This article is from WeChat official account:The Heart of Machine (ID: kexuedayuan), editor: Zhang Qian, Zenan, title picture from: Visual China
In recent days, probes targeting Mars have set off.
On July 30th, in the MARS 2020 mission successfully launched by NASA, the “Cosmos God 5” launch vehicle will be the latest generation of Mars rover Perseverance(Perseverance) on track.
Perseverance is the largest and most complex Mars detection system ever built. This next-generation Mars rover cost as much as US$2.7 billion and weighs 1,025 kilograms. It is the third probe launched by mankind in this “Mars season” after the UAE Hope and China Tianwen-1.
If all goes well, in 7 months, it will start collecting Martian rock samples, encapsulating them and burying them in a specific location, waiting for NASA to retrieve the earth. Perseverance will also look for signs of ancient alien life and use a microphone to capture the sound of Mars for the first time.
In addition to this, the most interesting experiment of Perseverance is the release of human’s first alien drone on the red planet-Ingenuity.
As planned, afterAfter 500 million kilometers, Perseverance will be in Jezero crater north of the Martian equator on February 18, 2021.(Jezero crater) Landing, after entering the Martian atmosphere, it will open a parachute, and then use the rocket to hover at a height of two meters to “lift” the rover to the ground. Unlike Curiosity, Perseverance has an autopilot system that can avoid huge rocks and guide itself to a safe location.
On Mars, Perseverance will spend at least one Martian year (approximately 687 Earth days) to explore nearby areas.
The area where Perseverance is scheduled to land. More than 3.8 billion years ago, a river injected a 45-kilometer-wide crater from this location. Of course, it was chosen to find evidence of ancient life on Mars.
Ingenuity: Scout sent by the rover
The history of using space probes to explore Mars runs almost throughout the entire history of human spaceflight, but these tools have some limitations. An orbiter flying around Mars can capture a wide range of Martian images, but the resolution is not high enough; the image captured by the rover launched to the surface of Mars has a high resolution, but the moving distance is limited, and many places are not suitable for the rover to enter .
Before, some human-made “Mars rover” have landed on Mars, but in order to adapt to the harsh environment of Mars surface with an average of -63 degrees Celsius and close to outer space, engineers will make them drive very slowly. The most well-known Rover, Curiosity, has been in operation for eight years and has only travelled 22 kilometers. On average, it has not climbed as fast as a snail.
So, NASA researchers thought about oneWays to expand the vision of the rover-drones.
This drone weighs only 1.8 kilograms, is mounted on the abdomen of the probe, and will try to take off in the harsh environment of Mars. This will be the first flight of a man-made aircraft on a planet other than the earth, or it will open up a new path to explore the solar system.
“The success of this flight test will add a new dimension to human space exploration,” said MiMi Aung, head of the Ingenuity project and head of the Jet Propulsion Laboratory.
NASA Black Technology: Only 1% of the atmosphere can fly
To equip the Mars rover with a drone. In fact, this idea is not difficult to think of. The real difficulty lies in: how to make it fly?
The gravity on the surface of Mars is approximatelyOnly one third of the Earth’s (38%), it seems easy to take off, but one thing is very fatal: the density of Mars’ atmosphere is only that of the Earth 1%. Since there is almost no air flow, it is very difficult to obtain the lift required for takeoff on Mars. Therefore, aircraft designed according to the aerodynamics of the earth cannot fly on Mars.
If you want to take off on Mars, the aircraft must be ultra-light, and the propeller must rotate very fast. But the propeller can’t turn too fast, because as the speed increases, the risk increases.
“No helicopter has ever flown under these conditions-this is roughly equivalent to taking off at an altitude of 30,000 meters on Earth,” said Bob Balaram, a member of NASA’s Jet Propulsion Laboratory technical team and chief engineer of the Mars UAV project. “The propeller cannot turn faster and faster, because its tip will be close to the speed of sound, and the next is supersonic speed. We don’t want it to reach the speed of sound because it will increase the turbulence effect.”
Usually when the moving speed is close to the speed of sound, a strong resistance will appear, causing the aircraft to vibrate strongly. This phenomenon is commonly known as the sound barrier. Even the wingtips of helicopter rotors are not easy to deal with. By the way: the speed of sound on Mars is 240m/s, one third slower than on Earth.
