Data Set Overview : This data set consists of the MESSENGER GRS uncalibrated observations, also known as EDRs. There are ten standard data products associated with the GRS sensor. A single EDR data file will contain the observations with a time tag corresponding to a given Earth day. One EDR contains a set of raw spectra data collected by the Ge detector and a second and third EDR (2 versions) contain raw spectra data collected from the shield detector. A fourth data product contains 10-ms cadence measurements of the total shield count rate. A fifth EDR contains the spectra accumulated due to anti-coincidence events in the Ge detector and the shield. A sixth EDR contains microphonics data associated with the cryocooler. The other four EDRs consist of information related to software rate counter telemetry, status telemetry, and diagnostic instrument status and command data.   Instrument Overview : The GRS detector is a high-resolution coaxial germanium crystal 50 mm in diameter and 50 mm in length, chosen for its radiation damage resistance and annealing capabilities. The detector is rigidly clamped in a hermetically sealed Al capsule pressurized with clean, dry nitrogen. The capsule is cooled to an operating temperature in the 80-95 K range by a mechanical cryocooler. A plastic scintillator anti-coincidence shield surrounds the germanium detector in its sides and back, for rejection of cosmic-ray background. Galactic cosmic rays continuously bombard the surface of Mercury, and through interactions with the surface, gamma-rays of discrete energies that are characteristic of specific elements are created. A fraction of these gamma-rays, as well as those from the decay of radiogenic elements escape from the surface, where they can be detected by the orbiting GRS. Gamma-ray fluxes are measurable at altitudes up to 1000 km and for gamma-rays up to about 10 MeV that emanate from depths of up to tens of centimeter beneath the surface. Detected fluxes are generally low and require numerous orbital passes over a specific region to obtain a statistically well-defined energy spectrum. The measurements of elements such as Fe, Si, Mg, Na, Al, Ca, Ti, K and Th by GRS will provide insight into distinguishing between different formation models for Mercury as well as other planetary evolution issues.  See the GRNS_INST.CAT file for more information and [GOLDSTENETAL2007] for full details.   Calibration Overview : This data set is NOT calibrated; it only provides the uncalibrated sensor measurements.   Parameters : The principal parameters when observing with the GRS are as follows:  * Accumulation Time: The accumulation time, in seconds, of the Ge detector.   Data : There are ten standard data products associated with the GRS sensor. A single EDR data file will contain the observations with a time tag corresponding to a given Earth day. One EDR contains a set of raw spectra data collected from the high purity Ge detector during a specified amount of time. These data are contained in 16,384 (2^14) channels, which can be used to create a histogram that shows the distribution of events (number of strikes) as a function of energy (channel number). Because of the low count rates usually encountered, accumulation times of minutes to hours are normal.  Two EDRs contain raw spectra data collected from the shield detector. The shield scintillator has a much lower energy resolution than the Ge detector, so events detected from the shield are binned in only 1024 channels. If events are found to occur in both detectors within some short time interval (of order microseconds), a coincidence condition is flagged; such events are usually caused by cosmic rays. A separate EDR contains the spectra accumulated due to anticoincidence events, to remove coincidence event background from cosmic rays.  Another EDR measures the total count rate at high time cadence (10 ms) in order to provide new insights into the charged particle environment around Mercury, particularly the energetic electron events.  The microphonics data are contained in an EDR and consist of a binned time series of fluctuations generated electronically that are associated with cryocooler vibrations. The microphonics data are used to help determine if the cooler is developing vibration issues. Data from the software event counters and associated data are stored in a separate EDR. Similarly, a separate EDR provides status data, which contains many engineering parameters, such as voltages, currents, temperatures, and modes. Another EDR contains information about the state of the instrument, with many parameters associates with the Analog-to-Digital converter event processing in the associated field-programmable gate array. A final EDR contains the time-tagged list of commands executed by the GRS instrument. It also records the success level of each command.

