Data Set Overview : This Galileo Probe Mass Spectrometer (GPMS) data set includes:  1. Jupiter atmospheric entry data from December 7, 1995. 2. Instrument characterization data; March - April, 1985. 3. Residual background data from Earth testing; 1985 - 1989. 4. Residual background data from space; 1989, 1990, 1992. 5. Characterization data from the refurbished Engineering Unit. NOT YET AVAILABLE - December, 1998 6. Sequence and conversion tables necessary to process the data.  This data set contains the Mass Spectrometer instrument data from the Galileo Probe mission that entered the atmosphere of Jupiter on December 7, 1995. The GPMS instrument operated for approximately 58 minutes (7000 steps). Approximately 50 minutes of the data are of high quality. Also included are data files necessary to characterize the operation and behavior of this instrument and data files needed to demonstrate the integrity of the GPMS instrument over the lengthy duration of the mission. Additionally, the Engineering Unit was refurbished to flight quality and has yielded data that help understand the results from the mission and these data are included with this data set. The data tables and conversion files required to process the raw data are also included. Documentation reviewing the steps necessary to go from telemetry to more useful (meaningful) data formats are included. Finally, in the entry data set Probe time and Probe descent pressure data are included. The pressure data are from the Atmosphere Structure Instrument. These last two data items will not be detailed further in this work.  In 'real' time (i.e., on December 7, 1995) the data were telemetered from the Galileo Probe to the Galileo Orbiter. These data were redundantly stored both in 'excess' orbiter memory and on a tape recorder. The initial data sent to Earth, beginning on December 10, 1995, were those stored in the Orbiter's memory. Following this, the data stored on the tape recorder were sent to Earth. Between December 1995 and July 1996, 37 files containing mission data were delivered to us. Some of these files contained unprocessed telemetry data (i.e., as it was received.) Other files contained data that had been checked and 'bested'. (Bested indicates data where error corrections have been applied.) In most instances each 'new' data file contained the existing data plus some new data. Effectively the data were 'redundantly' telemetered to the Earth *2?* times. The most useful (complete) data files are tagged with dates of February 5, April 16, and July 1, 1996. The reasons for this method of data return include:  1. The failure of the Orbiter high gain antenna. 2. The problems with the Orbiter's (sticking) tape recorder. 3. Time use allocations with the Deep Space Antenna Network. 4. The fact that Jupiter and Earth were located on opposite sides of the Sun in early 1996 resulting in a poor signal to noise ratio.  The Galileo Probe Mass Spectrometer instrument steps through a pre-programmed sampling sequence. Each measurement results in a count rate related to the mass programmed for that step. The nominal integration period for each step was 0.5 second. The data also yield a data bit indicating a detector sensitivity mode (LOW or HIGH) for that measurement. (At large count rates the instrument automatically switches to a LOW sensitivity mode so as to not overload and damage the detector.) Also returned with each measurement are two data bits of instrument 'housekeeping' information. Each GPMS Instrument minor frame (8 steps) yields two (2) housekeeping parameter values.  - - - - - - - - - -  A short mass spectrometer informational interlude. The GPMS instrument is also referred to as a Neutral Mass Spectrometer (NMS). Such an instrument is composed of an inlet system, an ionizer, ion optics (lenses), a mass filter and a detector. All of this is inside of a high-vacuum chamber. The function of the inlet system is to channel your sample to the mass spectrometer (ms). Because the ms requires a good vacuum, you must allow only a fraction of the incoming sample into the vacuum system. Calibrated leaks are used for this purpose. The mass filter allows only those ions with the proper mass to charge ratio (generally referred to as mass or Daltons or AMU) to pass. A mass filter 'works' because in the presence of electromagnetic fields in a vacuum, the trajectories of ions are predictable. The ionizer is often a heated filament designed to emit electrons with a defined energy (voltage). These electrons collide with gases entering the ionizer and a small fraction of the species acquire a charge. The larger the ionization energy, the more violent the effects. When all is working nicely, the ion acquires a unit charge. When the species is a molecule, it will usually break up into fragments; the exact fragmentation pattern is determined by bond energies and the ionization energy. Ion lenses are useful for directing the ions toward a specific target. A good detector of ions is an electron multiplier.  