The military-industrial scientific research system of the academic master.

October 2003, .

Early morning, 00:30.

Dongfeng Aerospace City.

It is mid-October in the northwest, and it is late at night, and the temperature has already become a little chilly.

Chang Haonan was wearing a coat and standing in the somewhat deserted hall of the command and control center.

At this time, there were less than nine hours left until the launch of Shenzhou V, and many staff members were still inspecting the equipment and did not appear here.

1500 meters away, the lake-blue launch tower stands tall, pointing to the sky. Three sets of rotating platforms are like powerful arms, tightly embracing the nearly 60-meter-high Long March F Yao- carrier rocket.

Of course, for safety reasons, the control center has no windows leading directly to the outside.

Chang Haonan could only see the situation at the launch site through one of the six large screens in front of him.

However, the ship-arrow combination was not the focus of his observation.

In fact, he had planned to return to the capital after the last full-course joint training two days ago, and personally command the Qingluan constellation to perform attitude maneuvers at the Danzhou Tracking and Control Station.

After all, it can't really play any direct role in the aerospace city.

In the end, it was the superiors who made the decision, stating that Comrade Chang Haonan, as a senior commander and basic R&D personnel of the project, would not be able to play a direct role even in Tanzhou since the satellite had already been launched. It would be better for him to stay in the launch center with the heads of other subsystems as per convention.

Of course Chang Haonan knew that the organization intended for him to witness this landmark moment for all of China.

But then again, there’s actually nothing wrong with what my superior said.

He is not a professional orbit controller, and no matter how capable he is on the ground, he can't do anything about the spacecraft that has already entered orbit.

So, I just stayed like this.

Moreover, by 2003, the communication network within the atmosphere had become relatively complete.

Even if he was in Suzhou's command and control center, he could still see the working conditions of the four Qingluan satellites.

At this moment, it is being displayed on another one of the six large screens.

Also presented are the instructions from Danzhou Station.

To some extent, it is equivalent to a "live broadcast" using a luxury dedicated line.

If necessary, he can even contact the other side and give instructions.

"The relay constellation's attitude maneuver is about to begin?"

At some point, Shen Junrong had come behind Chang Haonan.

As the chief person in charge of the measurement and control system of the manned space engineering project, he actually faced the same situation as Chang Haonan in the final period before launch.

Intellectually, I felt that I had to do something.

But the front-line tasks and personnel allocation are all flexible, and adding an old man like him in the mix might actually make things worse.

So I just came to Chang Haonan, ready to talk to someone and relieve the anxiety in my heart.

Chang Haonan nodded, but his eyes did not leave the big screen in front of him:

"In half an hour, Star 02 will enter the attitude maneuvering range."

As a relay communication satellite, the Qingluan constellation itself can also forward control signals, so it is less restricted by measurement and control resources.

However, the attitude and position determination of small satellites are highly dependent on magnetometers. For the sake of orbital accuracy, it is still necessary to avoid performing actions in high latitudes as much as possible.

Therefore, the time window reserved for each satellite is not large.

In several corners a little further away from the two, dozens of media workers were fiddling with their equipment.

Although the live broadcast plan was officially abandoned during the last rehearsal, Chang Haonan's suggestion was still adopted.

After confirming the success of the launch mission, Station C will broadcast a special program in the evening of the same day, reviewing the entire launch process in a fully recorded format.

And, that's not all.

The program will be broadcast just in time for the spacecraft to enter the 8th or 9th orbit.

That is the most suitable stage in the plan for relay communication testing.

Therefore, after reviewing the launch-orbital process, the program will seamlessly transition to a quasi-live broadcast with a delay of 8-10 minutes, directly presenting the situation inside the spacecraft to people all over the world.

In this respect, Shenzhou V has an advantage.

That is, the astronauts will not enter the orbital module during the entire process, but will stay in the less sensitive return module.

Therefore, the content that needs to be cut off is mainly limited to some voice during the call between heaven and earth, rather than the pictures.

This saves the trouble of coding in the middle.

It can be said that the only problem next is whether Chang Haonan and his team's "Qingluan" constellation can stably maintain sufficient relay communication time...

……

At exactly 02 a.m., Qingluan was the first to enter the pre-planned maneuvering range.

"Attention all units. According to the Gaojing orbital monitoring calculation, we are now confirming the target aircraft's attitude adjustment path..."

Zhang Weiyong's voice came from the headphones.

Controlling a satellite is not like driving a car, and it certainly does not involve technicians directly operating it with devices such as steering wheels or joysticks. Instead, commands are entered into the control program, which are then executed by the satellite.

And now, it is time to make the final confirmation before the order is issued.

At this time, Shen Junrong next to him also picked up another pair of headphones and put it to his ear.

He was just listening casually at first, but not long after, he showed a look of surprise.

"Your attitude maneuvers follow a sinusoidal path?"

