Who said that breaking up is always hard to do? Airbus Defence and Space Spain has developed a clamp band four times larger than that used for satellites to ensure flawless separation of the ATV-4 from its launcher
The launch of the fourth Automated Transfer Vehicle (ATV) ‘Albert Einstein’, which is currently docked to the International Space Station, stretched the limits of the largest separation system ever built by European industry. A clamp band four times larger than that used for conventional satellites was designed and produced by Airbus Defence and Space Spain to enable attachment of this space freighter to the launcher and perform subsequent separation of these two stages.
There are two especially critical moments during any spacecraft launch that prompt the applause of the personnel in the control tower: one is just after the launch and the other is when the spacecraft separates from the rocket. Any error during either of these so-called ‘single failure points’ and the mission is inevitably doomed to failure.
The launcher’s separation system consists of a clamp band and a series of ejection springs that must be capable of withstanding extreme tension and vibrations during the launch. “The clamp band is like an enormous belt that is tightened accordingly depending on the nature of the element it has to secure, resulting in differing degrees of tension,” explains Javier Rivas, head of separation systems at Airbus Defence and Space Spain. The greater the spacecraft’s mass and dimensions, which determine the loads borne during flight and the diameter of the clamp band, the greater the difficulties and technological challenges that must be overcome. With a total weight of approximately 20.2 tonnes, ATV-4 was the heaviest payload ever placed in orbit by an Ariane launcher, requiring a clamp band with a diameter of four metres. “The band was installed with a tension of around five tonnes, while the vehicle it held weighed 20 tonnes,” Javier points out.
Separation: the moment of truth
The first stage separations take place two minutes after the ATV is launched, with the boosters, the fairing and the cryogenic stage being progressively jettisoned before the ATV itself is released approximately 63 minutes after launch. “Our system must be completely reliable. Any failure would result in the loss of years of hard work carried out by teams working across the whole of Europe,” stresses Alejandro Durán, manager of the separation system programme at Airbus Defence and Space Spain.
The separation process takes place in a matter of milliseconds. An electric signal activates a pyrotechnic device that triggers a massive pressure increase inside a chamber. This then propels a mechanical cutting device – similar to those used for cold cutting of sheet metal – which severs the steel bolt fastening the band, thereby releasing the ATV. The vehicle has to make a clean break without any jolts or perturbations of any kind, and ensuring this becomes increasingly difficult the greater the diameter of the clamp band.
In addition, large amounts of energy are released when the band opens at one end as it tries to assume its natural diameter. It takes 10 brackets known as ‘clamp band catchers’ to capture it and hold it in its final position for the rest of the mission. “The concept is as simple as it is effective. It means that the success of the entire ATV mission is hanging in the balance for the few milliseconds it takes to achieve separation,” says Alejandro. “I don’t know of anyone who has launched a vehicle as heavy as the ATV with a system like ours,” adds Javier.
Airbus Defence and Space Spain also supplies this component with a diameter of approximately two metres for the multiple launch systems of the Vega and Soyuz launchers, although nothing compares to the major challenge posed by ATV. Development work on this separation system for the European Space Agency began back in the year 2000. “It was a big call to take on this project, given that Airbus Defence and Space Spain’s experience at that stage was limited to one-metre clamp bands for launching conventional satellites,” Javier says. “The whole team really had to rack their brains and put a lot of hours into this programme.” The development and complex certification process took nearly eight years until ‘D-Day’ finally arrived; the launch of the first ATV, the ‘Jules Verne’, on 9 March 2008. “Although we had tested it thousands of times and knew that it worked, we were so relieved following the success of that first flight because nobody had ever developed a system like ours.”
As Alejandro sums up: “It was worth it to see the satisfaction of all the people who have worked on this system. A large percentage of the staff at Airbus Defence and Space Spain have been involved directly or indirectly in its development and manufacture – particularly if we take into account the two structures for the external and avionics modules that we also supply for the ATV. And I think that each and every one of us can proudly say we’ve played a part in this programme.”