After more than 6 years, the launch record of the mainland's "one arrow and many stars" was finally broken again - at 11:06 on February 27, 2022, the Long March 8 (hereinafter referred to as "Changba") Yao'er carrier rocket was successfully launched, and a total of 22 satellites were successfully sent into the predetermined orbit.
Compared with the "one arrow and 20 stars" of the Long March 6 on September 20, 2015, the increase in the number of launch satellites by only 10% seems to be far from enough for it to tear out the space for brushing screens in the airtight media platforms blocked by Russian-Ukrainian news – but in fact, this launch will have a profound impact on the development of space technology on the mainland.
As a rocket type positioned for commercial applications, the Changba Yao-2 rocket is a bold attempt, and "launching a multi-orbit satellite with one arrow" is just one of them.
The Long March 8 Yao-2 carrier rocket adopts non-toxic and non-polluting propellant, the whole arrow is about 48 meters long, the diameter of the core stage is 3.35 meters, the diameter of the core stage is 3.0 meters, the take-off weight is about 198 tons, and the take-off thrust is about 240 tons, which can realize the carrying capacity of 3 tons in the sun-synchronous orbit. Image source China Aerospace Science and Technology Group Weibo "one arrow and many stars"
At 5:28 a.m. on September 20, 1981, the Storm 1 carrier rocket took off from Jiuquan Base (the predecessor of Jiuquan Satellite Launch Center). After 7 minutes and 20 seconds, the three satellites (three scientific experiment satellites of Shijian-2, Shijian-2A, and Shijian-2B) separated from the rocket one by one and entered the predetermined orbit. So far, after the former Soviet Union, the United States and the European Space Agency, China has become the fourth country to master the "one arrow and multiple satellites" launch technology.
"One arrow and multiple stars", that is, carrying multiple satellites on a launch vehicle. At present, a total of 6 countries in the world have mastered this technology. After 27 years of realizing "one arrow and multiple stars" on the mainland, India and Japan have also launched their own "multi-star" rockets. In the decade since, the record for the number of satellites launched at one time has continued to be rapidly refreshed, and by 2017, the number of satellites carried by India on a rocket has reached three figures, successfully achieving "one arrow and 104 stars".
Things have progressed here, and the layman may have returned to the taste. When the number of satellites carried by a single rocket increases to a certain value, the changes caused by the simple increase in the number may only stay in the category of quantitative change. In other words, the number of satellites launched is not necessarily proportional to the degree of proficiency of space technology.
At present, the "one arrow, many satellites" technology is divided into two categories: one is to launch all payloads into the same orbit; the other is to launch different satellites into their respective orbits. The former is the method used by India's "one arrow and 104 stars" and most of the starlink satellites, and the latter is the method used by the long eight remote two. Two types of launches, corresponding to different launch vehicle requirements.
The first type of launch mission is to shut down the last sub-stage of the launch vehicle, and only need to release the satellites in turn. Among them, the main issue to consider is the possibility of collisions after the release of each satellite. The solution to this problem is not difficult, that is, to control the speed or time when the satellite is released, so that it is slightly different.
As for launching multiple satellites into different orbits, it is not so simple. It requires the launch vehicle to meet the technical level of the former on the basis of entering the initial orbit, but also after entering the initial orbit, still have the ability to change orbit, which is not a conventional launch vehicle can do. It requires a complete process solution for satellites from "getting in the car" to "getting out of the car".
Taking the long eight remote two as an example, the first step is to rationally arrange these satellites in the rocket fairing. The 22 satellites carried by the Changba Yao'er mission belong to 7 different satellite manufacturers, and the size, size and weight of each satellite are quite different, so when laying out, first consider how to effectively use the space inside the fairing.
Image source China Aerospace Science and Technology Group Weibo
Combined with the mission requirements, the design team sorted out the traditional satellite structure and designed a new three-layer multi-satellite distributor, which finally provided a three-layer "seat" for the "passenger". The three-layer multi-star distributor consists of a tapered bracket, a central load-bearing cylinder and a disc platform from bottom to top. In the end, the layout of the 22 satellites was: the conical bracket (following the structure of the Changba Yaoyi rocket) carried 2 satellites, the central load-bearing cylinder carried 14 satellites, and the disc platform carried 6 satellites.