In addition, the design team of Perseverance also set the size of the drone and determined that the detector can accommodate a micro drone with a blade diameter of 1.2 meters.
After clarifying these limitations, engineers at NASA’s Jet Propulsion Laboratory (JPL) set out to design the first Martian drone.
They limited the weight of the drone to around 1.8 kg, which benefited from the advancement of lightweight electronic equipment. If it was placed a few decades ago, lightweight electronic computers, sensors, cameras, gyroscopes, etc. had not yet been invented, and it would be almost impossible to build such a lightweight drone.
The final design of the drone looks like a long-legged spider wearing a complex headdress. Its main body is a box with four legs extending from the box to make the body stand upright.
Four carbon fiber blades and a solar panel are installed on the top of the drone. The design speed of these blades can reach 2,400 revolutions per minute. For drones, this is extremely fast speed. In contrast, a traditional helicopter rotates every minuteThe speed is only 450 to 500.
The Ingenuity drone is about the same weight as your laptop. I don’t know how many black technologies are contained in it.
However, the UAV is only half of the success, the key is to ensure that it can fly on Mars. “In addition to design, you have to consider a question: “How to test? “Because no one has done this before.” MiMi Aung said.
Fortunately, NASA’s JPL laboratory is equipped with a huge test room that can be used for this work. This is a huge room called “Space Simulator”, which can create a completely vacuum environment and can also simulate various extreme temperatures that the drone may face after leaving the earth. In order to simulate the atmosphere of Mars, they pumped the space simulator into a nearly vacuum environment, and then filled it with carbon dioxide, so that the atmosphere density similar to Mars was obtained.
In addition to the atmosphere, gravity is also a problem to be solved. In order to simulate gravity on Mars, engineers tied a string to the drone. This string and related devices are called Gravity Offload System, which can provide upward pulling force.
During the first few flight tests, the research team found that the blades of the test drone were constantly swinging up and down. Because the blades are relatively slender, this tendency to swing also occurs on ground helicopters, but the heavy atmosphere reduces this effect.
In order to solve this problem, they made the propeller blades very hard, much harder than ordinary helicopters of the same size on the earth.
The team conducted dozens of flight tests under various extreme conditions, and the minimum test temperature reached minus 90 degrees. After the test was completed, they folded the drone and put it into the Perseverance probe.
After Perseverance reaches Mars and finds a suitable location, it will release Ingenuity and let it complete its mission independently.
Perseverance dropped Ingenuity on the surface of Mars and then drove away.
Wright Brothers moments on Mars
“If successful, it will be comparable to the moment when the Wright brothers succeeded in flying.” MiMi Aung said. During the 90-day remote self-check period after Perseverance landed on Mars, her team had a month to test the drone. In the future, we may be able to see drones searching for astronauts and performing various missions on distant Mars.
The “Ingenuity” plan will complete four short-distance flights. Each takeoff will have a larger and farther target. The planned flight time will not exceed 90 seconds. But in a short time, Ingenuity can fly to 4.It is 6 meters high, and the horizontal movement distance is about 50 meters.
Due to the long delay in communication between Earth and Mars (3~22 minutes one-way), all these flights are required Is autonomous. The design team will send a list of instructions to the drone, which will perform all the steps by itself. In the plan, the drone will capture images while flying, and Perseverance may also take some images of Ingenuity hovering in the air.
As the first UAV to take off on an alien planet in history, the missions performed by “Ingenuity” are mainly technical verification, proving that the aircraft has value in future Mars missions.
Although it has just launched into the sky, engineers have begun to design a larger drone weighing about 20 kilograms. The next generation of Ingenuity will be able to carry more important scientific payloads and better cameras than it is now. “But before you learn to walk, you must try to crawl.This is the meaning of Ingenuity,” Balaram said. “I hope we can achieve the ‘Wright Brothers’ moment of success and complete a controlled flight for the first time on another planet.”
Reference content:
https://www.nature.com/articles/d41586-020-02257-w
https://www.theverge.com/2020/7/29/21339544/nasa-mars-helicopter-ingenuity-perseverance-rover-flight-date
This article is from WeChat official account:The Heart of Machine (ID: kexuedayuan), editor: Zhang Qian, Ze Nan