# UKF-Based State Estimation for Electrolytic Oxygen Generation System of Space Station
## 2 Operation Analysis and Working Principle of EOGS
### Operation Analysis of EOGS  
The role and working process of the electrolytic oxygen system in the environmental control life insurance system are shown in Figure 1. During the operation of the space station's ECLSS, the EOGS receives materials from the urine treatment system and the water treatment system, generates deionized water after certain treatment, and then uses electricity to electrolyze the deionized water to generate oxygen and provide it for the astronauts in the cabin. If there are some faults in the electrolytic oxygen system and oxygen supply is insufficient, astronauts are required to promptly open the redundancy spare oxygen cylinders in the space station to continue supplying oxygen for them.  
The specific work flow of EOGS is shown in Figure 2. The specific operation process of the whole system is that the electrolytic water first enters the circulating water storage tank, and then enters the electrolytic core after being pressurized by the circulating pump together with the water that was not completely electrolyze  
Figure 1: The operation of ECLSS in space station.  
pump plays a role in providing fixed flow water for the electrolytic core. The electrolysis of water by the electrolytic core has certain electrolysis efficiency. Only a part of the electrolytic water can produce electrolysis reaction in unit time, generating oxygen and hydrogen, and generating water vapor due to the reaction heat. The other part of water changes into water vapor. It carries the electrolysis heat and oxygen from the anode to leave the electrolysis unit. Then, after the heat exchanger completes the heat exchange, it is separated from the hydrogen at the water gas separator. The oxygen gas enters the cabin, and the water enters the circulating water storage tank. The hydrogen generated by the reaction carries a small amount of water and heat away from the cathode. After heat exchange, it needs to be separated with water and then discharged from the tank. The separated water also needs to enter the circulating water storage tank for reuse. The core component of the oxygen production system of space station is the electrolytic core, which is composed of several electrolytic cells described above. The whole oxygen production system is composed of circulating water tank, water vapor separator, pipeline and other components. The water source of the electrolyzed oxygen production equipment includes human metabolic water, mainly urine. Since the battery of the electrolysis oxygen production system can provide stable direct current, the direct power supply of the electrolysis oxygen production system comes from the battery of its own system. The electrolysis oxygen production system is integrated into the space station's power supply plan as a whole, and the electrolysis battery's electricity comes from the space station's power bus. The overall power of the space station comes from PV. Hydrogen production and fuel cells are key technologies to achieve the mutual transformation of hydrogen energy and electric energy. Fuel cell and electrolytic oxygen production can be placed in the same equipment. When the electric energy is sufficient, more electrolytic oxygen production can be carried out to produce hydrogen and oxygen, which can be stored for later use. When electricity is scarce, the electrolysis oxygen production system is turned into a fuel cell system, which uses the reaction of hydrogen and oxygen to generate electricity to charge the electrolysis battery, reducing the dependence on the space station's electricity.