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Lunar Orbit X-Ray Data Tables (LDP)


Availability: At NSSDC, Ready for Offline Distribution (or Staging if Digital)

Time span: 1971-07-30 to 1971-08-04


This data collection consists of two tables holding time ordered event count rates from the Apollo 15 X-Ray Flourescence Spectrometer for all channels of the three proportional counters (unfiltered, magnesium filter, aluminum filter) and the solar monitor. The first table (A15C_XRFS_71_NORMAL_1.TAB) holds data from the Apollo 15 XRFS set to normal modes with all three counters measuring the same energy ranges. The second table (A15C_XRFS_71_DOUBLE_2.TAB) holds data from the Apollo 15 XRFS set to extended mode with detector 1 (unfiltered) measuring with the energy boundaries for each channel doubled. The X-Ray Spectrometer was carried aboard the Apollo 15 Command and Service Module and took measurements from lunar orbit. It also had K alpha and Fe55 calibration sources. The first Apollo 15 lunar XRFS data are from 306608 seconds GET (Ground Elapsed Time, or time since launch), 30 July 1971 at 2:44 UT on the fourth orbit and the final data were taken at 794934 GET, 4 August at 18:23 UT on the 73rd orbit.

The values give the measurement mode of the instrument, the time, orbit, spacecraft position and orientation, and the event counts, normally for 8-second intervals, for the three proportional counters and the solar monitor. The normal energy range for the first 7 channels of the first three counters (detector 1 unfiltered, detector 2 magnesium filter, and detector 3 aluminum filter) was between 0.75 and 2.75 keV, broken into seven equal energy ranges: 0.75-1.04, 1.04-1.32, 1.32-1.61, 1.61-1.89, 1.89-2.18, 2.18-2.46, and 2.46-2.75 keV. The solar monitor measured the range from approximately 1 to 3 keV, divided into seven equal intervals. An eighth channel recorded all x-ray events with energies higher than the upper level. However the solar monitor data was not useful due to saturation effects.

Each row in the table represents one set of measurements and contains 45 numbers in the order: one integer (I3) designated NFLAG; eight real numbers (F11.2,7F9.2) designated ANS(1) through ANS(8); and 36 integers (36I6) forming an array designated ISPEC(I,J), where I ranges from 1 to 4 and represents the counter used: I=1, detector 1, beryllium windowed counter, no filter; I=2,detector 2, beryllium windowed, magnesium filtered counter; I=3,detector 3, beryllium windowed, aluminum filtered counter; and I=4, solar monitor ; and J ranges from 1 to 9 and represents the energy channel: J=1-7, seven energy regions into which the energy readings were divided; J=8, all x-ray events above the upper level discriminator; and J=9, all non X-ray events. The ISPEC values are ordered in each row as ISPEC(1,1), ISPEC(1,2), ISPEC(1,3), etc. The values of NFLAG are: 14, normal mode; 96 calibration mode; 144, energy boundaries for detector 1 doubled; 224, calibration mode with energy range for detector 1 doubled.

These data were restored and made available as part of the Lunar Data Project at the NASA Space Science Data Coordinated Archive with assistance from Michael Bielefeld. The data and more detailed information on the formats are available online at:

Alternate Names

  • Lunar X-Ray Data Tables (LDP)


  • Planetary Science: Geology and Geophysics

Additional Information



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



NameRoleOriginal AffiliationE-mail
Dr. David R. WilliamsGeneral ContactNASA Goddard Space Flight

Apollo Lunar X-Ray Information/Data at NSSDCA

Lunar X-Ray Flourescence Data Tables On-line

Apollo 15 Lunar X-Ray Data Set Record
Apollo 16 Lunar X-Ray Data Set Record
Apollo 15 X-Ray Magnetic Tape Data Set Record
Apollo 16 X-Ray Magnetic Tape Data Set Record

Related Information at NSSDCA

Lunar Data Project
Apollo Home Page

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