The Lyman-alpha Solar Telescope (LST) for the ASO-S mission – II. design of LST

Abstract

As one of the three payloads for the Advanced Space-based Solar Observatory (ASO-S) mission, the Lyman-alpha (Lyα) Solar Telescope (LST) is composed of three instruments: a Solar Corona Imager (SCI), a Lyα Solar Disk Imager (SDI) and a full-disk White-light Solar Telescope (WST). When working in-orbit, LST will simultaneously perform high-resolution imaging observations of all regions from the solar disk to the inner corona up to 2.5 R⊙ (R⊙ stands for the mean solar radius) with a spatial resolution of 4.8″ and 1.2″ for coronal and disk observations, respectively, and a temporal resolution of 30 – 120 s and 1 – 120 s for coronal and disk observations, respectively. The maximum exposure time can be up to 20 s due to precise pointing and image stabilization function. Among the three telescopes of LST, SCI is a dual-waveband coronagraph simultaneously and independently observing the inner corona in the HI Lyα (121.6±10 nm) line and white light (WL) (700±40 nm) wavebands by using a narrowband Lyα beam splitter and has a field of view (FOV) from 1.1 to 2.5 R⊙. The stray-light suppression level can attain <10−6 B⊙ (B⊙ is the mean brightness of the solar disk) at 1.1 R⊙ and ≤5×10−8 B⊙ at 2.5 R⊙. SDI and WST are solar disk imagers working in the Lyα line and 360.0 nm wavebands, respectively, which adopt an off-axis two-mirror reflective structure with an FOV up to 1.2 R⊙, covering the inner coronal edge area and relating to coronal imaging. We present the up-to-date design for the LST payload.