| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set consists of the MESSENGER NS uncalibrated observations,
also known as EDRs. There are nine standard data products associated
with the NS sensor. A single EDR data file will contain the
observations with a time tag corresponding to a given Earth day. The NS
Full Science Spectra EDR contains the five spectra histograms collected
by the NS when in 'Full Science' mode. This EDR replaces the NS Spectra
EDR as a result of a flight software update in February 2006. The NS
Short Science EDR contains just three of the spectra histograms
collected by the NS, in contrast to the five spectra histograms in the
Full Science Spectra EDR. Other EDRs contain events data, galactic
cosmic ray spectra, gamma ray burst data, time-correlated counts,
critical NS status information, and calibration and diagnostic
information.
Instrument Overview
===================
The NS sensor consists of three scintillators, each wrapped separately
and coupled to separate photo-multiplier tubes. The three scintillators
are sensitive to neutrons of different energies: thermal neutrons
(0.025 - 1 eV), epithermal neutrons (1eV - 500 keV), and fast neutrons
(500 keV - 7 MeV). The first and third scintillators are lithium
(6Li)-glass scintillators (LiG1 and LiG2) which respond to a
combination of thermal and epithermal neutrons. The middle scintillator
is a borated plastic scintillator (BPS) that responds only to
epithermal and fast neutrons due to its electronics setup. The
interaction of galactic cosmic rays with the surface of Mercury
produces neutrons, some of which escape the surface and produce a
neutron signal that can be measured by the orbiting NS sensor. The
measured neutron energy spectrum reflects the transport properties of
the surface composition and is sensitive to depths down to about 1 m.
Thermal neutrons are sensitive to a variety of elements, including Fe,
Ti, Gd, Sm, Cl, and C. Epithermal neutrons are mostly sensitive to H
abundance. Fast neutrons can provide a good measure of average atomic
mass. For the MESSENGER mission, the NS sensor will establish and map
the abundance of H over most of the northern hemisphere of Mercury,
providing significant new information regarding the potential presence
of water ice within and near permanently shaded craters near the north
pole.
See the NS_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 NS are as follows:
* Actual Accumulation Period: The actual accumulation period for
software counters and energy histograms.
* GCR Mode: Sets the state for the galactic cosmic ray coincidence
mode. 1= Doubles, 2=triples, 3=either.
* Log Compression: Identifies when the log compression data mode has
been enabled. The NS flight software uses 32-bit to 16-bit log
compression on software counters when the log compression data mode is
enabled. 0=no log compression. 1=log compression enabled.
* Event Mode Length: Event mode data length specifies the number of
items containing data in the event mode fields and has a value of
0-255.
* Gamma Ray Mode: Sets whether the NS is in 'gamma burst' mode.
* BP Channel Upper Limit: Sets the highest BP channel that will be used
as part of the source of the gamma-ray burst BP counts.
* Burst Threshold: Sets the burst lower pulse threshold.
* Status Interval: Defines the interval at which status is reported.
Values are given in seconds.
* Macro Learn: Sets whether macro learn mode is enabled or not.
0=not learning. 1=learning.
* Monitor Response: Sets whether monitor response is enabled (=1) or
disabled (=0).
* Write Enable: Sets whether memory write is enabled (=1) or
disabled (=0).
* Capture Energy Limit: Sets the capture energy limit.
* Power Management: Power management bit register. Defines various
circuit parameters, including normal and sleep modes.
* Gain Dac: Controls BP channel gain by changing ADC reference.
* BP Charge Reset: BP charge reset.
* BP Prompt Threshold: Sets the BP prompt trigger threshold.
* BP Secondary Threshold: Sets the BP secondary trigger threshold.
* LG1 Trigger Threshold: Sets the LG1 trigger threshold.
* LG2 Trigger Threshold: Sets the LG2 trigger threshold.
* Screen on DQ: Set calibration/diagnostic mode to screen out data with
DQ bit set. 0=No screen. 1=screen.
