Formation Flying is conceptually different from the usual satellite constellation, which is not designed to build a single large sensor, but to multiply the number of sensors for increasing the ground coverage or the number of sensor types.

• The sensor is distributed and would have required too large a structure (masts, area) with a single spacecraft approach. The signals (RF or optical) from the spacecraft are combined in a coherent way. Changing formation geometry enables sensor reconfiguration.
• Applications correspond to those of a large antenna, telescope or interferometer in fields such as astronomy, Earth science/observation, positioning, and so on.
• The spacecraft are generally close to each other (instead of distributed around the globe in a constellation) and the relative control/knowledge can be in direct relationship with the sensing wavelength, and therefore very demanding. Particular sensing geometries can involve a nonnatural orbit trajectory, with continuous thrusting and closed loop control.
• Constraints on storage and telemetry may lead to in-flightmerging of signals through intersatellite links and distributed processing.
• Formation accuracy and proximity, as well as optimization of ground operation resources, mean that a large amount of onboard autonomy is required. This is also driven by significant distance of operations and contingency handling facilities.
• Guidance, Navigation and Control systems are more demanding, as they typically need to operating on both a central and decentralized mode, as well as the GNC requirements are unprecedented for several science missions.
• Testing of Formation Flying systems before flight is also a new area, where several spacecraft might need to be active to perform end to end tests.