This article is from WeChat official account:Tencent Space (ID: qqtaikong), author: Joe Hui, from the title figure: vision China

At 19:50 on July 30, 2020, Beijing time, a “Cosmic God Five” (Atlas-V) launch vehicle The Cape Canaveral Space Base in the United States was launched into space, this time it was carried by NASA’s Perseverance(Perseverance) nuclear-powered Mars The car is expected to arrive on Mars in February next year.

The “Perseverance” rover can be regarded as an upgraded version of the “Curiosity” rover that landed on Mars in 2012. It is equipped with the latest scientific detection instruments and focuses more on the exploration of potential signs of life on Mars.

In addition, the “Perseverance” rover will also undertake a Mars sampling mission, collecting Mars rock and soil samples in preparation for future Mars sampling and returning missions. It is reported that the total cost of this mission to Mars exceeds 2.4 billion US dollars.

It is very interesting that this launch, in addition to the “Perseverance” rover, is also equipped with a small Mars helicopter that can conduct aerial reconnaissance near the landing area of ​​the rover. Once successful, it will become the first controllable aircraft to fly on other planets.

This helicopter, named “Ingenuity” (Ingenuity), weighs only 1.8 kilograms and is powered by two counter-rotating propellers. The rotational angular speed can reach 2400 revolutions per minute. The speed of horizontal movement is 10 meters per second and the climbing speed is 3 meters per second. For the details of this small helicopter, there is a special chapter later.

1. What is the difference between this US mission to Mars and China’s mission to Mars?

On July 23, China used the Long March 5 carrier rocket to send the “Tianwen-1” into orbit to Mars. This is the first time that China has launched a Mars rover, and plans to use this mission to complete the mission to Mars. The complexity and difficulty of the three forms of detection, circling, landing, and patrol are very high.

Legend: On July 23, 2020, the Long March 5 rocket launched on the “Tianwen-1”.

Specifically, it means sending the Mars Orbiter, Mars Landing Platform, Mars Rover, and ancillary equipment to Mars at one time. The total weight is 5 tons. Only the Long March 5 rocket can be delivered.

The US “Mars 2020” mission is mainly to send the “Perseverance” rover to the surface of Mars. The total weight of the Mars rover plus the attached landing equipment is 3.9 tons, which is lighter than our “Tianwen No. 1”. It is launched by the Space God V541 rocket, which has a smaller capacity than the Long March V.

Legend: The nuclear battery is located at the rear of the Perseverance rover.

The “Perseverance” Mars rover is 3 meters long, 2.7 meters wide, 2.2 meters high, and weighs 1,025 kilograms. It is powered by nuclear power. In a little expansion, it uses the heat released by the decay of the plutonium 238 nuclear decay to generate electricity through thermocouples. The power is not too large, it can only provide continuous 110 watts of electrical energy, but this method can completelyGet rid of the dependence on the sun’s radiation, and can continue to drive the rover to move on Mars steadily. In addition to nuclear batteries, two lithium-ion rechargeable batteries are also installed to provide instant high-power electricity.

Legend: The nuclear battery of the Yili train car.

But this kind of nuclear power also has its shortcomings. Firstly, the cost is high. Secondly, as time goes by, the radioactive elements continue to decay, and the output power will decrease year by year, but it can be used for at least 14 years. The details of this nuclear power supply are described in a special chapter later.

Our country’s rover weighs about 240 kilograms, almost twice the weight of the Yutu lunar rover, and is expected to work for at least 90 Martian days. This weight is between NASA’s “Opportunity” and “Perseverance” rover. Specifically, the “Opportunity” rover weighs 185 kg, and the “Perseverance” rover weighs more than 1,000 kg.

Label: China’s Mars Exploration Project released the Tianwen-1 Mars Rover.

my country’s Mars rover has four solar panels, six wheels, and two towering antennas. It looks like a butterfly. Limited by the light and temperature on Mars, the best working time for the rover is around noon on Mars. At this time, there is plenty of sunlight and can provide sufficient power for the scientific instruments on board. Sunny during the dayAt that time, the rover will also store part of the electric energy in the battery for night use.

In addition, scientists also thought of an ingenious way to absorb solar energy using phase changes of matter. On the top of the rover, there is a device called a heat collecting window, which contains n-undecane. During the day, when the temperature rises, this substance absorbs heat and melts; at night, when the temperature drops, this substance releases heat and solidifies. Using this method, the rover can be guaranteed to spend the long cold night safely. This new way of using heat is the first in the world.

In terms of the details of scientific missions, there are also differences between the US Mars missions and my country’s Mars missions, so we will not compare them here.

2. What is the difference between the Perseverance rover and the Curiosity rover?

At the beginning of the article, we also mentioned that the “Perseverance” rover can be regarded as an upgraded version of the “Curiosity” rover that has landed on Mars before. It is based on the “Curiosity” rover. It is a directional design, but the two are very different in many details.

Legend: Curiosity rover (left) and Perseverance rover (right) (art drawing).

The “Perseverance” has a longer body than the “Curiosity”, about 13 cm long. Perseverance is heavier than Curiosity. Perseverance weighs 1,025 kg and Curiosity weighs 899 kg. The extra weight is mainly due to the heavier equipment carried by Perseverance.

The “Perseverance” Mars rover is equipped with 23 cameras, most of which are in color. The “Perseverance” mast camera has a better zoom function, can shoot high-definition video And panorama. The “Curiosity” rover only has 17 cameras installed, and only four are color cameras.

