Missions involving formation flying and rendezvousing in Space are already being planned for the future. Formation flying involves distributing different elements of an instrument between several satellites and having them fly in concert. This means the instrument in question can be larger than would be possible on a single satellite and therefore more efficient. Keeping the satellites in a stable formation requires high precision technologies for control and navigation.

The purpose of the Prisma mission is to test, in orbit, the manoeuvres and techniques used in formation flying and rendezvousing. Two satellites will fly in concert on the same low Earth orbit, with the principal satellite (‘Mango’) being mobile while the secondary satellite (‘Tango’) follows a fixed trajectory.

Prisma is a Swedish programme financed by the SNSB1. It is being developed as a multilateral cooperative project with CNES, the German Space Agency (DLR2) and the Danish Technical University (DTU). CNES is participating in the project, jointly with Spain’s CDTI3, by providing a radiofrequency metrology system together with software allowing it to be used in orbit for the FFIORD4 experiment.
The primary objective of the experiment is to validate the radiofrequency metrology sensor. It will be carried on both Mango and Tango and unlike GPS this kind of equipment can be used to monitor the relative positions and orientation of two satellites flying on different orbits. The other part of the CNES experiment will involve in-flight testing of the algorithms required for monitoring a set of satellites during the deployment and operational phases of future formation flying missions.

As well as flying in formation, which will also be tested with the help of GPS receivers (supplied by DLR), Prisma will attempt to perform rendezvous autonomously. This involves satellites working in close proximity guided by an optical sensor (supplied by DTU). All these operations will be carried out autonomously and require the use of onboard software which will also be validated as part of this demonstration mission.

By participating in the development of formation flying technologies, CNES is staking out a leading position for the design of future missions such as Simbol-X, Pégase, or Darwin.

^{1 Swedish National Space Board
2 Deutches Zentrum für Luft- und Raumfahrt
3 Centro para el Desarrollo Tecnológico Industrial
4 Formation Flying In-Orbit Ranging Demonstration}

_{Last updated : January 2010}