonintegrated optic flow measurements. The method using nonintegrated optic flow measurements is shown to have some practical advantages, such as eliminating the need to define input sensitivity functions and having a measurement Jacobian that is easier to derive analytically. Also, the state estimates obtained with the nonintegrated method are proven to have minimum variance compared with those fro...

Reconstruction of Rosetta's Thermal Radiation Effects Using Orbit Determination Results

The Rosetta mission to rendezvous with a comet requires accurate deep-space navigation. The main objective of our research is to develop a thermal radiation model of the spacecraft that can be included in the orbit determination process. This paper describes our preliminary thermal model, and a validation process using past orbit determination data. We numerically dierentiate the velocity from the long-arc orbit solutions to approximate the acceleration acting on the spacecraft. After accounting for the gravitational acceleration, we compare two models of the remaining nongravitational acceleration: one using only a solar radiation pressure (SRP) model, and an improved model that also includes the acceleration from thermal radiation. We show that the improved model can account for approximately 97 to 99% of the nongravitational acceleration, whereas the SRP-only model accounts for approximately 90 to 95%. Thus, including the thermal radiation model will enhance the mission’s existing orbit determination process.