The J_2 invariant relative configuration of spaceborne SAR interferometer for digital elevation measurement

A 3-craft formation configuration is proposed to perform the digital elevation model （DEM） for the distributed spacebome interferometric synthetic aperture radar （InSAR）, and it is optimized by the modified ant colony algorithm to have the best compatibility with J2 invariant orbits created by differential correction algorithm. The configuration has succeeded in assigning the across-track baseline to vary periodically and with its mean value equal to the optimal baseline determined by the relative height measurement accuracy. The required relationship between crafts＇ magnitudes and phases is formulated for the general case of interferometry measure from non-orthographic and non-lateral view. The J2 invariant configurations created by differential correction algorithm are employed to investigate their compatibility with the required configuration. The colony algorithm is applied to search the optimal configuration holding the near-constant across-track baseline under the J2 perturbation, and the absolute height measurement accuracy is preferable as expected.

Research on the slow orbit feedback of BEPCⅡusing machine learning

Background:Long-term orbit stability is a key performance indicator in synchrotron radiation facilities and colliders nowa-days,in which the orbit correction and corresponding slow orbit feedback system are indispensable.Conventional method of orbit correction uses response matrix based on SVD algorithm,which becomes less effective after a long operation due to the fact that response matrix measurements cannot be taken during normal operation.Purpose:The purpose of this paper is to integrate machine learning model into the slow orbit feedback process and to automatically update the model online to better correct the orbit shifts.Methods:In this paper,we propose a method for slow orbit feedback of storage ring based on machine learning.Training the neural networks by using online data sets,which can establish the mapping relation between BPMs and correctors,and being updated automatically,without using extra time to remeasure the response matrix.Results:The experiments in this paper are all conducted and verified in the upgrading project of Beijing Electron-Positron Collider.By the way of learning automatically,the updated neutral network is closer to the real machine model,and the orbit after correction shows a smaller fluctuation relative to the golden orbit.Conclusion:Using the online data sets which reflect the response of orbit to correctors in real time to update the neural network can increase the orbit stability.

Error analysis and lattice improvement for the C-ADS Injector-Ⅰ

The injector Scheme- 1 （or Injector- I ） of the C-ADS linac is a 10 mA 10 MeV proton linac working in C／V mode. It is mainly comprised of a 3.2 MeV room-temperature 4-vane RFQ and twelve superconducting single-spoke cavities housed in a long cryostat. Error analysis including alignment and field errors, and static and dynamic ones for the illjector are presented. Based on detailed numerical simulations, an orbit correction scheme has been designed, which shows that with correction the rms residual orbit errors can be controlled within 0.3 mm and a beam loss rate of 1.7× 10-6 is obtained. To reduce the beam loss rate further, an improved lattice design for the superconducting spoke cavity section has been studied.

An equivalent ground thermal test method for single-phase fluid loop space radiator

Thermal vacuum test is widely used for the ground validation of spacecraft thermal control system. However, the conduction and convection can be simulated in normal ground pressure environment completely. By the employment of pumped fluid loops＇ thermal control technology on spacecraft, conduction and convection become the main heat transfer behavior between radiator and inside cabin. As long as the heat transfer behavior between radiator and outer space can be equivalently simulated in normal pressure, the thermal vacuum test can be substituted by the normal ground pressure thermal test. In this paper, an equivalent normal pressure thermal test method for the spacecraft single-phase fluid loop radiator is proposed. The heat radiation between radiator and outer space has been equivalently simulated by combination of a group of refrigerators and thermal electrical cooler（TEC） array. By adjusting the heat rejection of each device, the relationship between heat flux and surface temperature of the radiator can be maintained. To verify this method,a validating system has been built up and the experiments have been carried out. The results indicate that the proposed equivalent ground thermal test method can simulate the heat rejection performance of radiator correctly and the temperature error between in-orbit theory value and experiment result of the radiator is less than 0.5 C, except for the equipment startup period. This provides a potential method for the thermal test of space systems especially for extra-large spacecraft which employs single-phase fluid loop radiator as thermal control approach.