Chapter 1086 Low and Medium Orbit Communications

The question of necessity was overcome almost the moment Guo Lin stated the project expectations.

However, before the plan can be actually implemented, its feasibility needs to be determined.

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

But it is already July, and there are only three and a half months left until the planned launch window for the first manned spacecraft.

As the most important project at the moment, Shenzhou V cannot be delayed for non-technical reasons.

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

Otherwise you will miss the time window.

Including Luan Wenjie's first thought after listening to the report was to postpone the project appropriately.

But this matter is special after all, and 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, ready to ask for his opinion——

Due to the huge scale of manned space projects, in order to facilitate the integration of resources from various systems, the commander-in-chief is always held in name only by a senior leader.

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

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

"Boss Shen, do you think it would be more appropriate to wait until we carry out Mission No. 6 to conduct this test?"

Luan Wenjie asked tentatively.

This suggestion is not made casually.

In fact, Chinese technicians have been very clear from the very beginning about the disadvantages of relying solely on ground measurement and control networks.

To this end, the plan also specifically planned the "Tianlian" series of synchronous orbit relay communication satellites.

The first launch is planned to take place before the Shenzhou VII mission, around 2007-2008.

The reason why Luan Wenjie is interested in this medium- and low-orbit relay communication constellation is largely to pave the way 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 you a lot of unnecessary trouble.

It should be said that Luan Wenjie's ideas are indeed more prudent.

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

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

But objectively speaking, from the perspective of 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 was rejected by NASA for various outrageous reasons.

It would be a lie to say that I wasn't holding my breath.

The opportunity is right in front of you now. If you miss it, you will never get it again.

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

Although this relay communication test can only be regarded as an external accessory of the Shenzhou V project, and no matter what happens it will not affect the launch mission itself, 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’s not like no one has ever tried to use medium and low-orbit satellites for relay communications.

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

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

"The relay communication systems of the United States and the Soviet Union, as well as the one we are currently planning to build, all operate in geosynchronous orbits. Although low and medium orbits obviously have large capacity, low latency, and flexible networking, there are still a few questions that require your serious answers."

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

This kind of trial by three judges must be nothing new to Chang Haonan.

But for Zhang Weiyong and others, the feeling of oppression is still quite 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 satellites is much greater than that in the GEO orbit, which also brings 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 acted calm and composed, quickly answered in a serious manner:

"In the past, communication satellites had to rely on OFDM technology to achieve wide beams due to their narrow frequency domain. This technology was used to improve the system's frequency band utilization and meet the needs of business and the increase in the number of users. OFDM signals are composed of multiple orthogonal subcarriers. 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 the satellite will be highly sensitive to frequency deviation."

"But the satellite used in this test is only facing individual targets and receiving stations. In addition, a Ka-band signal with a narrow beam is selected, which does not put much pressure on the frequency band utilization. Therefore, 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 is naturally very familiar with these principles.

However, complex systems often affect the entire system, and the problem cannot be solved simply by 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 serious loss of Ka-band during free space propagation, hydrometeors in the atmosphere and atmospheric turbulence will have a serious impact on signal stability. In addition, low and medium orbits also mean that the signal needs to be relayed more than once during transmission. This multi-hop network will further reduce the reliability of the data stream. How can you ensure the low latency and high capacity you are aiming for?"

However, facing the seemingly increasingly aggressive questions, Guo Lin, who was a little reserved at first, suddenly relaxed.

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

But if you ask him about multi-hop networks, he is not sleepy anymore:

"Mr. Shen, regarding the high transmission delay and low transmission rate caused by multiple relay nodes, our Electronic Technology System has cooperated with Aviation Power Group over the past year or so and has basically developed a complete solution with network coding technology as the core. We have tested it on three platforms: ground vehicles, stratospheric airships, and early warning aircraft. The result is that the throughput has increased by an order of magnitude compared to traditional networks."

"Although it is impossible to completely restore the working environment of orbital space in the atmosphere, at least in principle, it can fully meet the application requirements of a decentralized communication network within four hops..."

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

He used to be the deputy director of the Commission of Science, Technology and Industry for National Defense. Although he had left the post long ago, he still had some understanding of the systems under the former Commission of Science, Technology and Industry for National Defense.

Aviation systems are not strong in the field of communications.

If he could come up with something big in this area that even he didn't know about...

Shen Junrong quickly thought of an answer.

"Aviation Power Group..."

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

"Is it Comrade Chang Haonan and his group?"

Obviously, this name still has some weight.

"Yes."

Guo Lin nodded quickly:

"In fact, relying on Mr. Chang's technology, we have successfully developed a theater-level communication and 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:

"In fact, the main part of this project was previously handled by Mr. Chang himself, but now he is busy with the establishment of a new model project, so he entrusted the subsequent testing tasks to us..."

Many factors combined together finally caused the balance in Shen Junrong's heart to gradually tilt.

Of course, this is a serious matter.

The process to be followed is still indispensable:

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