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Apollo 15 CCIG Lunar Atmospheric Density Plots (PDS)


Availability: Archived at NSSDC, accessible from elsewhere

Time span: 0071-07-31 to 0073-09-12


This PDS data set holds data digitized as part of the Lunar Data Project from experimenter-generated, 35-mm microfilm reels containing plots of lunar atmosphere density measurements and instrument temperature as a function of time. Each frame consists of two plots with a common abscissa. The abscissa gives the time of the measurement in the form DDD/HH/MM where DDD is day of year, HH is hour, and MM is minute. All times are Greenwich Mean Time (GMT). The lower plot gives measurements of the equivalent density for a nitrogen lunar atmosphere in particles per cubic centimeter on a logarithmic scale that ranges from 10 E4 to 10 E10 [10 E4 = 10 x (10 to the 4th power) = 100 000.] The upper plot gives the instrument temperature on a linear scale from 0 to 400 Kelvin. Each frame holds 15 hours of data.

In the normal operational mode the basic cycle repeated five measurements (separated by 2.4 s), three measurements (separated by 40 s), and 16 seconds of calibration and auto-zeroing every 2.5 min. Each of the measurements is represented by one point on the graph. In a ground commanded special mode, one measurement was obtained every 2.4 s, with no other measurements being performed. There is no note on the plots indicating which mode the instrument is in.

The actual raw signal returned by the instrument was the current measured by the sensors. The sensors were calibrated in pre-flight tests using a pure nitrogen (N2) atmosphere. The values shown on the plots have been converted from the sensor-measured current reading to the equivalent nitrogen atmosphere density using the calibration curves of the appropriate gage and temperature sensor. The results are expressed in terms of the nitrogen concentration which would produce the observed current after correcting for temperature. The response of the instrument depends to a rather modest degree on the composition of the gas, which is not known, but it is assumed the true value will vary from this nitrogen concentration by a factor smaller than 2.

This is PDS Data Set ID A15A-L-CCIG-3-ATMOS-DENSITY-PLOTS-V1.0 held on Volumes A14CCG_0001 to A14CCG_0004. The data are available online at:

Alternate Names



  • Planetary Science: Atmospheres

Additional Information



Questions and comments about this data collection can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail
Prof. Francis S. JohnsonData ProviderUniversity of Texas, Dallas
Dr. David R. WilliamsGeneral ContactNASA Goddard Space Flight
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