Mission design study of an RTG powered, ion engine equipped interstellar spacecraft.

摘要

This research explores a variety of mission and system architectures for an unmanned Interstellar Precursor Mission (IPM) spacecraft with a Radioisotope Thermoelectric Generator (RTG) powered Ion Engine using Xenon propellant, traveling on a (direct) ballistic escape trajectory to the undisturbed Interstellar Medium (∼200 AU). The main goal of this work was to determine the relationship between the propulsion system design parameters and the ensuing escape trajectory. To do this, an orbit simulator was created in Matlab using a fourth order Runge-Kutta numerical integration method to propagate the thrusting spacecraft's trajectory through time. The accelerations due to the Sun's gravity and the Ion Engine thrust were modeled separately and then combined into a single total acceleration vector at each time step, with the thrust direction assumed to be in the direction of the spacecraft's instantaneous velocity vector. The propellant of the thruster was also designed to be completely consumed by the time of engine cut-off (ECO), meaning a constant propellant mass flow rate. Simulations were run for burn times of 5, 10 & 15 years, with heliocentric launch velocities of 0, 5, 7, 10 & 12 km/sec from a circular 1 AU Earth orbit, and with RTG supplied engine input powers of 1000, 1500 & 2000 W. A total of 45 simulations were run for the circular 1 AU case, as well as additional comparison simulations for launches from an elliptical Earth orbit at perihelion and aphelion.;The results of these simulations yielded many interesting results on the total fly-out times to 200 AU, which ranged dramatically from ∼35 to ∼140 years depending on the propulsion system settings and orbital initial conditions, as well as descriptions of the ECO distances from the Sun for each mission. The simulations also revealed the inherent gravitational maneuver inefficiency felt by all low thrust spacecraft, which becomes more apparent under certain conditions. Relations between launch velocity and the various characteristics of the escape trajectory were also shown. Finally, the propulsion system model showcased many details about the performance of the Ion Engine, including the consequence that increasing the input power level to the engine will result in a greater increase of thrust when operating at shorter engine burn times.