* No Compression Science Data: Science data mode enabled (=1) or
disabled (=0).
* Fast Compression Science Data: Fast compression of science data
enabled (=1) or disabled (=0).
* Log Compression Science Data: Log compression of spectra enabled
(= 1) or disabled (=0).
* Diagnostic Data Packet: Diagnostic packet enabled (=1) or
disabled (=0).
* Spare Data Packet: Spare data packet enabled (=1) or disabled (=0).
Used to enable gamma burst mode packets.
* HV1 Enabled: HV1 (BP) enabled (=1) or disabled (=0).
* HV2 Enabled: HV2 (LG1 and LG2) enabled (=1) or disabled (=0).
* Early Capture Start: Early capture window start time.
* Early Capture End: Early capture window end time.
* Late Capture Start: Late capture window start time.
* Late Capture End: Late capture window end time.
Data
====
There are nine standard data products associated with the NS sensor. A
single EDR data file will contain the observations with a time tag
corresponding to a given Earth day.
The NS Full Science Spectra EDR contains the five spectra histogram
arrays. Three of the spectra histogram arrays are from single events in
the three scintillators (LiG1, LiG2, and BPS). The data for LiG1, LiG2
and BPS have 64 channels; the channels are correlated to the energy
deposited in the scintillators. These three spectra are created by
event energies that arrived as a single event with no time correlation
to the other sensors. The other two spectra histogram arrays consist of
time-correlated events in the BP scintillator. The time-correlated
early spectrum is a histogram of prompt BP events that had a delayed BP
event occurring during the early capture window, while the
time-correlated late spectrum is similar but occurred during the late
capture window. Both of these spectra histogram arrays have 256
channels. The orbital neutron flux is significantly higher than the
gamma-ray flux, and thus the accumulation times for the NS instrument
can be smaller than that for the Gamma Ray Spectrometer (GRS); at low
and moderate altitudes, a 20 second integration time is a reasonable
assumption.
The NS Spectra EDR also contains the same five spectra histogram arrays
present in the NS Full Science Spectra EDR. A flight software update
replaced the NS Spectra EDR with the NS Full Science Spectra EDR in
February 2006. After this software update, the NS Spectra EDR is no
longer created.
The NS Short Science EDR contains a subset of the data in the NS Full
Science Spectra EDR. Specifically, it contains only three of the five
spectra histogram arrays: single event data from the BP scintillator
and the two time-correlated spectrum. This EDR may be generated as a
result of telemetry constrained situations.
The NS Events EDR contains event data collected by the NS in 'Science
Data' mode. The events data are transmitted in the same science
telemetry packet that contains the NS spectra data. The event-mode data
are event-by-event time series data of fast neutron events, rather than
energy histograms.
The NS Galactic Cosmic Ray EDR contains LiG1 and LiG2 galactic cosmic
ray spectra. The NS Gamma Burst EDR contains data collected in the
'gamma burst' mode and are of astrophysical interest. Gamma-ray bursts
are detected as counts that exceed a settable threshold over background
as determined by a running average of a counter.
The NS Time-Correlated Counts EDR contains data collected in the 'TC
Counters' mode. It contains the time-correlated early counter, whose
value equals the summation of every channel in the early time-
correlated spectra, and the time-correlated late counter, whose value
equals the summation of every channel in the late time-correlated
spectra.
The NS Status EDR contains critical state information recorded in the
NS status telemetry packet. The NS Calibration/Diagnostic EDR contains
calibration data recorded in the NS calibration/diagnostic telemetry
packet.
|
| CONFIDENCE_LEVEL_NOTE |
Confidence Level Overview
=========================
The NS EDR data are the least processed data set released for the NS.
Data presented here are an accurate representation of the NS data as
received from the spacecraft, with minimal timing and no spatial
processing.
