AAS 16-229 DEVELOPMENT OF A TOOL FOR ANALYZING ORBITS AROUND ASTEROIDS Julian Niedling * , David Gaylor † , Marcus Hallmann ‡ , and Roger Foerstner § In this paper orbit dynamics around asteroids are analyzed. Since asteroid orbital environ- ments are some of the most highly perturbed environments in the solar system, it is of partic- ular interest to demonstrate the effects of gravitational perturbations, solar radiation pressure (SRP) and solar gravity. In order to show and compare the importance of satellite and as- teroid properties, the theory of asteroid dynamics is applied on both the relatively massive asteroid Eros and the relatively small asteroid Itokawa. Special orbits, such as terminator orbits and hovering, are analyzed through the example of both asteroids. The analyses are performed using a tool written in MATLAB, which allows to parametrically study orbits around asteroids. The tool is capable of analyzing stability of orbits around asteroids, de- signing terminator orbits and determining Δv, thrust magnitude and propellant for hovering. INTRODUCTION Even though asteroids’ physical properties like size, shape and heliocentric orbital elements can be roughly estimated from Earth-based ground observations, a complete characterization of mass distribution, compo- sition, shape, rotational properties, etc. can only be performed by a spacecraft in the close vicinity of the particular asteroid. Due to the lack of apriori information, it is challenging to develop accurate and detailed mission plans for asteroid missions. Asteroid gravity fields are relatively weak, very irregular and not well known when compared to a planet’s gravity field. Additionally, the Sun’s gravity field and solar radiation pressure (SRP) still must be taken into account when analyzing forces acting on a spacecraft orbiting aster- oids. These irregularities and perturbations affect the satellite’s motion which results in unique trajectories around the asteroids. Regardless of the mission or scientific purpose, it is of particular interest to achieve stable motion around the asteroid. In order to avoid mission failure or complete loss of the satellite, the spacecraft should neither escape on a hyperbolic trajectory nor crash into the asteroid’s surface. If an orbit tends to be unstable, it should be either avoided, or thrust must be applied in order to stabilize the spacecraft’s motion. Generally, the choice of orbit must be compatible with the mission objective. The MATLAB tool ADONIS (Analysis and Design of Orbits around asteroids and Numerical Investigation of Stability), has been developed, which analyzes orbits around asteroids. It analyzes stability and simulates and visualizes the spacecraft’s trajectory, including potential escape hyperbolas or collisions with the asteroid’s surface. The tool has the capability to analyze the following three types of orbits: frozen terminator orbit, body-fixed hovering and inertial hovering. It also computes the Δv and thrust magnitude required for orbit maintenance and outputs various parameters of interest. The MATLAB script gathers input parameters which are necessary for asteroid mission design: satellite characteristics, force models and asteroid characteristics and ephemeris. Furthermore, the satellite orbit initial state can be defined and propagated for a certain time. An asteroid database comprising all recently known asteroids on Jet Propulsion Laboratory (JPL) Small- Body Database Search Engine provides required asteroid orbital elements and characteristics. By defining the asteroid identification number (ID) and mission date, the asteroid position is determined. Moreover, the asteroid dimensions can be approximated by three semi-major axes. ADONIS computes asteroid and Sun * M. Sc., University of the German Armed Forces, Institute of Space Technologies and Space Applications, Munich. † Prof., University of Arizona, Department of Aerospace and Mechanical Engineering, Tucson. ‡ Dipl. Ing., Deutsches Zentrum fuer Luft- und Raumfahrt (German Aerospace Center), Bremen. § Prof., University of the German Armed Forces, Institute of Space Technologies and Space Applications, Munich. 1