It has been a week of increased fear for the Mars Helicopter team as we prepare for a major aviation challenge for Ingenuity. We transferred instructions to the flight, which took place on Monday, July 5 at. 02:03 PT, and waited nervously for the results to arrive from Mars later that morning. The atmosphere in the control room on the ground was jubilant as we learned that ingenuity was alive and well after completing a journey that stretched over 625 meters of challenging terrain.
Plane 9 was not like the planes that came before it. It broke our records for flight duration and cruise speed, and it nearly quadrupled the flight distance between two airports. But what really set the flight apart was the terrain that Ingenuity had to negotiate during its 2 minutes and 46 seconds in the air ̵
Flying with open eyes
In each of its previous flights, Ingenuity jumped from one aerodrome to another over largely flat terrain. During the planning of the flights, we even took care to avoid overflying a crater. We started by dipping into what looks like a heavily eroded crater, then continued to descend over sloping and undulating terrain before climbing again to emerge on a flat plain to the southwest.
It may seem strange that the details of the terrain would be just as important as for a vehicle driving through the air. The reason has to do with Ingenuity’s navigation system and what it was originally designed for: a short technology demonstration at a carefully selected experimental test site.
When we as humans look at moving images of the earth, like those taken by Ingenuity’s navigation camera, we instantly have a pretty good understanding of what we’re looking at. We see rocks and ripples, shadows and texture, and the ups and downs of the terrain are relatively clear. Invention, however, does not have human perception and understanding of what it is looking at. It sees the world in the form of individual, anonymous functions – essentially dots that move with time – and it tries to interpret the motion of these dots.
To make that job easier, we gave Ingenuity’s navigation algorithm a little help: We told it that these features are all located on flat ground. It freed the algorithm from trying to find variations in terrain altitude and made it possible to concentrate on interpreting the motion of the functions by the movements of the helicopter alone. But complications arise if we then try to fly over terrain that is not really flat.
Differences in terrain elevation will cause features to move across the field of view at different speeds, and Ingenuity’s navigation algorithm “still assumes” that the ground below is flat. It does its best to explain the movement of the functions by changes in the movements of the helicopter, which can lead to errors. Most importantly, it can result in errors in the estimated course, causing the helicopter to fly in a different direction than intended.
Get ready for a bumpy flight
The assumption that the ground is flat is baked into the design of the algorithm, and we can not do that when planning the flights. what we able to to do is to anticipate the problems that will arise as a result of this assumption and to mitigate them as much as possible in terms of how we plan the flights and the parameters we provide the software.
We use simulation tools that allow us to examine the probable outcome of the flight in detail before we complete it. For Flight 9, a key adjustment of the plane was to reduce our speed at the crucial moment as we dipped into the crater. Although it cost to extend the flight time, it helped mitigate early course errors that could grow into a major cross-track position error. We also adjusted some of the detailed parameters of the navigation algorithm, which so far we have not had to touch on previous flights. And we chopped out a much larger aerodrome than in previous flights with a radius of 164 feet (50 meters). We ended up landing approx. 47 meters away from the center of the airport.
In the week ahead, Ingenuity will send back color images that Perseverance researchers look forward to studying. Photographed in these images are rock carvings showing contacts between the large geological units on the floor of the Jezero Crater. They also include a system of fractures, which the endurance team calls “Raised Ridges,” which the rover’s researchers hope to visit in part to investigate whether an ancient subterranean habitat might be preserved there.
Finally, we hope the color photos give the closest look yet at “Pilot Pinnacle,” a place of eruptions that some team members believe may detect some of the deepest aquatic environments in the ancient Jezero Lake. Given the tight mission plan, it is possible that they will not be able to visit these cliffs with the rover, so Ingenuity may offer the only option to study these deposits in detail.
Written by Håvard F. Grip, Chief Inventor Pilot and Ken Williford, Deputy Deputy Project Researcher