In this perspective, we outline that a space borne gravitational wave detector network combining LISA and Taiji can be used to measure the Hubble constant with an uncertainty less than 0.5% in ten years, compared with the network of the ground based gravitational wave detectors which can measure the Hubble constant within a 2% uncertainty in the next five years by the standard siren method. Taiji is a Chinese space borne gravitational wave detection mission planned for launch in the early 2030 s. The pilot satellite mission Taiji-1 has been launched in August 2019 to verify the feasibility of Taiji. The results of a few technologies tested on Taiji-1 are presented in this paper.

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To achieve the neutralization control requirements of the radio-frequency (RF) ion microthruster (μRIT) in the 'Taiji-1' satellite mission, we proposed an active neutralization control solution that is based on the carbon nanotube field emission technology. The carbon nanotube field emission neutralizer (CNTN) has the characteristics of light weight, small size, and propellantless, which is especially suitable for the neutralization control tasks of ion microthrusters. The Institute of Mechanics, Chinese Academy of Sciences, in collaboration with Tsinghua University, has successfully developed a CNTN to meet mission requirements. On the ground, the feasibility of cooperation working between μRIT and CNTN was fully verified, as well as the simulation and experimental study of neutralization control strategy, which finally passed the engineering assessment test. Since the launch of 'Taiji-1' satellite on 31 August, 2019, the RF ion micropropulsion system has successfully completed nearly one hundred test missions in space. The test results indicate that CNTN does not have performance degradation, and the neutralization control strategy is effective.