Helicopter dreams of Mars | Space

The video looks like a clickbait on YouTube: the worst drone pilot of all time. A small rotorcraft helicopter films maniacally around a closed chamber, such as a crazy winged insect, until it inevitably ends up splashing! "The accident was phenomenal," MiMi Aung laughs infectiously. "It's a really fun video."

Entertaining but also enlightening. The video showed that it was theoretically possible to stay high on Mars – in an atmosphere 100 times thinner than Earth – and helped convince NASA to give the go-ahead for the development of the first plane to be shipped to another planet. Eighteen months later, in the same 25-foot room of the Jet Propulsion Laboratory (JPL) in Pasadena, California, a larger autonomous model was flying, rotating, and moving from one side to the other. no problem. The team behind the Mars helicopter calls it their Wright Wright-at-Kitty Hawk moment.

Earlier this year, another model, the flying model, was successfully tested in the room. Although weighing less than four pounds, this complete vehicle contains everything needed to fly independently to Mars. In a few months, it will be set at the belly of a six-wheeled rover in anticipation of the March 2020 mission. If all goes well, the rotorcraft will be deployed on the Martian surface in 2021, where it will attempt five historic flights at over the next 30 days. "This is changing the game," said Aung, project manager for the Mars helicopter. "At the moment, we are exploring deep space in orbit or with mobile devices, but we have no vehicles that take advantage of the airspace. This will allow us to reach places that are impossible to reach with rovers or even astronauts. "

Gravity on the red planet is about 38% of what it is on Earth, but the thin atmosphere was what many smart people thought was a show. Of course, less air means less lift. For conventional aircraft, this translates into extremely long, high-speed take-offs, and even more difficult landings. But a helicopter seemed to be a potential alternative since, unlike a fixed-wing aircraft, its blades create their own airflow to generate lift. As Aung explains, "A helicopter or a rotary wing aircraft can get the required speed on the blades when it is stationary.

In theory at least. But in practice, no one knew if the blades could be turned fast enough to support the engines, avionics and flight controls of the body of the fuselage, not to mention the cameras, radios and antennas. In short, all the components needed to make the ship. useful on Mars. To grasp the challenge, consider that the highest altitude ever reached by a helicopter on Earth was about 40,000 feet. On Mars, the weak atmosphere would be like flying a helicopter at 100,000 feet.

Larry Young, a rotorcraft at NASA's Ames Research Center in Silicon Valley, began studying the issue in 1997. "At first I was a little skeptical," he says. "However, with an additional first-order analysis using aerodynamic knowledge for micro-rotorcraft and other micro-air vehicles (which I was also studying at the time), as well as information on weight trends derived from HALE. [high-altitude and long-endurance] plane, I concluded that a helicopter Mars of less than 100 kilograms [220 pounds] could actually be possible. "

Hinged tests of an ultra-light four-blade rotor with an eight-foot diameter and an eight-foot diameter built by Micro Craft were made in the environmental test chamber N-242 to Ames. The success of this program prompted Young to publish a document that qualified the viability of the concept.

Meanwhile, independently, Bob Balaram, a JPL engineer, attended a conference on robotics in San Francisco. In a presentation on the proposed miniature helicopters, Balaram realized that the Reynolds number (which expresses the performance of an aerodynamic profile depending on the density and viscosity of the aircraft). The air in which it evolves) would be about the same as that of a helicopter with a larger wing in the air more thinner. "So it has evolved," he says.

Stanford University provided an eight-inch-diameter rotor mounted on a pivot in the JPL vacuum chamber, which was pumped to simulate the atmosphere on Mars. When the blades turned at 7000 rpm, the pivot changed angle, which showed that sufficient elevation could be generated to fly in the Martian environment, assuming, of course, that the vehicle was light enough. Unfortunately, the funds for the program never materialized.

