| DATA_SET_DESCRIPTION |
Content: Notes Data Set Overview Science Objectives Mission Phase Definition Data and Data Processing Quality of Stage 2 Archived Data Creating Meaningful GCMS Archive Data File Names Structure of the DATA Directory & Comments Document Subdirectory Extras Subdirectory Dataset Review : NOTES : 2006-06-20: ATMOSPHERIC DESCENT (ENTRY) DATA The decision was made to not integrate the Titan Entry atmsophere data(altitude, pressure and temperature at the time of each mass spec. scan)into the direct atmosphere mass spectrometer data set files. These data canbe found in the HASI and/or the DTWG data sets that are a part of thisHuygens Probe data set. 2006-07-26: DOWNLOADING NOTICE If you are downloading files from multiple DATA subdirectories, be aware thatthe same file names are used in the different folders. If your systemdownloads all files to one subdirectory, it is likely that you will overwriteexisting files with the result being that the affected file(s) will notcontain the expected data. : Data Set Overview: Gas Chromatograph Mass Spectrometer (GCMS) Instrument: The GCMS uses a quadrupole mass filter with a secondary electron multiplierdetection system and a gas sampling system providing continuous directatmospheric composition measurements and batch sampling through three gaschromatographic columns. The mass spectrometer used five electron impact ionsources with available electron energies of either 70 or 25 eV. Three ionsources served as detectors for the gas chromatographic columns and two werededicated to direct atmosphere sampling and Aerosol Collector Pyrolyser (ACP)gas sampling, respectively. The multiple ion source approach allowed rapidswitching between sample systems and prevented cross-contamination. Theinstrument was also equipped with a chemical scrubber cell for noble-gasanalysis and a sample-enrichment cell for selective measurement ofhigh-boiling-point carbon-containing constituents. The mass filter producedflat-top mass peaks that allowed rapid scanning in 5-ms steps of unit valuesof mass to charge (m/z) ratios over a range from 2 to 141. The nominaldetection threshold was at a mixing ratio of 10^-8. Pressure reduction from the ambient pressure, ~3 to ~1,500 hPa (~1.5 bar),during the probe's descent to the vacuum level of <10^-4 hPa was achieved withmicrometre-sized glass capillary arrays. A choice of two capillary arrays ofdifferent gas conductance was used for the direct atmosphere ion source tocover the wide pressure range during the descent. Gases were removed from theion sources by conductance limited getter and sputter ion pumps. The maximumion source operating pressure was 10^-4 hPa and the mass filter pressure wasalways kept below 10^-6 hPa. The ambient atmosphere was sampled from flowthrough a tube whose inlet was near the apex of the probe fairing and whoseoutlet was at the rear of the probe. The pressure difference created betweenthe inlet and outlet owing to the motion of the Probe caused the atmosphericgas to flow through the tube during the descent. To prevent condensation andto cause rapid evaporation of condensates that might flow through the gassampling system, the inlet section, upstream from the sampling area, washeated up to 80 deg. C, and reached temperatures that depended on gas flowrates through the inlet line. The measurement sequence was pre-programmed. Direct atmospheric samples weretaken nearly continuously during the entire descent, interrupted only when theACP samples and the contents of the rare-gas and the sample-enrichment cellswere analysed. The sample inlet system and the mass spectrometer were sealed under vacuumuntil exposed to the ambient atmosphere after jettison of the probe's heatshield. The descent sequence was properly executed during the mission.However, ion source 5, serving as the detector for the N2-CO separationcolumn, ceased operation owing to an electrical malfunction early in thedescent. This resulted in the loss of all data from this column, and inparticular the measurement of the CO height profile. Coincidentally, externalperturbations affecting the Huygens probe motion were also experienced at thesame time. Science Objectives: Written PRIOR TO the Huygens Mission Titan Atmosphere Entry Event-----------------------------------------------------------------Titan is unique in the solar system in several respects. The dense atmosphereis still chemically reducing, even though Titan is small enough to allowhydrogen to escape readily from its gravitational field. The majorconstituents of the atmosphere, nitrogen and methane, are continuously brokenapart by a combination of solar UV, impinging electrons from Saturn?smagnetosphere, and a steady flux of cosmic rays. The resulting molecularfragments recombine to form a variety of new species, many of which weredetected for the first time by Voyager 1. The existence of still more complexcompounds is manifested by the ubiquitous, surface-hiding aerosol blanket. Inaddition to hydrocarbons and nitriles, the atmosphere is known to contain CO,CO2 and externally delivered H2O. The origin of this atmosphere, the processesinvolved in its evolution, the end products and their subsequent fate as theyinteract with the surface remain to be elucidated. A particularly interestingaspect of this investigation is the possible relevance of the chemicalevolution currently occurring on Titan to some of the prebiotic syntheses thattook place on the early Earth. It is the purpose of the GCMS to provide anaccurate analysis of Titan?s atmospheric composition along the descenttrajectory of the Huygens Probe. The instrument is a follow-on to others usedin making measurements of the atmosphere of Venus and Jupiter (see thereferences cited near the end of this document>. Written AFTER the Huygens Mission Titan Atmosphere Entry Event--------------------------------------------------------------Data were collected for two hours and 27 min from an altitude of 146 km to thesurface. The Huygens probe and the instrument survived the surface impact,allowing data collection of gases evaporated from the surface for anadditional 69 min. UNFORTUNATELY, the loss of the Probe to Orbiter 'A' datachannel resulted in a failure to receive 50% of the GCMS data! Saturn's largest moon, Titan, remains an enigma, explored only by remotesensing from Earth, and by the Voyager and Cassini spacecraft. The mostpuzzling aspects include the origin of the molecular nitrogen and methanein its atmosphere, and the mechanism(s) by which methane is maintained in theface of rapid destruction by photolysis. The Huygens probe, launched from theCassini spacecraft, has made the first direct observations of the satellite'ssurface and lower atmosphere. Here we report direct atmospheric measurementsfrom the Gas Chromatograph Mass Spectrometer (GCMS), including altitudeprofiles of the constituents, isotopic ratios and trace species (includingorganic compounds). The primary constituents were confirmed to be nitrogen andmethane. Noble gases other than argon were not detected. The argon includesprimordial 36Ar, and the radiogenic isotope 40Ar, providing an importantconstraint on the outgassing history of Titan. Trace organic species,including cyanogen and ethane, were found in surface measurements. Determining the composition of the atmosphere of Titan and the nature of theaerosols making up the surface-hiding haze layers are two of the primaryobjectives of the Cassini-Huygens mission. Whereas nitrogen (N2) and methane(CH4 ) were well established as the major atmospheric constituents after theVoyager 1 encounter, the vertical distribution of methane, the isotopic ratioof N in N2 and the abundances and isotope ratios of noble gases, includingradiogenic 40Ar, were not measured by the Voyager remote-sensing observations.Similarly, photochemically produced trace gases in the upper atmosphere hadbeen identified by the