Periodic Reporting for period 2 - FALCon (Formation flight for in-Air Launcher 1st stage Capturing demonstration)
Période du rapport: 2020-09-01 au 2022-11-30
Historically, nearly all launch vehicles have been expendable. However, the growing importance of sustainability gave way to cheaper launch technology via recovery and reuse of the respective launch vehicles. Since 2015, the 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 higher 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 of lowering the cost of space access and one unique method of reusing launch vehicle stages stood out technically and economically: the innovative “In-Air-Capturing” method, the centerpiece of the FALCon project.
Contrary to the method used by SpaceX, which relies on vertically landing the first stage by reigniting the engines, the “In-Air-Capturing” method requires a first stage to be winged. After burn-out of the first stage’s engines, the first stage continues on a suborbital trajectory, and re-enters the atmosphere by decelerating with its wings. Once it is subsonic, it is awaited by a towing aircraft, equipped with a capturing device that is 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.
To reach the goal of having a future reusable European launch vehicle, using the In-Air-Capturing method, the technology needs to reach maturity. 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 aim is to demonstrate “In-Air-Capturing” by using subscale demonstrators at relevant flight conditions.
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 of lowering the cost of space access and one unique method of reusing launch vehicle stages stood out technically and economically: the innovative “In-Air-Capturing” method, the centerpiece of the FALCon project.
Contrary to the method used by SpaceX, which relies on vertically landing the first stage by reigniting the engines, the “In-Air-Capturing” method requires a first stage to be winged. After burn-out of the first stage’s engines, the first stage continues on a suborbital trajectory, and re-enters the atmosphere by decelerating with its wings. Once it is subsonic, it is awaited by a towing aircraft, equipped with a capturing device that is 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.
To reach the goal of having a future reusable European launch vehicle, using the In-Air-Capturing method, the technology needs to reach maturity. 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 aim is to demonstrate “In-Air-Capturing” by using subscale demonstrators at relevant flight conditions.
• Development and Production of a subscale demonstrator models for the “In-Air-Capturing” demonstration
The “In-Air-Capturing” was to be 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. 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, permissions for both vehicles were obtained to perform flight tests. The subscale vehicles are now qualified for the next phase of testing, to perform formation flight and capture demonstrations.
• 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 were developed and produced. An environmental perception system was developed that is based on a fusion of camera-based perception and LiDAR-based perception. These technologies were successfully tested on ground and in-simulation, and are flight-ready for further demonstrations.
• 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 were 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 6-DOF simulation framework has been set up that allows for the simulation of several possible scenarios of “In-Air-Capturing”. External disturbances coming from vibrations of the rope, wake of the aircraft as well as environmental factors like wind have been considered. Similar flight control logic was maintained between subscale and full-scale scenarios to ensure that the technology is accurately represented and demonstrated.
• "In-Air-Capturing" Roadmap development and comparison with other return methods
The development roadmap for “In-Air-Capturing” has been defined in cooperation with the European stakeholders. Maturation plans for the different relevant technical areas are explained. The TRL-goal of IAC is set to 6 with target date 2029 for a technology development roadmap oriented on a large-scale launcher and its RLV lower stage. Based on the latest development roadmaps the next steps after FALCon in the time frame up to 2026 are identified.
Through comparitive studies, the advantage of the IAC recovery mode compared to VTVL resulting in significantly smaller and lighter stages has been established. Depending on the architecture and the operational scenario, “In-Air-Capturing” can allow significant launch cost reductions compared to the vertical landing.
The “In-Air-Capturing” was to be 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. 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, permissions for both vehicles were obtained to perform flight tests. The subscale vehicles are now qualified for the next phase of testing, to perform formation flight and capture demonstrations.
• 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 were developed and produced. An environmental perception system was developed that is based on a fusion of camera-based perception and LiDAR-based perception. These technologies were successfully tested on ground and in-simulation, and are flight-ready for further demonstrations.
• 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 were 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 6-DOF simulation framework has been set up that allows for the simulation of several possible scenarios of “In-Air-Capturing”. External disturbances coming from vibrations of the rope, wake of the aircraft as well as environmental factors like wind have been considered. Similar flight control logic was maintained between subscale and full-scale scenarios to ensure that the technology is accurately represented and demonstrated.
• "In-Air-Capturing" Roadmap development and comparison with other return methods
The development roadmap for “In-Air-Capturing” has been defined in cooperation with the European stakeholders. Maturation plans for the different relevant technical areas are explained. The TRL-goal of IAC is set to 6 with target date 2029 for a technology development roadmap oriented on a large-scale launcher and its RLV lower stage. Based on the latest development roadmaps the next steps after FALCon in the time frame up to 2026 are identified.
Through comparitive studies, the advantage of the IAC recovery mode compared to VTVL resulting in significantly smaller and lighter stages has been established. Depending on the architecture and the operational scenario, “In-Air-Capturing” can allow significant launch cost reductions compared to the vertical landing.
The state-of-the-art of the knowledge level with regards to reusability technologies was significantly enhanced. On a system level, different reusability methods were compared and evaluated to gather insight of the challenges and advantages linked to each method. From payload performance perspective, the “In-Air-Capturing” method shows for all investigated configurations the best results without any exception. It provided the smallest stages capable of delivering the specified payload mass.
Formation and Mission Control scenarios were set up and vehicle models for 6-DOF simulation for both subscale and full-scale scenarios. The knowledge gained on aircraft modifications, flight control algorithms, simulation framework set-up and the development and operation of autonomously flying UAVs have already pushed beyond state-of-the-art within FALCon. Major step forward with full-scale simulations by structured approach generated for research and future developments. Intricate models in propulsion, aerodynamics including wake turbulence, flight dynamics and controls were established and the principal feasibility of the innovative procedure has been confirmed.
Flight certified subscale demonstrators for both towing aircraft and reusable launch vehicle were built within <100 kg weight class. The autonomous vehicles can not only be used for future demonstrations of "In-Air Capturing", but also similar technologies like air-to-air refueling. An autonomous capturing device was also comprehensively designed to demonstrate the agility and accuracy required for the method. Furthermore, the models will be used to test and verify new and safety critical control concepts for the demonstrators before going into flight tests.
With valuable contribution from many European stakeholders, the path to further development of "In-Air Capturing" including immediate next steps has been defined.
Formation and Mission Control scenarios were set up and vehicle models for 6-DOF simulation for both subscale and full-scale scenarios. The knowledge gained on aircraft modifications, flight control algorithms, simulation framework set-up and the development and operation of autonomously flying UAVs have already pushed beyond state-of-the-art within FALCon. Major step forward with full-scale simulations by structured approach generated for research and future developments. Intricate models in propulsion, aerodynamics including wake turbulence, flight dynamics and controls were established and the principal feasibility of the innovative procedure has been confirmed.
Flight certified subscale demonstrators for both towing aircraft and reusable launch vehicle were built within <100 kg weight class. The autonomous vehicles can not only be used for future demonstrations of "In-Air Capturing", but also similar technologies like air-to-air refueling. An autonomous capturing device was also comprehensively designed to demonstrate the agility and accuracy required for the method. Furthermore, the models will be used to test and verify new and safety critical control concepts for the demonstrators before going into flight tests.
With valuable contribution from many European stakeholders, the path to further development of "In-Air Capturing" including immediate next steps has been defined.