100 days, 1000 meters, a new starting point

Today marks the 13th month that Tianwen-1 has been traveling in space and pursuing its dream on Mars. It is also the day that the Zhurong Mars rover has safely spent 100 days on Mars. It is also a critical day for the mileage to exceed 1,000 meters!

Today, the Mars rover, which has successfully completed its mission, is still surviving on the distant red planet, breaking new records and creating infinite possibilities. Every step of the Mars exploration is closely accompanied by the Mars team of the Beijing Aerospace Flight Control Center. Let us once again understand my country's first Mars exploration mission through their voices and get closer to this Chinese Mars rover living on a "foreign planet".

"Fall! Fall! Fall!"

From last summer to this spring, the flight control team accompanied "Tianwen-1" through the four seasons of the year. The long journey did not blur everyone's goal. All the companionship was for a smooth arrival and a smooth landing. Before this day came, the flight control team went through more than two months of fierce battles. Before the landing of the national heavy weapon that has been guarded for 10 months, it is necessary to understand the environment of the destination before you dare to send your baby there with confidence. How can it be more secure? Of course, you have to look again and again and confirm repeatedly. They completed 4 orbit maintenance in the parking orbit, first 2 test imaging of the destination, and then 18 formal imaging photos. This is not enough to feel at ease, and adding 3 backup imaging is considered solid. This kind of excellence and cautious attitude is very similar to parents who repeatedly inspect schools before applying for volunteers. The sleepless working hours are all a reflection of careful planning for the future. High-resolution imaging detection provides terrain data support for the landing on Mars, and a three-dimensional and comprehensive model has been established. After confirming the objective environment, they also conducted equipment self-inspection on each subsystem of the probe body, charged the Mars rover, and performed static calibration through the star sensor and inertial measurement unit to keep the protagonist in a good state before going on stage. On May 14, the flight control team entered the control hall early and methodically implemented the final parameter injection before entry, descent, and landing. To ensure the smooth implementation of the separation of the two devices, the orbiter needs to descend into the separation orbit before separation. Only after confirming that everything is normal can the order be issued to allow the two devices to separate. There are only 3 hours between the two operations. Excluding the time required for telemetry command issuance, there are only 2 hours left for interpretation. Everyone must evaluate and make decisions on the status and control effect of the device in a short period of time. If the conditions for separation are not met, other plans must be made. This is a test of comprehensive technical experience and courage. Fortunately, after the status evaluation, everything is normal and the orbit descent can be implemented as planned. Control began. Every second of the 17-minute light travel time was a torment for every team member. During their waiting, the telemetry indicating the completion of the orbit reduction finally arrived. Everyone quickly requested the delayed telemetry data during the orbit reduction. The data showed that everything went smoothly, the detector was in normal working condition, and the separation of the two devices could be implemented as planned. The separation command was issued and the separation procedure was implemented as planned. During this period, the detector did not transmit data back to the ground. Everyone had no way of knowing the status of the Mars rover, and what was left for the drivers was an anxious wait all night. According to the plan, after waiting all night, at 7 a.m. on May 15, the lander will enter the Martian atmosphere and face the "terrifying 9 minutes" that the world's Mars exploration missions are daunting. After deceleration, hovering to avoid obstacles and buffering, it can successfully reach Mars. On the 15th, the personnel in various positions who had been up all night swept away their sleepiness and watched the data sent back little by little confirm the results they had longed for in their hearts. Although they knew that it was not a real-time result, everyone in the on-site command position still shouted that exciting voice unconsciously to the three-dimensional simulation animation - "Land! Land! Land!" The landing was successful! “The first time a Chinese person left his mark”

On the day of landing, General Secretary Xi Jinping sent a congratulatory message: "You have the courage to challenge and pursue excellence, and have made our country a world leader in planetary exploration. The motherland and the people will always remember your outstanding contributions! I hope you will continue to work hard, carefully organize and implement the scientific exploration of Mars patrols, adhere to scientific and technological self-reliance, carefully promote major aerospace projects such as planetary exploration, accelerate the construction of a strong aerospace country, and make new and greater contributions to the noble cause of exploring the mysteries of the universe and promoting human peace and development!" The General Secretary's earnest exhortation encouraged the Mars rover drivers who would take over the subsequent exploration missions. From this day on, it was really the turn of the Mars rover drivers to work hard. How to drive the "Zhurong" from the landing platform to the surface of Mars was the first problem they had to face when they started their Mars roaming. "The way Zhurong transmits information to the ground is divided into direct communication and forwarding through the orbiter. The communication between Zhurong and the orbiter is mainly carried out in the far-Mars arc at night and the near-Mars arc at noon. As the time difference between the Earth and Mars accumulates, the communication window will shift. This way of information transmission makes it impossible to observe the execution effect in real time, which increases the difficulty for the flight control pilots to judge the status and control the behavior of Zhurong, and requires them to fully consider all possibilities before the mission. After repeated deliberation and many studies and discussions, everyone made a complete analysis of the decision-making implementation process and various emergency branches. Before leaving, the flight control pilots controlled Zhurong to carry out a top ring shot, looked around, reconfirmed the direction of the ramp deployment, and reconstructed the three-dimensional environment of the Mars surface. This was the first A reconstruction of the Martian surface environment is to build a Martian world in the mind of "Zhurong". At the same time, everyone has to calculate and confirm the ramp angle, ramp skewness angle and ramp deployment status again. "Zhurong" needs to go to Mars through the transfer mechanism like "walking on a tightrope", which can be understood as a ladder, and whether the ramp angle of the ladder is appropriate is crucial. Secondly, the drivers here also need to determine the subsequent path for the Mars rover, what the road it is about to take looks like, whether it will "hurt its feet", whether there are "roadblocks", whether it will affect subsequent planning, etc. Many problems were confirmed in their repeated inspections. Before departure, the flight control driver also conducted a self-inspection of the Mars rover, and evaluated that the working conditions, vehicle conditions and road conditions of "Zhurong" and the orbiter were all normal, and the Mars gallop was unstoppable.