Voyager Infrared Radiometer and Spectrometer (IRIS),but the fate of these constituents remained obscure. To what extent did theyform more complex molecules, for example, before condensing and precipitatingon the surface? The Gas Chromatograph Mass Spectrometer (GCMS) on the Huygens probe wasdesigned to help answer these and other questions concerning the atmosphere ofTitan, to measure isotope abundances, and to attempt to analyse condensedphases (including isotope ratios) on the surface. The GCMS composition and isotopic measurements provide important constraintson models of the formation of Titan and its atmosphere in particular, and ontheories of the protosolar nebula and the origin and evolution of planetarysystems and atmospheres in general. It is thought that planetary atmospheresare generated in two principal ways: by accretion of a portion of the solarnebula, or by impact of gas-rich planetesimals. A variation on the theme ofsolar nebula accretion is a subnebula in the region surrounding a giant planetsuch as Saturn. The giant planets seem to be an example of a blend of solarnebula accretion and degassing from planetesimals, because Jupiter has aproportional endowment of heavy noble gases and other heavy elements (relativeto hydrogen) that is greater than existed in the solar nebula. The rarity ofnoble gases in the atmosphere of Earth has long been viewed as strong supportfor a planetesimal influx, and the near absence of noble gases from Titan, aswe will discuss later, provides more support for this hypothesis. Except for36Ar, heavy primordial noble gases were not detected by the GCMS instrument,yielding an upper limit for 38Ar, krypton and xenon below mole fractions of10^-8 . The mole fraction of 36Ar is (2.8 +- 0.3) x 10^-7. This value willbecome more precise with further work. The photochemistry of nitrogen and methane leads to the formation of complexhydrocarbons and nitriles. Methane is also key to themaintenance of the thicknitrogen atmosphere. The nitrogen atmosphere would gradually condense in theabsence of warming resulting from the hydrocarbon haze and the H2-N2 andCH4-N2 collision-induced opacity in the infrared. The height dependence of themethane abundance in the well-mixed atmosphere could not be determined untilthe Huygens probe measurements were carried out. Results of the data analysisshow that the mole fraction of methane is 1.41 x 10^-2 in the stratosphere,increasing below the tropopause, levelling off at 4.9 x 10^-2 near thesurface. The uncertainty in these methane measurements is +-5%. Rapid increaseof the methane signal after landing suggests that liquid methane exists on thesurface, together with several species of higher molecular weight. GCMSisotopic measurements of carbon, nitrogen, hydrogen and argon further help toconstrain atmospheric evolution and composition models. The isotopic ratio of12C/13C is 82.3 +- 1, of 14N/15N is 183 +- 5, and of D/H is(2.3 +- 0.5) x 10^-4. Radiogenic 40Ar was detected at a mole fraction of(4.32 +- 0.1) x 10^-5. Mission Phase Definition: Each operation of the GCMS instrument(s) falls into one of five categories. Phase Description--------------+---------------------------------------------------------------pre-delivery Ground Check-Out and Entry simulation testing and calibrationat GSFC work done with the unit flown to Titan. 1997 (May - September)--------------+---------------------------------------------------------------post-delivery Ground Check-Out testing performed at KSC before and afterat KSC the mechanical and electrical integration of the flown GCMS with the Huygens Probe 1997 (June - September)--------------+---------------------------------------------------------------post-launch Flight Check-Out testing during the CRUISE Mission phaseCRUISE beginning in October 1997 and ending in December 2004--------------+---------------------------------------------------------------ENTRY Titan Atmosphere DESCENT (Entry) Mission: 2005-01-14--------------+---------------------------------------------------------------post-entry GCMS SPARE Instrument Ground Check-Out and calibration andat GSFC characterization testing done at GSFC. 1997 - ?--------------+--------------------------------------------------------------- Pre-delivery instrument operations at GSFC:-------------------------------------------One Entry Simulation test was performed with the unit flown to Titan duringMay 1997. No gases were introduced into the instrument. The data representinstrument residual background. Valves and heaters were functional. Thisdata is archived in the /DATA/19970506_DESCENT_BENCH/ folder. Instrument Calibration testing done pre-delivery: ------------------------------------------------- Much work was performed on the sensor in the laboratory to evaluate its performance. Brief summaries of selected studies are included in the /DOCUMENT/PRELAUNCH_CALIBRATION/ folder of this archive. The data from these tests is both poorly documented and the data files are archived using formats that are poorly documented and difficult to recover. At the time of the first data delivery, we will NOT be archiving any of this data. We are working to recover the data files and will archive these when possible. Post-delivery instrument operations at KSC:-------------------------------------------The flown GCMS instrument was delivered to the facilities at the Kennedy SpaceCenter for integration with the Huygens Probe craft. It was operated severaltimes to verify its operation and performance. These tests were performedbefore and after mechanical and electrical integration with the Huygens Probeand before and after the final 'closure' of the spacecraft. These tests were allperformed using a SUN Workstation and, because of storage space issues, thefiles were archived in compressed formats on various media. Much of the hardwarenecessary to read these archive media is no longer available. We are working toresolve these issues. The data that has been recovered is included with thisdataset. Additional data will be added to the archives as it is recovered. Post-Launch operations - CRUISE mode:-------------------------------------Following launch on October 15, 1997 the GCMS instrument was operated 21times. Sixteen of these were Flight Check-Out tests, performedapproximately every six months. These are called Type 1 (FCO1), Type 1B(FCO1B) or Type 2 (FCO2) tests. The FCO1B test is a slightly modified FCO1test. Additional details about the FCO1 and FCO2 tests are documented in thefile /EXTRAS/DOCUMENTS/FS_CRUISE_OPS.PDF. One important change that was madeafter the cruise operations document was finalized was that no operations ofthe GCMS valves were allowed. The Cruise Checkout Scenario 1 (Flight Check-Out Type 1 & 1B) tests are doneto verify the proper operation of the GCMS instrument. The instrument ispowered on in its pre-T0 configuration to allow the electronics and massspectrometer (MS) hardware to warm-up and stabilize. (T0 is defined as thestart time of the Entry mission. This time is 'declared' either by agravity-switch or by software. During the testing, software defines theT0 time.) Ion source #5 is primarily used but all of the ion sources areoperated for short intervals and return data for programmed test sequences.When the GCMS is first powered on for a FCO test, the ion pumps were NOTturned on. This was done so that a relatively large residual background gassample would be present for MS analysis and so that the test could monitorthe operation of the ion pump when it was turned on. These data are used toevaluate the health of the GCMS Instrument. The Flight Check-Out tests 2, 4,6, 8, 10, 12, 13, 15, 16, NO_PREHEATING and PREHEATING are all Type 1 orType 1B tests. As the data is first processed by the SUN Workstation astandard packet of graphs is produced for each test. These packets arearchived in the /EXTRAS/FLIGHT_CHECKOUT/ folder. The