Abstract One of the highest priority objectives in the study of small bodies in the solar system is to measure the detailed grainscale elemental and isotopic composition of solid surface materials in a known setting on the body. In many cases sample returns are not feasible and the only practical option is to make measurements in-situ with landed science packages. The reflectron time-of-flight (TOF) mass spectrometer, a relatively new technique, is based on the use of a small laser to remotely ablate and ionize a tiny sample of surface material, followed by measurement of the TOF of the ions as they go from the surface point of vaporization to the detector. The instrument is designed such that the TOF of each ion is proportional with high resolution to the square root of its mass, and a complete elemental and isotopic abundance spectrum of the surface measurement point can be formed for each laser pulse. An instrument using this concept was flown on the Phobos mission and much smaller versions appropriate for use on a lander are in development. Reflectron TOF mass spectrometer designs can be both small and low power, very appropriate for a lander science package.