At the end of last month, at Cape Canaveral Air Force Station, located in the middle of the Atlantic coast of Florida, the United States, a huge Atlas V launch vehicle will be "Mars 2020 Rover" launched into the sky, the beginning of the spacecraft's seven-month journey into space, and its destination is the red planet - Mars, which is most talked about by the people of the Earth. The spacecraft's destination is the red planet - Mars - that most people on Earth love to talk about.
▲An early concept of a Mars helicopter design program
Since NASA really started to explore extraterrestrial planets, the idea of flying within the atmosphere of other planets has been brewing and fermenting in the minds of NASA scientists, from the initial concept to the final "Mars helicopter". From the first rough idea to the final "Mars Helicopter", it took more than half a century. In fact, in the early stages of extraterrestrial exploration, science and technology were far less advanced than they are today, which led NASA scientists to "fantasize" without having any way to actually try to design and test them. That hasn't changed until the last decade or so.
It's fair to say that advanced materials and computer technology, as well as autonomous flight control, are the three key technologies that have given NASA scientists the confidence to build a "true extraterrestrial vehicle.
▲The Mars helicopter is being tested
However, in the end, the basic technology is there, whether it can really fly or another thing, NASA scientists are still facing the last layer, but also the most important obstacle : the Mars atmosphere is extremely thin, from the quantitative indicators, its average air density is only as high as the Earth's atmosphere, the average density of the air, the average density of the air, the average density of the air, the average density of the air, the average density of the air is only as high as the Earth's atmosphere. Its average air density is only 1 percent of the density of the Earth's atmosphere, and to fly at that density is roughly equivalent to flying at an altitude of more than 30,000 meters above sea level on Earth. This means that on the surface of Mars, there is almost no air to generate enough lift to hold up an aircraft for flight.
The greater the challenge, the greater the interest of some eager scientists, but they seem to have gotten off on the wrong foot early on. If you consider that the world's first truly flying fixed-wing airplane predates the helicopter by more than three decades, it's easy to see why NASA scientists initially focused all their attention on fixed-wing aircraft.
But after building and refuting their designs countless times, at some point, one of the scientists had a breakthrough idea:
"Well, why don't we try a helicopter? Why don't we try a helicopter? "
Of course, no one took the idea particularly seriously at first; if aerodynamically straightforward fixed-wing airplanes don't work, why would complex helicopters really work? Why would a complex helicopter really work, if the density of the Martian atmosphere is such that a helicopter could really get enough lift?
But some of the NASA scientists who heard about this "whimsical" idea quickly went ahead and did a few quick empirical calculations, and they came up with a "stunning" result: Though just barely up to snuff, it seems that a purpose-built helicopter would actually be able to fly through the Martian atmosphere.
▲An artistic rendering of a "Mars helicopter" flying on the surface of Mars
As the NASA team explored the concept of a "Mars helicopter" more and more, they came to realize that it was a very viable idea indeed. To that end, they began to consider a variety of designs, including a quadcopter similar to a DJI drone and several other multi-rotor vehicles, as well as a more conventional single-rotor helicopter with a tail rotor.
The final design, however, took the form of a helicopter equipped with a ****-axis counter-rotating dual rotor design, a ****-axis main rotor design most commonly seen in the work of the Soviet Union's (Russia's) Kamov Design Bureau, in which the two rotor blades are mounted up and down the same main axis, with the rotors steering in opposite directions in order to counterbalance the counter-torque between the two.
This **** axis configuration of the "Mars helicopter" is about 49 centimeters high and weighs less than 1.8 kilograms, which can be said to be quite lightweight, NASA scientists named it "machine spirit" (Ingenuity). The newest version of the Ingenuity is a new version of the Ingenuity, which will be released in the next few months, and will be available in the next few months.
▲ "The top of the helicopter is equipped with solar panels, which can provide battery life for the machine
In addition, the NASA team also needs to consider how to combine the helicopter with the Mars 2020 rover, which has been named the Mars 2020 rover, with the Mars 2020 rover, which has been named the Mars 2020 rover. " Combined with the rover named "Perseverance" (Perseverance) is the main equipment of the United States to carry out the 2020 Mars exploration program, it will be on Mars to search for evidence of the existence of ancient life, and collect rock and soil samples, and in the final mission return to Earth.
▲Photo of the Perseverance rover and the Spirit helicopter, the difference in size and magnitude of which can also be seen in this picture
▲The Mars helicopter under test
In order to combine the two helicopters into a single vehicle, it is important that the rover and the Spirit helicopter are not separated from each other. "In order to make the helicopter as light as possible, NASA engineers used composite materials, such as carbon fiber foam core for the rotor blades. In addition, they considered a number of "outside contractors" when selecting advanced microcomputers and avionics components. These compact, lightweight electronic components are basically impossible to see on NASA's previous spacecraft, but in order to minimize the weight of the Mars helicopter, NASA engineers had no choice.
▲Observing the design of the rotor blades of the Mars helicopter model, you can see that the shape of the blades is very different from that of a conventional helicopter on Earth
Of course, in the thin atmosphere of Mars, a helicopter obviously can't leave the ground just by reducing its own weight. Another key design feature of the Kirin is its rotor system. We know that the main rotor of a helicopter on Earth usually rotates at 400 to 500 rpm, but the Kirin's rotor rotates at 2,800 to 3,000 rpm, which is almost as fast as the rotor of a conventional single-rotor helicopter with a tail rotor on Earth, and the rotor of a tail rotor on a conventional single-rotor helicopter with a tail rotor on Mars.