Cruise Checkout Scenario 2 (Flight Check-Out Type 2) tests are similar tothe Type 1 tests. During a Type 2 test, selected parameters are varied toevaluate the 'fine-tuned' status of the GCMS instrument since the ageing ofthe electronics or vibrations or the thermal condition of the instrumentcould cause changes to the tuned condition of the GCMS. Had detrimentalchanges been observed, software patches could have developed and uploadedto correct the condition. No problems were identified! The Flight Check-Outtests 1, 3, 5, 7, 9, 11 and 14 were Type 2 tests. The standard package ofinstrument health graphics created as the SUN workstation processed thetelemetry is archived and available for review in the/EXTRAS/FLIGHT_CHECKOUT/ folder. Two of the tests were planned pre-entry battery depassivation tests, to beperformed shortly before the probe was released from the orbiter, wherelittle instrument data was returned. The purpose of these tests was thatthe probe batteries needed to be 'exercised' to insure optimal performanceduring Titan entry: the data from these tests is located in the folders/DATA/20040919_BAT_DEPSV1/ and /DATA/20041205_BAT_DEPSV2/. In 2003 a decision to have a spacecraft option available to allow the probe'selectronics system to warm-up, called a 'pre-heating' option, required theupload of a software patch to the GCMS instrument: 1 data folder resulted fromthis activity: /DATA/20031206_PATCHING/. The patched GCMS was then tested toverify both the non-pre-heating and the pre-heating operations modes. Thesedata are archived in the /DATA/20031209_NO_PREHEATING/ and the/DATA/20031213_PREHEATING/ folders. Be aware that the total files size of thepre-heating folder is large because the GCMS was powered on and producingdata for ~7 hours as opposed to the traditional ~3 hours necessary with thestandard Flight Check-Out tests. ***************************************WHY PRE-HEATING? See [LEBRETONETAL2005]*************************************** Titan Atmosphere Entry - DESCENT:---------------------------------Data were collected for two hours and 27 min from an altitude of 146 km to thesurface. The Huygens probe and the instrument survived the surface impact,allowing data collection of gases evaporated from the surface for anadditional 69 min. The failure of the 'A' telemetry channel between the Probeand Orbiter meant that we only received ~50% of the data generated by theGCMS instrument. The mass spectrometer has 5 sample input ports. During the sequence there aretimes when it is desireable to monitor the samples from all 5 sources. Thegeneration of this volume of data greatly exceeds the total data bandwidthalloted to the Probe Mission. The design of the MS instrument, with 5 inputsbut 1 quadrupole mass filter and electron multiplier detector dictates thatonly 1 of the data sources can be monitored at any time. This does reduce thebandwidth demands on the data system but the creation of a full MS sweepapproximately every 1 second still creates a large volume of data: enough toexceed the bandwidth alloted to the GCMS instrument. Many iterations wereevaluated relative to the question of how to select the data for telemetry.It was concluded that attempting to select which of the 5 MS data sourcesyielded the 'most meaningful' data from a single mass sweep was too risky.Thus, when multiple data sources are being monitored, the data packetizerselects data from Source 1 then from Source 2 then from Source 3 etc. andrepeats the sequence for the 'active' data sources. This means that if only1 data source is activated then the temporal resolution for that source willbe ~1 second. When 4 or 5 data sources are simultaneously active, thetemporal resolution of the data from each source will be ~4 or ~5 secondsrespectively. These temporal resolutions assume that both telemetry datachannels are functioning correctly. The probe to orbiter telemetry system utilizes two independent communicationchannels; designates the 'A' and 'B' channels (streams). The original missionplan suggested that the instruments use these channels redundantly: i.e.,all data packets be sent to both channels. The GCMS team decided that a lowrisk solution to the data volume problem would be to send sequential datapackets from each data source alternately to each channel: i.e., sweep 1 goesto the 'A' channel, sweep 2 goes to the 'B' channel, sweep 3 goes to the 'A'channel etc.. The only exception is the Housekeeping Type 2 data which isdeemed important enough to be sent redundantly to both data channels. Thiseffectively doubles the volume of GCMS data returned. Using this techniqueeven if one data channel failed the GCMS would still return the volume ofdata specified in the original mission plan, albeit with lower temporalresolution. And, in fact, one data channel did not work and so the GCMSteam lost ~50% of the data generated by the instrument. As programmed, the GCMS was powered on in pre-T0 time to warm up andstabilize its components. Unlike the Flight Check-Out tests, no data wasmade available for this pre-T0 operation. T0 was declared by the probe atUTC 2005-01-14T09:10:20.760 at which time power was applied to the GCMSinstrument. Refer to the /DOCUMENT/ subdirectory where the document(s)DESC_FM_08F or WORKING_SEQUENCE reveal the exact timings and details and toBLOCK_DIAGRAM to identify the component heaters and valves indicated. The GCMS instrument's operations can be categorized as indicated in the tablethat follows. The actual temporal resolution of the data during each phaseis indicated for the DESCENT MISSION where the 'A' telemetry channel failedto function. (All times indicated in the table, below, assume T0 to betime 0. s.) Sampling Event(s) What's Happening as the GCMS falls through Atmosphere----------------------+-------------------------------------------------------Pre-T0 GCMS is powered on for warm-up and component stabilization. Data system is operating but data is NOT forwarded to the Probe's data system.----------------------+------------------------------------------------------- Sampling temporal resolution ~2 s.Residual Background Apply power at time 0 s. Turn ion sources on from 9 - 17 s. Set key inlet system valves to their entry state. Probe fires the GCMS Inlet & Outlet Pyros at 50 & 53 s.----------------------+------------------------------------------------------- Sampling temporal resolution ~2 s.Direct Atmosphere Open valve VZ at 52 s. Open VL1 at 56 s. Only IS1 isvia Leak 1 being monitored so sampling occurs at ~2 s. intervals. VL1 is a 'large' leak intended for use in the lower pressure (upper) atmosphere. Open/Close VS7 & collect EC1/Rg sample from 1500 - 1545 s.----------------------+------------------------------------------------------- Sampling temporal resolution ~2 s.Instrument Background Close VL1 at 1748 s. & VZ at 1800 s. and monitor instrument pump-down & background samples for 89 s. Begin flowing H2 by opening the puncture valve IV.----------------------+------------------------------------------------------- Sampling temporal resolution ~2 s.Rare Gas Cell Open VL3 & begin sampling the Rare Gas sample volume.via Leak 3 Continue this analysis for 91 s.----------------------+------------------------------------------------------- Sampling temporal resolution ~2 s.Enrichment & RG Cells At time 1980 s. open valve VE and add the content ofvia Leak 3 the Enrichment Cell to the Rare Gas sample. Continue this analysis for 90 s.----------------------+------------------------------------------------------- Sampling temporal resolution ~2 s.Instrument Background Close VL3 at 2070 s. and monitor instrument pump-down & background sample for 90 s. Open puncture valve IVA to connect the ACP to the GCMS inlet system.