DESCRIPTION |
The Supra-Thermal And Thermal Ion Composition (STATIC) instrument is designed to measure the ion
composition and distribution function of the cold Martian ionosphere, of 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 degree x
90 degree field-of-view, combined with a time-of-flight (TOF) velocity analyzer with 22.5 degree
resolution in the detection plane. The TOF combines a -15 kV acceleration voltage with ultra-thin
carbon foils to resolve H+, He++, He+, O+, O2+, and CO2+ 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**11 eV/cm**2-s-sr-eV) while maintaining adequate sensitivity to resolve tenuous
pickup ions at apoapsis (~10**3 eV/cm**2-s-sreV), the sensor includes both mechanical and electrostatic
attenuators that increase the dynamic range by a factor of 10**3. The STATIC sensor is mounted on the
APP boom, along with NGIMS and IUVS, so that it can be pointed in the ram direction during periapsis
passes. During apoapsis, pointing of the APP is alternated between optimal viewing for IUVS and STATIC,
both of which depend on orbit parameters and local time.
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