How to "Drift" and step on the brakes of "Tianwen No. 1"
Author: reporter Zhang Lei
On February 10, 2021, the "Tianwen-1" Mars Rover successfully implemented the near-fire brake, completed the capture of Mars, and officially entered the ring-fire orbit.
At present, the various systems of the detector are in good condition, and the accuracy of entering orbit after near-fire braking is very high, which has won a "good start" for the smooth development of subsequent round-fire flights.
On Benhuo Road, how does "Tianwen No. 1" "drift" well, step on the brakes, and identify diverse and complex ring fire tracks?
All of these are inseparable from the interplanetary piloting of the orbital design team of the General Design Department of the Fifth Academy of Aerospace Science and Technology Group.
Now, let us listen to what the track design team of "Tianwen No. 1" says...
Midway corrections and deep space maneuvers are required on the road to rush
Since its launch on July 23, 2020, the "Tianwen No. 1", which set foot on the Benhuo Expressway, has completed four midway corrections and a deep-space maneuver.
Unlike the Chang'e series of probes flying in the earth and moon space, the "Tianwen-1" is on an interstellar voyage, and it has completely separated from the earth's gravitational field three days after launch.
In order to ensure that it can run into the fire smoothly, the Fifth Aerospace Academy has carefully designed the optimal flight path for it, and formulated detailed and comprehensive control strategies to help "Tianwen No. 1" fly accurately in navigation.
On the highway where the fire transfers, the "Tianwen No. 1" has been in a state of unpowered flight for a long time. It will inevitably be affected by the deviation of orbit, the deviation of control and other perturbation factors, and it will deviate from the predetermined orbit.
In order to get closer to the theoretical orbital flight, it needs to turn the "steering wheel" gently, step on the "throttle" slowly, and adjust the flight direction and speed in detail through midway correction.
On the high-speed road, deep-space maneuvering is a drifting skill "Tianwen-1" needs to master.
Compared with midway correction, deep-space maneuvering is a more controlled orbital maneuver, which enables the probe to enter the orbital surface of Mars from the earth's revolution surface through a large turn or drift, and accurately aim at Mars for flight.
"From the perspective of orbital design, deep-space maneuvering is mainly to adjust the size and inclination of the probe's orbit around the sun to meet the needs of reaching Mars." The orbital director Zhou Wenyan explained.
There is only one chance, the brakes must be accurately pressed
After the 4th midway correction, "Tianwen-1" maintained a steady flight trajectory and arrived near Mars.
On the days when the Chinese people celebrate the Spring Festival, Mars ushered in new seekers.
From the ground fire transfer orbit to the ring fire orbit, it is necessary to achieve Mars capture through near-fire braking, so as to complete the smooth connection of the heliocentric orbit and the fire center orbit.
"Tianwen No.1" needs to accurately identify the high-speed road signs to Mars, brake slowly, and drive cautiously on the "ramp" leading to the ring fire track.
"For orbital design, the brake force of near-fire braking is extremely elegant-if you step on it too lightly, you will fly away from sparks; if you step on it too hard, it will have a huge impact on the subsequent flight sequence." Designer Gao Shan described it vividly.
After completing the fourth midway correction, "Tianwen No. 1" entered the appropriate window period. The brakes must be accurately stepped on, that is, through near-fire braking to achieve Mars capture, and step into the predetermined ring fire orbit in one step.
For "Tianwen No. 1", there is only one chance for near-fire braking, because the next suitable window period is 2033.
Another great challenge to orbit control is communication delay.
Because the probe is too far away from the earth, the communication between Tianwen-1, which is about to enter the orbit of the ring fire, and the earth has been delayed for more than 10 minutes-which means that real-time monitoring and rapid response to the capture of Mars cannot be carried out.
Faced with such a "visual blind zone", the orbital design team coordinated the control system to analyze nearly a thousand fault conditions, determined key parameters and thresholds, and compiled nearly two hundred fault plans to ensure that the Mars rover cannot be on the ground. In the case of real-time control, make appropriate judgments and reactions to possible situations.
Guaranteed "parking" through complex track control
This is the first time that a Chinese spacecraft has arrived near Mars. It is very difficult to design the orbit to achieve the three goals of "orbiting, landing, and patrol" at one time.
The "Tianwen-1" Mars rover consists of an orbiter and a landing patrol.
In order to ensure the smooth landing of the landing patrol on Mars, "Tianwen-1" needs to use complex orbital control to ensure "parking."
It is reported that after the completion of Mars capture, the "Tianwen No. 1" entering the ring fire orbit will face a greater test: a plane maneuver at the far fire point, adjustment of the orbital inclination of the flight, and laying the foundation for subsequent "parking" work; When returning to the near-fire point, "slowly step on the brakes", step into the parking phase modulation orbit, and adjust the orbital cycle to ensure that the trajectory passes through the predetermined landing point; when the parking phase modulation orbit reaches the near-fire point again, "Tianwen No. 1" needs to brake for the third time to enter the parking track, and maintain the landing area on the track several times to take pictures and images of the landing area to ensure that the landing patrol can be landed at the predetermined time and place.
"After properly completing the previous steps,'Tianwen No. 1'slowed down again and entered the parking track, took images of the landing area, and selected a suitable location to complete the last step of'parking'-the orbiter separated from the landing patrol and landed The rover enters the Martian atmosphere." The staff of the orbital design team emphasized.
(Reporter Zhang Lei)