MAVEN SupraThermal and Thermal Ion Compostion (STATIC) Instrument

The MAVEN SupraThermal And Thermal Ion Compostion (STATIC) instrument is designed to measure the ion composition and distribution function of the cold Martian ionosphere, the heated suprathermal tail of this plasma in the upper ionosphere, and the pickup ions accelerated by solar wind electric fields. STATIC operates over an energy range of 0.1 eV up to 30 keV, with a base time resolution of 4 seconds. The instrument consists of a toroidal “top hat” electrostatic analyzer with a 360 ∘ × 90 ∘ field-of-view, combined with a time-of-flight (TOF) velocity analyzer with 22.5 ∘ resolution in the detection plane. The TOF combines a − 15 kV acceleration voltage with ultra-thin carbon foils to resolve H + , He + + , He + , O + , O 2 + , and CO 2 + ions. Secondary electrons from carbon foils are detected by microchannel plate detectors and binned into a variety of data products with varying energy, mass, angle, and time resolution. To prevent detector saturation when measuring cold ram ions at periapsis ( ∼ 10 1 1 eV/cm 2 s sr eV ), while maintaining adequate sensitivity to resolve tenuous pickup ions at apoapsis ( ∼ 10 3 eV/cm 2 s sr eV ), the sensor includes both mechanical and electrostatic attenuators that increase the dynamic range by a factor of 10 3 . This paper describes the instrument hardware, including several innovative improvements over previous TOF sensors, the ground calibrations of the sensor, the data products generated by the experiment, and some early measurements during cruise phase to Mars.