----------------------+------------------------------------------------------- Sampling temporal resolution ~2 s.Direct Atmosphere At time 2160 s. open VL2 and begin sampling the Directvia Leak 2 Atmosphere using Leak 2. The flow rate through Leak 2 is ~28% that of Leak 1. Leak 2 is used in the higher pressure (lower) atmosphere. Collect GC Sample 1 volume from 2340 - 2370 s. Collect GC Sample 2 volume from 3150 - 3180 s. Collect GC Sample 4 volume from 5130 - 5160 s. ------------------------------------------------------- Sampling temporal resolution ~8 s. At time 2368 s. begin sequentially monitoring IS1, IS3, IS4 & IS5. This changes the temporal resolution to ~ 8 s except as noted during ACP sampling.----------------------+------------------------------------------------------- Sampling temporal resolution ~8 s.GC Sample Injections GC Sample 1 (Grab Sample #1) at 2400 s. Continue monitoring GC Sample 2 (Grab Sample #2) at 3210 s. Direct Atmosphere----------------------+------------------------------------------------------- Sampling temporal resolution ~2 s.ACP MS Sampling ACP Sample 1 (Ambient T): 3886 - 3970 s. via. Leak 4 ------------------------------------------------------- Sampling temporal resolution ~10 s. 3970 - 4066 s. ------------------------------------------------------- Sampling temporal resolution ~2 s. ACP Sample 2 (250 deg.C): 4066 - 4150 s. ------------------------------------------------------- Sampling temporal resolution ~10 s. 4150 - 4375 s. ------------------------------------------------------- Sampling temporal resolution ~8 s. ACP Sample 3 (600 deg.C): 4375 - 4445 s.GC Sample Injection ACP - GC Sample 3 at 4388.625 s. of ACP Sample ------------------------------------------------------- Sampling temporal resolution ~10 s. 4445 - 4800 s.----------------------+------------------------------------------------------- Sampling temporal resolution ~8 s.GC Sample Injection GC Sample 4 (Grab sample #3) at 5190 s. Continue monitoring Direct Atmosphere----------------------+------------------------------------------------------- Sampling temporal resolution ~2 s.ACP MS Sampling ACP Sample 4 (Ambient T): 5935 - 6010 s. via. Leak 4 ------------------------------------------------------- Sampling temporal resolution ~10 s. 6010 - 6115 s. ------------------------------------------------------- Sampling temporal resolution ~2 s. ACP Sample 5 (250 deg.C): 6115 - 6190 s. ------------------------------------------------------- Sampling temporal resolution ~10 s. 6190 - 6415 s. ------------------------------------------------------- Sampling temporal resolution ~2 s. ACP Sample 6 (600 deg.C): 6415 - 6485 s. ------------------------------------------------------- Sampling temporal resolution ~10 s. 6485 - 6499 s. IS2 (ACP-MS) is powered OFF at 6501 s.----------------------+------------------------------------------------------- Sampling temporal resolution ~8 s.GC Sample Injections GC Sample 5 (Direct) at 6511 s. directly from GC Sample 6 (Direct) at 7320 s. ambient atmosphere GC Sample 7 (Direct) at 8131 s. Continue monitoring Direct Atmosphere----------------------+------------------------------------------------------- Sampling temporal resolution ~8 s.Surface Sampling Huygens Probe Lands at 8871 s. Direct Atmosphere MS and GC sampling with a temporal resolution of ~8 s. continues as programmed.GC Sampling GC Sample 8 (Direct & Surface) at 8941 s. on surface & GC Sample 9 (Direct & Surface) at 9751 s. Contiue monitoring GC Sample 10 (Direct & Surface) at 10561 s. Direct 'Atmosphere' Last GCMS MS data at 13047.125 s.----------------------+------------------------------------------------------- Post-Mission Calibration and Characterization at GSFC:------------------------------------------------------A GCMS identical to the instrument flown on the Huygens Mission resides in thelaboratory at GSFC. During the cruise phase of the mission, this instrumentwas occasionally operated using the simulated probe electronics interfacewith ground checkout (GCO) test sequences identical to the flight checkout(FCO) sequences performed on the flown instrument. This 'spare' GCMS willbe used to study and simulate the performance of the instrument used atTitan in the hopes to better understand the results. Issues that need to bestudied include the 'calibration' of the instrument with various gas samplesused to simulate the entry conditions (gas composition, pressures,temperatures.) We also need to evaluate the performance of the GC and MSinstruments and their subcomponents. The data resulting from this work andrelevant to the understanding of the GCMS results will be added to the archivesby 2008. Data and Data Processing::(Refer to the document /EXTRAS/DOCUMENTS/EIDB_A2.PDF for details.) The biggest problem with the processing of data from the GCMS instrumenthas been the lack of person continuity of those persons manipulating thedata. Those persons who created the original hardware, hardware interfacesand software long ago moved to new projects leaving only minimal and crypticinstructions. Over time at least six people have been responsible fordata processing and monitoring the instrument's health. Again, thedocumentation and instructions leave more than a little to be desired. The operation of the GCMS Instrument generates the following types of data: Instrument Data Type Operation Frequency--------------------------+---------+-----------------------------------------Unit resolution | All |mass sweep at 70eV | |--------------------------+---------+Unit resolution short | FCO2 | mass sweep at 70eV | |--------------------------+---------+Unit resolution low power | FCO1 | mass sweep at 70eV | FCO1B | Approximately every 1 second | FCO2 | the GCMS instrument performs--------------------------+---------+-------+ a mass sweep analysisUnit resolution | All | | on one of the ionmass sweep at 25eV | | | source samples.--------------------------+---------+ |Unit resolution short | FCO2 | Once | mass sweep at 25eV | | every |--------------------------+---------+ 64 |Unit resolution low power | FCO1 | scans | mass sweep at 25eV | FCO1B | | When more than 1 ion | FCO2 | | source is being--------------------------+---------+ | monitored, the numberHousekeeping Type 1 | All | | of ion sources being--------------------------+---------+-------+-------------+ monitoredHigh resolution | All | | determinesmass sweep at 70eV | | | the--------------------------+---------+ A block of 8 Hi-Res | frequencyHigh resolution short | FCO2 | scans is done | at which mass sweep at 70eV | | once every 320 | each--------------------------+---------+-------+ scans or | sourceHigh resolution | All | Once | approx. | is checked.mass sweep at 25eV | | every | once |--------------------------+---------+ 64 | every |High resolution short | FCO2 | scans | 307 | mass sweep at 25eV | | | seconds |--------------------------+---------+-------+-------------+-------------------Telecommand | All | When a software patch (Telecommand)Acknowledge | | is sent to the GCMS.