|Institution:||Delft University of Technology|
|Full text PDF:||http://resolver.tudelft.nl/uuid:970c4214-7667-494e-afc9-1c2109600736|
The purpose of this thesis is to develop a methodology to design trajectories in order to achieve high ecliptic inclinations for the purpose of solar observation. Solar observatories have been launched since the dawn of the space era, and are still being designed today, however the solar poles have seldom been imaged. This is partly because gaining high ecliptic inclinations requires extremely high amounts of energy. The 1990’s Ulysses probe was the only spacecraft to ever do this, at the cost of a complex mission, involving limited payload and short observation times. Several studies have been done to address the issue, some proposing to use low-thrust propulsion and others multiple gravity assists of the inner planets. The mission presented in this thesis will use both to reach as high inclinations as possible while maintaining short times of flight and short orbital periods. Low thrust trajectory simulation is a very prolific area, and can be done in a number of ways. Since this research was performed at the University of Colorado, a low-thrust trajectory tool was already made available. This is modeled after the Sims-Flanigan approach, which approximates low-thrust trajectories with a finite number of small impulsive ΔV maneuvers. A large drawback of the tool is that it necessitates initial conditions to allow the optimizer to converge. The bulk of this research consisted in devising multiple gravity assist strategies and constructing methods of providing such initial conditions. The chosen gravity assist strategy consists of two phases. The first is the approach phase; here the spacecraft makes multiple transfers between Earth and Venus, with the final objective of increasing relative velocity at the arrival planet of the sequence. The initial conditions are provided using a novel version of the Gravity Assist Space Pruning algorithm. This analyzes the multiple gravity assist sequence one fly-by at a time, sequentially pruning away infeasible transfers, which reduces the bounds for the next leg. Next is the resonance phase: the spacecraft makes multiple resonant fly-bys of the arrival planet, gradually increasing inclination with each pass. Initial conditions here are provided using an original method which models rotations of the V∞ vector on a sphere, whilst representing fly-by maneuvers and resonances as parametric circles on the sphere. The final results analyze and compare five different gravity assist scenarios, ultimately selecting a simple Earth-Venus transfer, followed by 4 resonant Venus gravity assists. This allows to reach an inclination of 36.6 degrees in just about two years, all while utilizing previously flown spacecraft systems. Both initial conditions methods have proven very successful both in identifying potential ballistic trajectories, as well as to serve as inputs for the low-thrust trajectory tool used. Advisors/Committee Members: Noomen, R., Parker, J..