| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains Raw data taken by New Horizons
Student Dust Counter
instrument during the LAUNCH mission phase.
The SDC instrument was commissioned on March 2, 2006 and stepped
through a checkout of all instrument functionality successfully.
Following these activities, SDC collected science data
intermittently throughout the first year of the mission.
Note that some SDC data files have the same stop and start time
and a zero exposure time. The reason for this is that the start
and stop time for SDC data files are the event times for the
first and last events in the files, so for files that contain a
single event, these two values are identical.
Every observation provided in this data set was taken as a part of a
particular sequence. A list of these sequences follows:
Sequence IDs & start times (end times are the start times
of the following Sequence IDs) for the SDC instrument
during the LAUNCH phase of the New Horizons Mission
=========================================================
Sequence ID: COSD_001
Start UTC: 2006-03-02T00:00:00
Start SCLK: 1/0003563517:33543
Description: Turn-on; Noise Floor Calibrations; Stimulus Tests
Sequence ID: COSD_002
Start UTC: 2006-04-01T00:00:00
Start SCLK: 1/0006155517:32813
Description: Noise Floor Calibrations; Stimulus Tests
Sequence ID: COSD_003
Start UTC: 2006-07-14T00:00:00
Start SCLK: 1/0015141117:31672
Description: Science data collection
Sequence ID: COSD_004
Start UTC: 2006-08-16T00:00:00
Start SCLK: 1/0017992317:31481
Description: Science data collection
Sequence ID: JESD_PLACEHOLDER
Start UTC: 2007-01-01T00:00:00
Start SCLK: 1/0029915517:30912
Description: The SDC instrument did not have any sequenced data taken
during Jupiter encounter. This entry is only a
placeholder to cover any data that exist.
For the list of observations and their parameters, refer to
the data set index table (typically INDEX.TAB & CUMINDEX.TAB,
initially in the /INDEX/ area of the data set).
Time
====
There are several time systems, or units, in use in this dataset:
New Horizons spacecraft MET (Mission Event Time or Mission Elapsed
Time), UTC (Coordinated Universal Time), and TDB Barycentric
Dynamical Time.
This section will give a summary description of the relationship
between these time systems. For a complete explanation of these
time systems the reader is referred to the documentation
distributed with the NAIF/SPICE toolkit from the NAIF PDS node.
The most common time unit associated with the data is is the
spacecraft MET. MET is a 32-bit counter on the New Horizons
spacecraft that runs at a rate of about one increment per second
starting from a value of zero at
19.January, 2006 18:08:02 UTC
or
JD2453755.256337 TDB.
The leapsecond adjustment (DELTA_ET = ET - UTC) over this dataset
is 65.184s.
The data labels for any given product in this dataset usually
contain at least one pair of common UTC and MET representations
of the time at the middle of the observation. Other portions
of the products, for example tables of data taken over periods
of up to a day or more, will only have the MET time associated
with a given row of the table.
For the data user's use in interpreting these times, a reasonable
approximation (+/- 1s) of the conversion between Julian Day (TDB)
and MET is as follows:
JD TDB = 2453755.256337 + ( MET / 86399.9998693 )
For more accurate calculations the reader is referred to the
NAIF/SPICE documentation as mentioned above.
Processing
==========
The data in this data set were created by a software data
processing pipeline on the Science Operation Center (SOC) at
the Southwest Research Institute (SWRI), Department of Space Studies.
This SOC pipeline assembled data as FITS files from raw telemetry
packets sent down by the spacecraft and populated the data labels
with housekeeping and engineering values, and computed geometry
parameters using SPICE kernels. The pipeline did not resample
the data.
Data
====
The observations in this data set are stored in data files using
standard Flexible Image Transport Sytem (FITS) format. Each FITS
file has a corresponding detached PDS label file, named according
to a common convention. The FITS files have image and/or table
extensions; see the PDS label plus the DOCUMENT files for a
description of these extensions and their contents.
This Data section comprises the following sub-topics:
- Filename/Product IDs
- Other sources of information useful in interpreting these Data
- CODMAC Level 2 SDC data details
- Instrument description
- Visit Description, Visit Number, and Target in the Data Labels
- Unresolved Liens on the Data
Filename/Product IDs
--------------------
The filenames and product IDs of observations adhere to a
common convention e.g.
ALI_0123456789_0X0AB_ENG_1.FIT
^^^ ^^^^^^^^^^ ^^^^^ ^^^ ^\__/
| | | | | ^^
| | | | | |
| | | | | +--File type (includes dot)
| | | | | - .FIT for FITS file
| | | | | - .LBL for PDS label
| | | | | - not part of product ID
| | | | |
| | | | +-- Version number from the SOC
| | | | (Science Operations Center)
| | | |
| | | +--ENG for CODMAC Level 2 data *
| | | SCI for CODMAC Level 3 data *
| | |
| | +--Application ID (ApID) of the telemetry data
| | packet from which the data come
| |
| +--MET (Mission Event Time) i.e. Spacecraft Clock
|
+--Instrument designator
* For those datasets where the NH project is delivering
CODMAC Level 1 & 2 data (REX & PEPSSI), ENG and SCI apply
to CODMAC Level 1 & 2 data, respectively.