--------------------------+---------+-----------------------------------------Telecommand | All | When a software patch (Telecommand)NOT Acknowledge | | is sent to the GCMS--------------------------+---------+-----------------------------------------Housekeeping Startup | All | Once shortly after Power ON--------------------------+---------+-----------------------------------------Housekeeping Type 2 | All | Every 40 scans--------------------------+---------+-----------------------------------------Housekeeping Idle | All | As needed to satisfy the requirements Subpacket | | of the GCMS to Probe Data interface--------------------------+---------+-----------------------------------------High Speed Housekeeping | All | ~every 10 seconds--------------------------+---------+-----------------------------------------Medium Speed Housekeeping | All | every 10 scans--------------------------+---------+-----------------------------------------RAM Dump | Dump | As commanded--------------------------+---------+-----------------------------------------IORAM Dump | Dump | As commanded--------------------------+---------+-----------------------------------------EEPROM Dump | Dump | As commanded--------------------------+---------+----------------------------------------- As noted previously, the probe to orbiter communication uses two independenttelemetry channels; called the 'A' and the 'B' channels. Each of the probe'sdata system channels is expecting to receive data from the instrument(s) atapproximately a constant rate. This rate does vary depending on the prioritiesassigned to the probe's data system at any specific time. With the GCMSinstrument, insuring that data is always available for the probe to pick-up isaccomplished by having the instrument's data system utilize two data buffersand putting the (GCMS) data into either the channel A or B buffer. The probethen picks-up (pulls) the data from the data buffers as it wishes. The GCMSinstrument's data system maintains a record for each data type of the datachannel most recently used. Thus it can alternately direct the sequential datafrom each source into the correct (A or B) data buffers. The only exceptionsare the Housekeeping Startup and the Housekeeping Type 2 data packets whichare deemed important enough to be pushed into both data buffers to force dataredundancy. The GCMS also maintains a continually refreshed data packet,called a Housekeeping Idle Data Packet, that is pushed into the instrument'sdata buffer in those instances when no other instrument data is availble. The Huygens Probe's data system packages the GCMS data with that from theother instruments plus probe housekeeping data and transmits this to theCassini Orbiter. The Orbiter then repeats this and forwards the data tothe Deep Space Network Antennas on Earth. This process is then reversed atJPL and ESA/ESOC and the data are separated into files: each file containsdata relevant only to a single instrument. The instrument teams then pick-uptheir data file(s) from the Huygens Data Distribution Server at ESOC. Thistelemetry file is in binary format and requires special software to process. When the mission was developed, the only computers with sufficient power tohandle the processing of this type of large data file were the SUNworkstations. The GCMS data was processed in 'real' time as it was acquired bythe hardware interface integrated with the SUN workstation. This also meantthat, in order to process the telemetry data downloaded from ESA, we had tochannel the telemetry data through the hardware interface in order to have thesoftware accept the data for processing. Several of these workstations and thecustom developed software needed to process the telemetry files were assembled.This allowed us to process the data. This was all completed in the early 1990s.These people were then transferred to other projects. This meant that most of uswere able to process the data only by following the directions provided to usand that it was not possible to handle the data in any new and special way. The first stage of data processing yields a number of data files, listedbelow. Each 'archive' file contains the data from one of the telemetrychannels, A or B, for one of the data packet types but the data remains inbinary stream format. The mergem.dat file is an ASCII text file containingselected mass sweep data extracted from the gcmsswpA and gcmsswpB files.Additional details about these files are in the GCMS_EAICD Document. gcmsackA.archive gcmsackB.archive gcmsbinA.archive gcmsbinB.archive gcmsdumpA.archive gcmsdumpB.archive gcmshkhsA.archive gcmshkhsB.archive gcmshkIA.archive gcmshkIB.archive gcmshkIIA.archive gcmshkIIB.archive gcmshkmsA.archive gcmshkmsB.archive gcmshksA.archive gcmshksB.archive gcmsidleA.archive gcmsidleB.archive gcmsnackA.archive gcmsnackB.archive gcmsswpA.archive gcmsswpB.archive gcmssw.archive mergem.datThe software that creates these 'archive' files also creates a standardpackage of graphs for each type of instrument operation: FCO1, FCO2 andDESCENT. These plots were used to evaluate the instrument's health followingeach in-flight (CRUISE) test. These plot packages are available for reviewin the /EXTRAS/FLIGHT_CHECKOUT/ subdirectory as multipage PDF documents. In late 2003 it was determined that desktop computers had become powerfulenough (large enough hard drives, enough memory and fast clocks) and thatunix software had become available such that the telemetry file could beprocessed, at least to a limited extent, on these platforms. In 2005 itwas discovered how to read and process the binary stream 'raw' telemetryfile using programs running in the Microsoft Windows environment. Theend result of these works is this rather sizeable set of archived data. The binary stream telemetry file and the 'archive' files were first processedto the Stage 1 level. These files consist of 8-bit ASCII TEXT values. All ofthe resulting Stage 1 files are included in the PSA/PDS archives. This hasbeen done to allow users to reprocess the data in the event that they haveissues with what we have done. Additional information about the files inthese archives are contained in the GCMS_EAICD document. The Stage 1 workstation 'archive' mass sweep files (gcmsswpA & gcmsswpB) havebeen further processed for the purposes of the PDS/PSA archives to createfiles containing data for each ion source and operating condition. Theresulting files are: GCMS_1FA_STG1 Ion Source 1, Fractional sweeping, 25 eV ion energy GCMS_1FS_STG1 Ion Source 1, Fractional sweeping, 70 eV ion energy GCMS_1UA_STG1 Ion Source 1, Integer sweeping, 25 eV ion energy GCMS_1US_STG1 Ion Source 1, Integer sweeping, 70 eV ion energy GCMS_2UA_STG1 Ion Source 2, Integer sweeping, 25 eV ion energy GCMS_2US_STG1 Ion Source 2, Integer sweeping, 70 eV ion energy GCMS_3UA_STG1 Ion Source 3, Integer sweeping, 25 eV ion energy GCMS_3US_STG1 Ion Source 3, Integer sweeping, 70 eV ion energy GCMS_4US_STG1 Ion Source 4, Integer sweeping, 70 eV ion energy GCMS_5US_STG1 Ion Source 5, Integer sweeping, 70 eV ion energyYou will find an example of the first few lines from several of these filesin the file /EXTRAS/DATASET_RELATED/SAMPLE_TABLE_FILES_STG1.PNG. The first 20columns of data and the very last column are added during data processing.Columns 1 - 3 contain the mass sweep time. Columns 10 - 20 contain the mostrecent values of selected data from the instrument Type 2 and Idlehousekeeping data. All other data columns are the data directly from theworkstation '*.archive' files. Additional details about the content ofeach column are available from the GCMS_EAICD document and from the LABELfiles associated with each data table file. The Stage 1 files are of little direct value to most users because they, ingeneral, associate 'mystery units' with the data. Selected housekeeping filesand all of the mass sweep (scan) data have been processed to yield Stage 2data files. In Stage 2 housekeeping data files the values have beenconverted to meaningful values: such as volts, amps, Bars etc.. For Stage 2 processed data, the mass sweep data has been converted tocounts/second and selected useful data and a column labels (row 1) have beenadded. Columns 1 - 3 contain time data. For Direct Atmosphere measurements(ion source 1), we had hoped to fill columns 4 - 6 with ambient atmosphericdata - BUT REFER TO THE NOTE BELOW! For the other data sources columns 4 - 6 areundefined. Columns 7 - 10 contain selected values extracted from the Type 2 andIdle Housekeeping data (refer to the GCMS_EAICD document.) Columns 11 & 12contain the Start and End 'mass' values for the mass sweep. Columns 13 - 154contain the mass sweep data. Columns 155 - 169 contain the 'totals' data for thescan. Refer to the GCMS_EAICD document and to the LABEL files associated witheach data file for additional details. You can review samples of selected Stage2 data files in the file /EXTRAS/DATASET_RELATED/SAMPLE_TABLE_FILES_STG2.PNG. ------------------------------NOTE - AMBIENT ATMOSPHERE DATA------------------------------When the Stage 2 processed data files were finalized, the actual entry data(DESCENT trajectory) was not available for general distribution. The datacolumns have been filled with the value ZERO (0.)