In addition, the rotor speed of the Spirit is 2,800-3,000 rpm, almost as fast as the tail rotor on a conventional single-rotor helicopter with a tail rotor on Earth.
In addition, the rotor blades on the Spirit have a special shape and a low Reynolds number airfoil. If you've ever seen a helicopter's rotor blades, you'll notice that the Mars Helicopter's rotor blades aren't quite the same as all the helicopter rotor blades you've ever seen, and they're much more similar to a thick, tapered shape, and at the root of the rotor blades, the chord ratio is roughly four times as high as that of a conventional helicopter. "chubby".
In the Mars helicopter blade design, there is another important factor to consider is its stiffness. Because the density of the Martian atmosphere is particularly low, which means that the air resistance is not so big, lower aerodynamic resistance brings another problem is that there will be a higher level of vibration of the paddle, in order to reduce the vibration level, the paddle's stiffness will have to be designed to be relatively high.
▲Scientists simulated the Martian environment in the lab, and then tested the helicopter
And at high rotational speeds, this new paddle is also capable of generating more lift.
Designing and building a "Mars helicopter" after figuring out the mechanics isn't much of a challenge for NASA at this stage, but testing and verifying that the helicopter "really flies" in the Martian atmosphere is a challenge on Earth. Martian atmosphere" is the really challenging one - NASA scientists need to find a way to replicate the unique environment of Mars in the lab.
The NASA team ended up testing at the Jet Propulsion Laboratory in Pasadena, California, a facility dubbed the "25-foot space simulator," a cylindrical facility that is now nearing its 60th birthday, but " old and strong," where engineers can test some of the extreme conditions of space and, of course, simulate the environment of Mars.
▲NASA scientists are setting up a "Martian helicopter" in the lab for testing
The facility's air can be pumped out, other gases are pumped in, the temperature can be varied from minus 195 degrees Fahrenheit to 93 degrees Fahrenheit, and lighting equipment can be directed toward the top of whatever is being tested. The light-emitting device can shine a bright light toward whatever is being tested, thus reproducing the solar radiation environment of planets that are not protected by an atmosphere similar to that of the Earth's. Over the years, a variety of spacecrafts have been built and tested. Over the years, a variety of spacecraft and extraterrestrial probes have been tested in this facility, including Voyager, Curiosity, and Perseverance.
▲The "Smart" Mars helicopter under test
Dimensionally, the facility is a little over 25 feet in diameter (1 foot ≈ 0.3 meters) and about 85 feet tall, which makes it ideal for flight tests of such small helicopters. With temperature control, the facility is fully capable of simulating the huge temperature variations of Mars, such as the 15 to 21 degrees Celsius environment at midday in summer and the ultra-low temperature of -107 degrees Celsius at midnight in winter. The facility also has an array of fans on one wall to replicate the effects of the crosswinds that can occur on Mars from time to time.
While the facility is able to simulate most of the actual environment on the surface of Mars, there is one point that it cannot simulate, and that is the gravity of Mars. Considering that the gravitational pull of Mars is only about 1/3 that of the Earth, the NASA team ended up using a compromise, which was to hang a rope from the ceiling, hang the helicopter on one end, and install a counterbalance on the other end, thus simulating the actual Martian gravity.
▲NASA scientists working in the lab to test the helicopter
In 2014, NASA built the first prototype of a Mars helicopter, which was smaller and more powerful than the current helicopter. That prototype was smaller than the current "Spirit" and was not yet equipped with an autonomous flight system, but was instead remotely maneuvered from lab to lab by manipulators. At the end of the test, the NASA team came to an important conclusion: the Mars Helicopter program was able to generate the level of lift they needed, but it was very, very difficult to maneuver in the simulated Martian environment.
▲The image shows the protective shell of the Spirit Mars helicopter, which would have fallen off and been disposed of after it landed on Mars in one piece
In this case, in 2016, the NASA team developed a second prototype, this time with a more sophisticated microcomputer and flight control system. sophisticated microcomputers and flight control systems, and its autonomous flight capabilities were somewhat improved, enabling it to at least hover autonomously under certain conditions. Two years later, NASA's third prototype was born, and this time, its flight control system was even better, basically in the laboratory environment to complete the autonomous flight project required by the test team.
As it stands now, much of the Martian terrain that NASA is most interested in -- steep cliffs, oddly shaped caves, and rocky potholes -- can't be reached by rovers that move around on the ground on wheels. So they need a vehicle to explore these sites, which may well go a long way toward understanding the history of Mars, just from a scientific perspective.
▲The capsule containing the Perseverance rover and the Spirit Mars helicopter is housed in the fairing of the Atlas V launch vehicle
Of course, all of the NASA team's work has been done in the lab so far.
Of course, all of the NASA team's work has been done in the lab so far, and it remains to be seen whether a unique, purpose-built unmanned helicopter will be able to land on the surface of Mars, take off, and fly autonomously in the unique environment of the surface, as envisioned by the design team.
▲After landing on Mars, the Perseverance rover will pull away from the Spirit helicopter so that it can start up for takeoff
Once all of Spirit's tasks have been completed successfully, the rover will be able to fly to the surface. Once all of the "Kirin's" activities have been completed, the larger "Kirin" 2 helicopter will likely land on Mars at the next available opportunity, laying the groundwork for further scientific exploration, and, in NASA's defense, they've already begun to conceptualize the development of a human rover to Mars: Imagine that. : Imagine an unmanned helicopter scouting and route-planning and itinerary management for a ground-based rover carrying astronauts to safely explore the surface of Mars, which is likely to be formalized in the second half of the century.