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In nov 2019 and sept 2020 the CNSA launched CZ-4B Y38 and CZ-4B Y41. Based on different images I noticed that this Long March 4B had grid fins. On CZ-4B Y41 the grid fins from Y38 were reused making it the first reused component in the Chinese space program
What is the CNSA trying here? are they trying to test components for a future reusable launcher? or do they serve another purpose?
TLDR the main purpose of the grid fins is to steer the spent 1st stage away from populated areas when it's falling to the grond.
CZ-4B targets SSO and is mostly launched from T-SLC (Taiyuan Satellite Launch Center). China currently operates 4 SLCs, T(Taiyuan), J(Jiuquan), X(Xichang) and W(Wenchang). While J-SLC launches into the desert and W-SLC into the ocean, spent rocket parts (strap-on boosters, rocket stages, payload fairings) from T-SLC and X-SLC do fall onto populated areas and has been a pain since day 1 of their operations.
This is the news piece from Xinhua News Agency on 2019-11-3 regarding the grid fins on CZ-4B Y38. I'll try my best to make a translation (Translating from official Chinese news source is hard).
新华社北京11月3日电（记者 胡喆）记者从中国航天科技集团获悉，11月3日由该集团八院抓总研制的长征四号乙运载火箭成功发射，将卫星送入预定轨道，此次发射任务还成功实施了基于栅格舵系统的一子级落区控制飞行演示验证。 Xinhua News Agency, November 3rd (2019), reported by Hu Zhe. We have known from CASC that, on November 3rd, a CZ-4B launch vehicle that was developed by 8th Institute of CASC was launched successfully, putting a spacecraft into planned orbit. This launch mission also completed successful demonstration and verification of 1st stage falling zone control based on grid fin system.
据八院有关专家介绍，此次采用的栅格舵是一种高效的新型气动稳定和控制舵面，具有很好的升力特性，紧贴箭体折叠安装，使用时再展开，不影响主任务飞行。栅格舵系统飞行试验的成功，将大幅改善落区安全环境，为后续垂直起降重复使用运载火箭的研制奠定坚实的基础。 According to relevant experts at 8th Institute, the grid fin used in this flight is a new type pf highly efficient aerodynamic stabilizer and control surface. It has very good lift characteristics. It is installed folded, close to the surface of the rocket body and unfolds when in use. Its presence does not affect the flight mission. The successful flight experiment of the grid fin system will significantly improve the safety of the (1st stage) falling zone. It also lays solid foundation for the development of future vertical landing reusable launch vehicle.
近年来，随着我国经济社会的发展，落区环境安全成为大众关注的焦点。一子级栅格舵落区控制系统的作用，就像给无控的一子级装上一对“聪明灵活的翅膀”，使一子级落区范围缩小85%以上，将极大改善落区安全环境，尽量避免大规模人员疏散和生命财产损失，是积极履行社会责任和发展绿色航天的必然选择 In recent years, with the development of the society and domestic economy, the safety of the falling zone attracts great public attention. The 1st stage grid fin falling zone control system is like adding a pair of "smart and agile wings" to the previously uncontrolled 1st stage, such that the size of 1st stage falling zone is reduced by more than 85%. This will tremendously improve the safety of the falling zone, and to a considerable degree, avoid large scale evacuation of personnel, loss of life, and damage to property. (The use of such system) is the inevitable choice (by CASC) to fulfill social responsibility and develop a eco-friendly aerospace enterprise.
