Platinum Metals Rev., 1970, 14, (4), 123
Rhodium Plated Langmuir Probes for Sounding Rockets
At the Radio and Space Research Station, Slough, rocket payloads are built for investigation of the production and density of ionisation in the D-region of the ionosphere at altitudes between 65 and 100 kilometres. Several different experiments are combined in each rocket flight, and one of these is a spherical Langmuir probe for measurement of electron density.
The probe consists simply of a conducting sphere, to which a programmed voltage is applied. The current to the probe, due to collection of electrons from the ionosphere, is measured and used to find the electron density as a function of height. It is essential that these probes have a very uniform surface contact potential; also spurious signals, due to photoemission of electrons from the surface by the sun’s radiation, must be made insignificant. For these reasons it is necessary for the probes to be rhodium plated and to be kept uncontaminated until they are exposed to the upper atmosphere.
Radio and Space Research Station Langmuir probes plated by Johnson Matthey Chemicals Limited have already been flown successfully on twelve flights of British “Petrel” research rockets and a similar number are to be flown in 1970–71. The plating work is again by Johnson Matthey.