For some satellites with large diameters that are not suitable for side mounting, the design team has designed a new disc platform above the central load-bearing cylinder to make the installation operation of large-diameter satellites more concise, and there is no interference from other satellites in the direction of separation.
Image source China Academy of Launch Vehicle Technology WeChat public account.
The satellites were finally successfully loaded into the fairing, and then the problem of getting them to "get off" safely and accurately was to solve the problem, which was one of the biggest problems encountered by the design team.
The first thing to consider is the safety of satellite near-field separation. In the process of separating the satellite from the arrow body, it is necessary to consider the different unlocking methods of the satellite and the movement deviation caused by the separation of energy. In some cases, these small deviations can reduce the distance between satellites, which in turn threatens the safety of the arrow body.
According to the different separation mechanisms of the satellites, the design team conducted multiple rounds of simulation calculations for all the arrow body and satellite deviations, so that the dynamic gap between the satellites in the near-field separation process was retained to ensure the safety of near-field separation.
"The greater the number of satellites, the greater the risk of collisions in orbit after separation, and far-field separation safety is also a key consideration for designers." Li Jinglin, who is in charge of ballistic design, introduced that the separation speed, separation direction and separation sequence are the key factors affecting the subsequent trajectory of the satellite. Staggering 22 satellites in a limited external separation orbit to avoid interference between two or two satellites is a challenge for designers.
22 satellites plus the end stage of the rocket is 23 separators, in order to ensure the safety of separation between each other, the design team to calculate and analyze the orbit parameters of each satellite operation, the relative distance between the two of the 23 separators for a long period of simulation, observation and assessment, and according to the satellite layout and design separation scheme, took 12 separation actions, in turn the 22 satellites gradually separated out, and by constantly adjusting the attitude of the final arrow body, to achieve the separation direction adjustment of different satellites, Ensure the safety of each satellite in the near and far field, so that 22 satellites can "get off" with peace of mind.
Specific to the design of the separation action, it is not an easy task. The analysis of the relative distance between the two of the 23 separators itself is very large, and on this basis, it is also necessary to maintain the space base visible in the rocket attitude adjustment process, which requires that the arrow body attitude adjustment angle cannot be too large. Under the attack of multiple requirements, the difficulty also increases: "This is an optimization problem equivalent to multiple objects, multiple constraints, long cycles, and needs to be solved through multiple rounds of iteration, and the amount of far-field separation calculations has increased several times than before." ”
To this end, the design team specially developed a multi-star far-field analysis tool, so that "through a simulation, the calculation of the respective velocity positions of the 23 separators can be automatically completed, as well as the calculation of the relative positions between the two, which not only greatly improves the calculation efficiency, but also improves the accuracy of the far-field analysis." ”
In the end, according to the separation method of each satellite, combined with various factors such as mission requirements, the second sub-stage made corresponding adjustments in the yaw and pitch angle, and the 22 satellites were finally successfully deployed into orbit in 12 times.
"This mission requires a total of 22 satellite separations, a total of 12 separation actions, creating a new record for China's aerospace." It can be said that the Long March 8 rocket in the separation of stars and arrows is like jumping a 'ballet', and the final release of 22 stars is like 'Tiannu Scattered Flowers'. Duan Baocheng, eighth deputy commander of the China Academy of Launch Vehicle Technology, concluded.
Customized for commercialization
If you have the heart to observe, it is easy to find that the Long Eight Yao-2 carrier rocket looks different from the previous rockets: the booster at the bottom is gone, becoming a complete "light rod" rocket.
In fact, this rocket without a booster is the new configuration of this type of rocket. Chen Xiaofei, deputy chief designer of Changba, said that compared with the Yaoyi rocket, the biggest difference in the shape of the Changba Yaoyi rocket is the cancellation of two boosters, from a two-stage and a half configuration to a two-stage tandem configuration.
On the left is the Yao'er rocket (pictured by Song Tao of China Aerospace Science and Technology Corporation), and on the right is the Yaoyi rocket (picture source China Aerospace News).
