Date of Award

January 2014

Document Type


Degree Name

Master of Science (MS)


Space Studies

First Advisor

Ronald A. Fevig


Near-earth objects (NEOs) are asteroids and comets that have a perihelion distance of less than 1.3 astronomical units (AU). There are currently more than 10,000 known NEOs. The majority of these objects are less than 1 km in diameter. Despite the number of NEOs, little is known about most of them. Characterizing these objects is a crucial component in developing a thorough understanding of solar system evolution, human exploration, exploitation of asteroid resources, and threat mitigation. Of particular interest is characterizing the internal structure of NEOs. While ground-based methods exist for characterizing the internal structure of NEOs, the information that can be gleaned from such studies is limited and often accompanied by large uncertainty. An alternative is to use in situ studies to examine an NEO's shape and gravity field, which can be used to assess its internal structure.

This thesis investigates the use of satellite-to-satellite tracking (SST) to map the gravity field of a small NEO on the order of 500 m or less. An analysis of the mission requirements of two previously flown SST missions, GRACE and GRAIL, is conducted. Additionally, a simulation is developed to investigate the dynamics of SST in the vicinity of a small NEO. This simulation is then used to simulate range and range-rate data in the strongly perturbed environment of the small NEO. These data are used in conjunction with the analysis of the GRACE and GRAIL missions to establish a range of orbital parameters that can be used to execute a SST mission around a small NEO. Preliminary mission requirements for data collection and orbital correction maneuvers are also established. Additionally, the data are used to determine whether or not proven technology can be used to resolve the expected range and range-rate measurements.

It is determined that the orbit semi-major axis for each spacecraft should be approximately 100% to 200% of the NEO's mean diameter and the two spacecraft should be in circular, near polar orbits. This configuration will produce trajectories, which exhibit reasonable stability over a period of roughly 24 hours. Corrective maneuvers will therefore be required with a frequency of approximately once per day. Due to the potentially rapid changes caused by the highly perturbed environment, it is likely that these maneuvers will need to be made autonomously. During the period between corrective maneuvers SST data collection will be possible. The expected range and range-rate measurements will be on the order of ±10-5 m and ±10-5 m/s respectively and can be resolved using proven technology.