Optimisation of Propellant Consumption for Power Limited Rockets

Abstract

In this thesis we look at the most cost-
effective trajectory for power limited rockets, i.e. the trajectory which costs the least amount of propellant. First some background information as well as the differences between thrust limited and power limited rockets will be discussed. Then the optimal trajectory for thrust limited rockets, the Hohmann Transfer Orbit, will be explained. Using Optimal Control Theory, the optimal trajectory for power limited rockets can be found. Three trajectories will be discussed: Low Earth Orbit to Geostationary Earth Orbit, Earth to
Mars and Earth to Saturn. After this we compare the propellant use of the thrust limited rockets for these trajectories with the power limited rockets. Here we made this comparison between a conventional thrust limited rocket with a specic impulse of 455 seconds and the VASIMR rocket for the power limited rocket. Also the initial mass of both rocket types was taken as
5 * 10^5 kg. Lastly, we take a look at a gravity assist. Gravity assists can help reduce propellant use even further. Therefore we will once more look at the trajectory for a power limited rocket
from Earth to Saturn. Only this time we use a gravity assist from Jupiter. Then we can see if the propellant use is indeed even lower when using the gravity assist. We find that the the power limited rocket becomes more fuel-effcient as travel time increases. Also using a gravity assist further reduces propellant consumption.