The Indian Space Research Organisation (ISRO) successfully launched the European Space Agency's (ESA) PROBA-3 satellite today, marking another milestone in its renowned Polar Satellite Launch Vehicle (PSLV) series. This mission, PSLV-C59, is the 61st commercial launch for ISRO’s workhorse rocket.

PROBA-3, part of the Project for Onboard Anatomy series, is the third satellite in ESA’s program and focuses on solar research. The mission aims to study the Sun's corona with unprecedented precision. It consists of two independently operated spacecraft: the Coronagraph Spacecraft (CSC), weighing 310 kg, and the Occulter Spacecraft (OSC), weighing 240 kg. Both satellites will orbit Earth in a highly elliptical trajectory, with their farthest point (apogee) reaching 60,500 km above the equator.

A key feature of PROBA-3 is its demonstration of "formation flying," a groundbreaking technique in space science. The two spacecraft will maintain a precise 150-meter separation in orbit to form a large-scale solar coronagraph. This configuration allows the OSC to cast a shadow that blocks direct sunlight, enabling the CSC to image and analyze the Sun's faint corona across the electromagnetic spectrum, including visible light, ultraviolet, and infrared wavelengths. The CSC can also capture polarized light, which provides critical insights into solar behavior.

PROBA-3's primary scientific goal is to observe the Sun's corona at 1.1 solar radii in visible light. This achievement would make it the most precise satellite for studying the Sun's outer atmosphere. The solar radius, used as a reference in this measurement, is approximately 695,700 km.

What sets PROBA-3 apart is its precision formation flying, where the two satellites autonomously maintain millimeter-level accuracy and arc-second angular alignment during six-hour sessions of their nearly 20-hour orbital cycle. Together, the pair effectively function as a virtual giant satellite, navigating independently without ground intervention.

Following their successful deployment, the spacecraft will undergo a preparatory phase involving safety tests by ESA, including collision avoidance simulations. Once these are complete, the satellites will enter a secure tandem orbit with no risk of collision or deviation. The satellites will repeatedly demonstrate advanced orbital maneuvers such as rendezvous, proximity operations, and coronagraph observations during their mission.

ESA describes PROBA-3 as a "laboratory in space," designed to validate cutting-edge technologies, including guidance, navigation, and control algorithms. It will test sensors and relative GPS navigation techniques previously evaluated in ground simulators. Additionally, the mission includes a rendezvous experiment to refine technologies for future applications, such as a Mars Sample Return mission or the de-orbiting of low-Earth satellites, contributing to the reduction of orbital debris.

This mission exemplifies the collaborative advancement of space technology, positioning ISRO and ESA at the forefront of innovation in satellite operations and solar research.