“YiThe rover “Li” is also equipped with two microphones, which can not only capture the sound of Perseverance landing on Mars, but also listen to the sound of wind on Mars and the sound of laser analyzers bombarding rocks.

Legend: Comparison of wheel styles between Curiosity rover and Perseverance rover.

The wheels of “Perseverance” are made of the same material as “Curiosity”, but the wheel diameter is larger and the width is narrower. The patterns on the wheels are also different and stronger.

“Perseverance” has stronger autonomy than “Curiosity” and can complete tasks more efficiently.

Caption: Like the Curiosity rover, the Perseverance rover also uses this aerial crane method for soft landing on Mars.

3. What important scientific instruments does the Perseverance rover carry?

Legend: Seven scientific instruments carried by the Perseverance rover.

1. Mastcam-Z: This is a zoom panoramic camera located on the mast, which can produce high-definition panoramic and stereo images; it can identify the composition of rocks on the surface of Mars, and it can also assist the rover. The power consumption is about 17.4 watts.

2. SuperCam: This is a laser ultra-distance analyzer that can use high-definition cameras, lasers and spectrometers to analyze the composition of rocks and soil on Mars from a long distance. The power consumption is about 17.9 watts.

3. PIXL: This is an X-ray spectrometer, which can use the principle of minerals to produce fluorescence from X-rays for more accurate analysis. Equipped with a macro camera, it can see very small particles of Martian sand. The power consumption is about 25 watts.

4. SHERLOC: This is an ultraviolet spectrometer that can use ultraviolet lasers to analyze minerals and organic substances. This will be the first ultraviolet Raman spectrometer on Mars. A high-resolution color camera is also installed on this instrument. The total power consumption is about 48.8 watts.

5. MOXIE: We know that carbon dioxide in the Martian atmosphere accounts for 95%. This instrument will conduct a very important experiment, which is to produce oxygen from carbon dioxide in the Martian atmosphere through chemical reactions. With oxygen, not only can it be used for breathing by astronauts who will land on Mars in the future, but oxygen is also the propellant for rockets. This instrument consumes about 300 watts.

6. MEDA: equivalent to a mobile weather station, capable of recording the temperature, pressure, wind speed, wind direction, relative humidity, and the size and shape of sand and dust in the Martian atmosphere. The power consumption is about 17 watts.

7. RIMFAX: This is a radar detector. This instrument uses radar to detect geological structures under the surface of Mars, with a resolution of centimeters. The power consumption is about 5 to 10 watts.

4. What are the key scientific goals of the Perseverance rover?

1. Look for traces of life on ancient Mars.

2. Collect rock and soil samples to prepare for future Mars sampling returns.

3. Explore the geological diversity of the landing area.

4. Validate new technologies for future Mars missions.

Legend: Perseverance Mars sampling container.

5. Where is the landing site of the Perseverance rover?

Caption: Perseverance will land on Mars at 18 degrees north latitude and 77 degrees west longitude (green circle); Curiosity’s landing area (red circle) ).

The Perseverance will land on Mars at 18 degrees north latitude and 77 degrees west longitude, in a crater named Jezero (Jezero Crater) place. This impact crater is 49 kilometers in diameter and was filled with water in ancient times, and it is rich in sedimentary clay. The “Perseverance” rover chose to land here in order to look for traces of life in the sediment.

This small helicopter is charged by the solar panel on the top, and the electric energy is stored in lithium ion batteries. It can fly for about 90 seconds after charging for one day! A color camera and a black and white camera are installed.

This helicopter cannot directly communicate with the earth. It has to relay information through the “Perseverance”. Therefore, it cannot fly too far away from the “Perseverance”. The farthest range is only 300 meters and the longest communication distance is 1 km.

Actually, this Mars helicopter project is mainly for technical verification, and it doesn’t give too many missions. The Martian helicopter has higher resolution than the orbiting satellite, and is more flexible and maneuverable than the Martian rover. Once the flight is successful, a whole new way will be added for future Mars exploration.

7. Nuclear power generation devices that do not rely on sunlight

Although solar power can also work on Mars, it sometimes encounters problems. When a dust storm occurs on Mars, Martian dust will block 90% of the sunlight, and the dust will also cover the battery panels. The “Perseverance” rover weighs about 1,000 kilograms and is a larger rover about the size of a small car. It is equipped with several high-energy-consuming instruments, so its energy demand is very high, so relying on solar power generation cannot meet the electricity demand.

Caption: Technicians at NASA’s Jet Propulsion Laboratory are installing a radioisotope heat generator (RTG) on the Curiosity. Plutonium-238 decays to provide the power needed for the mission.

The Perseverance rover uses a “Radioisotope Thermoelectric Generator”(Radioisotope Thermoelectric Generator, abbreviated as RTG) to provide electricity. The principle is that the heat generated by the decay of the radioactive isotope plutonium-238 is directly converted into direct current through a thermocouple device to provide the running of the rover and the use of various instruments and equipment.

Legend: The RTG uses plutonium dioxide (Plutonium-238), which has become very hot due to radioactive decay (left). The mushroom cloud raised by the atomic bomb dropped by the United States to Nagasaki, Japan in 1945 (right). The atomic bomb was code-named “Fatty” and the nuclear fuel used was plutonium-239.

The man-made isotope plutonium-238 has a half-life of only 88 years, which means that its radioactivity decays so quickly that it can be very hot. Plutonium-238 releases alpha rays, which are easily blocked. This substance cannot be used in nuclear bombs. RTG has no moving parts, so it is reliable, and radioactive materials can continue to generate heat for many years. In addition to being used to power the “Yili”, the waste heat can also be used for