Photo credit: www.esa.int

Exploring the Challenges of Formation Flying: ESA’s Proba-3 Mission

Operating a single satellite in orbit is a challenge in itself, but coordinating two satellites to fly in close formation adds a new layer of complexity. The European Space Agency (ESA) is set to launch its Proba-3 mission on December 4, 2024, from India, aiming to achieve precise formation flying at an astonishing proximity of around 150 meters. This distance is roughly equal to the length of one and a half football fields and will require incredible precision, measured to within a millimeter.

The Formation Flying Challenge

Damien Galano, the Proba-3 mission manager, elaborates on the unique aspects of this mission, stating, “Previous formation flying missions have maintained distances in the tens of kilometers. Proba-3 pushes the boundaries by keeping its satellites much closer, allowing for a visual effect where one satellite can cast a controlled shadow on the other. This shadowing effect will enable extended observation of the solar corona, which is significantly dimmer than the Sun itself.”

Choosing the Right Orbit

One of the critical decisions for the Proba-3 mission was selecting an appropriate orbit. A low Earth orbit was dismissed due to numerous factors that could destabilize the satellites’ positions: the stronger gravitational pull, air drag, and light interference from Earth. ESA’s Frederic Teston notes that initial simulations suggested that the frequent thruster adjustments required in a low orbit would deplete their propellant reserves in less than 30 minutes.

Instead, an elongated orbit was chosen, starting at an altitude of 600 kilometers and reaching up to 60,500 kilometers during each orbit cycle, which lasts 19 hours and 36 minutes. This approach resembles a rollercoaster, where the satellites speed up significantly in the lower parts of their trajectory but slow down as they ascend, spending more time near apogee, where they will execute their formation flying maneuvers.

Autonomous Precision Control

Given the vast distances involved, human intervention in formation flying is impractical. Proba-3’s satellites will operate autonomously, using a sophisticated combination of sensors and technologies to position themselves accurately relative to one another. This includes GPS receivers, optical cameras, and specialized sensors to monitor their alignment and distance with millimeter-level precision.

The process begins with star trackers that determine each satellite’s orientation in space, followed by precise calculations made by onboard navigation systems. During the formation flying phase, cameras will track LED patterns on the opposite satellite for relative positioning, while a laser system will provide the fine-tuning necessary for exact alignment.

Formation Flying Strategy

In the formation flying strategy, a leadership model is employed whereby one satellite takes the lead while the other follows. The Coronagraph satellite, equipped with a hydrazine propulsion system, will perform maneuvers to acquire and maintain formation, while the Occulter satellite uses a cold gas thruster system to adjust its trajectory subtly. These adjustments will occur approximately every ten seconds during active formation flying to counter external perturbations, such as solar radiation pressure.

Risk Management and Mission Lifespan

After six hours of formation flying, the satellites will transition back into parallel orbits. Each satellite is equipped with redundant systems and will autonomously execute collision avoidance maneuvers if necessary. Both craft are designed to last around two years, with projections suggesting they will re-enter Earth’s atmosphere five years after that due to their low perigee.

Proba-3: A Leap in Space Technology

Primarily a technology demonstration, the Proba-3 mission will not only focus on solar observation but will also trial various formation flying techniques, such as adjusting their baseline and orientation for different observational goals. This mission represents a significant step forward in our understanding of formation flying in space and may pave the way for future satellite constellations aiming for ambitious scientific and commercial objectives.

The Path Ahead

As the ESA prepares for this innovative mission, the global aerospace community watches closely, hopeful that Proba-3 will succeed in unveiling new insights about our solar system while showcasing the future of autonomous spacecraft operations.

Source
www.esa.int