As he said this, he turned to look at Chang Haonan, who was looking at one of the six screens with a focused expression.

This maneuver of the Qingluan system does not involve a change of orbit, so the "path" here does not refer to changes at the orbital level, but rather to the relationship between angular velocity and time during the attitude adjustment process.

"Yes."

This sudden question actually relieved a lot of the pressure on Chang Haonan's heart.

He took off his headphones and explained to Shen Junrong:

"Although the trapezoidal path has the highest utilization of time and actuator performance, it has a sudden change in angular acceleration, which may affect the satellite's workload, such as solar panels or liquid fuel in the tank. The sinusoidal path is easier to control in this regard."

As an expert in this field, the latter certainly understood the differences between different path planning, so Chang Haonan's answer did not resolve his doubts:

"But I've seen some of your satellite's design parameters. It's not the kind of satellite with a large flexible structure that's prone to divergent vibrations. The size and capacity of the fuel tank is very small... and it should be almost full at the moment, so there's no need to worry about liquid sloshing, right?"

As the name suggests, the trapezoidal path simply and crudely gives three constant acceleration values ​​during the attitude change process, allowing the angular velocity of the spacecraft to undergo three processes: uniform increase-uniform motion-uniform deceleration.

It is the simplest control principle that can be understood after learning high school physics.

It is also the least likely to cause problems.

Therefore, although there are many disadvantages, the trapezoidal path will basically be chosen if the conditions are met.

The integral of the sine function is a cosine function, which means that the change in angular acceleration is more complicated, especially for small MSIs with limited performance of actuators and control mechanisms.

The choice of Qingluan constellation seems to be a bit like looking for trouble.

But this time, Chang Haonan did not answer immediately, but just smiled mysteriously:

"Mr. Shen, you will know in a moment..."

Shen Junrong was stunned when he heard this, and then he laughed too.

He said no more and put an earphone to his ear again, waiting for Chang Haonan's performance.

While the two were discussing the issue, Qingluan 02 Star had already begun to adjust its posture.

In space, it is naturally impossible for a camera to stare at a satellite.

The small satellite project itself has little publicity value, and a 3D schematic diagram will not be made simply for intuitive purposes.

Therefore, what is displayed on the screen at this time is only the attitude angular velocity curve and the modal coordinate curve sent back by the sensor.

As for the satellite's movements...

Then you can only rely on your imagination.

As Zhang Weiyong issued attitude adjustment commands, the vertical coordinate of the angular velocity curve gradually began to increase from 0 upward, drawing a sinusoidal function curve on the coordinate system.

A little later, the modal coordinates also began to give data.

However, compared with the angular velocity curve with a near-perfect fit, a closer look at the modal coordinate data reveals that it contains a lot of irregular fluctuations that look like noise.

This is the flexible vibration mentioned by Shen Junrong earlier.

However, perhaps because of the sinusoidal path used, the amplitude in front of us will not have any effect on the satellite itself.

He could even see that after the satellite's angular velocity reached its maximum value, that is, after the angular acceleration returned to zero, the vibration had entered a convergence state.

Shen Junrong looked at Chang Haonan next to him, wondering what was special about this.

He even knew what was going to happen next—

In the second half of the attitude adjustment, angular acceleration reappears (negative acceleration) and the vibration will be strengthened again.

Once the entire adjustment process is completed, the vibration will slowly return to zero over the next 8-10 minutes or even longer.

But Chang Haonan did not move his eyes away. He just pointed at the screen, indicating Shen Junrong to continue watching.

But when the latter turned his attention back to the curve on the screen, he just stood there in a daze.

When the angular velocity starts to decrease again, the vibration level shown on the modal coordinate curve does not increase again.

Instead, it continues to weaken.

After another 120 seconds, Qingluan 02 Star finally located its new posture.

The vibration of the satellite accessories completely disappeared almost at the same time...

There was no subsequent gradual weakening process as he had expected.

Don't underestimate this difference.

In addition to affecting the working state of the equipment and the satellite itself, flexible vibration may also couple with orbital motion, thereby affecting the satellite orbit.

If the impact is large, then after the attitude adjustment is completed, it may even be necessary to make another orbit adjustment in order for the satellite to reach a suitable working state.

However, like the Qingluan 02 star in front of us, if the vibration ends almost synchronously with the attitude maneuver, this situation can be almost completely avoided.

only……

Even considering the size of a small satellite of 100kg and the sinusoidal path, this motion characteristic is a bit too outrageous.

Fortunately, at this time, Chang Haonan gave a further explanation:

"The advantage of the sinusoidal path is not only that it weakens the vibration caused by angular acceleration, but more importantly, there is no instantaneous mutation from the positive maximum value to 0. In other words, the induced vibration is more regular... Therefore, we have tried to apply active vibration suppression technology from the aviation field on the Qingluan series of satellites."

"And now it seems that the effect is quite good..."