Progress on the Chinese Gravimetry Satellite Missions

The Earth's gravity data encompass a lot of information, including characteristics of the Earth's shape, mass distribution, and its varying signals. As fundamental data, it is utilized in research related to geophysics, meteorology, hydrology, oceanology, geodesy, and more, demonstrating significant potential for further applications. As an effective method of observing the global gravity field, the gravity satellite missions have been developed well in this century. Some special gravity satellites such as CHAMP, GRACE, GOCE, and GRACE-FO have been successfully injected into orbit, belonging to the USA, Germany, and the EU. In China, the gravimetry satellite technique has been researched continually for the last 20 years, and the key techniques have been successfully broken through. The Chinese gravity satellite (Chinese Gravimetry Augment and Mass Change Exploring Mission, ChiGAM) has been launched successfully and is observing the Earth's gravity field respectively. Besides this, a gravity-wave observatory has been developed. As a first step, the TianQin-1 satellite was developed in 2019, in which the accelerometer and drag-free device were tested in orbit. In the second step, the TianQin- 2 satellite is planned to launch around the year 2026, which will test the laser inter-satellite ranging system and be used to precisely measure the Earth's gravity. Additionally, the satellite gravity gradiometer mission is being pursued. Some key engineering models, such as the gravity gradiometer and drag-free system, have been manufactured and tested, laying the foundation for the gravity gradiometer mission. In this paper, the status of the Chinese gravity satellite is briefly introduced, followed by an analysis of the main characteristics of each gravimetry satellite and the correlations and distinctions between them. Furthermore, suggestions are made for the direction and steps to develop the satellite gravimetry mission, in order to advance satellite gravimetry techniques and better meet the needs of oceanology, hydrology, seismology, and others.