The high energy cosmic-radiation detection (HERD) facility onboard China's Space Station

The High Energy cosmic-Radiation Detection ( HERD) facility is one of several space astronomy payloads of the cosmic lighthouse program onboard China's Space Station, which is planned for operation starting around 2020 for about 10 years. The main scientific objectives of HERDare indirect dark matter search, precise cosmic ray spectrum and composition measurements up to the knee energy, and high energy gamma-ray monitoring and survey. HERDis composed of a 3-D cubic calorimeter (CALO) surrounded by microstrip silicon trackers (STKs) from five sides except the bottom. CALO is made of about 10(4) cubes of LYSOcrystals, corresponding to about 55 radiation lengthsand 3 nuclear interaction lengths, respectively. The top STK microstrips of seven X-Y layers are sandwiched with tungsten converters to make precise directional measurements of incoming electrons and gamma-rays. In the baseline design, each of the four side SKTs is made of only three layers microstrips. All STKs will also be used for measuring the charge and incoming directions of cosmic rays, as well as identifying back scattered tracks. With this design, HERDcan achieve the following performance: energy resolution of 1% for electrons and gamma-rays beyond 100 GeV, 20% for protons from 100 GeV to 1 PeV; electron/proton separation power better than 10(-5); effective geometrical factors of >3 m(2) sr for electron and diffuse gamma-rays, >2 m(2) sr for cosmic ray nuclei. R&D is under way for reading out the LYSOsignals with optical fiber coupled to image intensifiedCCD and the prototype of one layer of CALO.