Data Set Overview : The data set consists of calibrated observations, also known as CDRs.  Each XRS observation results in four X-ray spectra. When an X-ray interacts with one of the four detectors, a charge or voltage pulse is generated. This signal is converted into one of 2^8 (256) channels, which are correlated to energy. Over a commanded integration time period a histogram of counts as a function of energy (channel number) is recorded. The EDRs are the number of events in each channel of the four detectors accumulated over the integration period. Channels above or below the useful energy range of the detectors are not saved or transmitted. The result is three 244- channel GPC histograms and one 231-channel solar monitor histogram, each of which is designated as a single X-ray spectrum.  In addition to the science data, associated instrument parameters are included.   Instrument Overview : The X-Ray Spectrometer (XRS) experiment is comprised of three identical gas proportional counters (GPC) that measure X-rays emitted from the surface of Mercury in the energy range from about 1 to 10 keV. X-rays in this energy range sample the planetary surface to depths of a few tens of microns.  See the XRSINST.CAT file for more information and [SCHLEMMETAL2007] for full details.   Calibration Overview : The supernova remnant X-ray source Cassiopeia-A (Cas-A) is being used for periodic in-flight calibration because of its relatively high intensity in the XRS energy range. Once or twice a year XRS is pointed to Cas-A for about 48 hours and then away from that source for another 48 hours to accumulate background measurements. These measurements provide an evaluation and calibration of the XRS anti- coincidence and rise-time discrimination background rejection systems.  This data set is NOT calibrated; it only provides the calibrated sensor measurements.   Parameters : The principal parameters when observing with the XRS are as follows:   * Integration Period: Normal (quiet Sun) or Flare. In Normal mode three different integration intervals are used, depending on distance to the planet. These may be set over a wide range, but the default values are:  Integration Collection Time Closest: 40 s 2000 s Mid-Range: 200 s 10000 s Greatest: 450 s 31200 s  In flare mode integration periods are automatically shortened to a pre-determined level, typically 20 s, for 60 minutes or less.  * Veto Event: Accept or reject events with a simultaneous signal from the anti-coincidence wires.  * Rise-Time Validation: Accept or reject events with an invalid rise time measurement.   Data : The XRS instrument telemetry conveys science data, configuration data and status (housekeeping) data. Several telemetry packets are used to downlink this information:  Status Housekeeping Packets Uncompressed Science Packets Compressed Science Packets Raw Sensor Data Packets  The useful science and housekeeping measurements from the telemetry are decompressed and decomutated and are correlated and accumulated into one binary table, which constitutes the primary experimental data record.  Each record of the table contains four energy spectra, housekeeping, status, and rate data for one integration period. The spectra correspond to the Mg-filtered detector (GPC1), the Al-filtered detector (GPC2), the unfiltered detector (GPC3), and the solar monitor (SAX). All the spectra have 256 bins, but only the highest 244 bins for the GPC and the highest 231 bins for the SAX are telemetered. All bins are 16 bits deep. There are five 32-bit rate counters for SAX and nine 24-bit rate counters for each of the three gas proportional counters.  Rate counters for all four detectors include raw, valid event, analyzed, pileup, and high-energy rates. The gas detectors also have counters for the veto-anode, veto, rise-pileup, and rise-rejection rates.  Housekeeping data provide voltage, current, and temperature readings measured at the end of each integration period. Also reported are record and software status, hardware settings and integration and reporting times.

Confidence Level Overview:The XRS CDR data are the calibrated data records released for the XRS. Theyinclude all of the EDR data plus other information such as detector energycalibration, engineering data conversions, and spatial data which will benecessary to convert raw XRS counts to planetary surface compositions.  Review:The XRS CDR was reviewed internally by the XRS team prior to release to thePDS. PDS also performed an external review of the XRS CDR.  