Confidence Level Overview : The GRS EDR data are the least processed data set released for the GRS. Data presented here are an accurate representation of the GRS 'raw' data as received from the spacecraft, with minimal timing processing, no data calibration, no unit conversion, and no spatial processing.   Review : The GRS EDR was reviewed internally by the GRS team prior to release to the PDS. PDS also performed an external review of the GRS EDR. Before the initial release, all functional modes were tested and reviewed, including bit-by-bit comparison with telemetry results from another tested program, GSEOS. In more recent releases, Ge detector science spectra are analyzed.   Data Coverage and Quality : Data reported are the minimally processed data received from the spacecraft during the the following mission phases: Launch, Earth Cruise, Earth Flyby, Venus 1 Cruise, Venus 1 Flyby, Venus 2 Cruise, Venus 2 Flyby, Mercury 1 Cruise Mercury 1 Flyby, Mercury 2 Cruise, Mercury 2 Flyby, Mercury 3 Cruise, Mercury 3 Flyby, Mercury 4 Cruise, Mercury Orbit, Mercury Orbit Year 2, Mercury Orbit Year 3, and Mercury Orbit Year 4. These mission phases are defined as:  Start time End time Phase 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 (028) 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)  These specific operational periods in relation to the mission phases were:  Start time End time Phase Name Date (DOY) Date (DOY) Sensor -------------------- ----------------- ----------------- ------ Launch 12 Aug 2004 (225) 13 Aug 2004 (226) Earth Cruise 10 Nov 2004 (315) 16 Nov 2004 (321) Ge Earth Flyby No Data Venus 1 Cruise No Data Venus 1 Flyby No Data Venus 2 Cruise 27 Mar 2007 (088) 30 Mar 2007 (089) shield Venus 2 Flyby 04 Jun 2007 (155) 08 Jun 2007 (159) shield Mercury 1 Cruise 26 Sep 2007 (269) 29 Sep 2007 (272) shield Mercury 1 Flyby 05 Jan 2008 (005) 15 Jan 2008 (015) shield Mercury 1 Flyby 13 Jan 2008 (013) 15 Jan 2008 (015) Ge Mercury 2 Cruise No Data Mercury 2 Flyby 03 Oct 2008 (277) 06 Oct 2008 (280) shield Mercury 2 Flyby 04 Oct 2008 (278) 06 Oct 2008 (280) Ge Mercury 3 Cruise 24 Sep 2009 (267) 27 Sep 2009 (270) shield Mercury 3 Flyby 28 Sep 2009 (271) 06 Oct 2009 (279) Ge Mercury 4 Cruise 02 Apr 2010 (092) 12 Apr 2010 (102) shield Mercury 4 Cruise 13 Apr 2010 (103) 15 Apr 2010 (105) Ge Mercury 4 Cruise 17 Sep 2010 (260) 24 Sep 2010 (267) shield Mercury Orbit 23 Mar 2011 (082) 03 Jun 2011 (154) Ge Mercury Orbit 11 Jun 2011 (162) 14 Jun 2011 (165) Ge Mercury Orbit 16 Jun 2011 (167) 05 Jul 2011 (186) Ge Mercury Orbit 20 Jul 2011 (201) 25 Jul 2011 (206) Ge Mercury Orbit 28 Jul 2011 (209) 06 Sep 2011 (249) Ge Mercury Orbit 08 Sep 2011 (251) 17 Sep 2011 (260) Ge Mercury Orbit Year 2 18 Mar 2012 (078) 15 Jun 2012 (167) shield Mercury Orbit Year 3 18 Mar 2013 (077) 17 Mar 2014 (076) shield Mercury Orbit Year 4 18 Mar 2014 (077) 17 Mar 2015 (076) shield  In this list, 'shield' means shield only and 'Ge' means Ge and shield. The GRS operational mode during most of the flyby time periods was a 'sleep mode' during which an operational heater maintained the cryocooler temperature at a constant value (to avoid temperature cycling of the cryocooler He seals) and the remainder of the instrument was shut down. Status data are continuously collected in this mode. Cryocooler exercises were conducted approximately every 6 months, but this is of engineering interest only.  Data from the cryocooled GRS high-resolution Ge detector were collected only during the full functional test in November 2004 and during the Mercury flybys in January and October 2008 and September-October 2009. This limitation preserves the lifetime of the limited-life cryocooler.  Data from the borated plastic shield were collected as part of a periodic cryocooler exercise; for the Venus-2 flyby (as another neutron detector to aid the NS); during the Mercury 1 Cruise in September 2007; for the Mercury 1, 2, and 3 Flybys.  A nonscience 'aliveness' test was conducted in August 2004.  The Ge detector energy resolution was somewhat degraded during Mercury Flyby 1 due to crystal displacement damage by cosmic rays, despite a 3-day anneal at 84C prior to the Flyby. To improve energy resolution for Flyby 2, the detector was kept at room temperature in July through mid-September in 'hot zombie' mode (no communication with the DPU to reduce memory usage and avoid upset events from cosmic rays). Then a 14-day anneal at 84C was conducted. After this, energy resolution was improved to nearly that found in the first cruise test shortly after launch.  