Tower Defense Strategy

How difficult is it to tow an asteroid?

To say it is difficult, it is too difficult.

From a technical point of view, whether it is towed from the front or propelled from the rear, as long as the asteroid is moved, it will interfere with the movement of its mass center of gravity. If the calculation of the mass center of gravity is slightly deviated, it is considered good not to fly out of the solar system, let alone Towed to the target location on the target track.

It's easy to say, and it's really easy, because the principle is very simple.

Just get a hook to fix the asteroid, and turn on the thrust to change its orbit. If the asteroid originally rubbed the earth ball, the thrust required for the change would not be very large.

If there is more time, say several hundred years, then there is even simpler. The tractor and the asteroid do not even need to be physically connected. As long as the tractor has a certain weight, relying on the universal gravitation between the two, it can slowly change the orbit of motion.

Most asteroids belong to two types, iron and ice.

Iron asteroids have an iron content of more than 70%, and a few can reach more than 80%, which are suitable for construction. Don’t think that iron is useless in space, but every kilogram of material going to the sky means a large stack of tickets behind it. The proportion of iron is obviously too large, so it is not used in space, but if it can be obtained from space at a reasonable price , It can still be used as the most commonly used material.

The ice is generally separated from a comet or the Kuiper belt is knocked out of the regular orbit by other celestial bodies. It is suitable for fuel. As for daily use, it depends on how it is affected by cosmic rays and radiation. With the existing technology of Tuqiu, it is difficult to completely purify the radiation in it in a short period of time. However, in case of emergency, it can consume more electricity, strictly control the temperature and distill a few more times, and it is not impossible to drink, but it is necessary to prepare a space medical system. Say it again.

No matter what type of asteroid, it can bring tremendous help to the construction or supply of a new space station, and it is much easier to develop it than to build an industrial chain on the moon.

After a comprehensive discussion, country C decided to give it a try.

This kind of thing is not enough by country C alone. Country F stated that it can coordinate the help of global observing agencies under the premise of keeping secrets to the outside world. Of course, it needs money.

Country F's influence on the earth ball has not expanded to the whole world, but the wonderful national temperament of Country F makes her very popular. If you give money, no one will refuse her. An example is that she will follow others behind her back. Country C cannot do it, because of the strategic and hostile relationship led by Country A, many things cannot be done with money.

With the help of the network of country F, the asteroid capture project launched a global astronomical search.

This kind of project has been under the leadership of the research institute of country A, and there have been several related global cooperations. So this time, country F will pay for it, and everyone is familiar with it.

Within a few days, country C found alternative targets from a large amount of feedback data.

There are three in total.

The diameter of No. 1 is twelve meters, and the length is slightly larger than the diameter. The total mass is estimated to be over 13,000 tons. The advantage is that its trajectory is closest to low orbit. With the help of Homan transfer action (full force reverse thrust before and after perigee), there is capture It is possible that the weight is too large, and the space system is not sure that it will reserve enough fuel in orbit before it enters the perigee.

The second candidate has a smaller diameter, only seven meters in diameter. The data has been repeatedly confirmed by multiple high-altitude observatories. According to spectral analysis, its rock composition is slightly higher (lower density), and it may be the first time to pass the earth ball. Its estimated weight is only 1,500 tons. The flaw is that the perigee height exceeds 2,000 kilometers.

The No. 3 is the largest, more than 20,000 tons, but it also has a little advantage. It is an asteroid that was captured by the earth and moon systems decades ago. Now its orbital speed has stabilized. It uses the Hohmann transfer maneuver to change it into Near circular orbit, the actual energy consumption will not be more than that of No. 1. But because it is too heavy, it still requires a huge expense to lower the orbit later.

After discussion, country C decided to arrest the number two. It could not be too far-reaching. At least the capture ability was verified.

Country F and Country R expressed that they can support a rocket each. They also want to be more generous in the future. They can have more voice in the sky. However, their national power is limited and their mobilization power is far less than that of Country C. They can only mean meaning.

Due to the rich docking experience, this time the load was also sent to low-Earth orbit to dock into a catcher.

The catcher is divided into three parts, the main body, the fuel tank, and the additional thruster. Only the main body is put in place by the rocket of the R country at one time, and the other things are assembled on orbit.

Although the limit has accelerated regardless of the cost, the time is still relatively long.

During this period, a third level two monster, the hypnotist, greeted the surface.

It is the kind of colorful goldfish that has a huge phantom and mimics other first-level monsters into its own.

There are misfortune and luck, both of which are because hypnotists are relatively timid.

Because of being timid, the hypnotist doesn't like to fly, but swims in the sea for a long time. As a result, there are no suitable weapons on the earth ball that can effectively attack it.

At the same time, because of his timidity, the hypnotist would not go deep inland after landing, but he would quickly return to the sea after a little damage. At the same time, the speed at which it moves in the sea is not as suffocating as a star breaks several time zones a day.

Finally, when the cargo ran to the junction of West Central Continent and Central Central Continent for the third time, it was locked down because of the shallow water depth. Three nuclear-armed countries dropped bombs continuously, killing it offshore.

After the hypnotist passed by, and two more level one monsters passed, and country C singled out one, the asteroid capture operation officially began.

First, through the UN notification, Congress C launched a high parabolic ballistic missile.

In fact, it is not a ballistic missile, it is a missile that was prepared in low orbit in advance, and there is also a missile that has not been activated by the first-level rocket.

