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Proba-3 is the first ESA space mission to use precise formation flying technology for the first time. It demonstrates the maturity of this technology and, at the same time, uses it to conduct scientific observations of the solar corona, under conditions never achieved until now.
Proba-3 is an ESA space mission that uses precise formation flying technology for the first time. Its objective is to demonstrate the maturity of this technology and, at the same time, use it to perform scientific observations of the solar corona, under conditions never achieved until now. Precise formation flying technology allows the two Proba-3 satellites to be positioned with a relative position accuracy of millimetres and a pointing precision of thousandths of a degree.
The mission’s commissioning period was completed in July 2025, at which time the ESA declared the mission objectives achieved.
Now in the routine operation phase, the satellites will demonstrate the capabilities of such technology for use in future scientific missions by performing a set of typical formation flying operations in orbit:
The success of Proba-3 demonstrates that small, independent, and easy-to-launch platforms can replace bulky structures, such as telescopes, and work as a single entity achieving high performance. In 2025, several approach operations were carried out, notably one at a distance of 30 m in November 2025.
Proba-3 also performs scientific observations, taking images of the solar corona through a coronagraph instrument placed on one of the spacecraft. Formation flying technology involves placing one of the two Proba-3 satellites in front of the instrument’s lens, thereby blocking the solar disk and creating an artificial eclipse in flight. Doing this in space, at a distance of 150 m and with observation periods of up to 6 continuous hours per orbit, achieves unprecedented performance in coronagraphy; therefore, the Proba-3 mission provides results of great value to the scientific community.
In 2025 alone, Proba-3 accumulated data equivalent to 4,000 solar eclipses. Its data, together with measurements taken by other sun observation satellites such as Proba-2 or SOHO, now allow for a better understanding of how coronal mass ejections (CME) are generated and transmitted from the centre of the sun to the outer corona.
Another particularity of this mission is that most operations on Proba-3 are carried out fully autonomously, without ground intervention to actively control the formation, but always with a monitoring team behind it. The Proba-3 satellites coordinate their own operations based on a predefined timeline where their activities are specified.
They must also be capable of making autonomous decisions in the event of failures during these operations, breaking the formation and putting the satellites into a safe configuration until the problems can be further investigated from the ground.
The space segment of Proba-3 is composed of two satellites. The first, called the Coronagraph Spacecraft (CSC), contains the primary instrument (coronagraph). The second satellite, called the Occulter Spacecraft (OSC), carries an occulting disk that covers the solar disk as seen from the other satellite.
The OSC, as the lead entity for the formation flying system, also integrates the main metrology units used for formation flying, specifically a laser system and a set of cameras part of a vision-based system. The two satellites are launched in a stacked configuration, with the OSC mounted on top of the CSC and the CSC’s solar array folded.
Orbit | High Elliptical Orbit (HEO) |
Launcher | PSLV-XL (ISRO) |
Ground station | Antennas of INTA (Spain) and SSC (Chile, Australia) |
Lifetime | 2 years |
Satellites | Coronagraph (300 kg/300W) |
Metrologies | Laser-based system (FLLS) |
Payloads & Experiments | ASPIICS (Coronagraph) |
Operation | Autonomous operations for 7 days |
The Sener technology group has led, as Prime Contractor, the development of the Proba-3 mission system, encompassing both the space segment and the ground segment, in close collaboration with an industrial team formed by Airbus Defence and Space in Spain, GMV, Redwire, and Spacebel, which included a broad industrial consortium of more than 29 companies from 17 different countries.
Sener also led the industrial team that operated the satellites during the in-orbit commissioning phase, which was completed in July 2025. Since then, the satellites have been operated under the responsibility of the ESA.
Proba-3 is part of the ESA’s General Support Technology Programme (GSTP), and Spain’s participation has been made possible thanks to the support of the CDTI (Centre for the Development of Technology and Innovation).
Sener has also been responsible for the design, manufacture, and testing of some of the satellite units:
The two Proba-3 spacecraft were launched together by the Indian Space Research Organisation’s (ISRO) PSLV-XL launcher. This vehicle provided the necessary power at a reasonable cost to place the combined 550-kilogram pair into their highly elliptical (or elongated) orbit, which required ascending to 60,000 kilometres from Earth before descending to just 600 kilometres.
Sener, as the Prime Contractor, developed the satellite platform and the formation flying system for this pioneering space mission.
The ESA’s Proba-3 space mission was launched on 5 December 2024.
The Proba-3 mission is marking a milestone in space exploration thanks to its innovative formation flying approach and its miniaturised satellites.
This technology allows for the creation of a modular system in orbit capable of functioning with the precision of a single piece, thanks to its millimetre-level operation. In this way, formation flying enables the creation of complex structures, such as telescopes, which would be very costly to launch into space due to the dimensions required during operation.
This technology opens new frontiers in astronomy, geodesy, and Earth observation. Specifically, as Proba-3 is capable of generating its own solar eclipses, it allows for very long-duration observations of the solar corona, achieving unprecedented precision.
