<p>The Neutral Particle Detector (NPD) is a new type of instrumentation for energetic neutral atom (ENA) diagnostics. This thesis deals with development of the NPD sensor designed as a part of the plasma and neutral particle packages ASPERA-3 and ASPERA-4 on board Mars Express and Venus Express, the European Space Agency (ESA) satellites to Mars and Venus, respectively. It describes how the NPD sensors were designed, developed, tested and calibrated. </p><p>It also presents the first scientific results obtained with NPD during its operation at Mars. </p><p>The NPD package consists of two identical detectors, NPD1 and NPD2. Each detector has a 9^o x 90^o intrinsic field-of-view divided into three sectors. The ENA detection principle is based on the surface interaction technique. NPD detects ENA differential fluxes within the energy range of 100 eV to 10 keV and is capable of resolving hydrogen and oxygen atoms by time-of-flight (TOF) measurements or pulse height analysis.</p><p>During the calibration process the detailed response of the sensor was defined, including properties such as an angular response function and energy dependent efficiency of each of the sensor sectors for different ENA species. </p><p>Based on the NPD measurements at Mars the main scientific results reported so far are:</p><p>- observation of the Martian H-ENA jet / cone and its dynamics, </p><p>- observations of ENA emissions from the Martian upper atmosphere, </p><p>- measurements of the hydrogen exosphere density profile at Mars, </p><p>- observations of the response of the Martian plasma environment to an interplanetary shock, </p><p>- observations of the H-ENA fluxes in the interplanetary medium.</p>

The Neutral Particle Detector (NPD) is a new type of instrumentation for energetic neutral atom (ENA) diagnostics. This thesis deals with development of the NPD sensor designed as a part of the plasma and neutral particle packages ASPERA-3 and ASPERA-4 on board Mars Express and Venus Express, the European Space Agency (ESA) satellites to Mars and Venus, respectively. It describes how the NPD sensors were designed, developed, tested and calibrated. It also presents the first scientific results obtained with NPD during its operation at Mars. The NPD package consists of two identical detectors, NPD1 and NPD2. Each detector has a 9o x 90o intrinsic field-of-view divided into three sectors. The ENA detection principle is based on the surface interaction technique. NPD detects ENA differential fluxes within the energy range of 100 eV to 10 keV and is capable of resolving hydrogen and oxygen atoms by time-of-flight (TOF) measurements or pulse height analysis. During the calibration process the detailed response of the sensor was defined, including properties such as an angular response function and energy dependent efficiency of each of the sensor sectors for different ENA species. Based on the NPD measurements at Mars the main scientific results reported so far are: - observation of the Martian H-ENA jet / cone and its dynamics, - observations of ENA emissions from the Martian upper atmosphere, - measurements of the hydrogen exosphere density profile at Mars, - observations of the response of the Martian plasma environment to an interplanetary shock, - observations of the H-ENA fluxes in the interplanetary medium.