ESA GNC Conference Papers Repository

As part of the Space Rider’s (SR) verification and validation campaign of the Guidance, Navigation and Control (GNC) system for the flight under the parafoil phase, a series of Scale Down Flight Test (SDFT) are envisioned for phases C/D of the project. These tests have the following objectives for what concerns GNC: increasing the maturity level of the Parafoil GNC (PGNC), de-risking especially its novel terminal guidance approach in view of flight and for drop tests, provide a preliminary assessment of the real-life achievable landing accuracy, test onboard wind estimation, test robustness of GNC to perturbations and modelling errors, ensure predictability of the developed GNC for guiding and controlling a parafoil in real non-modellable conditions, test effect of online wind updates. The scaled test flights will also serve to improve the knowledge of the system’s dynamics and, therefore, the representativeness of the mathematical models used in the functional simulators. The use of scaled testing is beneficial in terms of the risk/cost relationship and of the time required to reach flight and the amount of test flights that can be carried out. In addition, for SDFTs failure is indeed an option, due to the limited cost and time of repairing damage, enabling an agile approach and short time to flight. Due to the scaled nature of the test vehicle, some differences will exist with respect to the full-scale case. Nonetheless, this is not considered a problem since it will be possible to mimic the trajectory behavior of full parafoil: the onboard control can be designed limiting the max heading rate, which will be smaller for larger parafoils, and it is possible to tune the controllers to simulate larger parafoil response (slower step response times). In addition it will be possible to exercise the full chain: wind measurements, processing, upload to GNC, and onboard use, and see the impact on the actual GNC behavior in the real environment. The impact of the operations and details of the full chain ground to GNC cannot be easily tested in a modelled environment, due to the difficulties in simulating the atmospheric random behavior. The proposed vehicle will be based on a COTS paramotor, that will be procured and modified to include the required sensors and actuators, and comply with test range and air safety regulations. The envisioned global vehicle mass is approximately 100-200kg. The aim of using a paramotor platform is to allow carrying out autonomous tests, without requiring an additional vehicle to drop the parafoil. The concept of operations for the test is as follows: (1) take off under remote control (RC), and reach a sufficient altitude for free flight; (2) switch off engine and start autonomous PGNC flight, with operator for RC takeover in case of safety needs, also during unpowered glide; (3) at the end of the unpowered autonomous glide, the operator restarts the propeller, and controls the vehicle in a climb to allow repeating a new unpowered autonomous glide; (4) at the end of the flight campaign the operator will steer the vehicle to a safe landing location and perform landing. No stringent requirements on landing velocity besides typical landing conditions for paramotor survival apply. The aim is to allow fast repetition of tests, keep human in the loop for safety, and allow a large number of glides to be executed in a single test flight. With a parafoil L/D of 3.5-3.8, it is assumed that the tests shall be carried out in a range of approximately 1500 m maximum altitude, 6000 m horizonal radius (based on line-of-sight conditions to pilot and TM/TC availability). Visual range flight is foreseen, with operator always ready and enabled to recover manual control (manual “safe mode”). The development of such platform is carried out by SENER Aeroespacial, developer of the PGNC algorithms and design authority of the GNC for the SR re-entry phase. This paper presents the development, characterization, and performances of such SDFT system.