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The SWING project (Small Workshop for Innovative GNC) was born in 2015 out of the realization that the guidance, navigation and control (GNC) algorithms employed by multicopter drones in wide use today share many features with those of launch vehicles. Not only that, but they are also quick and easy to implement, inexpensive and backed by a dynamic Open Source community, allowing teams to build a complete vehicle and easily adjust its flight program.
Fuel sloshing has been chosen as the first concrete case study. Sloshing characteristics—frequency, damping, etc.—are typically determined using shakers that generate vibrations of different frequency and intensity or by numerical simulations. In pilot studies, sloshing is replaced by pendula with the same properties to simplify calculations.
As far as we are aware, no other experiment has yet been devised to compare how a rocket behaves when filled with liquid and with an equivalent pendulum. This type of experiment is difficult to perform with a launcher but can be envisaged with a drone.
The teams at CNES’s Launch Vehicles Directorate (DLA) have developed an experimental device in which water in a tank can be replaced by an equivalent pendulum. The device is hooked up to a drone, which cycles oscillations at different amplitudes and frequencies. The experiment is performed first with the liquid and then repeated with the pendulum to verify that the pendulum is modelling parameters correctly.
A first quadcopter-type vehicle was used to validate the concept, after which the SWING team partnered with AERACCESS in 2017 to devise a more powerful octocopter (with eight propellers) capable of carrying the experiment payload of 8 kg.
Tests are being conducted at Brétigny-sur-Orge—a nod to history, as the drones take off only a few hundred metres from where CNES’s first facilities were located in 1962.
On the strength of results obtained from the sloshing study, other algorithms will be able to be tested on this platform in the years ahead. Multi-rotor drones even have the potential to represent a fully-fledged test method. This avenue is also being explored by our partners at ESA (landing algorithms), DLR (navigation and guidance by optical sensors) and NASA (flight-control algorithms).