On April 29, the Long March 5B carrier rocket was successfully launched at the Wenchang Space Launch Site in Hainan. It successfully sent the Tianhe Core Module, the first spacecraft of my country’s space station project, into the scheduled orbit, and the launch mission was a complete success.
According to Gan Keli, deputy commander-in-chief of the space station, in the development of the core module, the Eighth Research Institute of China Aerospace Science and Technology Corporation undertook the power subsystem, docking and transposition mechanism subsystem, measurement and control communication products, resource module structure and assembly and The task of cable network development. Among them, the power subsystem is one of the four key technologies for the mission of the entire core module, acting as the future space station “space power station”.
First use of large-area flexible solar panel wings
According to Luo Bin, deputy chief designer of the space station, the Tianhe core module uses a large-area deployable flexible solar cell wing for the first time, with a double-wing deployment area of up to 134 square meters. This is the first time that my country has adopted a flexible solar wing as an energy source for a spacecraft. . The flexible solar wing integrates four brand-new technologies, including large-area lightweight, repeatable development and high reliability, 10-year long life in orbit on low orbit, and high load-bearing capacity with rigidity and flexibility.
Compared with the traditional rigid and semi-rigid solar cell wings, the flexible wings are small in size, large in deployment area, and high in power-to-weight ratio. A single wing can provide 9kW of electric power for the space station, which can meet the normal operation of all equipment in the cabin, and also It can completely guarantee the daily life of astronauts in the space station.
Compared with the traditional rigid and semi-rigid solar wing, the flexible wing is only one book thick after being folded, which is only 1/15 of the rigid solar wing. The substrate is made of ultra-thin lightweight composite materials, and the coating thickness of the glue layer used to protect the space environment is also strictly controlled.
Whether the flexible wing can be successfully deployed is directly related to the success or failure of the space station mission. The core module solar wing uses 6 active mechanisms to unfold in three dimensions and five steps, just like doing a set of “space broadcasting operations.”
First, the 15-round pyrotechnics “warm-up movement” detonated to release the fixation of the solar wing and the small column bulkhead; then the lifting mechanism “pitch motion” to raise the solar wing from the bulkhead; then, the locking mechanism was deployed to “expand the chest” “Motion” expands the two solar cell arrays to both sides, and the restraint release mechanism “rotating motion” releases the constraints of the storage box; finally, the “stretching motion” of the stretching mechanism drives the solar battery wings to fully expand. Each prescribed action has undergone a large number of ground verification tests to ensure standard posture, skill and smoothness.
The unfolding process lasts for 40 minutes, and several stretch mechanisms are pushed out one by one, driving the solar wing to unfold outward, and it is like an accordion being slowly unfolded, so it is vividly called the “accordion” unfolding method.
Another special function of the core cabin solar battery wing is that the entire wing can be disassembled and transferred on orbit. Taking into account that after the completion of the subsequent space station construction, the solar cell wings of the core cabin will be blocked, which will affect power generation. The two solar cell wings can be disassembled and transferred outside the cabin by the astronauts and robotic arms, and installed in the experimental cabin for subsequent launches. On the tail truss, and rebuild the power supply channel on orbit, this is also known as the “on-orbit energy expansion function.”
Good long-term living conditions with “lithium”
When the space station runs into a shadow area where the sun cannot be irradiated, the entire cabin is powered by a lithium-ion battery. How to ensure the safety of lithium batteries? After long-term research, the research personnel of the 811 Institute of the Eighth Academy have designed a long-life, large-capacity, and high-safety lithium-ion battery that meets the operational needs of the space station from multiple perspectives such as development, use, and replacement.
According to reports, the biggest safety problem of lithium batteries is “thermal runaway.” In this regard, the space station lithium battery has adopted a variety of effective measures during the development: from the source, ceramic diaphragms are used to provide good internal short-circuit prevention measures; flame-retardant materials are used in the battery pack to prevent high temperature from burning; in the battery pack Use pressure relief materials to provide space for the expansion of the single battery; use a fully enclosed lithium-ion battery box structure design to provide a safe and reliable environment for the cabin.
There are 6 sets of lithium-ion batteries in the core compartment of the space station, each with 66 single cells. The difficulty when using lithium batteries is to achieve overcharge protection for each single battery. The researchers of 811 Institute have designed a set of intelligent lithium battery management system to realize high-precision, high-reliability, and high-safety lithium battery charging control.
For example, the first domestic use of high-precision lithium battery collection system, so that the acquisition accuracy is higher, and the control points are more accurate; the first domestic use of high-efficiency, high-voltage and high-power charging modules, the three-level protection mechanism is enabled during charging, and electricity is guaranteed under any circumstances. Safe; at the same time, temperature monitoring is implemented during the charging process. When the charging temperature is higher than the set safe temperature value, the battery charging of the unit is immediately stopped.
During the space station’s more than 10 years of in-orbit operation, astronauts need to regularly replace lithium batteries in orbit. How to ensure the safe operation of astronauts without affecting the normal power supply of the space station?
The developers have provided “double insurance” for the lithium battery replacement operation. The core compartment has two power channels. When one of the channels needs to be replaced with a battery, the other channel is used as the main power supply. And each power channel adopts the “2+1” unit working mode. When the battery in any unit needs to be replaced, the unit is powered off, and the remaining two units can ensure the normal power supply of this channel.
In addition, when astronauts replace lithium batteries, the high-voltage battery pack poses a safety hazard. To this end, the developers installed two parallel section switches in the lithium-ion battery module. By reducing the voltage of the battery pack to the safe voltage range of the human body, it meets the 36-volt safety voltage requirement of the human body and protects the personal safety of the astronauts during on-orbit maintenance.
Millions of tests to ensure foolproof
The core cabin is the aircraft with the longest life design requirements in my country. The 10-year flight in orbit puts forward the highest requirements for the long life of all products.
As an extra-vehicle product, the solar wing has to face an extremely harsh space environment. In addition to experiencing 88,000 ±100°C high and low temperature cycles, it also has to withstand atomic oxygen, plasma, ultraviolet radiation, and ionization radiation in the low-orbit environment. And other space environment tests.
In order to make the solar battery wing have good adaptability to the space environment, the flexible solar battery wing development team of the 805 Institute of the Eighth Academy has carried out more than 3 years of program demonstration and comparison work, gathered top experts from related industries in China, and summarized 5 impacts. The key research project for the long life of the solar wing has undergone a large number of ground simulation long life tests.
For example, the tension mechanism on the solar wing is a set of constant force spring rope system. Through its continuous expansion and contraction, it can ensure the sufficient rigidity and attitude control of the solar wing in the high and low temperature environment. The life test requirement of the tensioning mechanism is 88,000 times, but in order to ensure that it is “slacks, flexible” and “safe” in the 10-year on-orbit conditions, the team has gone through many years of research and completed 400,000 heat cycles on the ground. Vacuum fatigue life test and 1 million normal temperature and normal pressure life tests have fully verified the high reliability and long life of the product.