Review
======
The NS EDR was reviewed internally by the NS team prior to release to
the PDS. PDS also performed an external review of the NS EDR.
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, Mercury Orbit Year 4 and
Mercury Orbit Year 5.
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)
Mercury Orbit Year 5 18 Mar 2015 (077) 30 Apr 2015 (120)
A nonscience 'aliveness' test was conducted in August 2004. The first
full function test was conducted April-May 2005. In August and
September 2005 and March 2006, engineering tests were conducted to
determine origin and magnitude of gain changes in a Li-glass detector
channel. A second full function test was conducted in June 2006 after
new software was uploaded. In January 2007 a calibration period was
begun and the NS was left on. The NS was off from mid-October 2007
through mid-December 2007 and from February 26, 2008 through March 28,
2008.
The NS had four off periods during the Mercury 3 Cruise phase:
Nov. 2008 - Jan 2009; July 2009; Four days in August 2009; Two days in
early September 2009. The NS had one off period during the
Mercury 3 Flyby period due to the spacecraft safing event that occurred
during the Mercury 3 Flyby.
The NS had three off periods during the Mercury 4 Cruise phase:
Oct. 2009 - Dec. 2009; four days in May 2010; and three days in Dec.
2010.
The NS had one off period during the Mercury Orbit phase in March 2011.
This off period was two days prior to Mercury Orbit Insertion (MOI) and
continued during the first week of orbit operations.
During the data delivery from May 18, 2011 to September 17, 2011, the
NS was shut off for nine consecutive days when the MESSENGER spacecraft
passed through its first long eclipse period. The specific off period
was from May 24, 2011 21:34:49 to June 3, 2011 0:17:49.
During the data delivery from May 18, 2011 to September 17, 2011, the
high voltage (HV) to the LG and BP sensors was shut down three times
during spacecraft thrusting maneuvers. Each time, the HV was shut down
for approximately four hours while the spacecraft was near apoapsis.
The specific times for the HV shut down are:
June 15, 2011 16:12:08 - June 15, 2011 20:30:16;
July 26, 2011 17:40:16 - July 26, 2011 21:55:16;
September 7, 2011 11:38:16 - September 7, 2011 16:05:50.
During the data delivery from September 18, 2011 to March 25, 2012, the
NS HV to the LG and BP sensor was shut down four times. Three times,
the HV was shut down during spacecraft thrusting maneuvers. The
specific times for these HV shut downs are: October 24, 2011 18:29:00 -
October 24, 2011 23:16:00; December 5, 2011 12:36:00 - December 5, 2011
17:18:00; March 2, 2012 22:09:22 - March 3, 2012 02:47:54. The HV to
the LG and BP sensors was shut down a fourth time during a large solar
particle event when the NS sensors were safed because of the large
charged particle flux. The times for this HV shut down period were:
March 7, 2012 0:24:42 - March 12, 2012 15:50:42.
During the data delivery from March 26, 2012 to September 17, 2012, the
NS HV was shut down once from April 16, 2012, ~18:00 UTC to
April 21, 2012, ~0:00 UTC for the MESSENGER spacecraft change from
12-hour orbit to 8-hour orbit.
During the data delivery from September 18, 2012 to March 17, 2013, the
NS HV for the BP sensor was shut down twice: first from
September 20, 2012 at 09:40 UTC to September 24, 2012 at 17:38 UTC when
the NS BP sensor went into safe mode due to an energetic particle
event; second on March 16, 2013 from 06:53 UTC to 08:00 UTC when the NS
BP sensor went into safe mode due to an energetic particle event.
During the data delivery from March 18, 2013 to September 17, 2013, the
NS HV was shut down six times into safe mode due to high rates from
energetic particles: 1) April 24, 2013 to April 25, 2013;
2) May 2, 2013, 8:45 UTC to May 2, 2013, 9:16 UTC; 3) May 21, 2013,
8:57 UTC to May 21, 2013, 9:32 UTC; 4) May 21, 2013, 17:02 UTC to
May 21, 2013, 17:33 UTC; 5) June 21, 2013 to June 24, 2013;
6) August 19, 2013 to August 22, 2013. Due to engineering
considerations, the NS_CAD2013233ZZZ product was not ncluded in this
delivery.