----------------------------- As stated, above, columns 13 - 154 contain the mass sweep data from the scanstarted at the time indicated in column 1. The start and end masses for thesweep are identified in columns 11 and 12. The mass step increment is either1 (integer or unit stepping) or 0.125 (fractional stepping). To allow for adequate resolution over the entire m/z (mass) range of 0.5 -141.25, dual RF voltages are used with the GCMS's quadrupole mass filter.The high frequency RF covers the m/z range 0.5 - 19.875. The low frequencyoscillator is used to cover the m/z range 20.0 - 141.25. At the start of eachscan and every time the oscillator frequency is changed the instrumentre-initializes the quadrupole frequency parameters. After each initilizationthe first data point obtained is of questionable quality because thecircuitry and system require time to settle and stabilize and so in allinstances the sampling step is repeated. This dictates that the first valueof every sweep should be considered to be invalid and so the sweep actuallybegins with sample #2. This also means that the first sample following anoscillator frequency change should be considered as invalid. Most of the scansare performed using unit stepping with start and end (m/z) values of 2 and141 and so samples 1 and 20 (data in columns 13 and 32) are consideredinvalid. The situation is more complicated during fractional scanning.Again, the data from Sample 1 (column 13) is always considered to be invalid.During fractional scaning the GCMS must change RF during the scan includingm/z 20. The GCMS performs full high-resolution mass scans (m/z 0.5 - 141.25)by performing 8 sub-scans. The m/z ranges of the individual sub-scans are: 0.50 - 18.000 18.125 - 35.500 35.625 - 53.125 53.250 - 70.750 70.875 - 88.375 88.500 - 106.000 106.125 - 123.625 123.750 - 141.125Notice that mass 20 occurs during the second high-resolution sub-scan, atsample 17 (column 29) thus this value is to be ignored in favor of the validsample for mass 20 recorded in the next column. A graphic sampling of thestructures and content of these Stage 2 processed files can be reviewed inthe file /EXTRAS/DATASET_RELATED/SAMPLE_TABLE_FILES_STG2.PNG. The use oforange background indicates those readings considered to be invalid. For thecase of the fractional scans, a pink background highlights the start and endmass values for that scan where mass 20 occurs. In the case of the files containing unitary mass stepping data (integer valuesweeps). the label (row 1) is used to simplify the identification of them/z (mass) value of the column's data. The labels will look something like'X1', 'M2', 'M3', ..., 'X20', 'M20', ..., 'M#' where the number followingthe 'M' indicates the m/z of the data in the column. Those columns with the'X' in the label correspond to the initiation of the scan or the firstoccurrence of m/z : 20 and should be considered to be invalid. For the ion source 1 files with fractional mass stepping (high resolution)data the typical column label will be 'FR2', 'FR3', ..., 'FR142' where theselabels denote the fractional sample (number): i.e., 2, 3, ..., 142. Usersof these data files must determine the appropriate m/z assignment for therow of data of interest using the start mass value (column 11) and rememberingto ignore the first sample and the first sample when m/z : 20 occurs. Users of the Stage 2 processed data files need keep in mind that these datahave been processed to convert the data to meaningful values. Referring to theGCMS_EAICD the reader will note that raw data values of 0 - 127 convertdirectly to counts per sample. Larger raw data values convert to counts persample using the formula counts/sample : (raw - 128)^2: i.e., the instrument'sdata system square rooted the original data. To convert to counts per secondthe user must know that the sampling period is 4.592 milliseconds. With theseStage 2 results, we have attempted to also remove the most obvious knownidiosyncrasies (defects) of the GCMS data. Refer to one example, below.Additional data corrections are still necessary and will be done when wearchive the Stage 3 data products. For example, counting system (electronics)dead time and missed data resulting from 'pulse pile-up' conditions are wellknown problems. These conditions necessitate only small corrections with lowcount rates but can require significant corrections when the count rate islarge. These CORRECTIONS have NOT yet been INCLUDED in the Stage 2 processeddata files associated with this document. ****** EXAMPLE OF SECONDARY DATA PROCESSING REQUIRING MANUAL CORRECTION ******Too much input signal causes the detector (counting system) to overflow. Thesystem was not designed to detect and flag this condition. In most instancesthis is obvious as we process the data *BUT* we must manually correct the databased on our determination that it has occurred. One example of data showingthis situation is available in the /EXTRAS/DATASET_RELATED/ subdirectory ineither of the files GCMS_OVERFLOW_EXAMPLE_STG1.PNG orGCMS_OVERFLOW_EXAMPLE_STG2.PNG. The behavior flagging this as a secondarycounter overflow problem is the drop in the data value (at time ~-1470)followed immediately by the large jump.****************************************************************************** All of the instrument housekeeping (health) data files are archived asStage 1 processed data. These values are of minimal use unless the user isfamiliar with the instrument's basic operation. The following tablesidentify selected TYPE 2 and IDLE HOUSEKEEPING parameters and reveal thevalues needed to convert the raw data (Stage 1) to more meaningful Stage 2processed values. All conversions require that the raw data (Stage 1) be converted to 'volts.'The conversion formula is: Volts : (counts * 0.0201) - 0.037. In the tablethe uA indicates micro-amps and A indicates amperes. The other values areobvious. TYPE 2 Housekeeping:-------------------- Label In English Conversion------------------------------------------------------------------------------ANODE1A Anode 1 current uA:4.223*VANODE2A Anode 2 current uA:4.209*VFILI1A Filament 1 current A:0.3141*VFILI2A Filament 2 current A:0.3131*VEMIS2A Emission 2 current uA:5.003*VEMIS1A Emission 1 current uA:5.003*VH2CLPR Column Pressure of H2 Bars:0.918*VFBSTRNG FB String (V) Volts:84.55*VANODE3A Anode 3 current uA:4.007*vANODE4A Anode 4 current uA:4.012*vFILI3A Filament 3 current A:0.3228*VFILI4A Filament 4 current A:0.3219*VEMIS4A Emission 4 current uA:4.777*VEMIS3A Emission 3 current uA:4.768*VH2RESP H2 Cylinder Pressure Bars:5.336*VANODE5A Anode 5 current uA:4.2168*VANODE6A Anode 6 current uA:29.9908*VFILI5A Filament 5 current A:0.3183*VBACURNT BA Gauge Current A:0.2658*V+0.155BAEMIS BA Gauge Emission uA:31.7463*V-.18EMIS5A Emission 5 current uA:5.021*VSHELLP Instrument Shell Pressure Bars:0.32131+0.19920*VPOS13_MON +13 V Mon Volts:2.907*V5R_MON +5 Reference Voltage Monitor Volts:1.0989*VACP_PRB1 ACP transfer line Pressure #1 Bars:0.918*V-0.354ACP_PRB2 ACP transfer line Pressure #2 Bars:0.918*V-0.3545R_FC_MON +5R Mon Volts:2.0*VEM1HV Multiplier 1 High Voltage uA:9.837*VEM2HV Multiplier 2 High Voltage uA:9.837*V IDLE Housekeeping:------------------ Label In English Conversion---------------------------------------------------------Anode 1 Anode1A uA : 4.223*VAnode 2 Anode2A uA : 4.209*VFil1I Fil1A A:0.3141*VFil2I Fil2A A:0.3141*VFil_Emis2 Emis2A uA : 5.003*VFil_Emis1 Emis1A uA : 5.003*VBiasM2 FBSTRNG 84.550*VAnode3 Anode3A uA : 4.007*VAnode4 Anode4A uA : 4.012*VFilI3 FilI3A A : 0.3228*VFilI4 FilI4A A:0.3219*VFil_Emis4 Emis4A