Chapter 1086 Medium and low orbit communications


    The issue of necessity was overcome almost the moment Guo Lin stated his expectations for the project.


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


    Although Zhang Weiyong and others 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 now it’s July, with only three and a half months left before the planned launch window for the first manned spacecraft.


    As the number one project in the world right now, Shenzhou 5 cannot be delayed due to non-technical reasons.


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


    Otherwise, you will miss the time window.


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


    But this matter is special after all. Even if he is the leader of the space agency, he cannot make the decision alone.


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


    Due to the huge scale of the manned space project, in order to facilitate the integration of resources from various systems, the overall commander is always assumed by senior leaders.


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


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


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


    Luan Wenjie asked tentatively.


    This suggestion is not given casually.


    In fact, China''s technical personnel have been very clear about the disadvantages of relying solely on ground measurement and control networks from the beginning.


    To this end, the "Skylink" series of synchronous orbit relay communication satellites are also specially planned in the plan.


    It is planned to launch the first one before the Shenzhou-7 mission, that is, around 2007-2008.


    The reason why Luan Wenjie is interested in this low-to-medium orbit relay communication constellation is largely to provide a front-line for the Tianlian system.


    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 Shen Junrong''s analysis just now, he has realized the publicity value of this matter.


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


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


    Especially since 1994, China has applied many times in the hope of participating in the International Space Station project, but has been rejected by NASA for various outrageous reasons.


    To say that I wasn’t holding my breath was definitely a lie.


    Now the opportunity is in front of me. After passing this village, there is no such store.


    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 5 project, no matter what happens, it will not affect the launch mission itself. But if the plan is made but cannot be executed, or something goes wrong in the middle of the execution, then The effect is counterproductive.


    After all, it’s not like no one has tried using mid- and low-orbit satellites for relay communications.


    However, the eventual bankruptcy of the famous Iridium satellite project still cast a haze on this technical route.


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


    "The United States and the Soviet Union, as well as the relay communication system we are currently planning to build, all work in geosynchronous orbit. Although the medium and low orbits obviously have large capacity, small delay, and flexible networking, there are also several problems that require you to Answer carefully."


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


    Chang Haonan must have been used to this kind of three-court trial. But for Zhang Weiyong and the others, the sense of oppression is still quite enough.


    The three of them immediately sat up straight.


    "First of all, the relative angular velocities of satellites in low and medium orbits between the satellite and the earth and between the satellite and the satellite are much larger than those in GEO orbits, which also brings stronger Puller frequency deviation and Doppler change rate. Have you considered any solutions? "


    When faced with the boss''s question, even Zhang Weiyong, who had acted calmly outside before, quickly answered in a clear-eyed manner:


    "In the past, communication satellites achieved wide beams due to their narrow frequency domain range. They generally needed to rely on OFDM technology to improve system band utilization and meet business needs 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 at the transmitting end and the local oscillator frequency at the receiving end, the orthogonality between the sub-carriers will be seriously affected, thus showing extremely high sensitivity to frequency deviation. "


    "However, the satellites used in this test are only oriented to individual targets and receiving stations. Moreover, they also chose to implement Ka-band signals with narrow beams. There is not much pressure on band utilization, so filter multi-carrier technology can be used As a candidate to enhance the system’s anti-frequency offset performance…”


    “…”


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


    However, complex systems often affect the whole system, and problems 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 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 became more relaxed—


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


    But if you want to 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. It is a complete solution with technology as the core and 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.


    To say that he could do something big 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."


    (End of chapter)