During the data delivery from September 18, 2013 to March 17, 2014 the
NS HV for the BP and/or LG sensor was shut down 6 times: 1) for
approximately two hours on October 25, 2013; 2) October 28, 2013,
16:00 UTC to October 29, 2013 02:00 UTC; 3) For less than an hour on
November 5, 2013; 4) For less than an hour on December 14, 2013;
5) December 26, 2013 07:00 UTC to December 31, 2013 20:00 UTC;
6) For less than an hour on Jan 25, 2014.
During the data delivery from March 18, 2014 to September 17, 2014 the
NS HV for the BP and LG sensors was shut down twice for a few hours for
spacecraft thrusting maneuvers. These times were June 17, 2014 at
12:00 UTC and September 12, 2014 at 13:00 UTC.
During the data delivery from September 18, 2014 to April 30, 2015 the
NS HV for the BP and LG sensors was shut down for a few hours for
spacecraft thrusting maneuvers.
These days were September 28, 2014 around 07:44 UTC,
October 24, 2014 around 16:00 UTC, and
January 21, 2015 around 19:30 UTC.
The specific operational periods in relation to the mission phases
were:
Start time End time
Phase Name Date (DOY) Date (DOY)
----------------- ----------------- -----------------
Launch 12 Aug 2004 (225) 13 Aug 2004 (226)
Earth Cruise 18 Apr 2005 (108) 23 May 2004 (143)
Earth Flyby 16 Aug 2005 (228) 16 Aug 2005 (228)
Venus 1 Cruise 07 Sep 2005 (250) 11 Sep 2005 (254)
07 Mar 2006 (066) 11 Mar 2006 (070)
16 Jun 2006 (167) 16 Jun 2006 (167)
21 Jun 2006 (172) 22 Jun 2006 (173)
Venus 1 Flyby No Data
Venus 2 Cruise 31 Jan 2007 (031) 22 May 2007 (142)
Venus 2 Flyby 23 May 2007 (143) 20 Jun 2007 (171)
Mercury 1 Cruise 21 Jun 2007 (172) 17 Oct 2007 (290)
Mercury 1 Cruise 21 Dec 2007 (355) 30 Dec 2007 (364)
Mercury 1 Flyby 31 Dec 2007 (365) 28 Jan 2008 (028)
Mercury 2 Cruise 29 Jan 2008 (029) 25 Feb 2008 (056)
Mercury 2 Cruise 29 Mar 2008 (089) 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)
11 Jan 2009 (011) 07 Jul 2009 (188)
22 Jul 2009 (203) 18 Aug 2009 (230)
23 Aug 2009 (235) 01 Sep 2009 (244)
04 Sep 2009 (247) 15 Sep 2009 (258)
Mercury 3 Flyby 16 Sep 2009 (259) 29 Sep 2009 (272)
01 Oct 2009 (274) 12 Oct 2009 (285)
Mercury 4 Cruise 09 Dec 2009 (343) 21 May 2010 (141)
26 May 2010 (146) 03 Dec 2010 (337)
06 Dec 2010 (340) 03 Mar 2011 (062)
Mercury Orbit 04 Mar 2011 (063) 16 Mar 2011 (075)(for MOI)
23 Mar 2011 (082) 24 May 2011 (144)
03 Jun 2011 (154) 07 Mar 2012 (067)
12 Mar 2012 (072) 17 Mar 2012 (077)
Mercury Orbit Year 2 18 Mar 2012 (078) 16 Apr 2012 (107)
21 Apr 2012 (112) 20 Sep 2012 (264)
24 Sep 2012 (268) 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)
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 NS 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.
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