Data Coverage and Quality:Nineteen mission phases: Launch, Earth Cruise, Earth Flyby, Venus 1 Cruise,Venus 1 Flyby, Venus 2 Cruise, Venus 2 Flyby, Mercury 1 Cruise, Mercury 1flyby, Mercury 2 Cruise, Mercury 2 flyby, Mercury 3 Cruise, Mercury 3 flyby,Mercury 4 Cruise, Mercury Orbit, Mercury Orbit Year 2, Mercury Orbit Year3, Mercury Orbit Year 4 and Mercury Orbit Year 5.These mission phases are defined as:  Start time End timePhase Name Date (DOY) Date (DOY)----------------- ---------------- ----------------Launch 03 Aug 2004 (216) 12 Sep 2004 (256)Earth Cruise 13 Sep 2004 (257) 18 Jul 2005 (199)Earth Flyby 19 Jul 2005 (200) 16 Aug 2005 (228)Venus 1 Cruise 17 Aug 2005 (229) 09 Oct 2006 (282)Venus 1 Flyby 10 Oct 2006 (283) 07 Nov 2006 (311)Venus 2 Cruise 08 Nov 2006 (312) 22 May 2007 (142)Venus 2 Flyby 23 May 2007 (143) 20 Jun 2007 (171)Mercury 1 Cruise 21 Jun 2007 (172) 30 Dec 2007 (364)Mercury 1 Flyby 31 Dec 2007 (365) 28 Jan 2008 (28)Mercury 2 Cruise 29 Jan 2008 (029) 21 Sep 2008 (265)Mercury 2 Flyby 22 Sep 2008 (266) 20 Oct 2008 (294)Mercury 3 Cruise 21 Oct 2008 (295) 15 Sep 2009 (258)Mercury 3 Flyby 16 Sep 2009 (259) 14 Oct 2009 (287)Mercury 4 Cruise 15 Oct 2009 (288) 03 Mar 2011 (062)Mercury Orbit 04 Mar 2011 (063) 17 Mar 2012 (077)Mercury Orbit Year 2 18 Mar 2012 (078) 17 Mar 2013 (076)Mercury Orbit Year 3 18 Mar 2013 (077) 17 Mar 2014 (076)Mercury Orbit Year 4 18 Mar 2014 (077) 17 Mar 2015 (076)Mercury Orbit Year 5 18 Mar 2015 (077) 30 Apr 2015 (120) No XRS data were collected during Earth Flyby or Venus 1 Flyby phases. TheXRS was on for some of each of the other seventeen mission phases. Duringthese planned operational periods, the XRS functioned nominally and the dataquality was good. Specific XRS operational periods were:  Start time End timePhase Name Date (DOY) Date (DOY)----------------- ---------------- ----------------Launch 30 Aug 2004 (243) 30 Aug 2004 (243)Earth Cruise 07 Feb 2005 (038) 11 Feb 2005 (042) 14 Apr 2005 (104) 14 Apr 2005 (104) 09 Jul 2005 (190) 13 Jul 2005 (194)Earth Flyby No DataVenus 1 Cruise 16 Jan 2006 (016) 13 Feb 2006 (044) 06 Sep 2006 (249) 10 Sep 2006 (253)Venus 1 Flyby No DataVenus 2 Cruise 27 Jan 2007 (027) 31 Jan 2007 (031)Venus 2 Flyby 26 May 2007 (146) 20 Jun 2007 (171)Mercury 1 Cruise 21 Jun 2007 (172) 08 Aug 2007 (220) 17 Aug 2007 (229) 25 Aug 2007 (237) 21 Dec 2007 (356) 30 Dec 2007 (364)Mercury 1 Flyby 31 Dec 2007 (365) 21 Jan 2008 (021)Mercury 2 Cruise 28 Mar 2008 (088) 02 Jun 2008 (154) 11 Jun 2008 (163) 21 Sep 2008 (265)Mercury 2 Flyby 22 Sep 2008 (266) 20 Oct 2008 (294)Mercury 3 Cruise 21 Oct 2008 (295) 19 Nov 2008 (324) 15 Jan 2009 (015) 04 May 2009 (124) 07 May 2009 (127) 17 May 2009 (137) 28 Aug 2009 (240) 01 Sep 2009 (244) 04 Sep 2009 (247) 15 Sep 2009 (258)Mercury 3 Flyby 16 Sep 2009 (259) 29 Sep 2009 (272)Mercury 4 Cruise 22 Jan 2010 (022) 03 Dec 2010 (337) 06 Dec 2010 (340) 03 Mar 2011 (062)Mercury Orbit 04 Mar 2011 (063) 16 Mar 2011 (075) 23 Mar 2011 (082) 07 Mar 2012 (067) 12 Mar 2012 (072) 17 Mar 2012 (077)Mercury Orbit Year 2 23 Mar 2012 (083) 17 Mar 2013 (076)Mercury Orbit Year 3 18 Mar 2013 (077) 17 Mar 2014 (076)Mercury Orbit Year 4 18 Mar 2014 (077) 17 Mar 2015 (076)Mercury Orbit Year 5 18 Mar 2015 (077) 30 Apr 2015 (120) The XRS gas proportional counters were intentionally powered down on 7 June2007, following the Venus 2 flyby. The solar monitor remained on throughoutthe Venus 2 Flyby phase. During Mercury 1 Cruise the gas proportional counters were on from August 4-8,August 17-24, and December 21-30. The solar monitor was on for all of theindicated time periods. The XRS gas proportional counters were intentionally powered down on 15January 2008, following the Mercury 1 flyby. The XRS was powered down on 21January 2008. The XRS was powered up on 28 March 2008 and remained on until 3 June 2008.They were turned on again on 11 June 2008 and remained on throughout theremainder of the Mercury 2 Cruise phase and the entire Mercury 2 Flyby phase.During the Mercury 2 Cruise phase the aluminum filtered gas proportionalcounter safed itself for 1 hour on two separate occasions, 28 August (241)and 7 September (251). These two safing events were caused by excessivecount rates in the anti-coincidence wires of the counter. The gasproportional counters were intentionally powered down on 7 October,following the Mercury 2 flyby. The solar monitor remained on throughout theMercury 2 Flyby phase. The solar monitor remained on during Mercury 3 Cruise until 19 November 2008.The entire XRS was powered up again on 15 January 2009. The gasproportional counters were intentionally turned off on 22 January 2009 andthen powered up again on 7 May 2009. The entire instrument was powered offon 17 May 2009. The XRS was powered up on 28 August 2009 and was powered down on 1September 2009 due to spacecraft safing. After spacecraft recovery, XRS waspowered up on 4 September 2009 and remained on until 29 September 2009.Power down was again due to spacecraft safing. During the Mercury 4 Cruise phase of the mission, the GPCs were powered onprimarily for Cas-A observations, 22 January 2010 to 29 January 2010,30 