Bees land like spacecraft
A recent paper published in the PNAS journal, the Proceedings of the National Academy of Sciences of the United States of America, found that honeybees land using a surprisingly simple strategy solely based on estimating the time left to land. Such a quantity, called time-to-contact and measured by the expansion of optic flow, was found to be roughly constant during a series of observed bee landings. Scientists were so amazed of the discovery that Mandyam Srinivasan, professor of visual neuroscience at the University of Queensland, and one of the investigators, declared the experiments revealed bees were “doing something very neat and very elegant" that aeronautical engineers simply had not considered before.
Actually, engineers had. In 2008, an article from Hérissé et al. appeared, featuring a MAV landing by keeping the optic flow divergence constant. This is exactly the strategy followed by the honeybees. Moreover, in a work published in 2012 in the Journal of Guidance, Control and Dynamics, scientists at the European Space Agency's Advanced Concepts Team (ACT), generalized the concept and applied it to spacecraft landing.
"Many engineers are currently drawing inspiration from biologists. But sometimes science could work in the opposite direction." said Guido de Croon, now assistant professor at the Delft University of Technology and one of the leading scientists of the work performed at ESA.
But spacecraft and MAVs are not bees. So the researchers at the ACT decided to go further and improve what nature had designed for the insects and also designed a second landing strategy that, instead of keeping the rate of change of the time-to-contact constant, would make it exponentially decrease. Such a landing was shown to be efficient in terms of propellant consumption on simulated spacecraft Moon landings and faster in general.
"When landing a spacecraft, low propellant, not energy consumption is crucial. Bees do not care as much about that, so it is only normal that we could find a better use of time to contact than the one developed in nature" said Dario Izzo, the scientific coordinator of the Advanced Concepts Team and main investigator in the simulated spacecraft landings.
This work is important not only in the context of spacecraft, but in the broader area of UAVs. Preliminary experiments on quadrotors were performed both at ESA and TU Delft indicating that the use of time-to-contact is simple and effective (a video showing the results in simulation and on a real drone can be found here).
Related links:
- A Drone landing at ESA/ESTEC premises using time to contact. (video)
- The paper from Hérissé et al. proposing to keep the optic flow divergence constant during a MAV landing.
- The paper from the European Space Agency improving such a strategy and adopting it in spacecraft.
- The paper recently appeared in PNAS proving that bees do the same.