The drivers planned the UHF communication work near Mars. At 6:15 on May 21, the drivers recorded the Martian day work on the orbiter and successfully forwarded it to the rover, which drove away on the eighth Martian day. Although everything was normal, in order to deal with the failure of the rover, the corresponding fault handling work must also be planned in place. Once the rover's working condition is abnormal, emergency handling can be in place in time. These are all carried out simultaneously.

On May 22, the images of the rover's telemetry and obstacle avoidance camera during its departure began to be downloaded. The teleoperation hall of the Beijing Center was very quiet, and the drivers stared at the screen. As time passed, the image data was downloaded, and everyone breathed a sigh of relief. It was stable! The 20 pairs of images collected by the front and rear obstacle avoidance cameras were clearly presented to everyone, and the process of the rover's departure was recorded in this set of images. The last image of the rear obstacle avoidance camera showed that "Zhurong" had successfully left the landing platform and stepped steadily onto the surface of Mars. For the first time, China's imprint was engraved on this red planet!

"Everything is working fine!"

During the more than 300 days that Tianwen-1 was on its journey to Mars, behind the "everything is normal" seen by the news media and the public was the flight control team of the Beijing Aerospace Flight Control Center who tracked and monitored day and night, discovered and dealt with one problem after another, turning each "extraordinary" situation into "extraordinary".

Before the first mid-course correction, the team keenly discovered that the temperature of a single device on Tianwen-1 was too high, which was crucial to the rover's landing on Mars.

How to "use medicine accurately" to control the temperature at a more reasonable value, everyone has made a detailed plan. Based on the impact of sunlight on the temperature of the whole device, the flight control team controlled the attitude adjustment of "Tianwen-1" to fly at a small angle to the sun to avoid direct sunlight. After taking a dose of medicine, the temperature of "Tianwen-1" gradually dropped, and it was able to fly smoothly to Mars. In order to improve the reliability of the descent and landing process, the flight control team organized and formulated an implementation plan for orbit control to be advanced by 1 hour, from 5 hours before entering the Martian atmosphere to 6 hours, increasing the flight control decision-making criteria and timely margin. They formulated an implementation plan to adjust the orbit control target of the orbiter from 265 kilometers near the perigee to 440 kilometers, so that the communication coverage time between the ground and "Tianwen-1" is longer, and the ground's judgment on the fire situation has become more reliable. They also adjusted the trigger parameters of the parachute, optimized the working conditions of the parachute opening, formulated an implementation plan for fire adjustment based on the imaging results of the landing area, and continuously improved the emergency plan, etc. The team did a lot of work to make the landing and departure of the Mars rover safer and more reliable.

After successfully maneuvering the rover away, the mission entered the patrol and exploration phase.

According to the implementation process determined by the plan and flight procedures, the team carried out surface work in a mode of "perception-detection-mobility" with a cycle of three Martian days. However, the overall project puts forward the requirement of "efficient mobility and efficient detection", and decides that the Mars rover will carry out detection in a cycle of "mobility-perception" with one Martian day. After the limited remote operation team members had just experienced the high-intensity work rhythm of the release and separation stage, they were not resting and turned to higher-intensity work again. The original 22 hours under the three-day process were compressed to 8 hours, which required efficient coordination and close cooperation between the overall remote operation, planning, imaging, positioning, remote control, telemetry and other positions, and once again engaged in a tough battle with the participating systems.

In order to run faster and go further, the Mars rover once again ushered in a change in its mobility mode.

The Mars rover has been adjusted from "ground-planned blind movement" to "ground-planned blind movement plus autonomous obstacle avoidance movement on the device", that is, from one step and one movement to two steps and two movements. The daily movement distance of the Mars rover has been expanded to about 20 meters, and the work intensity of the remote operation team has been further increased. The time difference between the Earth and Mars is a 40-minute dynamic time difference set daily, and the ground operation team needs to synchronize with the Mars rover. According to the Martian time schedule, the seemingly insignificant 40 minutes, when added up, is equivalent to reversing day and night every 15 Martian days for ground staff. Efficient long-distance movement plus dynamic time difference between the Earth and Mars is a challenge that cannot be underestimated for the Mars rover remote operation team with limited personnel, but in the face of exploring the mysteries of the red planet, they did not back down, just to protect the Chinese Mars rover, observe more cosmic beauty from a Chinese perspective, and discover more scientific results.

The engineering goal has been achieved, but the pace of exploring Mars will not stop, and the pursuit of excellent survival goals will not be relaxed!