The Aestus upper stage engine was tested on the P4.2. The engine delivers a thrust of around 27.5 kilonewtons and is powered by dinitrogen tetroxide (N2O4) as an oxidizer and mono-methyl hydrazine (MMH) as fuel. In 2008, an Ariane 5 ES rocket with an Aestus engine tested in Lampoldshausen was launched for the first time towards the International Space Station (ISS). On board was the unmanned space freighter Automated Transfer Vehicle (ATV). This European space transporter weighed around 20 tons: a real heavyweight.
The last mission for the Aestus engine involved four Galileo satellites, each weighing 700 kilograms. To ensure that the satellites were launched smoothly, the Aestus engine was tested for flight around three years before the launch with a total of eight ignition tests and a long-term test followed by a re-ignition. As the engine was newly produced for the Galileo mission, a so-called "Ariane Research and Technology Accompaniment" (ARTA) campaign ensured this flight acceptance. To this end, an identical engine underwent a total of 115 ignition tests as well as a test profile with a long hot run and – after a simulated free flight phase without propulsion - a short re-ignition. Finally, four further long-term tests followed, each with four re-ignitions.