This is also a last resort, because according to repeated calculations, without cutting off a section of the asteroid's head to continue to reduce its weight, at least another ten cans of fuel will be sent up in order to drop it to the perigee 1000 kilometers orbit.

In short, the missile launches first, the ignition timing and trajectory are all calculated repeatedly through super-calculation, but the shape of the cut and the subsequent trajectory offset have to be luck.

In the official action, the missile hits accurately.

A group of satellites in low orbits that have adjusted their attitudes to face the asteroids, take pictures and take pictures of the side band and the side band, and quickly calculate the orbital offset of the remaining subjects.

According to the plan, the best result is to go up a missile and directly brake the asteroid's speed to the level of an artificial satellite, so that the subsequent fuel consumption is relatively small, and you can even consider using the trap in the future.

But the explosion of this thing, without enough preparation time and site survey, certainly can not be so accurate.

In the end, the remaining body of less than a thousand tons is still two hundred meters faster than the artificial satellite at the same altitude.

It doesn't look like much, but it takes a thousand tons of things to get a speed of two hundred meters per second, and it consumes a huge amount of fuel even in space.

However, the missile attack still greatly reduced the speed of the asteroid, so its orbit has undergone tremendous changes. The apogee distance has been reduced from three million kilometers to... just about to be caught and hit by the moon.

It's a bit too close, I can only get on it.

The trap that was on standby at an altitude of 1800 kilometers continued to ascend and merged with the asteroid before perigee 1900 kilometers.

What? Fragment?

The fragments thousands of kilometers away are distributed non-uniformly on the spherical surface and scattered at non-uniform speed, most of which are away from the direction of the earth ball, and there is almost no chance that the trap will be hit directly.

After more than ten hours of fine-tuning the orbit, the trap grabbed the asteroid's main body, and only three hours and twelve minutes were left from the perigee when it was punched and grasped.

After the capture, it entered a more intense stage. Through the data returned by the various sensors of the main body of the capture, the surface country C mobilized dozens of supercomputers to calculate various aspects, the position of the overall mass center of gravity, and how to adjust the overall thrust direction. Follow-up What is the thrust direction and so on.

One hour and fifty-two minutes remaining from the perigee.

The catcher ignited for the first time after a successful capture, and only used 2% of the thrust.

Here is a feedback of the previous calculation parameters. The moving direction of the asteroid, whether the grasping structure is displaced, etc., will determine the next strategy.

With one hour and twenty-six minutes remaining from the perigee, the propulsion strategy was slightly adjusted, and the thrust was increased to 16%.

What needs to be explained is that the propeller used in space this time is very different from the one used on the ground. It is the type of engine prepared for the lunar landing plan. The thrust is small and the fuel burning speed is relatively slow, but per ton of fuel. The number of meter seconds (specific impulse) produced is greater.

In terms of specific numerical comparisons, the first stage of the rocket used on the surface has a specific impulse between 200 and 300. Even in an ultra-thin atmosphere above 90 kilometers, the specific impulse does not exceed 320. The specific impulse value used this time has reached 450, and the same fuel has a lot more thrust.

Why doesn't the ground use such a powerful engine?

First, the ground ratio cannot be improved. The surface performance of this type of engine is not as good as that of a normal first-class engine.

Second, there is no way to make it bigger. To obtain additional specific impulse, the fuel needs to be pressurized additionally, and it is pressurized after combustion. If it is slightly larger, the material will melt. Because it is not very large, it is calculated with a mechanical unit such as kilonews. The actual thrust is very small, and acceleration cannot be given at all in the environment of high gravity.

In short, relying on the fuel prepared before, the propulsion group composed of five thrusters, after the capture is completed, it must be pushed for thirty to thirty-two minutes to run out of fuel, unlike ordinary rockets, which takes a few hundred seconds. Burn hundreds of tons of fuel.

The asteroid was one hour and ten minutes away from the perigee, and the trap engine stopped, quietly waiting for the opportunity of Hohmann's transfer.

The perigee time limit is 18 minutes and 50 seconds, and the engine starts at full power!

Then there is the long Homan transfer time.

The asteroid's orbits based on ground observations and calculations keep changing apogee, from hitting the moon to being bounced by the moon, and then twisting back into an orbit around the earth, and then the apogee keeps getting closer to the earth ball.

Perigee (front) in the past seventh minute ~www.wuxiaspot.com~ The trap is turned off again, and the remaining fuel is 8%. The previous perigee has become an apogee.

Perigee (current), 600 kilometers above the ground, and a half-round orbit about 90 minutes.

To make good use of fuel, the next step is to wait until the current perigee before performing the Homan transfer maneuver.

In the first capture operation, when the capture device finally ran out of fuel, the target asteroid's perigee was 600 kilometers, and the apogee was 900 kilometers. It did not reach the expected best state, at least not the worst.

Although it is still far away from the space station, the height fluctuations of this kind have made it possible to refuel.

Asteroids are preparatory materials. No personnel, power, or equipment are in place for the new space station, and there is no need to get it in place now.

In addition, when the asteroid enters the corresponding orbit and enters a relatively stationary and sufficiently close position with the space station, it also needs to wait for a window. The most recent window takes eight days, and there is only one window every ten days thereafter.

Country C's actions were too big this time, and countries with outer space observation capabilities expressed shock and demanded country C to give a reasonable explanation.