uA : 4.777*VFil_Emis3 Emis3A uA : 4.768*VPres2 H2ResP Bars : 5.336 * VAnode5 Anode5A uA : 4.217*VAnode6 Anode6A uA : 29.9908*VFilI5 FilI5A A : 0.3183*VFilI6 BACURNT A : 0.2658*V + 0.155FilEmis6 BAEMIS uA : 31.7463*V - .18FilEmis5 Emis5A uA : 5.021 * VSHELL_PRES SHELLP Bars : 0.32131+0.19920*VPOS_30VL 6.63 * VPOS13_MON 2.907*V5R_MON 1.098*VIMON1 A:0.00779*Counts-0.07288IMON2 A:0.007118*Counts-0.1851Multana1 Multana1A uA : 2.0*VMultana2 Multana2A 0.3*V5R_FC_MON 2.0*VEM1_MON EM1_HV uA : 9.837*VEM2_MON EM2_HV uA : 9.837 * V When the HOUSEKEEPING data is Temperature, the Celsius scale is used withthe following conversions: Standard Temperatures: T(C) : 1/[M1 + M2*ln(abs(Rtherm))+M3*(ln(abs(Rtherm)))^3] - 273.15 Enrichment Cell Temperatures: T(C) : 1/[M4 + M5*ln(abs(Rtherm1))+M6*(ln(abs(Rtherm1))^3] - 273.15 where: M1 : 0.0024983939203 M2 : 0.00024717631804 M3 : 3.75056e-7 M4 : 0.0008253 M5 : 0.0002045 M6 : 1.144e-7 Rtherm : Vmon * 18.7 / (5REF - V) Constants below are for temps T_EC1 and T_EC2Rtherm1 : Vmon * 3010.0 / (5.0 - V) where '5REF' is the scaled value for '5REF' in Volts. Stage 3 Data Processing:------------------------Following our post-mission calibration and characterization with the spareGCMS instrument we will integrate this information into the data set andforward the fully corrected STAGE 3 data files to the PDS/PSA for archiving. Quality of the Stage 2 Archived Data::The archived data in all folders has been processed to the Stage 2 level. Thecounts telemetry has been examined and the low counts data (raw telemetryless than 128) and the square rooted counts data (raw telemetry 139 - 255)have been converted to counts per sample and then counts per second. Theprocess of checking for counter overflow requires an examination of theresults from the Stage 2 processing and is a laborious process. ONLY THEDESCENT DATA HAS BEEN EXAMINED AND CORRECTED FOR COUNTER OVERFLOW! Anexamination of the in-flight (FCO) testing data will show that the overflowproblem is occasionally present and has not yet been corrected. None of thecounts data have been corrected for the known multiplier and counter problemsof simultaneous pulse arrival and electronic recovery time issues. Theseissues have minimal effects on low count rate data but can become an issuewith higher count rates. Following the careful examination of all of thedata and the completion of mission simulation efforts in the laboratory, wewill release Stage 3 processed data where all of the known data set issueshave been resolved. The archived instrument TYPE 2 and IDLE HOUSEKEEPING DATA have been processedand converted from raw units to more meaningful values expressed in volts,(micro)-amps, (milli)-Bars and such. For the DESCENT ONLY data, the HIGH-and MEDIUM-SPEED HOUSEKEEPING have also been converted to the meaningfulvalues. Creating Meaningful GCMS Archive Data File Names::There really is a method to the madness with the data file names. Refer to theGCMS_EAICD document for additional details and a listing of all possible data(named) products. ----------------------------+-------------------------------------------------File Name Translation----------------------------+-----------------------------------------------------------------------------+------------------------------------------------- Form of ALL file names----------------------------+-------------------------------------------------GCMS_[stuff]_STG#.EXT REQUIRED FORM of file name and extension Limited to '27.3' format. # : Stage (level) of data processing 1 8-bit (unprocessed) values 2 counts/second values 3 All Stage 2 data corrected for instrumental and experimental issues----------------------------+-----------------------------------------------------------------------------+------------------------------------------------- Mass Scan Data Stage 1 and Stage 2 Processed Data----------------------------+-------------------------------------------------GCMS_# Data Source (Ion Source Number) 1 Direct Atmosphere Sampling Rare Gas & Enrichment Cell Sampling 2 ACP MS Samples 3 GC Column 1 4 GC Column 2 5 GC Column 3 (NO DESCENT DATA)GCMS_1$ Scan type (mass increment stepping) F Fractional (0.125 per step) U Unitary (1. per step)GCMS_1U$ Ionization Energy A 25 eV S 70 eVGCMS_1US_$_ Special Operating Options X Short Scan, CO2 only Z Low Power Scan, CO1 & CO2 only----------------------------+------------------------------------------------- Mass Scan Data Stage 2 Processed Data only----------------------------+-------------------------------------------------GCMS_1US_B# GCMS Instrument Background Sample # 1 9 - 56 s. 2 1800 - 1889 s. 3 2070 - 2160 s.GCMS_1US_L# Data through Leak # 1 9 - 1748 s. 2 2160 s. - end 3 1889 - 2070 s. 4 3896 - 3970 s. 4 4076 - 4145 s. 4 4376 - 4450 s. 4 5936 - 6010 s. 4 6116 - 6190 s. 4 6416 - 6487 s.GCMS_1US_L1_GRABEC Direct Atmosphere MS data during the time the Rg + EC sample was collected 1500 - 1545 s.GCMS_1US_L2_GRABGC# Direct Atmosphere MS data during the time GC 'GRAB' Sample # was collected 1 2340 - 2370 s. 2 3150 - 3180 s. 4 5130 - 5160 s.GCMS_1US_L3_RG MS Data via Leak 3 (Rare Gas Cell Sampling) at times 1889 - 1980 s.GCMS_1US_L3_RGEC MS Data via Leak 3 (Rare Gas + Enrichment Cell Sampling) at times 1980 - 2070 s.GCMS_2US_S# MS Data via Leak 4 for ACP Sample # 1 3886 - 3970 s. 2 4066 - 4150 s. 3 4375 - 4445 s. 4 5935 - 6010 s. 5 6115 - 6190 s. 6 6415 - 6485 s.GCMS_3US_GC1_S# MS Data from IS3, GC Column 1, Sample # 1 Grab Sample #1 at 2400 s. 2 Grab Sample #2 at 3210 s. 3 ACP Sample at 4388.625 s. 4 Grab Sample #4 at 5190 s. 5 Direct Atmosphere Injection at 6511 s. 6 Direct Atmosphere Injection at 7320 s. 7 Direct Atmosphere Injection at 8131 s. 8 Surface Sample at 8941 s. 9 Surface Sample at 9751 s. 10 Surface Sample at 10561 s.GCMS_4US_GC2_S# MS Data from IS4, GC Column 2, Sample # Same as GCMS_3US_GC1_S#GCMS_5US_GC3_S# MS Data from IS5, GC Column 3, Sample # Same as GCMS_3US_GC1_S#----------------------------+------------------------------------------------- Combined and time ordered Housekeeping Data converted to Real World values----------------------------+-------------------------------------------------GCMS_HK_HS_STG2 High Speed HousekeepingGCMS_HK_IDLE_STG2 Housekeeping Idle Data PacketsGCMS_HK_MS_STG2 Medium Speed HousekeepingGCMS_HK_TYPE2_STG2 Type 2 Housekeeping Data----------------------------+------------------------------------------------- Files from the SUN workstation necessary to create/verify all subsequent files.----------------------------+-------------------------------------------------GCMS_TELEMETRY_STG1 Telemetry data stream as Stage 1 processed fileGCMS_HK_$_ACK_STG1 Command Acknowledge response from the GCMS indicating that the telecommand sent to the instrument was considered to be valid.) A gcmsackA.archive B gcmsackB.archiveGCMS_HK_$_HS_STG1 High Speed Housekeeping Data A gcmshkhsA.archive B gcmshkhsB.archiveGCMS_HK_$_IDLE_STG1 Idle Housekeeping Data Packet A gcmsidleA.archive B gcmsidleB.archiveGCMS_HK_$_MS_STG1 Medium Speed Housekeeping Data A gcmshkmsA.archive B gcmshkmsB.archiveGCMS_HK_$_NACK_STG1 Command NOT-Acknowledge response from he GCMS indicating that the telecommand sent to the instrument was NOT verified as valid. A gcmsnackA.archive B gcmsnackB.archiveGCMS_HK_$_SOFTWARE_STG1 Startup/Software Packet from workstation A gcmshksA.archive B gcmshksB.archiveGCMS_HK_$_TYPE1_STG1 Type 1 Housekeeping Data A gcmshkIA.archive B gcmshkIB.archiveGCMS_HK_$_TYPE2_STG1 Type 2 Housekeeping Data A gcmshkIIA.archive B gcmshkIIB.archiveGCMS_ALL_$_STG1 Copy of workstation gscmbin$.archive file A gcmsbinA.archive B gcmsbinB.archiveGCMS_SWEEPS_$_STG1 Copy of workstation gcmsswp$.archive file A gcmsswpA.archive B gcmsswpB.archive----------------------------+------------------------------------------------- Data Products Created from other processed files.