Chapter 373

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

Because it's relatively simple.

TURNING ON MATLIB ON THE COMPUTER, GU LU BEGAN TO WORK HEAVILY.

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

The first part is the Earth-Moon transfer phase.

At this stage, the Chang'e-4 probe will be launched from the Long March carrier rocket on Earth, so that the probe will leave the Earth's orbit and fly to the moon to achieve the Earth-Moon transfer.

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

Then, the probe continued to move near the moon.

When the probe reaches the predetermined orbit, the near-moon braking is completed.

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

Because when the probe flies near the Moon, its velocity relative to the Moon is greater than the Moon's escape velocity of 2.38 km/s, and if it does not slow down, the probe will fly away from the Moon.

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

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

This part of what Gu Lu needs to do is much more troublesome than the Earth-Moon Transfer Stage.

The first point is that Gu Lu must determine the amount of braking in the braking process in the near month.

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

But if the braking volume is too large, the consequences will be even more serious.

Because the probe will hit the moon directly!

Therefore, it is necessary for Gu Lu to accurately measure one of them.

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

Gu Lu has a lot of experience to learn from.

Gu Lu took a stack of scratch 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 scratch paper.

After Gu Lu's careful calculation, the whole process of near-moon braking is obtained:

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

The near-moon braking adopts a 7500N variable thrust engine.

The near-moon braking process will last 290 seconds.

After the 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 process of braking the entire near-moon.

The process is not complicated, it is simply a matter of slowing down the probe and propelling it into a preset orbit.

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

The third stage is to fly around the moon.

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

The perilunar point of the elliptical orbit around the Moon is 100 km, and the apogee is 400 km.

You only need to clarify these two data and draw a simple orbital chart.

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

Then, so far, the first part of Gu Lu's work is basically completed.

After the Chang'e-4 probe lifted off from the Earth until it entered the elliptical orbit around the Moon, the entire orbit was easily mapped by Gu Lu.

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

Wu Zheng can easily draw this orbital diagram by finding a mathematician, or even a doctoral student who knows a little bit about physics.

This part of the work is only incidental.

What really needed Gu Lu to work hard was the setting of various parameters and orbits throughout the moon landing stage.

............

The moon landing phase refers to the process by which a probe descends from an elliptical orbit around the moon to the surface of the moon.

It is also the core and most difficult part of the entire lunar exploration program.

At the beginning, the Chang'e-4 probe was supposed to fly around the moon in an elliptical orbit around the moon with a perilunar point of 100 km and an apogee of 400 km.

Then, the orbit descent control will be carried out to enable the Chang'e-4 probe to enter a predetermined landing preparation orbit on the far side of the moon at an altitude of about 15 kilometers at the perilunar point and about 100 kilometers at the apogee altitude.

This is just the beginning.

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

The whole power descent process will be divided into 6 stages, namely the main deceleration section, the rapid adjustment section, the approach section, the hovering section, the obstacle avoidance section, and the slow descent section.

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

Gu Lu needs to be calculated one by one.

This requires a considerable amount of computational work.

Gu Lu sighed lightly, moved his fingers, clenched the pen and began to work.

First of all, there is the final reduction 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 of the navigation, guidance and control system (GNC system) and the centroid and attitude dynamics models of the small lunar probe.

The influence of thrust eccentricity and deflection of each engine is considered in the model, and the discrete operating characteristics of the GNC system are considered.

Then, the guidance law of the main deceleration section under the condition of horizontal velocity constraint at the end is studied.

Based on the correspondence between the orbital parameters of the Kepler orbit and the terminal motion parameters, the terminal motion parameter constraints are transformed into the orbit parameter constraints, so that the trajectory planning problem is transformed into the finite thrust orbit change problem, and then the guidance law is obtained by the least squares correction method.

Next, the guidance law of the main deceleration section under the condition of end height constraint is studied.

Subsequently, the dynamic equation under the guidance inertial polar coordinate system is established, and the target constraint quantity is taken as the state quantity, and the pseudo-spectroscopy method can be used to conveniently obtain the values of some parameters.

On this basis, according to the configuration of a given engine, the range of the final reduction section is studied, and the orbit characteristics in the range are studied, the quaternions are taken as parameters, and the deviation quaternions are introduced to construct quasi-Euler angles to eliminate the duality of the target attitude, and the attitude control is designed by using the time optimal control of the perturbation double integral system, and an optimal control solution is obtained.

In this way, all the data on the final reduction section is obtained.

When to enter this stage, how much power is used in the engine force, what is the thrust angle, and how long is the braking time.

These values were all obtained by Gu Lu after complex calculations.

However, this is the first of six phases.

This took Gu Lu more than an hour.

There are five other stages that follow, which are also quite complex.

"Go ahead!"

Gu Lu looked up and glanced at the time on the wall watch, it was already more than seven o'clock in the evening.

Gu Lu didn't have the heart to eat dinner, and directly knocked on a bottle of fatigue medicine, and continued to start to follow the liver.

At the current rate, he's probably going to be all-nighter.