PROBA3s

PROBA3s is a European Space Agency technology-demonstrator concept consisting of two formation-flying micro-satellites designed to study the solar corona with an artificial eclipse. The two spacecraft operate in a tightly controlled formation at a separation of tens to hundreds of meters, enabling a long-baseline coronagraph on a compact platform.

Its primary objective is to validate autonomous formation flying and high-precision relative positioning in space, including metrology, navigation, and propulsion needed to maintain the formation over extended periods. The mission also demonstrates a coronagraphic imaging approach that suppresses direct sunlight to reveal the faint solar corona, supporting solar physics and space weather research.

Design features include a leading spacecraft that carries an occulting structure to block the solar disk and a trailing spacecraft that houses the telescope and detector. Precision alignment is achieved through a combination of laser or optical metrology, star trackers, sun sensors, and micro-propulsion. Telecommunications links support inter-satellite communication and data downlink to Earth.

Outcome and significance: PROBA3s serves as a technology demonstrator for formation flying and high-contrast imaging in space. By proving precise relative control and metrology in a two-satellite system, the mission informs the development of future space telescopes and solar-observation platforms that require stable, long-baseline configurations.