Data Set Overview : This data set comprises a reduced, subsampled set of the data returned from the Apollo 15 Heat Flow Experiment (HFE) from 31 July 1971 through 31 December 1974. The experiment consisted of two probes placed by the Apollo 15 astronauts in holes drilled in the lunar surface near the Apollo 15 Lunar Surface Experiments Package (ALSEP) site to measure the thermal conductivity. For more information on the experiment and instrumentation see the instrument.cat file in this directory. The data consist of a set of ten ASCII tables with time, temperature differences, and average temperatures readings measured by the thermocouples in the heat flow probes and probe cables. The data have been restored and reformatted from binary data held on magnetic tapes at the NASA National Space Science Data Center (NSSDC) under NSSDC ID of PSPG-00093 (old NSSDC 71-063C-06A).   Data : The data for each probe are divided into 5 files. All numbers in the files are of the form E14.7 (e.g. [1.8388079E+10]). The first column in each file contains the time in milliseconds from 24 hours before the beginning of the year in which the mission was launched. (Apollo 15 was launched in 1971, so the time in milliseconds is measured from 00:00 UTC on 31 December 1970. For example, the elapsed time in milliseconds at 01:00 UT on 1 January 1971 would be 90,000,000. The leap year 1972 and the single leap second added on each of 30 June 1972, 31 Dec 1972, and 31 Dec 1973 -- in which the heat flow timing of elapsed seconds would keep counting while the UT clock would be 'stopped' for a second -- were incorporated into the computed UT start and stop times in this data set.) The files are arranged in chronological order with a few exceptions noted at the end of this description. Files 1, 2, 4, and 5 contain the temperature difference between the upper and lower ends of the bridge (column 2) and the average temperature (column 3) in degrees Kelvin. File 1 is for the upper section gradient bridge (DTGx1, x is the the probe number), file 2 for the lower section gradient bridge (DTGx2), file 4 for the upper section ring bridge (DTRx1), and file 5 the lower section ring bridge (DTRx2). Note that for each bridge, the upper sensor is designated with an 'A' and the lower sensor with a 'B' (e.g. DTG11A and DTG11B), see the INST.CAT file for more details on the naming convention. File 3 contains the heater state (column 2), the reference bridge temperature (column 3), and the cable thermocouple temperatures (columns 4-7 corresponding to TC_1 through TC_4 respectively). The file naming convention is as follows: the first seven characters identify the Apollo mission and the heat flow experiment (A15_HFE); the next two characters identify the probe, P1 for probe 1, P2 for probe 2; finally, the last character before '.tab' gives the file number, 1 through 5. The files contained in this data set are:  A15_HFE_P1_1.TAB - Probe 1 upper section gradient bridge DTG11 (approximately 36 cm to 83 cm depth)  A15_HFE_P1_2.TAB - Probe 1 lower section gradient bridge DTG12 (approximately 91 cm to 138 cm depth)  A15_HFE_P1_3.TAB - Probe 1 heaters and thermocouples  A15_HFE_P1_4.TAB - Probe 1 upper section ring bridge DTR11 (approximately 45 cm to 74 cm depth)  A15_HFE_P1_5.TAB - Probe 1 lower section ring bridge DTR12 (approximately 100 cm to 129 cm depth)  A15_HFE_P2_1.TAB - Probe 2 upper section gradient bridge DTG21 (approximately -6 cm to 41 cm depth)  A15_HFE_P2_2.TAB - Probe 2 lower section gradient bridge DTG22 (approximately 49 cm to 96 cm depth)  A15_HFE_P2_3.TAB - Probe 2 heaters and thermocouples  A15_HFE_P2_4.TAB - Probe 2 upper section ring bridge DTR21 (approximately 3 cm to 32 cm depth)  A15_HFE_P2_5.TAB - Probe 2 lower section ring bridge DTR22 (approximately 58 cm to 87 cm depth)  Two numbering conventions exist in the literature for the thermocouples. We are using the convention that TC14 designates the thermocouple at the top of probe 1, TC13 is the cable thermocouple closest to probe 1, followed by TC12 and TC11. Probe 2 would have TC24, etc. (Another convention, seen in the Preliminary Science Reports, has the probe thermocouple designated as TC11, followed successively in the cable by TC14, TC13, and TC12.) The data are kept in separate files for each bridge because the measurement times were different.  The measurement time intervals for a given sensor would vary over the course of its operation, so it should be noted that the time sequences in the data sets do not necessarily follow a linear pattern. In normal operating mode a 7.25 minute measurement sequence is used to collect the ambient high- and low-sensitivity differential data from the gradient sensors and the thermocouple outputs. The same measurement sequence would be used when the heaters were commanded on for the low conductivity (0.002 W) mode, with the heaters activated in turn for typically 36 hours. For the high-conductivity (0.5 W) sequence, the ring bridge sensors were used and were read every 54 seconds. This mode nominally would last 8 hours. This mode could also be done without the heaters on, with measurements simply being made by the ring bridge sensors. This mode, known as a ring bridge survey, would be used approximately every 6 hours at first and less frequently later in the experiment. However, the data archived here only represent subsampled data, typically at 57 minute intervals.  The instrument was turned on 31 July 1971 and the first reading listed from probe 1 is at 19:47:59 UT. The first reading listed from probe 2 is at 19:48:52 UT. Because of the troubles with the obstruction in the probe 2 hole, probe 2 was not placed permanently in the hole until the end of the second EVA on 1 August at approximately 17:17 UT. Since the experiment was turned on the previous day readings from probe 2 were coming in before it was emplaced in the hole. In December 1975 the experiment began returning anomalous data and only operated intermittently starting on 28 April 1976. The experiment was commanded off from Earth on 15 January 1977. The heaters were turned on and off in the low power (0.002 W) mode in 1971 as follows, with the heater designation followed in parentheses by the depth of the heater, the date and time the heater was turned on, and the date and time the heater was turned off, in UT. For probe 1: H11 (36 cm, 30 Aug. 17:00 - 31 Aug. 17:00), H12 (83 cm, 4 Sep. 05:04 - 5 Sep. 16:55), H13 (91 cm, 26 Aug. 04:58 - 27 Aug. 16:57), H14 (138 cm, 2 Sep. 05:01 - 3 Sep. 16:55). For probe 2 only the bottom two heaters were used: H23 (49 cm, 24 Aug. 05:00 - 25 Aug. 17:01), H24 (96 cm, 7 Sep. 05:00 - 8 Sep. 17:00). In 1973 probe 1 heaters H11 and H12 were rerun in low power mode because they were strongly affected by diurnal variations. These times were chosen to minimize the effects of transient variations near the surface: H11 (36 cm, 13 Mar. 15:01 - 15 Mar. 15:00), H12 (83 cm, 14 Feb. 14:42 - 16 Feb. 02:26).  