Date of Award

Spring 1-1-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Aerospace Engineering Sciences

First Advisor

Daniel Scheeres

Second Advisor

George Born

Third Advisor

Hanspeter Schaub

Abstract

Based on the recommendations of the Augustine Commission, President Obama has proposed a vision for U.S. human spaceflight in the post-Shuttle era which includes a manned mission to a Near-Earth Object (NEO). A 2006-2007 study commissioned by the Constellation Program Advanced Projects Office investigated the feasibility of sending a crewed Orion spacecraft to a NEO using different combinations of elements from the latest launch system architecture at that time. The study found a number of suitable mission targets in the database of known NEOs, and predicted that the number of candidate NEOs will continue to increase as more advanced observatories come online and execute more detailed surveys of the NEO population.

The objective of this thesis is to pick up where the previous Constellation study left off by considering what orbit options are available for an Orion-class spacecraft upon arrival at a NEO. A model including multiple perturbations (solar radiation pressure, solar gravity, non-spherical mass distribution of the central body) to two-body dynamics is constructed to numerically integrate the motion of a satellite in close proximity to a small body in an elliptical orbit about the Sun. Analytical limits derived elsewhere in the literature for the thresholds on the size of the satellite orbit required to maintain stability in the presence of these perturbing forces are verified by the numerical model. Simulations about NEOs possessing various physical parameters (size, shape, rotation period) are then used to empirically develop general guidelines for establishing orbits of an Orion-class spacecraft about a NEO. It is found that an Orion-class spacecraft can orbit NEOs at any distance greater than the NEO surface height and less than the maximum semi-major axis allowed by the solar radiation pressure perturbation, provided that the ellipticity perturbation is suffciently weak (this condition is met if the NEO is relatively round and/or has a long rotation period) for orbits falling below the minimum threshold for guarding against its effects. NEOs as small as ≈ 20 m in diameter can be orbited by an Orion-class spacecraft, provided the rotation period is not too long (< 30 hours) if the ellipticity perturbation is strong. There are cases of small, very slowly rotating NEOs that cannot be orbited by an Orion-class spacecraft at any distance, but generally these NEOs are required to have severely elongated shapes in order to maintain the strength of the ellipticity perturbation in spite of their longer rotation periods. Finally, terminator frozen orbits are found to be the best orbit option for a manned mission to a NEO, since their stability in the face of multiple perturbations provides an ideal platform for conducting scientific observations of the NEO and launching astronaut excursions to the NEO surface.

Share

COinS