Telecommand decoder in a spacecraft payload signal processing unit

Abstract

AB3:Sääsatelliitin otsonitarkkailuinstrumenttia käytetään sään ja UV-säteilynennustamiseen ja ilmaston muutosten tarkkailuun. Satelliitinsignaalinprosessointiyksikköä ohjataan telekomennoilla. Työssäsuunniteltiin ja testattiin simuloimalla telekomentoväylän ja -dekooderintoiminnot.

Metop satellites 1-3 are objectives of the European Meteorological Satellite Organisation (EUMETSAT) for the operational meteorology for the next two decades. The ozone monitoring instrument (OMI) in the satellites measures distributions of ozone and other minor atmospheric constituents and aerosols, providing data e.g. for daily weather and ultraviolet radiation level predictions. In the long run, the data also contributes"'io climate monitoring and scientific research of the atmosphere. -The OMI-ImS (Imaging Spectrometer) is a proposed implementation for the OMI. Being a nadir-viewing instrument and based on nominal absorption wavelengths of constituents, it evaluates the distributions by comparing the spectrum of the solar irradiation reflected from Earth's surface with sun's known spectrum. The Front End Electronics (FEE) is a signal processing unit in the payload of the instrument and handles the science data acquisition and pre-processing as well as some supporting operations. The operation of the FEE is controlled via telecommands i.e. coded control messages by the master unit. -This thesis is part of the specification and developing project of the FEE. It consists of redefining the telecommand link within the payload and the functional and electrical design of the telecommand decoder in the FEE. Although the decoder does not directly relate to the science data acquisition, it has an important role to handle the control interface between the master unit and the rest of the FEE in a sophisticated way. The decoder receives and decodes the incoming telecommands and distributes the controls within the FEE. It also fetches and transmits the requested telemetry and performs some system level operations within the FEE. The redefining the telecommand link, on its behalf, aids the joining of the hardware oriented FEE to the other, processor oriented units. -The design starts with a design specification that lists the requirements and restrictions, specifies the interfaces and characterizes the operating principles. During the design, the radiation and reliability aspects, the characteristic features of the space oriented design, are also taken into account. Finally a preliminary design is depicted and its functionality verified.