March 2010 to 5 April 2010, 13 July 2010 to 19 July 2010, and22 October 2010 to 29 October 2010. Other time periods with GPC HV on were23 July 2010 to 29 August 2010, and 6 December 2010 to 23 December 2010.The solar monitor was powered up on 22 January 2010 and remained on for theremainder of this mission phase except for 4-5 December 2010. The XRS was powered off for orbit insertion maneuvers, 17-22 March 2011.Once in orbit, the XRS detectors were on continuously except where spacecraftoperations (eclipses) and instrument health and safety (temperature and countrate) required some or all of the detectors to be turned off. The XRS GPCs experienced a number of safing events during early orbit.During these safing events one or more of the GPCs safed due to high countrate and remained off for 1 hour until autonomous recovery. On 25 April thesafing limit for the GPCs was increased from 5000 s-1 to 10000 s-1 and theautonomous time to recover was reduced from 60 minutes to 5 minutes. MESSENGER experiences a hot planet/long eclipse season every ~88 days.During these times spacecraft periapse is over a sunlit portion of the planetand eclipses exceed 15 minutes. Initially, long eclipses required instrumentpower off for ~2 hours for each orbit due to spacecraft power limitations.Beginning in August 2012, this restriction was lifted and the GPCs remainedon during eclipse, but the solar monitor is still powered off when thermalmodeling shows that the temperature is likely to exceed the red limit(30 degrees C). In addition, when the solar monitor temperature exceeds ~19degrees C, spectra are dominated by electronic noise and are generally oflittle scientific value. Hot planet/long eclipse seasons are typically about2 weeks in duration. The sixteen seasons experienced so far began on25 May 2011, 21 August 2011, 15 November 2011, 11 February 2012, 8 May 2012,13 August 2012, 14 November 2012, 23 February 2013, 20 May 2013, 15 August2013, 14 November 2013, 1 February 2014, 7 May 2014, 1 August 2014, 31October 2014, and 27 January 2015. On 5 March 2012 a large solar particle event produced severe radiation damagein the XRS solar monitor. Above -10 degrees C leakage current in the solarmonitor was so high that spectra were of no scientific value. A two dayanneal at 100 degrees C, beginning on 20 March 2012, improved the situationsignificantly so that good solar monitor spectra could be collected up to ~+5degrees C. A second two day anneal, beginning on 3 April 2012, produced onlymarginal improvement. No other anneals were planned. After 22 March 2012,only solar spectra collected when the detector temperature is ~2 degrees C orless should be used for science analysis. During the remaining three years oforbital operations, solar particles events continued to be an issue for thesolar monitor, as described below. For the last ~6 months of orbitaloperations, scientifically useful solar monitor spectra are limited to thosewhen the detector temperature is less than ~1 degrees C. On 1 April 2012, the high voltage was increased on all three of the gasproportional counters to adjust for loss of gain in the detectors. The newhigh voltage settings are Mg filtered: 1437 volts, Al filtered: 1426 volts,and unfiltered: 1436 volts. The GPC voltages have remained at these levelsexcept for a period from 17 June 2014 to 2 October 2014, when the voltageswere set to the old values. On 28 February 2013, 11 May 2013, 4 June 2013, 29 August 2013, and 25November 2013 the solar monitor temperature exceeded its red limit and thedetector safed itself. In each case the solar monitor remained off forseveral days. Also, on 26 August 2013, the XRS was safed by a spacecraftautonomy rule. XRS remained off for about 1 day. On 20 August 2013 a large solar particle event caused the GPCs to safe andremain off for about 3 days. This solar particle event also affectedoperation of the solar monitor. The solar monitor noise level increased andthe detector no longer provided solar spectra above ~0 degrees C. A threeday anneal was performed 9-12 September 2013. This anneal increased theuseful upper level operating temperature of the solar monitor back to whereit had been prior to the 20 August 2013 solar event. On 1 September 2014 a large solar event caused the GPCs to safe. Theyremained off for about 1 day. On 24 March 2015 a large solar event caused the GPCs to safe.They remained off for about 1 day. Mission operations ended on 30 April 2015 with impact of the MESSENGERspacecraft on the surface of the planet. Limitations:This is a calibrated data set. It includes the data that are received fromthe spacecraft telemetry as well as calibration information and otherancillary data necessary for data analysis. No data gaps have beenidentified for any of the XRS operational periods other than those notedabove.