FALCon project – catching rockets with DLR in-air innovation
FALCon project – catching rockets with DLR in-air innovation
Artist's impression: winged rocket stage approaches converted airliner during coupling
DLR's patented in-air capture process is an innovative approach to recovering reusable space transporters. In this method, winged stages are captured mid-air and towed back to the launch site by a subsonic aircraft, meaning rocket stages do not need their own propulsion system. Between 2019 and 2022, the FALCon project, coordinated by DLR, investigated the key technologies for this technique in a Europe-wide consortium. In-air capture promises to be a climate compatible and cost-effective solution for returning medium to large reusable launch vehicle stages.
Artist's impression: The winged stage approaches the aerodynamic capture device in subsonic flight
Since 2019, research into in-air capture was carried out as part of the EU-funded FALCon project, ending in November 2022. A team of scientists and industry partners made significant progress towards Europe's goal of more sustainable space transport.
Image: 2/4, Credit:
DLR-SART
Overview of the in-air capture mission sequence
After a rocket launches and its second stage separates, continuing its ascent into space, the first stage falls back to Earth. Thanks to its design, it enters into horizontal flight and decelerates to a subsonic speed, approaching and then docking with an aerodynamic capture device mounted on an aircraft. It is then towed to the landing area.
When it comes to horizontally landing a rocket, there are two main approaches: with or without a dedicated propulsion system for a winged rocket stage. The FALCon project (Formation flight for in-Air Launcher 1st stage Capturing demonstration) focused on a solution for return flights without propulsion, and one innovative approach is 'in-air capture'. After the stage slows down while re-entering the atmosphere and transitions into horizontal flight using its wings, it is captured by a subsonic aircraft. The aircraft, towing a capture device attached to a rope, positions itself so that the rocket stage can dock.
Simulation of the laboratory-scale experiment planned for 2023 in Cochstedt
Animation: Capturing Simulation
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Animation: Capturing Simulation
Simulation of the laboratory-scale experiment planned for 2023 in Cochstedt
Once docked, the aircraft tows the stage to a landing site, where it is uncoupled mid-air and lands independently like a glider – similar to NASA's US Space Shuttle. This in-air capture method, using an aerodynamic capture system, is a technology patented by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR).
A cost-efficient and climate-compatible approach to returning space transporters
Research into this in-air capture return method made significant strides under the EU-funded FALCon project, which began in 2019. The project concluded in November 2022, with the scientists and engineers making substantial progress towards developing a sustainable transportation system for Europe.
Among the project's achievements were the creation of significantly refined simulation models and the development of a roadmap outlining the next steps towards a reusable European space transportation system, targeted for around 2035. From autonomous capture to towing, the project team tested the technical concept for the 'rocket catcher' through flight demonstrations using small-scale models at DLR's site in Cochstedt. Simulations were based on a reference model of a high-performance winged rocket stage with a return mass of 80 tonnes. They demonstrated that a converted airliner, such as the Airbus A340-600, would be a suitable towing aircraft.
The primary benefit of the rocket catcher system is that the returning stage does not require additional fuel, reducing the overall launch mass and fuel consumption. This allows more payloads to be transported into space.
Moreover, the amount of exhaust gas emitted by aircraft jet engines is far less than that of rocket engines. Since these engines operate at lower altitudes, their environmental impact can also be minimised by avoiding condensation trails (contrails). Further reductions in emissions could be achieved with hydrogen-powered aircraft engines, a technology currently under development.
Researching re-entry and landing technologies for Europe’s next-gen 'recycled rockets'
In contrast to a propulsion-free horizontal return flight, the 'fly-back' method equips the winged rocket stage with its own engines. These engines require additional fuel and ignite as soon as the stage reaches subsonic speed, meaning no towing aircraft is required to reach the landing site. However, this increases the launch weight of the rocket and so reduces the maximum payload.
DLR and the European space industry will continue to research horizontal landing concepts, both with and without propulsion, each of which – like vertical landing systems – offer its own set of advantages and disadvantages.
This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 821953. The German Aerospace Center (DLR) was responsible for coordinating the project, among other tasks. Additional partners in the FALCon project included Drone Rescue Systems from Austria, Embention Sistemas Inteligentes S.A. from Spain, Soft2tec (now nexonar) from Germany, the von Karman Institute for Fluid Dynamics (VKI) in Belgium, the Institute of Mechanics from the Bulgarian Academy of Sciences and Astos Solutions from Romania.