The nominal data returned from the mission comprised a series of measurement times, 8 series of temperature differences for each sensor bridge pair (4 from each probe), 8 series of average temperatures for each bridge pair, 8 series of cable thermocouple measurements, and a series of temperature measurements from the electronics box. The original data were sent to NSSDC written on four 7-track magnetic tapes (one for each probe) at 800-bpi by an IBM 1130 Model 2415 tape unit. The data were in 32-bit floating point binary and were separated into 5 files in standard IBM 1130 floating point two-word format.  Programs were written to read these tapes and translate them into fixed-width, flat ASCII tables at the NSSDC. The Apollo 15 tapes cover the time span from 19:47:59 UT 31 July 1971 to 21:14:17 UT 31 December 1974. The nominal density on the tapes is about one point (logical record) per hour, although some samples were done at a much lower time resolution.  A reformatting process was applied at NSSDC in June 2005 to the Apollo 15 Heat Flow Experiment tapes to produce a set of five data tables for each of the two different probes associated with the instrument. All data from a given probe are together in one 'file' as archived in the original data sets noted above. Each 'file' as mentioned in the documentation for the original data set is actually a group of physical records that make up only a part of the original archived file. The physical records are written blocked, with 100 logical records per physical record. Where the data did not fill a complete physical record at the end of a group, the original data had zero values inserted to fill out the 100-logical-record physical record.  The logical record size (in 4-byte words) is either 3 words (for files 1, 2, 4, and 5) or 7 words (for file 3). To make the data easier to use, NSSDC separated these groups of physical records into separate files (in the usual meaning of a file) by selecting the appropriate physical records from the archived data file. Thus each original binary archive file resulted in five new ASCII data files, matching the descriptions of the 'files' as described in the original data set documentation. In some cases, the number of physical records in the 'file' was found to be one less than indicated in the documentation. The new output files are written in ASCII, unblocked, and the records containing only fill values have been deleted.  In the NSSDC processing program written by H. K. Hills, a physical record of binary data was read in, then the order of the four-byte words in the record was inverted, making the records advance in chronological order (instead of last to first as in the original archived data set). Then the byte order (within a 4-byte word) was inverted to put the bytes together properly in the VAX word (because of the way the VAX handles input tape records). Then the sign, mantissa, and characteristic of the values were selected as bit strings and moved into their own separate computer words, after which the value of each data word was computed. In cases where the input word value was zero, the output value was set to a flag value of -9999 (or -9.999000E03). The logical three-word records or seven-word records were written out in ASCII directly to disk files with no blocking. Trailing filler records of zero values were deleted.  These new ASCII data tables have the records in nominal chronological order (i.e., the inverse of the order on the original tapes), but there are exceptions where the time of a given point is slightly less than the time of the previous point. The error occurs in the 6th to the 8th significant digit of the time. No such time irregularities were seen in most files, but there were numerous such cases in A15_HFE_P1_3.TAB. For A15_HFE_P2_3.TAB, there was only one timing irregularity. No attempt was made to remove these time discrepancies. There are also occasional anomalous temperature readings or data spike errors in column 3 (TEMP), which may be a result of telemetry errors, tape writing or reading anomalies, or other minor faults. These errors are in most cases very obvious, and we have not attempted to remove the anomalous readings.  The Apollo 15 heat flow data also contain some errors which occurred during transmission or conversion in the form of possible 'bit flips' that cause the differential temperature values to rapidly oscillate in a manner inconsistent with normal hear flow readings. The places where this occurs in the data are obvious. In particular, the 'bit flips' occur in column 2 (DELTA_TEMP) of the following data tables: A15_HFE_P1_1.TAB, A15_HFE_P1_4.TAB, A15_HFE_P2_1.TAB, A15_HFE_P2_4.TAB, AND A15_HFE_P2_5.TAB. We have not attempted to correct these anomalies because we have not been able to identify the cause and do not know the precise correction. We note that in general the use of heat flow data is for the study of long-term trends, and the preferred way of dealing with these corrupted data in most cases would be to ignore them..

This data set passed an external peer review that was held on 9 July 2012.  This data set contains only the data delivered by the Principal Investigator (PI) of the Heat Flow Experiment. The PI had already processed the data to temperature values. No further calibration information came with the data set. No original binary data are included in this data set. Raw, uncalibrated heat flow data exist for the last year and a half of the Apollo 15 experiment but without the proper calibration information the products in this data set supply limited information. We plan to archive the raw, uncalibrated heat flow data in the future.  Please be aware that the temperature readings measured by the cable thermocouples on the surface are not true surface temperatures due in part to the emissivity and heat capacity of the cable.