----------------------------+-------------------------------------------------GCMS_SWEEPS_ALL_TOTALS_STG2 Total Signal values extracted from the Stage 2 processed mass scan data files.GCMS_MOLE_FRACTION_STG2 Mole Fraction data for the most important species extracted from the processed Stage 2 data and submitted to the DTWG team.----------------------------+-----------------------------------------------------------------------------+------------------------------------------------- Structure of the DATA Directory & Comments:: /DATA/ Subdirectories:-----------------------19970506_DESCENT_BENCH Final Descent Sequence Check-out at GSFC19970802_MATED_CO1 Check-Out type 1 at KSC after probe mating19970805_MATED_CO2 Check-out type 2 at KSC after probe mating19970910_PRECLOSE_CO1 Check-out type 1 at KSC before probe reclosure19970913_POSTCLOSE_CO1 Check-out type 1 at KSC after probe reclosure19970919_CONTINGENCY Contingency check-out test at KSC19971023_F01 In-Flight Check-Out #119980327_F02 In-Flight Check-Out #219981221_F03 In-Flight Check-Out #319990915_F04 In-Flight Check-Out #420000202_F05 In-Flight Check-Out #520000728_F06 In-Flight Check-Out #620010322_F07 In-Flight Check-Out #720010919_F08 In-Flight Check-Out #820020415_F09 In-Flight Check-Out #920020916_F10 In-Flight Check-Out #1020030503_F11 In-Flight Check-Out #1120030918_F12 In-Flight Check-Out #1220031206_PATCHING GCMS Software Patching Verification Data20031209_NO_PREHEATING In-Flight testing No-Preheating entry scenario20031213_PREHEATING In-Flight testinf of preheating scenario20040320_F13 In-Flight Check-Out #1320040714_F14 In-Flight Check-Out #1420040914_F15 In-Flight Check-Out #1520040919_BAT_DEPSV1 Battery Depassivation #1 returned data20041123_F16 In-Flight Check-Out #1620041205_BAT_DEPSV2 Battery Depassivation #2 returned data20050114_DESCENT Titan Entry (DESCENT) Mission DataDTWG_MOLE_FRACTION Product generated from DESCENT & submitted to DTWG DOCUMENT Subdirectory:: BLOCK_DIAGRAM.PDF Simplistic block diagram of GCMS Inlet System.BLOCK_DIAGRAM.PNGDESC_FM_08F.ASC Sampling Sequence used by engineersDESC_FM_08F.PDFHUYGENS_GCMS.ASC Content of GCMS Instrument Article published in 'Space Science Reviews' (2002)HUYGENS_GCMS_EAICD_ASC GCMS_EAICD DocumentHUYGENS_GCMS_EAICD.PDFHUYGENS_GCMS_NATURE.ASC GCMS results published in 'Nature' (December 2005)HUYGENS_GCMS_NATURE.PDFHUYGENS_GCMS_SP1177.ASC ESA SP-1177 GCMS article (August 1997)HUYGENS_GCMS_SP1177.PDFWORKING_SEQUENCE.ASC Sampling Sequence as originally developedWORKING_SEQUENCE.PDFWORKING_TIMELINE.PDF Graphic of Sampling Sequence with MODEL Atmospheres Altitudes & Pressures shownWORKING_TIMELINE.PNG /DOCUMENT/HUYGENS_GCMS/ Files:------------------------------FIGURE_1.PNG Modeled MS & GC ResultsFIGURE_2.PNG Block Diagram, Key Instrument ComponentsFIGURE_2A.PNG Color version of FIGURE_2FIGURE_3.PNG Graphic of GCMS InstrumentFIGURE_3A.PNG Color version of FIGURE_3FIGURE_4.PNG Mission Timeline with annotationsFIGURE_4A.PNG Better resolution version of FIGURE_4FIGURE_5.PNG Figure of Ion Source, Lens, Quadrupole & Multiplier configuration. Includes vacuum (pumping) model.FIGURE_5A.PNG Color version of FIGURE_5FIGURE_6.PNG Photo of Ion SourceFIGURE_6A.PNG Better Photo of Ion SourceFIGURE_7.PNG Photo of Instrument MSFIGURE_7A.PNG Photo of Instrument MS with color backgroundFIGURE_8.PNG Photo of detectorFIGURE_9.PNG Photo of Getter Pump & its componentsFIGURE_10.PNG Photo of Ion PumpFIGURE_10A.PNG Photo of Ion Pump componentsFIGURE_11.PNG Block Diagram of ElectronicsFIGURE_11A.PNG Same ad FIGURE_11FIGURE_12.PNG Photo of electronics componentFIGURE_12A.PNG Color version of FIGURE_12FIGURE_13.PNG CADD cut-away drawing of instrument in its shellFIGURE_13A.PNG Color version of cut-away CADD drawingFIGURE_14.PNG Photo of electronics assembled around MS InstrumentFIGURE_14A.PNG Color Photo, same as FIGURE_14FIGURE_15.PNG Photo of shell of assembled GCMS instrumentFIGURE_15A.PNG Same as FIGURE_15FIGURE_16.PNG RF Amplitude vs. time showing mass scans & totals regionsFIGURE_17.PNG Modeled GC results for the 3 parallel columnsFIGURE_17A.PNG Color version of FIGURE_17FIGURE_18.PNG Annotated Sample of 'typical' Mass Spectrum DataFIGURE_19.PNG Block diagram of GCMS calibration system /DOCUMENT/HUYGENS_GCMS_NATURE/ Files:-------------------------------------FIGURE_1.PNG Integrated Titan results: Atmosphere, Rare Gas Cell & SurfaceFIGURE_2.PNG Methane Mole Fraction Results from TitanFIGURE_3.PNG Methane and Nitrogen data around time of surface landingTABLE_1.PNG GCMS determination of isotope ratios from Titan data /DOCUMENT/PRELAUNCH_CALIBRATION/ Files:---------------------------------------CALPRES.ASC Component characterizations & gas mixes usedCALPRES.DOCCALPRES.PDFCALPRES2.ASC Sub-system test descriptions & component characterizationsCALPRES2.DOCCALPRES2.PDFCALPRES3.ASC Sub-system & component testing descriptionsCALPRES3.DOCCALPRES3.PDFCALPRNT2.ASC Sample MS & GC descriptionsCALPRNT2.DOCCALPRNT2.PDFCALPRNTS.ASC Sample MS & GC with PHD informationCALPRNTS.DOCCALPRNTS.PDF EXTRAS Subdirectory:: /EXTRAS/ANIMATED_GIF/ Files:----------------------------ANIMATED_GIF_SCREEN.pdf Brief Overview of annotated Screen Display used for animated GIF files of the GCMS Sequence.GCMS_A2.gif Animated GIF of GCMS Sampling Sequence. Displays a MODEL Altitude Profile Insert.GCMS_P2.gif Animated GIF of GCMS Sampling Sequence. Displays a MODEL Pressure Profile Insert./EXTRAS/DATASET_RELATED/ Files:-------------------------------DATA_PROCESSING.PDF Details of processing the data from Stage 0 to Stage 3 (4) with examples.GCMS_OVERFLOW_EXAMPLE_STG1.PNG Sample of Stage 1 processed data exhibiting counter overflow condition.GCMS_OVERFLOW_EXAMPLE_STG2.PNG Sample of Stage 2 processed data exhibiting counter overflow condition.SAMPLE_TABLE_FILES_STG1.png Sample of selected data TABLE files proc'd to Stage 1 level showing labels and typical data content.SAMPLE_TABLE_FILES_STG2.png Sample of selected data TABLE files proc'd to Stage 2 level showing labels and typical data content. Examples of invalid data resulting from oscillator frequency changes are highlighted. /EXTRAS/DOCUMENTS/ Files:-------------------------EIDB_A1.pdf EID - appendix - telecommanding instrumentEIDB_A2.pdf EID - appendix - telemetry handlingFS_CRUISE_OPS.pdf FS instrument's in-flight cruise operationsGCMS_FS_USER_MANUAL.pdf GCMS FS User's Manual /EXTRAS/FLIGHT_CHECK_OUT/ Files:--------------------------------F01_CO2.pdf Type 2 in-flight check-out #1F02_CO1.pdf Type 1 in-flight check-out #2F03_CO2.pdf Type 2 in-flight check-out #3F04_CO1.pdf Type 1 in-flight check-out #4F05_CO2.pdf Type 2 in-flight check-out #5F06_CO1.pdf Type 1 in-flight check-out #6F07_CO2.pdf Type 2 in-flight check-out #7F08_CO1.pdf Type 1 in-flight check-out #8F09_CO2.pdf Type 2 in-flight check-out #9F10_CO1.pdf Type 1 in-flight check-out #10F11_CO2.pdf Type 2 in-flight check-out #11F12_CO1.pdf Type 1B in-flight check-out #12NO_PREHEATING.pdf Type 1B in-flight no-preheating check-outPREHEATING.pdf Type 1B in-flight preheating check-outF13_CO1B.pdf Type 1B in-flight check-out #12F14_CO2.pdf Type 2 in-flight check-out #14F15_CO1B.pdf Type 1B in-flight check-out #12BATTERY_DEPASSIVATION_1.pdf In-flight battery depassivation #1F16_CO1B.pdf Type 1B in-flight check-out #12BATTERY_DEPASSIVATION_2.pdf In-flight battery depassivation #2DESCENT_AS_CO1.pdf DESCENT mission plotted as type FCO1 check-outENTRY_PLOT_DESCENT.pdf DESCENT mission data Dataset Review: The tentative GCMS dataset was made available to the PDS and PSA teams in lateMarch 2006. The files were reviewed by Roland Thissen and Heidi L.K. Manningand their comments were made available to the GCMS team in early June.The work of the reviewersis greatly appreciated. The suggestions of the reviewers and the formattingerrors discovered by the PDS and PSA teams have been incorporated in this(June) revision to the dataset.
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