urn:nasa:pds:context:instrument:sws.a15a 1.0 1.7.0.0 Product_Context 2016-10-01 1.0 extracted metadata from PDS3 catalog and modified to comply with PDS4 Information Model urn:nasa:pds:context:instrument_host:spacecraft.a15a::1.0 instrument_to_instrument_host Apollo 15 Preliminary Science Report, NASA SP-289, 546 pages, published by NASA, Washington, D.C., 1972. reference.APOLLO15A1972 Bates, J.R., W.W. Lauderdale, and H. Kernaghan, ALSEP termination report, NASA Reference Publication Series, NASA-RP-1036, 162 pages, published by NASA, Washington, D.C., 1979. reference.BATESETAL1979 Clay, D.R., B.E. Goldstein, M. Neugebauer and C.W. Snyder, Apollo 15 - solar wind spectrometer experiment, Apollo 15 Preliminary Science Report, SP-289, pages 10-1 to 10-7, published by NASA, Washington, DC, 1972. reference.CLAYETAL1972 Clay, D.R., B.E. Goldstein, M. Neugebauer and C.W. Snyder, Lunar surface solar wind observations at the Apollo 12 and Apollo 15 sites, Journal of Geophysical Research, 80, 1751-1760, 1975. reference.CLAYETAL1975 Goldstein, B.E., D.R. Clay, C.W. Snyder and M. Neugebauer, ALSEP solar wind spectrometer plasma data as observed at the Apollo 12 and 15 landing sites, Jet Propulsion Laboratory, Contract NAS7-100, 1973. reference.GOLDSTEINETAL1973 SOLAR WIND SPECTROMETER Spectrometer not applicable not applicable Instrument Overview =================== The Solar Wind Spectrometer (SWS), designed to measure protons and electrons at the lunar surface, was part of the Apollo 15 Lunar Surface Experiments Package (ALSEP) package left on the Moon. It consisted of seven modulated Faraday cups opened toward different, but slightly overlapping, portions of the lunar sky. The instrument was used to observe the directional intensities of the electron (6-1480 eV) and positive ion (30-10400 eV) components of the solar wind and magnetotail plasma that strike the surface of the Moon. The scientific objectives of the SWS experiment were to measure electron charge fluxes at the lunar surface, study the interaction of the solar wind with the local magnetic field, determine if lunar limb shocks can be detected at dawn or dusk, measure solar wind conditions, make simultaneous comparisons with Apollo 12 data, and study time-dependent phenomena. Each Faraday cup had a circular opening, five circular grids, and a circular collector. The five circular grids were an aperture grid, a modulator grid, a screen grid, a screen plate, and a suppressor grid. These served to apply an AC modulating field to incoming particles and screen the modulating field from the sensitive preamplifiers. Sensor covers were over each cup to protect against dust during the extravehicular activities and the lunar module ascent. Charged particles entered the cup and a current amplifier determined the resultant current flow. Energy spectra of positively and negatively charged particles were obtained by applying fixed sequences of square-wave AC retarding potentials to a modular grid and measuring the resultant changes in current. One cup (number 7) was oriented vertically and the other six cups (numbered 1-6 clockwise) surrounded it symmetrically facing 60 degrees off vertical. The number 1 cup faced east on Apollo 15. The electronics were in a temperature-controlled container below the sensor assembly attached to a radiator. The instrument had deployed dimensions of 30.5 x 28.2 x 34.5 cm, a mass of 5.7 kg, used 12.5 Watts total power, and had an average data rate of 66.2 bits/second. A sequence of plasma measurements was made every 28.1 seconds, consisting of 14 energy steps spaced a factor of square root of 2 apart for positive ions and 7 steps a factor of 2 apart for electrons. Flux rates of 2.5E6 to 2.5E11 particles cm**-2 sec**-1 could be measured. A large number of internal calibrations are provided. The instrument as deployed had the east-west axis of the instrument 1 degree south of east and 2-degree slope to the east and a 2.5-degree splope to the north. The north-south axis was self-leveling. These were well within the 5-degree specifications for the instrument. The ALSEP central station was located at 26.13407 degrees North latitude and 3.62981 degrees East longitude on the lunar surface. The solar wind spectrometer was situated 4 meters north of the central station and was emplaced so that cup number 1 faced east and the point between cups 5 and 6 faced north. The instrument was deployed on 31 July 1971 and turned on with the sensor covers in place to provide background data at 19:37:10 UT. The covers were removed by command from Earth on 2 August 1971 at 18:07:32 UT, approximately one hour after lunar module ascent. The experiment performed well until 5 November 1971, when intermittent modulation dripping in proton channels 13 and 14 occurred. This intermittent, though scientifically usable, behavior continued until 30 June 1972, when the instrument experienced loss of science and engineering data. Analysis indicated that high-voltage arcing was occurring in the instrument electronics. To prevent the additional power consumption this entailed, the instrument was put into standby mode indefinitely. Tests were done periodically but no change in status was detected, and the solar wind spectrometer was permanently commanded off on 14 June 1974. This instrument description was provided by the NSSDC.