Zero distance
Uncover the mystery of Tianwen-1 Mars Orbiter
The image of the braking capture effect of Tianwen-1.
Photo courtesy of the Eighth Academy of China Aerospace Science and Technology Corporation
With the successful capture of Tianwen-1 by Martian gravity, its orbiter structure has also revealed the mystery.
The Tianwen-1 probe consists of an orbiter and a landing patrol device.
Among them, the "space all-rounder" orbiter has three functions: aircraft, communicator and detector.
Zhang Yuhua, deputy commander-in-chief of China's first Mars exploration mission probe system and commander-in-chief of the orbiter, said that during the nearly seven-month flight, the Tianwen-1 orbiter first served as a vehicle to send the landing patrol to the Mars landing orbit.
After the landing patrol is successfully released, the orbiter serves as a communicator to establish a relay communication link with the earth for the landing patrol.
After the communication work is over, the orbiter serves as a probe for scientific exploration of Mars.
"Slimming"
According to Dr. Du Dong from the Tianwen-1 orbiter structure team of the Eighth Academy of China Aerospace Science and Technology Corporation, in order to overcome the strong gravitational force of the earth and run to Mars, the total weight of the Tianwen-1 probe cannot exceed 5,000 kilograms, but in order to reach distant Mars , It also needs to carry at least 2500 kg of propellant, except for the 1300 kg weight share occupied by the landing patrol, the dry weight of the orbiter itself is strictly limited to 1200 kg.
"The 1200 kilograms of the orbiter includes the weight of the structure and various other equipment. It also takes into account the installation requirements of a variety of large-volume equipment such as a 2.5-meter expandable drive antenna, solar array, and high-resolution camera." Du Dong said, how Realizing efficient load-bearing and equipment installation under the condition of limited weight has become a "blocker" in front of the surround structure team.
Wang Jianwei, the chief designer of the orbiter structure, said that for a spacecraft, the lower the center of mass and the lighter the weight, the lower the launch cost. Therefore, the goal of structural configuration design is to minimize the center of mass, optimize weight, and take into account equipment installation. demand.
Around this core principle, the structure team has successively carried out multiple rounds of structural configuration demonstrations.
"The weight of the detector is one gram, and the cost of launching will be far more than one gram of gold." Du Dong said that in order to continue "weight reduction", the orbiter structure team also focused on the heaviest structural core component-the center bearing. The force cylinder, and innovatively adopted the "full composite material main bearing structure", and worked hard on the material, so that the orbiter can achieve efficient load bearing under the strict weight limit conditions.
"Fresh Eyes"
How can the Tianwen-1 probe find Mars on its own when it approaches Mars?
Zheng Xunjiang, an optical navigation expert at the Eighth Academy of China Aerospace Science and Technology Group, told reporters that the optical navigation sensor on the Tianwen-1 probe can use the captured images of stars and Mars to accurately calculate its own flight attitude, position and speed, and achieve relative Autonomous navigation on Mars.
"The optical navigation sensor is like the'eyes' of the Tianwen-1 Mars rover during the autonomous driving process." Zheng Xunjiang said.
According to him, during the process of approaching Mars, the probe relied on these "eyes" to observe the distance and direction of Mars in real time, allowing the flight control team to more intuitively confirm the flight orbit and attitude, and calculate the geometric center and geometric center of Mars in the image. Depending on the radius, Tianwen-1 can also obtain real-time position and speed information from the master through the optimal estimation algorithm.
Zheng Xunjiang said that in the past 7 years, during more than 2,500 day and night tackling key problems, the development team was either doing experiments or on the way to do experiments.
With the support of extensive test data, the team completed multiple rounds of optimization of the design plan, and finally completed the verification of all functions and performance under the worst conditions.
"This is the first time that my country has applied optical autonomous navigation technology in the process of interplanetary transfer." Zheng Xunjiang said that there is no previous engineering experience in China to refer to. The development team has explored a little bit and designed more than 100 test projects, large and small, and finally This makes China the second country in the world that has mastered and verified on-orbit Mars optical autonomous navigation technology.
"strongest brain"
The integrated electronic subsystem is called the "most powerful brain" of the Tianwen No. 1 surround device, and is responsible for the management and control of all the surround device information.
Zhang Yuhua said that during the exploration of Mars by the Tianwen-1 orbiter, the scientific instruments on the orbiter will generate a large amount of scientific data. These data must be sent back to the ground for research by scientists. In addition, the Optical navigation sensor and infrared navigation sensor data also need to be sent back to the ground for further analysis. The integrated electronic sub-system is responsible for processing and storing these raw data, and transmitting it back to the earth at the right time.
According to her, under normal circumstances, satellites orbiting the earth are controlled by the ground control center according to the satellite's real-time status and mission requirements.
But unlike earth satellites, the Mars Orbiter has a long time delay in communication due to its long distance to the ground, and it is often too late to rely on ground instructions to process the probe in real time.
In addition, there is a unique "sun transit" phenomenon in the communication between deep space probes and ground stations, that is, when the probe, the earth and the sun are in the same straight line, solar radiation will interfere with the radio frequency signal transmission between ground fires and cause communication interruption.
Therefore, during the "Sun Ling" period, the surround device must "take care of itself".
Zhang Yuhua said that in response to these situations, the development team of the orbiter integrated electronic subsystem has carried out a series of technical research, and designed a long-term deep-space exploration without an uplink command independent management mechanism, and the whole device is powered off and then restored. When necessary, it can "take care of yourself" and realize the ability of the orbiter to operate autonomously for more than 60 days.
She told reporters that Tianwen-1 has officially become a satellite of Mars since Huanhuo started.
In the follow-up, Tianwen-1 will undergo an orbital adjustment and two near-fire braking. By then, Tianwen-1 will be only 265 kilometers away from Mars.
After that, the Tianwen-1 rover will complete its photographing mission while circling, and carry out pre-selected landing zone exploration. It is planned to choose an opportunity to land on Mars from May to June 2021.
"High Definition Photographer"
On February 12, the National Space Administration released images of Tianwen-1 during its orbit on Mars.
The engineering survey sub-system for this shooting mission is the "photographer" behind the Mars capture blockbuster, designed and developed by the 509th Institute of the Eighth Academy of China Aerospace Science and Technology Corporation.
Zhang Yuhua said that in order to do a good job in visual monitoring of the working status of Tianwen-1 in orbit, the Mars Orbiter engineering survey team specially designed a set of "small blocks" with "small mass, small size, and low energy consumption". The engineering measurement sub-system includes a fixed telemetry probe, a short-distance telemetry probe and the national flag. The two fixed measurement sensors of the fixed telemetry probe are the two fixed telemetry probes that were taken during the capture process.
During the journey to Mars, the fixed telemetry probe monitored the status of Tianwen-1 all the way, completed the solar wing deployment process and the directional antenna deployment monitoring, and captured the earth while the directional antenna was deployed in place.
Zhang Yuhua said that since my country's first independent Mars exploration project was established, how to do a good job in visual monitoring of Tianwen-1's on-orbit flight has become one of the important tasks facing the development team.
The Mars Orbiter engineering survey team combined the entire flight process to design monitoring tasks such as solar wing deployment, directional antenna deployment, earth-moon photography, space selfies, Mars photography, and vehicle separation process.
She told reporters that in the next flight, the Mars Orbiter Engineering Measurement Sub-system will continue to carry out missions, continue to monitor the operation of the solar wing and directional antenna, implement visual monitoring of the separation process of the vehicle, and continue to work for the Tianwen-1 Escort the exploration journey.
China Youth Daily·China Youth Daily reporter Qiu Chenhui