Thermal design of the EarthCARE MSI-VNS instrument

The EarthCARE satellite mission objective is the observation of clouds and aerosols from low Earth orbit. The payload will include active remote sensing instruments being the W- band Cloud Profiling Radar (CPR) and the ATLID LIDAR. These are supported by the passive instruments BroadBand Radiometer (BBR) and the Multispectral Imager (MSI) providing the radiometric and spatial context of the ground scene being probed. The MSI will form Earth images at 500 m ground sample distance over a swath width of 150 km; it will image the Earth atmosphere in 7 spectral bands. The MSI instrument will be formed in two parts: the Visible, Near infrared and Short wave infrared (VNS) unit, and the Thermal InfraRed (TIR) unit. In the VNS optical unit, the ground scene is imaged onto four linear detectors via four separate optical channels. Driving requirements for the VNS instrument performance are radiometric accuracy, signal-to-noise ratio, optical image quality and coregistration. Driving requirements for the VNS instrument performance are the spectral sensitivity, the image quality, co-registration and the inter-channel radiometric accuracy. Derived thermal design requirements: • The Short Wave Infrared-2 (SWIR-2) detector needs to be cooled to a narrow temperature band around 230 K in order to meet the sensitivity requirements. • Thermal stabilization of optical housing and the detectors is required to meet het radiometric accuracy requirements. • Reduction of spatial and temporal temperature gradients in the optical unit is required to prevent distortions leading to reduced image quality and loss of co-registration between the channels. The following thermal design and analysis aspects will be covered: • Accommodation of the instrument on the EarthCARE spacecraft and its thermal environment. • A trade-off between passive and thermo-electric cooling of the SWIR-2 detector. • Thermal stabilization of the optical unit. • Interaction between finite element style internal thermo-mechanical model and the external thermal analysis using ESATAN/THERMICA. The VNS is current under development by an integrated TNO/Dutch Space engineering team. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.