Capability of solar electric propulsion for planetary missions

Historically, deep space exploration was initiated by a series of flyby missions that were propulsively and energetically modest. The basic energy barrier given by the use of chemical propulsion system was not a limiting factor. Later on, the use of gravity assists has enabled missions with enlarged velocity increments. Unfortunately, multiple gravity assists have the drawback to narrow dramatically the launch windows. Moreover, the cruise phases are extremely long with obvious impacts on the operation costs. The most promising solution for the future deep space missions is found in the use of the electric propulsion (EP). Owing to its high specific impulse, the EP enables very high velocity increments, higher payload ratios and the use of smaller launchers. In addition it allows to have more flexible launch windows and ultimately reduces the cruise time. possesses a variety of EP systems. Two main parameters characterise the performance of these EP systems: the specific impulse and the specific power. The first parameter is a measure of the fuel consumption, while the second is the main design driver for the on board power system. The increase in specific impulse enables missions requiring a large ΔV. However, in practice the maximum ΔV is limited to some 10 km/s, while a typical EP-based mission to Mercury requires 16 km/s. Hence, trajectories combining both low-trust and gravity-assist techniques have been devised for the ESAʹs BepiColombo mission. 1 is a precursor mission to test these system and mission aspects.