The Changba rocket is a new generation of main medium-sized carrier rockets in the mainland, and is also the commercial rocket with the strongest capacity in the mainland's low- and medium-orbit capacity, which successfully made its first flight in December 2020, filling the capacity gap of 3 tons to 4.5 tons in the continental sun-synchronous orbit carrying capacity, and can undertake more than 80% of the mainland's low- and medium-orbit launch tasks. The "light pole" Long March 8 Yao-2 carrier rocket without boost has a carrying capacity of 3 tons
Changba is aimed at the future launch market demand and specially built a type of rocket, as a rocket positioned in commercial applications, cost has become a factor that must be considered, Changba Yao'er rocket on this basis has made further adjustments and attempts.
Using a new configuration is one of the attempts. Hu Huibiao, director of the Changba Rocket Project Office, introduced that the use of the new configuration can achieve "multiple things in one fell swoop". In addition to testing the correctness, coordination and matching of the new configuration, and opening up the medium-sized main rocket market, reducing the two boosters can also alleviate the pressure of production, assembly and testing, shortening the development cycle and reducing the development cost.
"In the future, the demand for human beings to enter space is increasing, and the demand for space infrastructure construction is increasing, so it is urgent to change the launch site process and shorten the rocket development cycle." Xiao Yun introduced.
To this end, the Changba Yao-2 rocket also adopts the design idea of "modularization" and "combination". As early as the beginning of development, the designers fully took into account the state of the rocket without a booster and included it in the assessment envelope of the Yaoyi rocket. Therefore, the Yao-2 rocket does not need to make large-scale changes, only need to make adaptive adjustments for the payload and flight trajectory. In the end, from the successful first flight to the completion of the assembly general test and the factory conditions, the Changba Yao-2 rocket took only 1 year.
The height of the fairing was shortened from 8 meters to 5.4 meters. Image source China Academy of Launch Vehicle Technology.
In addition, the height of the fairing of the rocket has also been shortened from 8 meters to 5.4 meters, which reduces the loading of key parts of the whole arrow, and the launch cost is also reduced. Of course, this is not all due to cost considerations. From a technical point of view, because the satellites that need to be launched are smaller and lighter in weight, they do not need to use a fairing as large as the Long Eight Yaoyi rocket. From the perspective of aerodynamic appearance, a shorter fairing can reduce the load, relax the rocket launch release conditions, improve the probability of rocket launch, and lay the foundation for subsequent high-density launches.
The "sharing" model is also based on cost considerations – the cost of satellite carriers. The 22 satellites launched this time are mainly optical remote sensing satellites, which are mainly used for Earth observation, low-orbit Internet of Things communication, space science experiments, and can provide resource surveys, synthetic aperture radar data support, Internet of Things decentralized terminal data collection, on-orbit scientific tests and technical verification, and vessel information collection and processing in Hainan and the coastal areas of the province. These satellites are from 7 domestic commercial space companies. Of course, the cost is also shared by 7 companies.
"Simply put, it is a carpooling scheme that provides users with an affordable launch service, and the threshold is greatly reduced." Xiao Yun, commander-in-chief of the Changba rocket, said. With the successful exploration experience of the Changba Yao-2 rocket, the rocket academy has stronger confidence in promoting the normalization of shared launches.
At present, the fastest final assembly of the Long Eight rocket is 23 days. However, after the final assembly, from the Tianjin plant to the launch site, it is also necessary to carry out the process of fireworks installation and unit testing. If you build a final assembly test plant near the launch site, you can combine the launch site test and the factory test into one, save a series of testing, inspection, and transfer steps, compress the cycle of the rocket at the launch site, and adapt to the future market demand for the rapid launch of the Long Eight rocket.
Through the efforts of the Changba rocket team, at present, the construction of the Hainan assembly test plant has begun, and the launch station is also in the process of demonstration. Once completed, a Long Eight rocket launch can be achieved in a week, and it is expected to launch 50 times a year, and the future of the "Star Sea" is promising.
Resources
China Aerospace Science and Technology Corporation's "Changba New Configuration will implement the "One Arrow, 22 Stars" | What is "one arrow and many stars"? 》
China Academy of Launch Vehicle Technology "22 Stars: Sit in Line, Go Down, and Accurately Reach the Destination"
Science and Technology Daily "One Arrow 22 Stars! Long eight, record-breaking! 》