Apollo XRS Data

Data were taken from orbital X-ray spectrometers during sequential
orbits of Apollo service module during 15 and 16 missions.

For XRS data, Mg, Al, and Si intensities were derived from counts in
channels 1 through 8 from 3 differentially filtered detectors with
filter factors, or efficiencies for Mg, Al, and Si, were known from
pre-flight calibrations. Intensities and errorbars were calculated using
matrix inversion. From these data, Mg/Si and Al/Si intensity ratios were
calculated, and those were calibrated to Mg/Si and Al/Si abundance
ratios from landing site averages. Because Si abundance is nearly
constant, intensity ratios, and abundance ratios, represent Mg and Al
abundance to first approximation. Papers describing this technique are
included in the archive, along with the data. Ancillary data include
GET, Locational data (longitude, latitude), spacecraft/instrument
pointing data (yaw, pitch, and roll), and altitude, included for each
integration period, along with raw counts in each of the channels. All
ancillary data values are assumed to represent the mid-point in 8 second
integration periods.

Completeness

Modes: 16 (in table) indicates normal data, not in calibration mode, and
not 14 as described in label.

XRF Data: Raw counts given for each of 8 channels plus non x-ray events
for each detector (bare, Al filter, and Mg filter) and the solar
monitor.

Gaps: Within orbits, data not taken when surface not illuminated (dark
side). During some orbits, data was not taken because it conflicted with
other activities of service module. Extended Mode (twice the gain) data
taken periodically (nominally for two hours every six hours) (For Apollo
15, portions of orbits 7, 21, 22, 28, 29, 32, 33 36, 37, 40, 41, 44, 46,
50, 54, 57, 58, 61, 62, 65, 66, 69. 70; for Apollo 16, portions of
orbits 6, 7, 17, 20, 21, 24, 25, 28, 29, 32, 33, 36, 37, 41, 44, 45, 49,
53, 56, 57, 60, 61).

Calibration Data: Calibration data, with Mg and Mn (Fe55) K radiation
source moved into place on a 'calibration rod', taken periodically
during normal and extended modes (nominally, for 64 seconds every 16
minutes).

Pointing Information: Given for each integration period (row entry) in
table in terms of longitude, latitude, altitude, yaw, pitch, and roll,
allowing geometry to be determined.

References: Catalog entries for references and documentation give
published papers, along with descriptions of hardware (sensors,
collimators, filters), and algorithms for data reduction process.
Measurement units are indicated in label files.

Engineering/'housekeeping' data: Only pointing information, described
above, are given. No other telemetry data from spacecraft given.

Intelligibility

Data are available as ASCII Files. Data are sequential along orbits.
Orbits are sequential during course of mission. Separate tables for
normal mode and extended mode operation during course of mission.

Numbers of aligned properly in each column. Columns are separated by 1
or more spaces. Formatting matches data type (real or integer).

Ease of Viewing: in Print mode. ASCII file prints as long string of
numbers with break at end of line with noticeable indent and easily
recognizable repeating pattern. Still, lines are awfully long to display
in this format. Spreadsheet would be better.

Ease of Viewing: in Display mode. This works fine, as window can be set
to view only ancillary data, or each detector.

Interpretability

Data is consistent with information logged on printouts at the time of
Apollo missions.

Archive Quality

1\. Data have been stable for a couple of decades.

2\. Original data stored on magnetic tapes at NSSDC for Apollo 15 and
16. Original data not available form another source.

> Note: Images of Al/Si and Mg/Si created by filtering in Lunar
> Consortium format at Flagstaff on PDS demo disk and on floppy
> diskettes as bytes readable on Sun operating system. Old magnetic
> tapes of processed data also exist.

3\. The data are scientifically significant as direct geochemical
measurements of Al and Mg from the lunar nearside at 25 km resolution.
Nothing comparable is or will be available for some time to come. It is
unlikely that new data will improve on the resolution of this coverage,
where it is available. It will be important to compare new information
on major element abundances to this data, which was calibrated based on
ground truth from the lunar landing sites.