Bulk Ion Velocity Measurements in the Martian Ionosphere by M-MATISSE/3DVI: Prototype Performance Tests

The 3DVI (3-D Velocity for Ions) instrument is specifically designed for the M-MATISSE mission to measure, for the first time, the three-dimensional bulk ion velocity in the Martian ionosphere. The instrument consists of two sensor heads: a Retarding Potential Analyzer (RPA) and an Ion Drift Meter (IDM). Both sensors have a field of view defined by a 45° half-cone oriented toward the spacecraft ram direction. By exploiting the spacecraft’s orbital motion, the RPA and IDM determine the bulk ion velocity components parallel and perpendicular to the sensor boresight, respectively, with a sensitivity of 20 m/s.

Although sensors of this type have been widely used in previous space missions, their application to the Martian ionosphere requires specific design considerations. These arise primarily from the expected low bulk ion velocities in the lower ionosphere and the low plasma density in the upper ionosphere.

A prototype of the 3DVI instrument has been developed and tested using low-energy ion beams. The tests confirmed an angular sensitivity of 0.5° and a field of view of 30° half-cone, in agreement with the instrument requirements. In this presentation, we report and discuss the results of these performance tests.