Sliding electric contacts in space: Observations on existing technology and new trends in low-speed applications

It is shown that sliding electrical contacts employing silver/molybdenum disulfide composite brushes develop high contact resistances and contacts which exhibit a negative temperature coefficient of resistance. Such effects are due to the susceptibility of silver or molybdenum disulfide to atmospheric contamination, or to the electronic properties of intrinsic MoS2 or a combination of these. Improvement in contact reliability might be obtained by operating low speed slip rings without lubrication and employing alternative contact materials, such as alloys which better resist tarnishing. Such tarnish-resistant materials must be capable of withstanding the development of electrically-resistive films as a result of atmospheric exposure. Miniature slip rings operating without lubrication are shown to be effective for low current signal transmission. It is shown how metallic fiber brushes are capable of high current transmission at low brush loads such that lubrication may be unnecessary.