The GPMS Instrument:  1. Two inlets with larger leaks used on Inlet 1 than on Inlet 2. (Because the pressure is lower up high where Inlet 1 is used.) Micron sized (7 channel) capillary leaks are used. 2. Vacuum maintained by the use of ion and chemical getter pumps. 3. Quadrupole Mass Filter 4. Electron bombardment ionizer with 3 ionization energy options. 5. Several lenses are used to 'steer' the ions. 6. Electron multiplier is used as the detector.  - - - - - - - - - -  In order to translate the housekeeping data returned by the GPMS instrument, a table of conversion coefficients is required. The application of these conversion coefficients yields parameters in meaningful units (Volts, Amperes) instead of 'telemetry mystery units'. Also needed is a table indicating the GPMS parameters (mass, ionizer energy) associated with each step of the sampling sequence. These tables are parts of this data set. Contained in the instrument's housekeeping parameters are a GPMS SYNC PATTERN. These parameters are necessary to 'lock' the programmed sequence with the returned data.  Most of the GPMS data are in the form of standard mass sweeps. During these sequences the mass is incremented in integral (1) Atomic Mass Unit (amu) steps between sample integrations. Typically the sweep steps over a mass range from 2 to 150 amu with the ionizer set to operate at 75 volts. The circuitry associated with the electron multiplier (detector) normally starts its measurement in the HIGH sensitivity mode. When the count rate exceeds a defined threshold, (excessive signal yielding too much current in the multiplier) the system switches the detector to the LOW sensitivity mode. Occasionally measurements are made where the GPMS instrument is incrementing in 0.125 amu steps, is operating using ionization energies of 25 or 15 Volts, is set to measure specific mass values at chosen ionization energies, has been forced to use the LOW sensitivity detection mode of operation and such.  The overall GPMS sequence includes the following subsequences:  1. Instrument Background: Selected residual gases (masses) in the instrument are monitored as soon as power is applied and until Inlet 1 and Outlet 1 are opened to the atmosphere.  2. Photochemical Region: The molecules most likely to exist in the upper atmosphere probably evolved as a result of photochemical processes. Masses corresponding to the anticipated molecules are monitored. Selected masses are monitored at least once every 30 seconds. The collection of a sample by Enrichment Cell 1 was initiated. The enrichment cells work by pulling a large volume of sample across a sorbent material ('Carbosieve'). The hydrogen that dominates the Jovian atmosphere is pumped away using chemical getter pumps.  3. Below the Ammonia Clouds: It was believed that the uppermost clouds visible on Jupiter were composed of Ammonia and possibly including Hydrogen Sulfide. In this region a slightly modified sampling scheme was used. The inlet to the Enrichment Cell was closed and processing of this sample started.  4. Instrument Background: At this phase of the mission, the atmospheric entry models predicted the presence of a water cloud. To avoid problems that can arise if a drop of water entered the inlet of the mass spectrometer, it was decided to terminate direct atmospheric measurements and prepare the GPMS instrument for important special sequences. At this time, in the sequence, valves were closed to isolate the mass spectrometer from the Jovian atmosphere and instrument background measurements were obtained.  5. Rare Gas Measurements: Following the charging of Enrichment Cell 1, a valve was opened to allow those gases not sorbed by the enrichment cell material to (volume expand) enter the Rare Gas Cell. An additional getter pump helps remove any remaining hydrogen from the gas mixture. The gases remaining were expected to be primarily the Rare (Noble) gases. Following the completion of the instrument background measurements, valves were opened to allow these gases into the mass spectrometer for analysis.  