ESA GNC Conference Papers Repository

Precise landing on planets, moons and other larger celestial bodies requires a powered descent, hovering, and vertical landing. Similarly, recent and future concepts for re-usable launch vehicles (RLV) also involve a vertical take-off and landing. The development of guidance, navigation, and control (GNC) for this type of vehicles is a challenging task. To support this, a Vertical Take-Off and Landing (VTOL) vehicle has been developed for demonstrating the capability of conducting soft landings, smooth ascent, and hovering. The focus was put on a platform for testing new and advanced GNC algorithms that employ a base set of sensors and actuators typically present on such vehicles. It should represent a dynamics similar to a thrust vector controlled planetary lander or RLV, and should allow fast turn-around times as well as rapid prototyping capabilities for testing. Additionally, the platform should provide the option for an additional small payload, e.g., enhancing the on-board avionics with different or more precise sensors. The result of this platform development is EAGLE (Environment for Autonomous GNC Landing Experiments). Its lift-of-mass is about 28kg and it is powered by a jet engine with a maximum thrust of 400 N. The vehicle design allows for a flight time of a several minutes. For the main thruster a jet engine was preferred to a rocket engine in order to allow safer and easier handling of EAGLE. EAGLE has multiple actuator systems which resemble the typical control action employed on planetary landers or vertical landing RLV. A thrust vector control system within the exhaust stream of the main engine is the primary actuation system for lateral stabilization. The roll axis is controlled via pulsed thrusters of a cold gas system. The development included extensive testing and identification of actuators and sensors, before testing of the full integrated system in a tethered set-up. With a series of tethered flight experiments the verification and fine tuning of the whole GNC system was completed. During these hovering tests a large amount of measurement data were collected which have been compared to simulations, requirements, and assumptions of the EAGLE system. Each flight test was used to improve controller and navigation system to reach a high confidence in order to allow for less restricted testing, e.g., by loosening the tethers, and finally, entirely free flight. Among the first flights of the EAGLE demonstrator are tests within the ESA project <i>Upper Stage Attitude Control Design Facility</i> (USACDF) which is part of the FLPP3 program and lead by Airbus Defense & Space. The EAGLE vehicle will be used for testing and verifying new GNC algorithms for launch vehicles. The paper will present an overview of the EAGLE system, of its rapid prototyping capabilities, and of its baseline GNC system design. It will also explain how this experimental VTOL vehicle can be used for verifying new GNC algorithms for future planetary landers and re-usable launch vehicle. This paper will further detail the flight envelope and system capabilities of EAGLE. The most recent flight results will be presented together with the lessons learned from the flight tests executed so far.