A cosmic dust sensor comprising a unique array of sensors, sensor controls, and in‐flight calibrations was placed in a heliocentric orbit (0.99 to 1.088 a.u.) on 13 December 1967 on board the Pioneer 8 satellite. The ionization and momentum imparted by the impact of a cosmic dust particle upon a surface are measured by the sensor and used to determine the particle's direction, speed, and mass. Prelaunch calibration studies using the Goddard Space Flight Center electrostatic accelerator have shown that the sensors can measure kinetic energies of impacting particles as low as 0.6 ergs and momenta as low as 2×10−5dynes·sec.