Ion Data from Lunar Surface Becoming Newly Available

Volume 12, Number 4, December 1996
By H. Kent Hills

NSSDC personnel are completing the restoration of a large number of original data tapes from the Suprathermal Ion Detector Experiment (SIDE), which was part of the Apollo Lunar Surface Experiments Package (ALSEP) on the Apollo 12, 14, and 15 missions. The data are from the two sensors within the SIDE: the Total Ion Detector (TID) and the Mass Analyzer (MA). The TID measured a 20-channel differential energy spectrum from 10 eV/Q to 3.5 keV/Q. The MA measured a 20-channel mass spectrum at each of six energy levels from 0.2 to 48.6 eV. The sensors were directional, pointing in the ecliptic plane 15 degrees from the lunar local meridian. Because of the range of longitudes of the three mission landing sites, the look directions of the instruments were about 38 degrees west, 2 degrees west, and 19 degrees east of the Earth for Apollo 12, 14, and 15, respectively. Thus, at certain times during the lunar orbit, the detectors could see ion flows in the magnetosheath, but they never looked directly at the solar wind. During other times the detectors saw ion events of several different types; some appear to be mainly related to the Moon and others to the magnetotail. These instruments resulted in numerous publications and theses. The data have been used, for example, to determine the potential of the lunar surface, to determine the effective plasma screening length at the surface, to study the ion mass spectra, and to study magnetotail ion fluxes. There was also a rather controversial observation of water vapor ions for a limited time on one day, never to be repeated.

The three instruments were nominally identical but did vary in energy and mass levels. Mass resolution was coarse but could identify water vapor, neon, and argon. The range went to 1000 AMU for Apollo 12 and to 120 AMU for Apollo 15. Instrument descriptions and other results appear in the Preliminary Science Report for each of the Apollo 12, 14, and 15 missions: NASA SP-235 (1970), SP-272 (1971), and SP-289 (1972). Brief descriptions of the instruments and archived data sets may be found via the NMC World Wide Web (WWW) interface at http://nssdc.gsfc.nasa.gov/nmc/nmc_query.html by entering the appropriate ID into the query form: 69-099C-05, 71-008C-06, or 71-063C-05 for the Apollo 12, 14, or 15 instruments, respectively.

J. W. Freeman of Rice University was the principal investigator. NSSDC's H. K. Hills was a member of the experimenter team and is supervising this effort. With an additional processing step these data will significantly extend the time coverage of the presently archived SIDE data sets and will include data not previously examined. The level of effort spent on further processing will depend on the interest shown in these data.

The previously-archived data sets each cover from 1.8 to 3.3 years, and each is less than or about 300 MBytes. The newly-restored tapes cover an additional 1-2.6 years for each data set, with the latest data from November 1975.

Lunar image from SIDE

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Miranda Beall, beall@nssdca.gsfc.nasa.gov, (301) 286-0162
Hughes STX, Code 633, NASA Goddard Space Flight Center
Greenbelt, MD 20771, U.S.A.

Erin D. Gardner, gardner@nssdca.gsfc.nasa.gov, (301) 286-0163
Hughes STX, Code 633, NASA Goddard Space Flight Center
Greenbelt, MD 20771, U.S.A.



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Author:Miranda Beall
Curators: Erin Gardner and Miranda Beall
Responsible Official: Dr. Joseph H. King, Code 633
Last Revised: 10 JAN 1997 [EDG]