During Mercury Flyby 3, the GRS data were collected only up to approximately 6 minutes before closest approach, at approximately 661 km altitude, due to a S/C safing that occurred. The GRS was restarted once the S/C was promoted to operation, but the S/C was far from the planet by this time. It is estimated that only approximately 18 percent of the signal counts from the planet were obtained below 2500 km altitude, compared to previous flybys. After the Ge detector recooled to operational temperature, engineering tests were run involving Ge temperature and high-voltage changes.  The shield was operated during May 2009 for some engineering tests. Otherwise the GRS operational mode during the Mercury 3 Cruise was 'warm zombie' mode, which performs a relatively low temperature Ge anneal to reduce radiation damage. Also the operational heater maintains the cryocooler temperature, to avoid cycling of the cryocooler He seals. On September 2 2009, the GRS was brought out of warm zombie mode and a 3-day Ge anneal at 84C was then performed. After this anneal the Ge energy resolution appeared to be close to that obtained for Mercury Flyby 2.  During Mercury 4 Cruise, the GRS remained in warm zombie mode, except the shield was on for some spectral tests on shield-only data and the Ge detector and shield were on for some spectra tests on coincidence spectra between the shield and and the Ge detector.  Just before orbit insertion, the GRS was brought out of warm zombie mode, and the Ge crystal was annealed for 7 days at 84C. After a few days of orbital operations the Ge energy resolution was measured to be close to the same value obtained for the M3 flyby. S/C temperatures were somewhat higher than expected during orbital operations, but the GRS cryocooler was able to cool the Ge detector easily.  During orbital operation, the GRS remained on continuously, except for periods when the high voltage was down, for various reasons, including an X-class SPE (Solar Particle Event) that safed the detector, OCMs (Orbital Correction Maneuvers), and cryocooler temperature setpoint changes. Periods having conditions that lead to broad energy resolution, such as radiation damage revealed by a Ge temperature increase or large very low-energy noise, have also been removed. Not shown in the table of operational periods are periods of SPEs that did not safe the detector: SPE2 08-02-2011, SPE3 08-04/05-2011, SPE4 08-09-2011, and SPE5 09-08/09-2011. These time periods should probably be eliminated from analysis, due to count-rate saturation and strong activation of gamma-ray peaks.  Beginning on 11 October, 2011, the HPGe detector began registering anomalous counts in the low-energy (< 300 keV) portion of the spectrum. While these events are lower in energy than the gamma-ray photopeaks of interest, the resulting count rate during these periods is sufficiently high to degrade the energy resolution for the detection of all gamma rays, regardless of energy. The magnitude of the anomalous counts and corresponding degradation of the energy resolution varies, and all data acquired after 11 October, 2011 should be carefully evaluated for its energy resolution prior to analysis. Particular care should be taken prior to summing individual gamma-ray spectra with differing energy resolution to produce summed spectra for analysis.  The GRS operated in anomalous count rate mode for the remainder of its life. The high voltage (HV) was maintained at its nominal value of 3200 V until 18 November, 2011, when it was lowered to 2700 V. It returned to 3200 V on 21 November, 2011, which was followed by a change to 2400 V. These changes were implemented in an attempt to maintain the highest possible energy resolution in the presence of the increased leakage current.  A short detector annealing activity took place from 15 December, 2011 to 21 December, 2011. This was followed by the arrival of an energetic solar particle event on 26 December, 2011 to 27 December, 2011.  A detector annealing activity took place from 19 March, 2012 to 29 March, 2012. Following this activity the detector leakage current was observed to have increased significantly with a corresponding degradation in the leakage current.  From 30 March, 2012 to 11 April, 2012, the detector high voltage value was varied between 1500 to 2400 V to characterize the energy resolution of the system as a function of high voltage.  A detector annealing activity took place from 11 April, 2012 to 28 April, 2012. Following this activity, the detector was operated at 2400 V.  In an attempt to preserve the limited lifetime of the GRS cryocooler, the detector was kept warm from 5 May 2012 to 1 June 2012. This time period corresponded to a time of elevated spacecraft temperatures. On 8 June, 2012 a weeklong detector annealing activity began.  