As time progressed, the machines we use to explore Mars have become more complex and capable. Over the decades we went from static landers to mobile laboratories the size of a SUV. The increase in mobility brought the obvious benefit of allowing the study of multiple places in a single mission. Now, the Ingenuity helicopter is pioneering the next step: flight.
Designed to last 30 days and with the modest, if it can be called that, goal of demonstrating powered flight on Mars, the tiny aircraft has exceeded all expectations. So far, Ingenuity has flown 51 times, covering almost 12 km and racking up 1.5 hours of flight time. The small, JPL-built helicopter has achieved some truly impressive engineering feats.
The spacecraft’s body is a small box, with sides approximately 15 cm in length. It houses the flight computer, sensors, cameras, six lithium-ion batteries, and communications equipment. Four tiny landing legs stick out, giving the helicopter 13 cm of ground clearance. The most striking feature is, of course, the rotor blades. These have the arduous task of lifting the helicopter in the thin Martian atmosphere.
Air density on the Red Planet is only 1% that of Earth’s surface. To generate enough thrust, the propellers have to spin at 2400 rpm in opposite directions. The diameter of the rotor is a full 1.2 m. The helicopter has a mass of only 1.8 kg, and in Martian gravity, it still has 38% of its terrestrial weight. Atop the rotor sits a small solar panel and the antenna. It has the critical task of keeping the batteries powered for both flying and staying warm. It takes a day to charge up for a flight. For communications with Earth, Ingenuity uses the Perseverance rover as a relay, which in turn contacts mission control through various Mars orbiters.
Ingenuity reached Mars under the belly of the Perseverance rover. It lay on one side with two legs folded, protected by a cover. The cover was jettisoned on March 21, 2021, little more than a month after landing on Mars. Ingenuity was placed on the surface on April 3, then a period of static tests and checks followed. History was made on April 19, 2021, when the helicopter spun up its rotors, took off, reached an altitude of 3 m, hovered 40 s, then landed back safely. The location was named Wright Brothers Airfield, thus linking the two times powered flight has first been demonstrated on the two planets.
By successfully taking off and landing again, Ingenuity had fully reached its mission goals. However, the aircraft was still functional, so flights continued. Two more took place as part of the Technology Demonstration Phase, and two as part of a Transition Phase towards extended operations. Some software issues were encountered that sometimes prevented takeoff, but they were worked around. These two phases, which lasted until May 7, demonstrated up to 117 s of flight time and 270 m of ground distance covered.
Given the success of these flights, Ingenuity began the Operational Demonstration Phase. Since the helicopter has no science instruments, its main purpose is to scout the terrain ahead of Perseverance. Throughout the missions, the controllers have also pushed the limits of what can be done further and further. Currently, the altitude record is 18 m, the maximum distance traveled in a single fight is 709 m, and the maximum flight time is 170 s.
Surviving the long stay on Mars is not trivial for the small aircraft, designed to last 30 days. Like all vehicles on the planet, the dust has begun to collect on the surfaces, though this has not endangered power production. One of the biggest changes was coping with a 30% decrease in air density brought about by seasonal changes. To compensate, the speed of the rotor was increased to 2700-2800 rpm. Doing so posed some risks, such as excessive vibrations, and pushed the blade tips up to 80% of the speed of sound on Mars.
Both the rover and the helicopter are currently traveling up the basin of a dried-up river, where Perseverance is looking for signs of past life. As of now, the last flight, the 51st, took place on April 23, 2023, covering 191 m over 134 s. The area is rather narrow, so flights are greatly constrained by the keep-out zone of Perseverance. There is also the constraint of not losing radio connection with the rover, which is essential to keep up the communications.
The success of Ingenuity’s mission has built confidence and momentum for future helicopter probes. The biggest one is Dragonfly, an autonomous, nuclear-powered helicopter meant to launch toward Titan in 2027. The environment of the Saturnian moon is much more favorable for flight (even more than Earth) and the mission had already been selected before Ingenuity flew. However, the Mars helicopter has undoubtedly bolstered confidence in operating aircraft on other worlds.
As far as Mars is concerned, more Ingenuity-like helicopters are set to fly relatively soon. NASA and ESA aim to send spacecraft to Mars around 2030 to retrieve surface samples collected by Perseverance, and to bring them back to Earth. The rover is planned to be the primary means of handing them to the return rocket, but a backup plan is required, just in case. Two Ingenuity-derived helicopters will serve this role. They will be equipped with small wheels and a robotic arm so that they can reach the precise location of each sample tube and pick it up. The additional equipment would bump the mass up to 2.3 kg, which may require a lengthening of the rotor blades.
Concepts for missions further in the future call for even bigger helicopters. Scientists envision drones kept aloft by six rotors, massing up to 30 kg. These would be fully-fledged science missions, capable of traversing for up to 1 km and hovering for minutes. While limited in payload size, they would be able to collect data from previously inaccessible sites. These are just proposals for now, but the technology demonstration we just witnessed has greatly helped build confidence in them. We now live in a world where flight is possible not just on Earth, and exciting things lie ahead.