The idea remained on the shelves until 2012, when Aung was then running Charles Elachi, then director of the JPL, during a tour of the Autonomous Systems Division. In one of the laboratories, drones were used to demonstrate embedded navigation algorithms. Elachi addressed René Fradet, director of finance, and asked him, "Why do not we do this on Mars?" Balaram erased his previous research and informed Elachi of his findings. After thinking for a week, Elachi told Balaram: "I agree, I have money for your studies."

From the beginning, engineers had to meet a double challenge: to design a helicopter capable of flying on Mars while surviving the "seven minutes of terror" landing on the red planet, attached to the bottom of a rover from one ton. Packaging considerations limited the length of the blades to no more than 1.2 meters (four feet).

JPL commissioned AeroVironment, the Southern California-based advanced engineering company, which had created one of the first UAVs deployed in combat, the FQM-151 pointer, to create a test model at the same time. 1/3 scale. The vehicle was mounted on a vertical rail in JPL's 25-meter vacuum chamber, a national historic monument officially known as the Space Simulator, where all spacecraft built on site since 1962 were tested. With the blades rotating at 8,000 rpm (to make up for the small size), the drone produced enough lift to get out of the ground. This prompted JPL to invest a little more money to see how the model could fly without rail to keep it straight in the way. With Matt Keennon, AeroVironment's best drone, operating a joystick, the model was flying freely around the room. Too freely, in fact, hence the spectacular crash of the video Worst Drone Pilot Ever.

"Rotorcraft are very difficult to model," says Håvard Fjær Grip, a fixed-wing pilot who leads the Mars Guiding, Navigating and Control team. "When we flew the vehicle, we had anticipated that it would not behave exactly like the [computer] model, and that's not the case. But he did what he was supposed to do, showing that he could produce enough thrust to take off. "

Based on the 1/3 scale vehicle tests, NASA decided in January 2015 to fund the development of a complete iteration, known as the "Risk Reduction Vehicle". As a project leader, Aung realized that the program required a multidisciplinary structure. It brought together a team of scientists, engineers and technicians drawing on all the skills of NASA. In terms of full-time equivalents, the number of people never exceeded 65, but according to Aung, more than 150 people participated in the program at JPL, AeroVironment and NASA research centers in Ames and Langley.

Every decision regarding the design of the helicopter was filtered through the prism of the mass. Balaram, an inveterate backpacker whose office wall is dominated by a spectacular landscape picture taken in one of his campsites, has set the vehicle on a diet. "I used the same philosophy as that used with my backpack," he says. Each extra gram meant more energy to support it, which added even more weight, which required even more energy – a vicious circle that threatened the entire project. "There was a time when we had a crazy mass problem, and it was hard to stay within the limits dictated by physics," says Balaram.

To fit perfectly under the Mars rover, the team rejected a classic tail rotor in favor of a coaxial design with two horizontal blades rotating in opposite directions to cancel their respective torque. The rotors are mounted on a central mast. At the top of the mast, a solar panel recovers energy for lithium-ion batteries. At the bottom is a small cube of about 2 square feet. A smaller rigid container inside this fuselage contains most of the hardware (and software). Four narrow but flexible carbon fiber legs make up the low tech landing system.

The helicopter carries eight electric motors. The rotors are powered by a pair of custom-made, 23-pole, solid-state DC solid-state units filled with square copper wire that the AeroVironment Keennon is hand-wound using a microscope – an extremely tedious process that takes 100 hours per engine. The other six motors drive the cyclic trays attached to each of the rotors. (Cyclic platters change the angle of the blades to allow the helicopter to pitch, rotate and lace up.)

The lithium-ion battery system comes from the vaping industry. Mobile phone technology provides high-level processor and cameras: a 13-megapixel color device for taking high-resolution photos and a black-and-white camera to provide data to the relatively rudimentary visual navigation system. The low level processor comes from the world of the automobile; the laser range finder, from robotic applications. "It would not have been possible without commercially available commercial components," says Grip.