On 15 June, 2012, the GRS cryocooler failed after approximately 9,500 hours of operation. This compares favorably to the 8,000 hour mean lifetime for these coolers. The failure occurred during a routine detector cool down following the 8 June 2012 annealing activity. Several unsuccessful attempts to revive the cooler have been made. Without the ability to maintain the HPGe detector at cryogenic temperature, gamma-ray measurements are not possible. No Germanium data collected after June 15, 2012 will be supplied to PDS for archiving.  On 25 February, 2013, new flight software was uploaded to the GRS. The purpose was to optimize the capability of the instrument to characterize neutron emission from Mercury's surface by changing the gain of the shield spectrum. Additionally, a new data product was added (SCR), which produces 10-ms cadence measurements of the total shield count rate. Because the shield responds to charged particles, these measurements represent the highest time cadence samples of the energetic charged particle environment around Mercury. The first several weeks were devoted to parameter optimization, with official data collection beginning on 18 March, 2013.  Beginning on 9 September, 2014, a new data operations mode was implemented in which the SHI data is acquired at a higher time cadence when MESSENGER is within 500 km altitude of Mercury. During these periods, SCR data collection is temporarily suspended.  Periods of elevated count rates resulting from spacecraft-incident SPE events includes data collected on:  3-4 June, 2011; 1 August, 2011; 3-4 August, 2011; 8 August, 2011; 7-8 September, 2011; 21-23 September, 2011; 3-5 October, 2011; 14-15 October, 2011; 3-5 November, 2011; 17-18 November, 2011 22-23 December, 2011; 2 January, 2012; 23-31 January, 2012; 28-29 January, 2012;  Post-January 2012 flares are difficult to isolate in the count-rate anomaly compromised dataset. Care should be used when utilizing these data as they may also contain gamma-ray detections resulting from prompt and/or long-lived activation products. The count rate anomaly issue does not apply to data collected following the 25 February, 2013 flight software upload.  For measurements taken following the 25 February, 2013 software upload, the following times were compromised by SPEs:  15-16 March, 2013; 11-12 April, 2013; 21-22 April, 2013; 24-25 April, 2013; 12-15 May, 2013; 31 May - 1 June, 2013; 21-25 June, 2013; 19-23 August, 2013; 5 October, 2013; 11-14 October, 2013; 22-23 October, 2013; 25-30 October, 2013; 6-8 November, 2013; 19 November, 2013; 29 November - 1 December, 2013; 13-15 December, 2013; 25-28 December, 2013; 6 January, 2014; 8-10 January, 2014; 22-23 January, 2014; 26 January, 2014; 28-31 January, 2014; 11-12 February, 2014; 14-15 February, 2014; 18-20 February, 2014; 25 February - 2 March, 2014; 4 March, 2014; 12-14 March, 2014; 29 April, 2014; 1 May, 2014; 5 May, 2014; 4-5 June, 2014; 10-12 June, 2014; 17 June, 2014; 8-9 August, 2014; 1-5 September, 2014; 10-12 September, 2014; 25-27 September, 2014; 14 October, 2014.  The degree to which science data can be derived from these SPE-comprised periods varies on an event-by-event basis.  Periods with no science data, corresponding to instrument safing or operations activities include:  4-16 June, 2011; (Safed) 6-16 July, 2011; (GRS Annealing) 26 July, 2011; (Short safing event) 7 September, 2011; (Short safing event) 24-25 October, 2011; (Short safing event) 8-10 November, 2011; (Safing) 4-6 December, 2011; (Instrument Safing) 15-20 December, 2011; (Detector Annealing) 2-12 March, 2012; 24-25 April, 2013; (HV shutdown during OCM) 21-24 June, 2013; (Instrument Safing due to SPE) 20-22 August, 2013; (Instrument Safing due to SPE) 25-30 October, 2013; (Instrument Safing due to SPE) 26-28 December, 2013; (Instrument Safing due to SPE) 17 June, 2014; (HV shutdown during OCM) 1-5 September, 2014; (Instrument Safing due to SPE) 10-12 September, 2014; (Instrument Safing due to SPE)  Restrictions on data generation resulting from limited space on the spacecraft data record resulted in SCR products being suspended during the following periods:  14 December 2013 - 2 January, 2014; 16 January 2014 - 1 February, 2014;  SCR data acquired between 2 January and 16 January are subject to a time offset that will be fixed in a future delivery.   Limitations : This data set is minimally processed data. The data are received from the spacecraft telemetry and ingested into the MESSENGER Science Operations Center (SOC). No data gaps or corrupted data have been identified for any of the GRS operational periods. Although there may be some data not identified as missing or corrupted, such data should be minimal and a very small fraction of the available data.