Instrument Instrument designators ApIDs
=========== ================================== =============
SDC SDC 0X700
* Not all values in this range are used
There are other ApIDs that contain housekeeping values and
other values. See the documentation for more details.
Here is a summary of the types of files generated by each ApID
along with the instrument designator that go with each ApID:
ApIDs Data product description/Prefix(es)
===== ===================================
0x700 - SDC Science Data/SDC
Other sources of information useful in interpreting these Data
--------------------------------------------------------------
Refer to the following files for more information about these data
NH Trajectory table:
/DOCUMENT/NH_TRAJECTORY.*
SDC Field Of View definitions:
/DOCUMENT/NH_FOV.*
/DOCUMENT/NH_SDC_V###_TI.TXT
Instrument description
----------------------
Refer to the following files for a description of this instrument.
CATALOG
SDC.CAT
DOCUMENTS
SDC_SSR.*
NH_SDC_V###_TI.TXT (### is a version number)
SOC_INST_ICD.*
Visit Description, Visit Number, and Target in the Data Labels
---------------------------------------------------------------
The observation sequences were defined in Science Activity
Planning (SAP) documents, and grouped by Visit Description and
Visit Number. The SAPs are spreadsheets with one Visit Description
& Number per row. A nominal target is also included on each row
and included in the data labels, but does not always match with the
TARGET_NAME field's value in the data labels. In some cases, the
target was designated as RA,DEC pointing values in the form
``RADEC=123.45,-12.34'' indicating Right Ascension and Declination,
in degrees, of the target from the spacecraft in the Earth
Equatorial J2000 inertial reference frame. This indicates either
that the target was either a star, or that the target's ephemeris
was not loaded into the spacecraft's attitude and control system
which in turn meant the spacecraft could not be pointed at the
target by a body identifier and an inertial pointing value had to
be specified as Right Ascension and Declination values. The PDS
standards do not allow putting a value like RADEC=... in the PDS
TARGET_NAME keyword's value; in those cases the PDS TARGET_NAME
value is set to CALIBRATION.
Unresolved Liens on the Data
----------------------------
None exist at the present time.
Ancillary Data
==============
The geometry items included in the data labels were computed
using the SPICE kernels archived in the New Horizons SPICE
data set, NH-X-SPICE-6-LAUNCH-V1.0.
Reference Frame
===============
Geometric Parameter Reference Frame
-----------------------------------
Earth Mean Equator and Vernal Equinox of J2000 (EMEJ2000) is the
inertial reference frame used to specify observational geometry
items provided in the data labels. Geometric parameters are based
on best available SPICE data at time of data creation.
Epoch of Geometric Parameters
-----------------------------
All geometric parameters provided in the data labels were
computed at the epoch midway between the START_TIME and
STOP_TIME label fields.
Software
========
The observations in this data set are in standard FITS format
with PDS labels, and can be viewed by a number of PDS-provided
and commercial programs. For this reason no special software is
provided with this data set.
Contact Information
===================
For any questions regarding the data format of the archive,
contact the person whose PDS_USER_ID is MHORANYI
as described in PERSONNEL.CAT.
|
| CONFIDENCE_LEVEL_NOTE |
Confidence Level Overview
=========================
During the processing of the data in preparation for
delivery with this volume, the packet data associated with each
observation were used only if they passed a rigorous verification
process including standard checksums.
In addition, raw (Level 2) observation data for which adequate
contemporary housekeeping and other ancillary data are not available
are not reduced to calibrated (Level 3) data. This issue is raised
here to explain why some data products in the raw data set,
NH-X-SDC-2-LAUNCH-V2.0,
do not have corresponding data products in the calibrated data set,
NH-X-SDC-3-LAUNCH-V2.0.
Review
======
The data have been reviewed and validated by the instrument team
members, as well as by SOC personnel.
SDC updates for Data Sets V2.0
==============================
None of the formats for the Calibrated data will change. The data
file will look the same, including the data formats. The changes
are improvements to the processing code. There were 3 changes made
to the code:
Change to dust impact velocity assumption
-----------------------------------------
An assumption is needed for the the dust impact velocity to
calculate its mass. Before this update the pipeline used only the
normal component of the total velocity between the dust and
instrument (assuming the particle is in Keplerian orbit).
Now this has been changed to the total relative velocity of the
particle (still assumed to be in Keplerian orbit) and the
instrument.
Using multiple sensors for temperature correction
-------------------------------------------------
There are two thermistors on the analog board. The analog board
temperature is used for calibrating a particular channel on the
board. Before this update, for a given channel the temperature
of the closest thermistor to a that channel. Now a linear fit
to the temperatures is used.
New charge-velocity-mass calibration curve
------------------------------------------
The calibrated data contains the mass of the particle. The
charge to mass curve used to be
Q=3.18E17*m^1.3*v^3.0
where m is the mass, Q is the charge and v is the relative speed.
This was the Simpson-Tuzzolino curve. The new curve is a function
of detector temperature as well:
Q=(1.15E15+6.75E12*T)*m^1.052*v^2.883
where T is the temperature. A paper with this new calibration
curve will be submitted for publication in Spring, 2009.
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