Chapter 373

Gu Lu first calculated the orbit of the Chang'e-4 detector.

Because this is relatively simple.

Opening matlib on the computer, Gu Lu began to work intensely and busily.

The orbit of the Chang'e-4 probe can be simply divided into three parts.

The first part is the earth-moon transfer stage.

In this stage, the Chang'e-4 probe is launched from the Earth by the Long March launch vehicle, causing the probe to leave the Earth's orbit and fly toward the moon to achieve the Earth-to-Moon transfer.

Gu Lu entered a series of parameters and quickly figured out the orbit of the Chang'e-4 detector at this stage.

Then, the probe continued to move near the moon.

When the probe reaches the predetermined orbit, it will complete near-month braking.

The so-called near-moon braking is to slow down the satellite flying at high speed in the Earth-moon transfer orbit, complete the "space braking deceleration", establish a normal attitude, be attracted by the moon's gravity, and fly around the moon.

Because when the probe flies near the moon, its speed relative to the moon is greater than the moon's escape velocity of 2.38 kilometers/second. If it does not slow down, the probe will fly away from the moon.

If you want to fly around the moon, you must brake. You must brake the car and reduce the flight speed to within the moon's escape velocity, so that it can be captured by the moon's gravity.

Near-lunar braking is the most critical orbital control during the flight of a satellite or probe.

What Gu Lu needs to do in this part is much more troublesome than the Earth-to-Moon transfer stage.

The first point is that Gu Lu must determine the amount of braking during the braking process in recent months.

Although if the braking amount is too small, the probe will fly directly away from the moon.

But once the braking amount is too large, the consequences will be more serious.

Because the probe will hit the moon directly!

Therefore, Gu Lv is needed to accurately measure one of the degrees.

Fortunately, their project is the Chang'e-4 lunar exploration project, not Chang'e-1.

Gu Lu has a lot of experience to draw from.

Gu Lu took out a pile of draft paper and wrote and drew on it.

After obtaining a string of data, Gu Lu used matlib to build a model simulation.

Then, Gu Lu came to a result.

"7500n engine!"

Gu Lu circled the number on the scratch paper.

After Gu Lu’s careful calculation, the entire braking process in recent months was concluded:

When the Chang'e-4 probe was 850 kilometers away from the moon, it started braking near the moon.

In recent months, the brake adopts 7500n variable thrust engine.

The braking process will last for 290 seconds.

After braking is completed, the Chang'e-4 probe will be captured by the moon and successfully enter a 100km*400km elliptical orbit around the moon.

This is the braking process in recent months.

This process is not complicated. Simply speaking, it is to slow down the detector and advance it to the preset orbit.

Gu Lu simulated it on the computer and drew the entire orbit diagram.

The third stage is flying around the moon.

The flight around the moon is the simplest part, which refers to the process of the Chang'e-4 probe orbiting the moon in an elliptical orbit of 100km*400km.

The peri-lunar point of this lunar elliptical orbit is 100 kilometers, and the far-lunar point is 400 kilometers.

You only need to clarify these two data and draw a simple orbit diagram.

This part of the work is so simple that anyone with a little basic knowledge of high school physics can easily do it.

So, so far, the first part of Gu Lu's work has been basically completed.

From the time the Chang'e-4 probe took off from the Earth until it entered an elliptical orbit around the moon, Gu Lu easily plotted the entire orbit.

In fact, this part of the work does not need to be done at all.

Wu Zheng could find any mathematician or even a doctoral student who knew a little bit about physics to draw this orbit diagram easily.

This part of the work is just incidental.

What really required Gu Lu to put in a lot of effort was the setting of various parameters and orbits during the entire moon landing phase.

…………

The lunar landing phase refers to the process of the probe landing on the lunar surface from an elliptical orbit around the moon.

It is also the core and most difficult link of the entire lunar exploration plan.

At the very beginning, the Chang'e-4 probe was supposed to fly around the moon in an elliptical orbit with a distance of 100 kilometers from the peri-lunar point and 400 kilometers from the far-lunar point.

Then, de-orbit control is implemented to make the Chang'e-4 probe enter a predetermined landing preparation orbit on the far side of the moon with an altitude of about 15 kilometers at the peri-lunar point and an altitude of about 100 kilometers at the far-lunar point.

This is just the beginning.

After Chang'e-4 enters the landing preparation orbit, it needs to perform a powered descent at the perilunar point on the far side of the moon.

The entire power descent process will be divided into six stages, namely the main deceleration stage, the rapid adjustment stage, the approach stage, the hovering stage, the obstacle avoidance stage, and the slow descent stage.

Six stages, that means six different sets of system parameters are needed.

Gu Lu needs to calculate one by one.

This requires considerable computational effort.

Gu Lu sighed lightly, flexed his fingers, gripped the pen and started working.

First, there is the main deceleration section of the first stage.

Based on the configuration characteristics of Chang'e-4 in the data provided by Wu Zheng, Gu Lu established the working model and center of mass and attitude dynamics model of the small lunar probe's navigation, guidance and control system (GNC system for short).

The model takes into account the impact of thrust eccentricity and deflection of each engine, as well as the discrete operating characteristics of the GNC system.

Then, the guidance law of the main deceleration section under the terminal horizontal speed constraint was studied.

The corresponding relationship between the orbit parameters of the Kepler orbit and the terminal motion parameters is used to convert the terminal motion parameter constraints into orbit parameter constraints, thereby converting the trajectory planning problem into a limited thrust orbit change problem, and then obtain the guidance law through the least squares correction method

.

Next, the guidance law of the main deceleration section under the terminal height constraint was studied.

Subsequently, the dynamic equations in the guidance inertial polar coordinate system are established, and the target constraint is used as the state quantity. The pseudospectral method can be used to easily obtain the values ​​of some parameters.

On this basis, for a given engine configuration, the value range of the main deceleration section range was studied, and the orbit characteristics within this range were studied. Quaternions were used as parameters, and deviation quaternions were introduced to construct quasi-Eulerian

The angle is used to eliminate the dual value of the target attitude, and the attitude control is designed using the time optimal control of the perturbation double integral system, trying to obtain an optimal control solution.

In this way, all the data about the main deceleration section can be obtained.

When does it enter this stage, how much power should be used to generate power, what is the thrust angle, and how long is the braking time.

These values ​​were all obtained by Gu Lu through complex calculations.

However, this is the first of six stages.

This took Gu Lu more than an hour.

There are five other stages later, which are also quite complex.

"Keep going!"

Gu Lu looked up and glanced at the time on the clock. It was already past seven o'clock in the evening.

Gu Lu had no intention of going to dinner, so he drank a bottle of fatigue potion and continued to drink liver.
Chapter completed!