Hannover Messe Hall 22, as B12
On the 11. In February, the European Space Agency (ESA) took a historic step: It launched its first reusable space shuttle into space and safely brought it back to Earth. During the hellish ride through the atmosphere, SKF's special roller screws played a truly groundbreaking role.
Actually, the ESA wanted to test its "Intermediate Experimental Vehicle" (IXV) in November of last year. At this point, however, hardly anyone would have noticed, because at the same time, another ESA mission was preparing to land the first spacecraft ever on a comet: "Rosetta" and her lander "Philae" would have the IXV after more than ten years so definitely stolen the show.
While the touchdown on 510 millions of miles away is undoubtedly spectacular, the IXV is no less important to ESA. After all, the unmanned drone should pave the way for Europeans to become a reusable space shuttle. The first step has now been taken: Thanks to SKF's special roller screws, the ferry has safely drifted in the Pacific.
Architect of the IXV is Thales Alenia Space - Italy (TAS-I). For this project, TAS-I has contracted some 20 subcontractors, including Sabca (Société Anonyme Belge de Constructions Aéronautiques), a Belgian aerospace specialist. "So far, we have to buy in Europe a lot of technical know-how for re-entry systems," explains Sabca project manager Didier Verhoeven. Against this background, projects such as the IXV are enormously important in ensuring Europeans' future independence in space. "The re-entry trials and lessons learned on upcoming flights will help us strengthen our position as a major player in this strategic area," Verhoeven says.
For its maiden flight in space, the IXV had been catapulted by a Vega launcher on a suborbital journey. 320 km above the Kourou spaceport in French Guiana, the spacecraft stuffed with sensors has disengaged itself from the rocket and has continued to rise - to an altitude of around 450 km. From this vertex, the roughly 2 t heavy aircraft, the size of a small car, fell back to earth. He accelerated to a speed of well 27.000 km / h.
1600 ° C at 27.000 km / h
The problem is that as soon as a missile hits the top layers of the atmosphere at this speed, hell breaks loose. For example, the IXV's heat shield had to withstand temperatures above 20 ° C for more than 1600 min to prevent the ESA hopefuls from dissolving into a "meteor shower". It is equally important when re-entering that in this inferno of heat and vibration, the control of the spacecraft works flawlessly: If the required maneuvers can not be carried out as calculated, the same consequences threaten as with inadequate heat protection.
70 kN for steering
For this reason, Verhoeven & Co. at their factory in Haren, not far from Brussels, have paid special attention to the actuators, which ensure the control of the steering flaps at the rear of the IXV. When riding through the atmosphere, these flaps not only have to work fast and with high precision, but also extremely robust and reliable. For example, it is necessary for both flaps to hold their defined positions, each with a force of around 35 kN, so that the drone can race through the atmosphere on the desired path at any stage of reentry.
The actuators developed by Sabca are controlled by computers and powered by electric motors. "The actuators built by us for the IXV have their roots in a special design, so to speak," says project leader Verhoeven: "In principle, they come from the thrust vector control that we had already developed for the drive of the Zefiro nozzles in the Vega launcher. We have now adapted this control to the requirements of the IXV. "
Background of this approach was originally the limited budget: For cost reasons, it was necessary to reuse as many existing components. Meanwhile, mechatronic solutions in space technology are getting more and more popular anyway. "While we were working on the Ariane 5 launcher, hydraulic actuators were still the tool of choice," recalls Verhoeven. "Today, however, there is a clear trend in the aerospace industry towards electromechanical actuators. Ergo, we have chosen this solution not only for the Vega rocket but also for the IXV. "
Multi-talented roller screw drive
The core of these electromechanical actuators are high-performance roller screw drives. The fact that Sabca and Verhoeven rely on a SKF product is the result of tailor-made development: "SKF engineers have designed the roller screw drive to meet our exact requirements. So we were pretty sure he could withstand the tremendous vibrations, work fast and accurately, and help keep the valves in place, "says Verhoeven. "Because ruggedness, power, speed and precision are key to ensuring the correct tilt or roll angle of the IXV during the reentry phase, through symmetrical or asymmetric flap adjustment." comparatively small parts of the whole system, they had to fulfill an extremely responsible task at the heart of the actuators.
The demanding job of these linear drives, however paradoxical it may sound, also included their absolute immobility. Actually, the "brake system" of the actuators already played a significant role in the launch of the rocket: the system's support springs had to be able to withstand the enormous vibrations, especially when igniting the engines. Neither when lifting off the ground nor in space could it come to a so-called cold deformation, which possibly prevents the release of the brake and thus later - when re-entering the atmosphere - would have caused the flaps lose their now indispensable mobility.
Accordingly, project manager Verhoeven and his colleagues have tested the system: "We lubricated the brake with a special grease and then tested it in 1000 cycles under vacuum conditions. There was not a single case of cold deformation. "In addition, the actuators including brakes from 2013 to 2014 X were subjected to many other climate, vacuum, shock and vibration tests, without serious problems to emerge.Of course, Didier Verhoeven looked skyward with his pulse on "flight day" and watched all available information from the control center. For 100 min, the ESA experts had collected as much data as possible before the IXV touched down in the Pacific Ocean. "We are proud to be involved in this project. It is the first step on a very long journey that will hopefully culminate in a European manned space mission and its safe return to Earth, "concludes Verhoeven. He was all the happier that the flaps - also thanks to SKF - worked so well.
Picture above: The IXV of the ESA is about the size of a small car. At the lower rear are the two control flaps, which are operated by means of roller screw drives.