6. Enrichment Cell 1 Measurements: The processing of the gases in the enrichment cell consists of heating the cell to drive off those volatile materials sorbed on the 'Carbosieve' material. These gases were added to those already in the Rare Gas Cell and analyzed by the mass spectrometer.  7. Instrument Background: Following the evaluation of the contents from the special cells, additional instrument background scans were done.  8. Inlet 2: Inlet and Outlet 2 were opened to monitor samples directly from the deeper Jovian atmosphere. Most of the sequences done in this region consist of full mass scans because it was expected that more complicated molecules would exist at these higher pressures. In a similar fashion to that previously noted, Enrichment Cell 2 was charged with sample.  9. Enrichment Cell 2: Following sample processing, the contents from the second enrichment cell were analyzed by the mass spectrometer. These samples were superposed on the sample entering from the direct atmosphere.  10. High Resolution Scans: A single 0.125 amu per step mass scan was multiplexed into the sequence.   Parameters : The GPMS measurements yield a count rate for the sampling integration time; here nominally 0.5 second. The resulting count rate as a function of mass is a measure of qualitative and quantitative information about the atomic and molecular species entering the instrument. The actual integration period for each step is 0.48375 seconds. The observed count rate must also be corrected for the limitations of the detector circuitry. One well documented problem at higher count rates is pulse pile up where the events occurring at the detector are happening faster than the circuitry can recover. Data corrected for this effect are part of the data set.   Data - Atmospheric Entry : The operation of the GPMS instrument was expected to begin at an ambient pressure of 0.1 Bars. As the result of a probe problem, the actual start of the instrument's sequence began at a pressure of ca. 0.5 Bars. The data included in the file, GPMSDATA.DAT, include  Column 1: Sequence Step Column 2: Probe Time (Seconds after Major Frame/Minor Frame 0/0.) Column 3: Ambient Pressure (millibars) (from ASI measurements) Column 4: Ionization (electron) Energy (electron Volts) Column 5: Mass being sampled (amu) Column 6: Detector Sensitivity (HI or LO) Column 7: Uncorrected Count Data (counts per period) Column 8: Corrected Count Data (counts per period) Column 9: (Where present) Inlet System Operation Steps  The initial telemetry data forwarded by the project, in the form of System Data Manager (*.SDM) files, contained errors. (Note: *.SDM files are not included in the PDS data set.) The GPMS data were redundantly sent on both the 'A' and 'B' telemetry data systems. The Probe data were also stored both in the (excess) Orbiter's memory and on the Orbiter's tape recorder. The data from each of these were independently telemetered to the Deep Space Network antennas on Earth. As new batches of data were received on Earth and the Jupiter-Sun- Earth geometry improved, the quality of the telemetry data plus the error correction and besting procedures yielded a high quality raw data product. Eventually we identified and rejected only 2 readings from the final 7000+ values as being in error.  The data files (*.SDM files) consist of data records sized at 100 (8-bit) words. (The first data word is indexed (numbered) as zero.) These records are recorded as BINARY data (often referred to as a DIRECT ACCESS format.) The first 36 of these data words contain data system identification plus counter and time information. The remaining 64 (8-bit) words contain the telemetry for 1 minor frame of Galileo Probe data. All data not related to the GPMS instrument were 'zeroed' by the Galileo Probe Project office before we received a file.  Extracting the Probe telemetry yields Probe data records. The GPMS data occupy positions numbered 6, 7, 14, 15, 22, 23, 30, 31, 38, 39, 46, 47, 54, 55, 62 and 63. Two of the data records, from the data file nms0701a.sdm (July 1, 1996), are shown next. These data records are tagged with the mission date 12/07/95 and the time tag shown. Word 0 indicates the data system used (A or B). Words 36, 37 and 38 (Probe words 0, 1 and 2) show the Probe SYNC pattern. Word 40 (Probe word 4) is a counter.  ------------------------------------- Comments 6 0 92 0 1 0 64 0 0 Header (36 entries) 0 0 0 7 252 46 22 171 49 Data Stream >B< 7 252 46 22 171 33 7 252 46 22:46:08.247 22 171 33 134 5 48 22 82 227 248 197 73 0 66 100 0 39 Probe Data (64 Entries) 0 0 0 0 0 0 1 252 125 7 0 0 0 167 0 32 0 0 0 0 0 0 192 41 Multana : 3 168 125 93 156 0 0 64 26 0 0 0 0 0 0 0 29 81 228 205 83 0 123 0 25 0 0 0 0 0 0 192 24 Housekeeping : 67  ------------------------------------- Comments 5 0 92 0 1 0 64 0 0 Header (36 entries) 0 0 0 7 252 46 22 93 36 Data Stream >A< 7 252 46 22 93 36 7 252 46 22:48:09.093 22 93 36 134 5 48 22 116 228 248 197 73 0 65 73 0 31 Probe Data (64 Entries) 0 0 0 0 0 0 1 252 0 7 0 0 0 245 0 32 0 0 0 0 0 0 192 41 Multana : 3 14 125 93 156 122 0 64 26 0 0 0 0 0 0 0 29 0 228 206 83 204 7 0 25 0 0 0 0 0 0 192 24 Housekeeping : 67  Fortunately the Probe and GPMS minor frames are synchronized. Each Probe minor frame yields one minor frame of GPMS data. This GPMS minor frame of data yields 8 count rates and associated detector sensitivities plus two housekeeping parameters. These data are extracted from the data as indicated next.  | HIGH (Even No. Word) | LOW (Odd No. Word) | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | 7| 6| 5| 4| 3| 2| 1| 0| 7| 6| 5| 4| 3| 2| 1| 0| 8-bit +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |<-HK>| S||<--------Mantissa-------->| +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |15|14|13|12|11|10| 9| 8| 7| 6| 5| 4| 3| 2| 1| 0| 16-bit +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ msb lsb  where: msb : most significant bit lsb : least significant bit HK : GPMS Housekeeping bits (0 - 3) S : GPMS Sensitivity Bit (0 : HI, 1 : LO) Exponent : Count Exponent (0 - 7) Mantissa : Count mantissa (0 - 511)  Note: The GPMS data are log compressed. The success of this method requires that the counter always starts at 1. The combination: Mantissa : Exponent : 0 can NEVER occur!  To determine the uncorrected count data, the following rules apply:  If Exponent : 0 COUNT : Mantissa - 1  If Exponent > 0 COUNT : (512 + Mantissa) * 2 ^ (Exponent - 1) + 2 ^ (Exponent - 2)  As long as the count is less than, approximately, 1. E+7, the CORRECTED count rate is derived from the following relationship:  OBSERVED : TRUE * exp(-TRUE / z) where: OBSERVED : Raw (Observed, Uncorrected) Count data TRUE : Actual (Real, Corrected) Count data z : Constant value determined for this specific instrument z : 2.933 E+7  The housekeeping parameter values are derived as follows:  MULTANA : 64 * W(6) + 16 * W(14) + 4 * W(22) + W(30)  HK : 64 * W(38) + 16 * W(46) + 4 * W(54) + W(62)  where: MULTANA : Multiplier Analog Current: A measure of the current from the electron multiplier. HK : One of 32 repeating GPMS 'health' parameters. W(6)...W(62) : The value from the two data bits into which these housekeeping parameters are coded.   Data - GPMS Instrument Characterization : THESE DATA ARE NOT CONSIDERED TO BE QUANTITATIVE!  The GPMS instrument's capabilities were tested in March and April of 1985 in the laboratory at GSFC. These tests were performed using selected pure gases and gas mixtures to demonstrate that the instrument could detect these species. These tests were NOT meant to be quantitative! During these tests the leaks used with the enrichment cells were several hundred to a thousand times smaller than those used during the actual Jovian atmospheric entry. (This was done to prevent damage to the fragile components in the mass spectrometer's ionization source that would occur in the event of an air leak or a pressure surge.) The characterization gas handling system shown in the diagram NMSCLBR.GIF was used. This system is a recirculating system where the pressures and temperatures of the gas sample can be controlled.  The data file names indicate the GPMS instrument inlet (I1 indicates Inlet 1 and I2 indicates Inlet 2) by which the gas sample was introduced as well as the identity of the gas sample. The data files include the following:  File Name Inlet Gas Sample i1_h2s 1 Hydrogen Sulfide i1_hcn 1 Hydrogen Cyanide i1_hydr 1 Mixture of inorganic Hydrides i1_ph3 1 Phosphine i1_rg 1 Rare Gas Mixture i1_rgp 1 Rare Gas Mixture at selected pressures i2_alkan 2 Mixture of saturated alkanes i2_chmx 2 Mixture of saturated and unsaturated hydrocarbons i2_h2nh3 2 Ammonia plus hydrogen mixture i2_h2o 2 Water sample i2_h2s 2 Hydrogen Sulfide i2_hcn 2 Hydrogen Cyanide i2_hydr 2 Mixture of inorganic Hydrides i2_nh3 2 Ammonia i2_ph3 2 Phosphine i2_rg 2 Mixture of Rare Gases i2_unsat 2 Mixture of Unsaturated Hydrocarbons pfusim 1 & 2 90% hydrogen 10% helium mixture introduced using a pressure profile simulating the expected entry.   