The Negative Ions at the Lunar Surface (NILS) instrument on the Chang’E-6 mission

Abstract The Negative Ions at the Lunar Surface (NILS) instrument is a compact mass resolving negative ion and electron analyser flown on the Chinese Chang’E-6 mission to the Moon. NILS measures negative ions an electrons in the energy range of 3 eV/q to 3 keV/q with a mass resolution of m/Δm of about 2. The mass resolution is sufficient to separate charge converted solar wind protons and sputtered negatively charged atoms form the surface. An electro-magnetic electron suppression system allows to switch between electron and ion measurements. The fan-shaped field-of-view is divided into 16 discrete angular pixels that are scanned sequentially. For each viewing direction, an electron and an ion energy spectrum is acquired in 4.06 s. NILS has a mass of 919 g, excluding cables and multi-layer insulation. The power consumption is on average 2.7 W during nominal operations.