Synthesis of highly inclined and short period solar polar orbit with electric propulsion

Solar polar observation satellites should be in orbits highly inclined to the ecliptic plane. However, the delta-V required to achieve such orbit is too large to get with whichever propulsion system. From this situation, Ulysses, the only satellite on a high inclination orbit so far, used gravity-assist at Jupiter. Because Ulysses flew ballistically after Jupiter flyby, its orbit kept large and period was long. Therefore, solar polar observation time was short compared to orbit period and distance from the sun was about 2AU when observation. To solve these problem, a method called E-2-I conversion was invented. This method attains highly inclined and short period orbit ballistically by repeating Earth flyby after Jupiter flyby. Gravity-assist at Earth can make the orbit smaller, higher inclination and shorter period. Gravity assist at Earth affects weaker than that of Jupiter but by repetition of it can make semi-major axis of the orbit smaller than 1AU and inclination of it about 90 degrees. This is better for solar polar observation than that of Ulysses. However, there was still a problem. Because this method repeats Earth flyby, orbit period after each flyby must be rational number to meet Earth. Moreover, because of weakness of Earth gravity, Earth meeting period can become as long as 5 years and it takes 33 years to reach eventual orbit. In this study, we shortened the whole mission period drastically with low thrust continuous propulsion represented by electric propulsion. In previous study, optimization analysis has been made to increase the orbital inclination angle itself using continuous thrust, but no attempt has been made to combine optimization trajectory by continuous thrust and E-2-I conversion. This study uses continuous thrust not for changing orbit plane which demand huge delta-V but for changing orbit period on the same orbit plane. For example, in ballistic case, the best orbit period after the 1.5 years’ period orbit was 1.25 years not 1 year because Earth gravity is too weak to achieve 1 year period. Therefore, Earth meeting period became 5 years. However, even if it is impossible to change the orbit period from 1.5 years into 1 year by swing-by.