Chapter 1086 Low and Medium Orbit Communications

The question of necessity was almost crossed the moment Guo Lin spoke of the project's expectations.

However, before the plan is truly implemented, feasibility must be determined.

Although Zhang Weiyong and his team seem to have made some preparations, and there are ready-made platforms for small satellites under 100 kilograms, which do not require a long production cycle.

But it is already July, and there are only three and a half months left before the launch window of the first manned spacecraft in the plan.

As the top project at the moment, Shenzhou V cannot be postponed for non-technical reasons.

Therefore, this relay communication constellation cannot be affected by any accidents.

Otherwise, the time window will be missed.

Including Luan Wenjie's first thought after listening to the report, it is to postpone this project appropriately.

But this matter is special after all, even as the head of the space agency, he cannot make the decision alone.

So, he looked at Shen Junrong, who was sitting on the other side of the office, and prepared to ask for his opinion--

Due to the huge size of manned space projects, in order to facilitate the integration of resources from various systems, the commander-in-chief has always been a senior leader in name only.

Therefore, although the latter is nominally only the deputy commander-in-chief, he has a very high say in the operation.

What's more, the other party is also responsible for building the entire measurement, control and communication system.

"Mr. Shen, do you think this test... is it more appropriate to wait until the No. 6 mission is carried out?"

Luan Wenjie asked tentatively.

This suggestion is not just a casual one.

In fact, the technical staff of China have been very clear about the disadvantages of relying solely on the ground measurement and control network from the beginning.

For this reason, the "Tianlian" series of synchronous orbit relay communication satellites are also specially planned in the plan.

It is planned to launch the first satellite before the Shenzhou VII mission, that is, around 2007-2008.

The reason why Luan Wenjie is interested in this low- and medium-orbit relay communication constellation is largely to prepare for the Tianlian system in advance.

But for him, there is almost no technical difference between testing now and testing two years later.

On the contrary, it can save a lot of unnecessary trouble.

It should be said that Luan Wenjie's thinking is indeed more stable.

But after the analysis just now, Shen Junrong has realized the publicity value of this matter.

The Columbia accident is certainly a tragedy for the entire human space industry.

But objectively, from the perspective of the competition for discourse power, it is not entirely a bad thing.

Especially since 1994, China has applied many times, hoping to participate in the International Space Station project, but NASA has rejected them all for various outrageous reasons.

It is absolutely false to say that I am not holding my breath.

Now the opportunity is in front of us. If we miss this opportunity, we will never have it again.

But on the other hand, Luan Wenjie's concerns are indeed reasonable.

Although this relay communication test can only be regarded as an external accessory of the Shenzhou V project, no matter what happens, it will not affect the launch mission itself, but if the plan is well made but cannot be executed, or something goes wrong halfway through the execution, the effect will be counterproductive.

After all, it is not that no one has tried to use medium and low orbit satellites for relay communication.

But the famous Iridium project eventually failed, which still cast a shadow on this technical route.

Therefore, after careful consideration, he did not choose to answer immediately, but turned to the other side:

"The United States and the Soviet Union, including the relay communication system we are currently planning to build, all work in geosynchronous orbits. Although the medium and low orbits obviously have large capacity, low latency, and flexible networking, there are also a few questions that require you to answer seriously."

The atmosphere in the entire office suddenly became serious, and even the temperature seemed to drop several degrees suddenly.

This kind of three-court trial must be nothing new to Chang Haonan.

But for Zhang Weiyong and others, the sense of oppression is still a bit enough.

The three of them sat up straight immediately.

"First of all, the relative angular velocity between the satellite and the ground and between the satellite and the satellite in the medium and low orbit satellite is much greater than that in the GEO orbit, which also brings about a stronger Doppler frequency deviation and Doppler change rate. Have you considered a solution?"

Faced with the boss's question, even Zhang Weiyong, who had previously shown a calm and calm appearance, quickly answered in a serious manner:

"In the past, communication satellites had a narrow frequency domain range to achieve a wide beam. Generally, they needed to rely on OFDM technology to improve the system's frequency band utilization to meet business needs and the increase in the number of users. The OFDM signal is composed of multiple orthogonal subcarriers superimposed. When there is a frequency deviation between the carrier frequency of the transmitter and the local oscillator frequency of the receiver, the orthogonality between the subcarriers will be seriously affected, and then it will show extremely high sensitivity to frequency deviation. "

"But the satellite used in this test is only aimed at individual targets and receiving stations, and the Ka-band signal with a narrow beam is also selected. There is not much pressure on the frequency band utilization, so the filter multi-carrier technology can be used as a candidate to enhance the system's anti-frequency deviation performance..."

"..."

As a communications expert, Shen Junrong naturally knows these principles very well.

But complex systems often affect the whole body, and it is not easy to solve the problem by simply introducing a new technology.

Otherwise, Iridium would not have gone bankrupt so easily.

Therefore, almost as soon as Zhang Weiyong finished speaking, he continued to ask:

“But in addition to the severe losses suffered by the Ka-band during free space propagation, hydrometeors and atmospheric turbulence in the atmosphere will have a serious impact on signal stability, and the medium and low orbit also means that the signal needs to pass through more than 100 kilometers during the transmission process. Once relayed, this multi-hop network will further reduce the reliability of the data flow. How to ensure the low latency and high capacity you aim for? "

However, in the face of seemingly increasingly aggressive questions, Guo Lin, who was a little reserved at first, suddenly seemed to relax——

I may not know much about things in the satellite field.

But if you ask about multi-hop networks, he won’t be sleepy:

"Mr. Shen, regarding the problems of high transmission delay and low transmission rate caused by multiple relay nodes, our Electronic Technology System has cooperated with the Aerospace Power Group for more than a year and basically developed a network coding system. A complete solution with technology as the core has been tested on three platforms: ground vehicles, stratospheric airships and early warning aircraft. The result is an order of magnitude increase in throughput compared to traditional networks. "

"Although there is certainly no way to completely restore the working environment of orbital space in the atmosphere, at least in principle, it can fully meet the application needs of a centerless communication network within four hops..."

After hearing this answer, Shen Junrong's expression changed slightly.

He also served as deputy director of the Commission of Science, Technology and Industry for National Defense in the past. Although he has resigned long ago, he still has some understanding of the systems under the former Commission of Science, Technology and Industry for National Defense.

Aviation systems are not known for their expertise in communications.

If he was to say what great work could be done in this area that even he didn't know about...

Shen Junrong quickly thought of an answer.

"Aviation Power Group..."

He gently tapped the armrest of the sofa with his right hand:

"Is it Comrade Chang Haonan and the others?"

Obviously, this name still carries a certain weight.

"That's right."

Guo Lin nodded quickly:

"In fact, relying on Mr. Chang's technology, we have successfully developed a theater-level communication command system, so we will further consider testing it on a space-based platform."

Although it is not a project within the system, Shen Junrong has heard about the new data link.

At this time, Guo Lin added:

"Actually, the main part of this project was previously handled by Mr. Chang himself, but now he is busy with the establishment of new model projects, so he entrusted the follow-up testing tasks to us..."

Many factors came together, and finally the balance in Shen Junrong's heart gradually began to tilt.

Of course, this is a big deal.

The process that needs to be followed is still indispensable:

"You should integrate the relevant technical solutions into a report as soon as possible. This matter... needs to be discussed by the Manned Space Engineering Command before it can be decided."