The Large Area Detector (LAD) is the high-throughput, spectral-timing instrument designed for the eXTP (enhanced Xray Timing and Polarimetry) mission, a major project of the Chinese Academy of Sciences and China National Space Administration. The eXTP science case involves the study of matter under extreme conditions of gravity, density and magnetism. The eXTP mission is currently performing a phase B study, expected to be completed by the end of 2024. The target launch date is end-2029. Until recently, the eXTP scientific payload included four instruments (Spectroscopy Focusing Array, Polarimetry Focusing Array, Large Area Detector and Wide Field Monitor) offering unprecedented simultaneous wide-band X-ray timing and polarimetry sensitivity. The mission designed was however rescoped in early 2024 to meet the programmatic requirements of a final mission adoption in the context of the Chinese Academy of Sciences. Negotiations are still ongoing at agency level to assess the feasibility of a European participation to the payload implementation, by providing the LAD and WFM instruments, through a European Consortium composed of institutes from Italy, Spain, Austria, Czech Republic, Denmark, France, Germany, Netherlands, Poland, Switzerland and Turkey. At the time of writing, the LAD instrument is thus a scientific payload proposed for inclusion on eXTP. The LAD instrument for eXTP is based on the design originally proposed for the LOFT mission within the ESA-M3 context. The eXTP/LAD envisages a deployed >3 m2 effective area in the 2-30 keV energy range, achieved through the technology of the large-area Silicon Drift Detectors - offering a spectral resolution of up to 200 eV FWHM at 6 keV - and of capillary plate collimators - limiting the field of view to about 1 degree. In this paper we provide an overview of the LAD instrument design and the status of its maturity when approaching nearly the end of its phase B study.
The enhanced X-ray Timing and Polarimetry (eXTP) is an international cooperation flagship mission, equipped with four kinds of instruments, including 9 SFA (Spectroscopic Focusing Array) telescopes, 4 PFA (Polarimetry Focusing Array) telescopes, 6 WFM (Wide Field Monitor) cameras, and 40 LAD (Large Area Detector) modules. These payloads overall require about 11.5m2 for mounting on the same side of the satellite, with high alignment requirement between lines of sight of each instrument to guarantee the effective area and response performance of scientific payload, which is the most important driver for the satellite mechanical design. At the same time, the mirror assemblies and cameras of SFA and PFA telescopes are installed separately on the satellite, relying on the satellite structure to ensure the relative position accuracy. There are also factors such as payload field-of-view, sun shield, antenna accommodation, mechanical property to be taken care of in the satellite configuration design. According to the characteristics of payloads, an integrated configuration and structure design of eXTP satellite is proposed, with a high-rigid optical module providing large area for payload optics accommodation, a central cylinder as the primary force-taking structure of the satellite, a service module for platform equipment accommodation, and a detector module equipped with cameras of SFA and PFA. This paper introduces the mechanical design and analysis of eXTP satellite. The feasibility and performance of configuration and structure design are verified by simulation analysis.
The enhanced X-ray Timing and Polarimetry Observatory (eXTP) is a flagship international collaboration mission led by Chinese Academy of Sciences, with a large contribution from more than 20 European institutes. eXTP mission is designed to study the equation of state of ultra-dense matter under extreme conditions of strong density, gravity and magnetic field. The satellite carries four main instruments, including the Spectroscopy Focusing Array (SFA), the Large Area Detector (LAD), the Polarimetry Focusing array (PFA) and the Wide Field Monitor (WFM), enabling simultaneous spectral-timing-polarimetry studies of celestial sources in the energy range from 0.5-30 keV. The satellite will fly at a near-zero-inclination Low Earth Orbit, and is featured with long-time steady high-precision coaxial pointing, near realtime burst alert distribution, and follow-up maneuver capabilities. This paper describes the primary mission requirements and constraints, and presents an overall mission analysis including orbit analysis, pointing strategy, and board-ground communications, etc. The preliminary design of eXTP satellite is also introduced, including satellite overall configuration, observation modes, avionics architecture and development plan.
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