Data - Waiting for Launch : NMS85183, NMS88201 A89MY15, A89MY15A, A89JL19, A89SE14, A89SE14A B89MY15, B89MY15A, B89JL19, B89SE14, B89SE14A  These data are an important monitors of the 'history' and handling of the instrument. The data in these files indicates the cleanness of the instrument and that it remained (vacuum) leak free. (Note: files A89MY15A, B89MY15A and B89SE14A contain no data, and are not included in this archive.)  The data files are included for both the 'A' and the 'B' data streams and include:  July 2, 1985 instrument test at GSFC. This test was done immediately after the 'final' processing and sealing of the GPMS vacuum system.  July 19, 1988 test at GSFC. This is the last test with the instrument prior to its final delivery for processing and launch. The GPMS was allowed to perform a full sampling sequence with the enrichment cell heaters operational during this test.  May 15, 1989 ground MST testing at KSC (This Mission Sequence Test is intended to simulate the timeline and events expected at entry.)  July 19, 1989 'ground' Probe Baseline testing at KSC.  September 14, 1989 'onboard shuttle' Probe Baseline testing at KSC.   Data - Cruising in Space : A89OC26, A89OC27, A90DE04, A90DE04A, A92NO20, A92NO21 B89OC26, B89OC27, B90DE04, B90DE04A, B92NO20, B92NO21  The GPMS instrument was tested three times following its launch from the space shuttle. The data from both the 'A' and 'B' data streams is included with this data set. (Note: files B89OC27 and B90DE04 contain no data, and are not included in this archive.)  The data files include:  October 26, 1989 first turn on data from space December 4, 1990 Probe Baseline test (SFT) from space November 20, 1992 MST (full sequence) test from space   Data - Entry : A95DE07 B95DE07  Also included are the 'A' and 'B' string data from the entry on December 7, 1995. These data files are formatted identically to the files noted (above) that present the ground and space GPMS instrument testing results. The instrument's housekeeping data is also included in these data files.   Data - Refurbished Engineering Unit : *** NOT YET AVAILABLE at the beginning of 1999. ***  The Galileo Probe Engineering Unit was refurbished to 'Flight Quality' following launch. This instrument is in the laboratory at GSFC and is being used in attempts to simulate the observations from the mission.  *** NOT YET AVAILABLE at the beginning of 1999. ***   Data - Miscellaneous : NMSCOEFF, NMSSTEPS  The file NMSCOEFF.TAB contains the coefficients necessary to convert the GPMS raw housekeeping data into real world Engineering units. The file NMSSTEPS.TAB contains all of the details that have been programmed into the GPMS instrument's sampling sequence such as the mass, electron energy, and sensitivity conditions used for each step. This file also documents the instrument's inlet system operations and other parameters as programmed.   Software : The (IBM PC/Clone) executable program NMSSEQ.EXE is a self-extracting program that creates a set of files that display a cartoon of the GPMS instrument's operation. This file will create 3 files in the subdirectory from which it is run.

Confidence Level Overview :  Data Quality ------------ This data set is of high quality. The GPMS data were redundantly returned on the 'A' and 'B' data streams from the mission. Where data exist from both data streams, only two (2) points do not agree. The disagreements resulted at steps where one of the data streams was noisy or failing so it was not difficult to choose the correct data value. Additionally, the mass spectrometer and its housekeeping parameters also yielded verifications with regard to the correct choice for the data values.  CAUTIONARY NOTE: It appears that thermal problems, with either the Probe transmitter or the GPMS Instrument's data system or with both, caused the quality of the data to slowly degrade during the final 1000 (or so) measurements from the GPMS instrument. Investigation into this problem continues.