SOLAR PLASMA EXPERIMENT
In order to investigate the phenomena associated with the movement of plasma (charged particles of low energy and density streaming out from the Sun to form the so-called “solar wind”) in interplanetary space, Mariner carried a solar plasma spectrometer that measured the flux and energy spectrum of positively charged plasma components with energies in the range 240 to 8400 volts. The extremely sensitive plasma detector unit was open to space, consumed 1 watt of power, and consisted of four basic elements: curved electrostatic deflection plates and collector cup, electrometer, a sweep amplifier, and a programmer.
The curved deflector plates formed a tunnel that projected from the chassis on the spacecraft hexagon in which the instrument was housed. Pointed toward the Sun, the gold-plated magnesium deflector plates gathered particles from space. Since the walls of the tunnel each carried different electrical charges, only particles with just the correct energy and speed could pass through and be detected by the collector cup without striking the charged walls. A sensitive electrometer circuit then measured the current generated by the flow of the charged particles reaching the cup.
The deflection plates were supplied by amplifier-generated voltages which were varied in 10 steps, each lasting about 18 seconds, allowing the instrument to measure protons with energies in the 240 to 8,400 electron volt range. The programmer switched in the proper voltage and resistances.