FEEP thrusters are high performance devices designed to satisfy the most demanding requirements for very low thrust, high-accuracy applications. Originally developed for science missions, FEEP is an enabling technology for precision formation flying and accurate pointing applications. Initially proposed by ESTEC researchers in the mid-1970’s, the linear slit FEEP thruster was developed for µN applications by Centrospazio (later to become Alta) in the 90's. Today, Alta is the provider of FEEP thrusters in Europe.
FEEP Thruster Working principle. Left: diagram; Right: animation.
FEEP's unusual combination of very low thrust and very high specific impulse makes it quite unique even in the field of electric propulsion, let alone in the broader field of space propulsion, where it is far more common to deal with high thrust, low specific impulse devices. By using a liquid propellant (usually cesium, for its low ionization energy and high atomic mass) which is first ionized and then accelerated by means of a strong electric field, these devices can easily achieve specific impulses in excess of 10000 s with extremely high power efficiency at thrust ranging from a few µN to a few mN.
FEEP systems often represent the only viable option for drag-free satellite applications, such as the LISA Pathfinder and Microscope missions, where fine thrust resolution (0.1 µN) over a relatively wide thrust range (0.1 – 150 µN) is required. The micronewton FEEP system is developed under ESA funding (read here for ESA contribution to FEEP testing). Higher thrust versions of FEEP are suited to attitude control and orbit maintenance on small commercial satellites. Development and testing of two FEEP systems is presently underway: