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 and electrons in the energy range of 3 eV/q to 3 keV/q with a mass resolution m $/\Delta $ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>/</mml:mo> <mml:mi>Δ</mml:mi> </mml:math> m 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. Power consumption is on average 2.7 W during nominal operations.