Last week the Ingenuity helicopter carried out its sixth flight on Mars. The first of its explorer campaign for Ingenuity. But unlike the previous five flights, which it carried out without problems, the sixth flight was somewhat bumpy, with significant pitch and roll oscillations of more than 20 degrees, control commands and much larger than expected power consumption spikes.
The objective of the flight was to extend the flight envelope and demonstrate Ingenuity’s ability to take stereo images from the air of a region of interest to the west of its position. The flight was scheduled to climb to an altitude of 10 meters and travel 150 meters to the southwest at a rate of 4 meters per second; travel another 15 meters to the south while taking images pointing west; and then fly another 50 meters to the northeast and land.
But towards the end of the first 150-meter leg things started to get complicated and Ingenuity began to adjust its speed and pitch back and forth in an oscillating pattern that did not correspond at all to the program. Fortunately, despite these oscillations, Ingenuity’s flight control system was able to bring it to its destination without exceeding its stability limits. And it managed to land it about 5 meters from the planned point.
The problem came from the fact that Ingenuity takes pictures of the ground over which it flies to correct the data it receives from its inertial units, otherwise the position would become increasingly uncertain over time. It takes 30 images per second with the camera it carries in its belly and analyzes them to obtain data on its displacement and integrate them with what the inertial units, which measure its movements without “seeing” the outside world, tell it. And one of those images was lost. That wouldn’t have been too much of a problem except that all the other images from that one arrived at the navigation system with erroneous information about when they were captured. So the navigation system was faced with camera data that conflicted – very much conflicted – with what the inertial units were telling it.
Still the navigation system kept the commands it was sending to Ingenuity’s rotors within the margin necessary to keep it from capsizing in mid-air, which had been disastrous. And as it was coming in – more or less, remember that it was a bit lost – the algorithm that governs the landing came into action, which does not take the camera images into account at all; it simply makes sure that Ingenuity is in stable and level flight and brings it down.
This failure has never appeared before in ground tests, so we will have to see how to avoid it in the future. But at the same time the flight has shown how robust Ingenuity’s control system is. The helicopter suffered no damage and is ready to continue flying.