Even so, just about every design solution has created a new problem. For example, the blades were lightweight carbon fiber, which allowed them to spin as fast as possible. But they had to be strengthened when it turned out that the thin atmosphere of Mars lacked natural damping qualities that reduce the vibrations and catastrophic resonances on Earth. From the beginning, the team had hoped to save a few grams by equipping the upper rotor with a collective, which controlled the altitude but no cycle, which controlled the pitch and roll. (The lower rotor has both.) But these plans were abandoned when it became apparent that the helicopter needed more control authority. The team has "refined its tools", as Aung says, to lose weight elsewhere.

In May 2016, Aung and his company were confident enough to release the Martian helicopter into the 25-foot vacuum chamber. To compensate for Earth's gravity, the model had to be reduced to 850 grams. The electrical system, the computers and the avionics were thus removed from the vehicle and connected to the fuselage by a long fastener.

The fully autonomous risk reduction flight went off without a hitch. And yet, members of the team were sitting at the edge of the stone while they were watching. "People said," You were so under control, "Aung said, remembering the friendly words of his colleagues. "But we were so happy. There is no way to describe what we felt. "

This success has gone from a blip on NASA's radar to a goal to be monitored more closely. A new round of funding has funded two models of technical design, which could serve as a model for the current Mars helicopter, if, in reality, NASA decided to build it. Even at the beginning of the work, the team discovered that it had miscalculated the heat budget.

Two-thirds of the energy produced by the batteries was intended to keep them warm during the freezing nights of March, which proved more difficult than expected. The solar panel has been enlarged and additional battery cells have been added, which means more weight. Fortunately, Keennon's engines proved to be more energy-efficient than expected, saving mass. In the end, the vehicle weighed less than four pounds.

On January 9, 2018, EDM-1 entered the space simulator at JPL. In addition to being pumped to simulate the anemic Martian atmosphere, the chamber was largely filled with carbon dioxide to mimic the oxygen-poor environment of the red planet. To simulate Martian gravity, the vehicle was attached to a fastener called gravity unloading system, which essentially gave EDM-1 a thumbs up to stay in the air. The test flight was a slam dunk. But this time, instead of receiving a figurative gold star from NASA, the team got the copper ring – a coveted slot as a technology demonstrator for the March 2020 mission.

Scientists from NASA and JPL have already begun to think about the future of Martian helicopters. Aung says the thin atmosphere will probably limit them to 10 to 15 kilograms, which means they will not be big enough to carry humans. But they will be equipped with scientific instruments weighing up to 2 kilos. "Future versions of the Mars rotorcraft will be able to carry out sustained missions that will cover areas of inaccessible terrain and conduct" surface-interactive "scientific surveys such as soil and rock analysis and recovery. 'samples,' says Young. "Such vehicles could enter craters, fly near cliffs or other rock formations, or conduct low-level surveys of ancient riverbeds and deltas."

That said, the centerpiece of the March 2020 expedition will not be the helicopter but the mobile carrying it in space. While the rover's mission is expected to last nearly two years on Earth, the helicopter only has 30 days to do its job. The main objective is simply to demonstrate the feasibility of the concept. Hopes are high, but expectations are not. "We are not a flagship mission with a budget of one billion dollars," Balaram said. "We are a very thin little demo, at high risk of failure."

The batteries limit the flight time to 90 seconds and there is enough energy to launch once a day. The indicated speed will be maximum at 10 meters per second (about 22 miles to the hour), or two meters per second of ground speed while allowing up to eight meters of wind per second, altitude will be capped at 16.5 feet. As the helicopter's ability to map the terrain is marginal, it will land at the flat, clear spot from which it left. The most ambitious flight of the schedule provides for the vehicle to fly 500 feet before returning to the launch site.

And after that? To be determined. It is unclear how many cold cycles the components can survive, and there is no way for the helicopter to withstand the harsh Martian winter. As Aung says, "It is built to the standards of the technological demo, and it's not supposed to last forever." Vehicles built by JPL for Mars are reputed to be above their expectations. The Spirit and Opportunity rovers, designed to survive for about three months each, flourished for six years and fourteen years, respectively. So Balaram says the team has already nicknamed the Wendy helicopter.

Wendy? Why Wendy?

Balaram smiles and explains, "We are not dead yet."