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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. Gravitational wave astronomy has opened the door to test general relativity and the effect of gravity in the Universe. The authors present the capabilities of an overlap between space gravitational wave detectors LISA and Taiji to constrain the Hubble constant to 0.5%, in 10 years, and what can be learned from the satellite pilot Taiji-1 launched in 2019.

The Hall Micro Thrusters (HMTs) use cold gas or accelerated plasma dual mode to provide ultra-precise spacecraft altitude control. They were operated in space for the first time as part of the demonstration payloads on Chinese Academy of Science’s (CASs) Taiji-1 spacecraft since September 2019. Hall Micro Thruster Assemblies (HMTAs) were the actuators in drag-free control, and will compensate the nonconservative force for gravity wave observatories. The HMTAs meet the requirements of operating at 5–100 [Formula: see text] N of thrust with 0.7 [Formula: see text] N resolution and [Formula: see text]0.6 [Formula: see text] N/Hz[Formula: see text] (0.01–1 Hz) noise to deliver the nanometer-level precision control as fast as 30 ms measured by Gravitational Reference Sensor (GRS). A transfer function model in z-domain was fit and used to filter HMTs cathode voltage to predict GRSs thrust noise response. Simulations of a single or dual-frequency disturbance and the corresponding compensation demonstrated that HMTAs could deliver the required thrust profile expected. The capability to meet the requirements of thruster noise in drag-free control is critical for future missions because the acceleration noise on test mass directly relates to the gravity wave signa l. Preliminary in-orbit verification of Taiji-1 has showed HMTAs’ great potential in future, and the data in the experiments are presented in this paper.

(Ni, Fe)-codoped ZnO powder was synthesized by a sol-gel process, using oxalic acid zinc as the zinc source. Effects of the pH value of the precursor solution and the calcination temperature on the photocatalytic degradation efficiency of (Ni, Fe)-codoped ZnO powder were studied by using methyl orange as the degradation object. The structures, morphology and ingredients were characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. The results show that all the samples are polycrystalline with a nanocrystal size of about 20~30nm. The methyl orange solution (8 mg/L) was degraded by more than 50% in 12 hours under the irradiation of natural light in the presence of the (Fe, Ni)-codoped ZnO sample synthesized under these conditions: the doping concentrations of both Ni, Fe are 1%, the pH of the precursor solution is 7.5, and the calcination temperature is 375°C. The photocatalytic degradation mechanism of (Ni, Fe)-codoped ZnO powder is discussed qualitatively, based on the microstructure analysis.