The European Space Agency (ESA) plans to launch two satellites in 2017 that can move as a single object with submillimeter precision. The configuration could enable the creation of large space telescopes with long focal lengths. The Proba-3 mission — led by Salvador Llorente and colleagues at private engineering and technology group Sener — the first Spanish company to lead an ESA mission — will include two satellites weighing about 340 and 200 kg. There have been very few formation satellite missions, such as the Swedish Prisma project, and only in the near-Earth environment and with a level of precision of tens of centimeters. The first satellite, the blocker, will create an artificial solar eclipse to facilitate its companion satellite, the coronagraph, in examining the sun in unprecedented detail and gathering data. A similar technique was tried in 1975 on the Apollo-Soyuz mission. A European Space Agency project aims to demonstrate, for the first time, that two spacecraft can fly in formation with submillimeter precision. The Proba-3 mission will be led by Spanish company Sener. Courtesy of ESA – P. Carril. “The primary objective of this mission is to validate the precision formation flight technology and to be able to position both craft between 20 and 250 meters apart, yet always working together as if they formed a rigid structure,” Llorente said. The configuration also could be used to create large space telescopes with the lens and detector hundreds of meters apart. “If you wanted to build telescopes with long focal length, you could mount the lens on one of the satellites and the detector on the other, which was already proposed; for instance, in the case of the Xeus x-ray telescope,” he said. This eliminates the need for large deployable structures and reduces the mass of the launch as well as improves the position stability when compared with thermoelastic distortion with such a large structure. Proba-3 also will serve to validate several optical and laser sensors in addition to the algorithms required for future formation flight missions. Various experiments will help confirm that the system works properly, varying the distances between the satellites and their pointing direction. Rendezvous tests — orbital approach maneuvers between spacecraft in highly elliptical orbit — also will be performed and could be applied to missions such as the “Mars Sample Return,” which plans to pass a Martian rock from one craft to another. Prevention and emergency systems will be tested with the activation of engines and other devices to avoid the risk of the satellites colliding, “a situation that entails the premature end to any mission,” Llorente warned. The satellites will be launched in 2017 — several are being evaluated, including one from the US and another from India — and they will travel jointly together until they separate in a highly eccentric orbit. Their nearest point, the perigee, will only be 600 km from Earth. Each time they pass through this zone, they will be in free flight, but under well-controlled trajectories, the researchers say. The operations associated with precise formation flight will take place on the most distant section of the orbit, the apogee, more than 60,000 km away. At this point, the gravitational disturbances are minimized and do not complicate or make the maneuvers too costly. The formation technology will be tested, and the planned tests will be conducted in this region of the orbit. Other project partners are Astrium CASA Espacio and GMV, both of Spain, and QinetiQ Space and Spacebel, both of Belgium. The mission’s tracking station will be located in Redu, Belgium, but adjustments between the two spacecraft can be programmed automatically. Details of the Proba-3 mission appeared in Acta Astronautica (doi: 10.1016/j.actaastro.2012.05.029). For more information, visit: www.fecyt.es