Skip to main content

Formation flight for in-Air Launcher 1st stage Capturing demonstration

Periodic Reporting for period 1 - FALCon (Formation flight for in-Air Launcher 1st stage Capturing demonstration)

Reporting period: 2019-03-01 to 2020-08-31

Historically, reaching space has always been an adventurous and ambitious, but very costly endeavor. The huge demand of energy to reach orbit requires enormous and very complex and sophisticated launch vehicles. Commonly, nearly all parts of a launch vehicle in the past were expended and either fell into the ocean and were destroyed on impact or were deorbited and burnt up in the atmosphere after serving their mission. This gave way to the question, if it would not be cheaper to recover and reuse the respective launch vehicles.
In the past years new players have shown that reliable and rather cheap transportation to space with a reusable launch vehicle is possible. Since 2015, the private US-company SpaceX has been launching and landing the first stage of the Falcon 9 vehicle on a frequent basis either on land or on ships in the sea. This allowed them to offer transportation to space for very competitive prices and high launch frequencies.
For Europe’s access to space and its competitiveness on the global launcher market it is important to offer cheap and reliable transportation to space. In the past years, a range of studies were initiated at DLR to investigate the possibilities to lower the costs of space access and one method of reusing launch vehicle stages turned out to be offering very promising results, technically and economically: the innovative “In-Air-Capturing” method, the centerpiece of the FALCon project.
Contrary to the method used by SpaceX, vertically landing the first stage by reigniting the engines, the “In-Air-Capturing” method requires a first stage to be winged, similar to the Space Shuttle (see the figure attached). After burn-out of the first stage’s engines, the first stage continues on a suborbital trajectory, re-entering the atmosphere by decelerating with its wings. Then, once being subsonic, it is awaited by a towing aircraft, equipped with a capturing device that would be attached to the aircraft by a rope. The aircraft and the returning stage match their velocity and trajectory, reduce the distance between them and, subsequently, the reusable stage docks with the capturing device.
This patented “In-Air-Capturing” procedure has been studied in theory extensively at DLR since 2001. To reach the goal of having a future reusable European launch vehicle, using the In-Air-Capturing method, the maturity of this technology has to be increased. Together with a range of competent partners throughout the EU, the FALCon project was initiated to tackle this task and increase the know-how in Europe with respect to the In-Air-Capturing technology and reusable launch vehicles. Within FALCon, the unprecedented goal of demonstrating “In-Air-Capturing” by using subscale demonstrators at relevant flight conditions is aimed for. Further goals of this project are:

• Developing the necessary sensors and integrating their data and software to be used in-flight for an autonomous, successful and rapid connection of the two stages.

• Establishing an accurate simulation environment both for the planned flight tests as well as for the future full-scale “in-air-capturing”-application.

• A sound assessment of the in-air-capturing”-launch cost reduction potential by identifying suitable large-scale capturing aircraft and evaluating the necessary modification effort considering regulatory issues.

• Proposing a European development roadmap, first up to TRL of 6 and then estimating the effort for reaching the full-scale operational system with TRL of 9. This task is to be iterated jointly with the European stakeholders in agencies and industry.
• Development and Production of a subscale demonstrator models for the “In-Air-Capturing” demonstration
The “In-Air-Capturing” is demonstrated on a subscale level in FALCon by using unmanned aerial vehicles (UAVs) to represent the different vehicles involved in the full-scale scenario. The development and construction of the reusable stage demonstrator was successfully completed and two models are available to the FALCon team. Furthermore, the towing aircraft demonstrator was acquired, modified and first flight tests were performed. A capturing device capable of being full controllable around all three axes was built and tested in flight with very good results. In the 2nd part of the project, flight tests will be done both with the RLV demonstrator and the towing demonstrator carrying the capturing device. At the end of the project, a formation flight and finally coupling between the RLV demonstrator and the capturing device will be demonstrated.

• Formation Flight Procedures, Communication & Environment Perception
Since two vehicles have to approach each other while one of those vehicles tows an actively controlled capturing device, sophisticated communication procedures have to be established to allow for an autonomous formation flight. A mission and formation plan was established and hardware for the communication and location of the demonstrators was developed and produced. , An environmental perception system was developed that is based on a fusion of camera-based perception and LiDAR-based perception. The companion computer, capable of processing the information necessary for formation flight, was already successful built into the towing and RLV demonstrator. Next, the formation flight has to be tested in flight.

• Simulation of the subscale and the future full-scale “In-Air-Capturing”
The simulation of both the subscale as the full-scale scenario is an important aspect of the project. For the simulation framework, sophisticated models of the towing aircraft, the RLV stage, the capturing device and the rope attaching this device to the towing aircraft are developed. The aerodynamic database of the vehicles involved is backed up with CFD data. Especially for the capturing device a full CFD aerodynamic database was established. A hi-fi 6-DOF simulation framework is set up that allows for the simulation of several possible scenarios of “In-Air-Capturing”.

• In-Air-Capturing Roadmap development and comparison with other return methods
The “In-Air-Capturing” technology and possible launch vehicles using this technology have to be put into a European context, involving possible development steps on the way to a future reusable launch vehicle. Therefore, a preliminary roadmap involving reusable launchers with In-Air-Capturing was developed. This roadmap will be discussed with the European stakeholders in space. Furthermore, a comparison between different return methods was done to show the advantages and challenges of specifically the In-Air-Capturing method.
Already this early on into the project, the state-of-the-art of the knowledge level with regards to reusability technologies was enhanced. On a system level, different reusability methods were compared and evaluated to gather insight of the challenges and advantages linked to each method. Formation & Mission Control scenarios were set up and vehicle models for hi-fi 6-DOF simulation of the In-Air-Capturing were established. Furthermore, mounting an environmental perception system into an autonomously flying UAV to recognize a capturing device is unprecedented. The knowledge gained on aircraft modifications, flight control algorithms, simulation framework set-up and the development and operation of autonomously flying UAVs has already pushed beyond state-of-the-art within FALCon.
Wind-Tunnel Test Setup of the capturing device
Towing Aircraft Demonstrator APUS
FALCon team at progress meeting 1 in Sofia, Bulgaria in 2019
Overview of a In-Air-Capturing Mission
CFD Simulations of the towing aircraft wakefield for the full-scale scenario
The assembled RLV demonstrator model