| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains Raw data taken by New Horizons
Alice Ultraviolet Imaging Spectrograph
instrument during the PLUTOCRUISE mission phase.
PERSI-Alice (P-ALICE; also ALICE) is a spectrograph on the New Horizons
spacecraft that is sensitive to extreme and far UltraViolet (UV) light
(520-1870 Angstroms). The ALICE instrument comprises a telescopic optics
section and a spectrograph section that includes a diffraction grating
and a photosensitive two-dimensional (2-D) detector. The optics and
diffraction grating physical arrangement configure one detector
dimension as a spatial dimension and the other as spectral. ALICE has
two separate entrance apertures that feed light to the telescope section
of the instrument: the AirGlow Channel (AGC) aperture; the Solar
Occultation Channel (SOCC) aperture. Both apertures pass light to the
detector through a lollipop-shaped slit comprising two contiguous
sections: a narrow, rectangular slit with a Field Of View (FOV) of 0.1
by 4.0 degrees; a fat, square slit with FOV 2.0 x 2.0 degrees. ALICE has
two data-taking modes: pixel list mode records each detector/photon
event location (pixel i.e. spectral and spatial), interleaved with time
sequence events (hacks), allowing sub-second resolution of the photon
events; histogram mode summarizes the per-pixel photon event counts into
a 2-D histogram over all detector pixels, collected over an extended
time which can range from a few seconds to several days. From both
modes, the common data product is the histogram (derived on the ground
in the pixel list case), which is functionally equivalent to a
spectral-by-spatial spectrogram (2-D image); other data products are
also provided and described in this data set.
P-Alice Activities Overview: ACO-1 to ACO-8
===========================================
ACO-1 (Sept-Oct 2007)
Executed standard WakeUp sequence that includes memory/code checks, aperture
door performance test and pixelhack issue verification followed by two times
24 hour of decontamination and three one hour dark observations.
Performed pointing, flux and flatfield calibration on rho-Leo, airglow Solar
scattered light test down to 25deg, 115 frames histogram IPM scan, Ralph
interference test, three deep dark sky stares of 8 hours total each, pointing
flux and HV optimization observation on gamma-Grus, SOCC pointing and flux
calibration on Spica, pointing and short wavelength calibration on HD93521 and
SOCC pointing and flux calibration on zeta-Pup
Concluded activities with the standard Button-Up sequence that includes code
and parameters refresh.
ACO-2 (Oct-Nov 2008)
Executed standard WakeUp sequence that includes memory/code checks, aperture
door performance test and pixelhack issue verification followed by 48 hour of
decontamination and three one hour dark observations.
Adjusted countrate limit and HV rampup parameters. Performed Pointing and Flux
verification on rho-Leo, 456 frames pixellist IPM scan and REX2 interference
test.
Concluded activities with the standard Button-Up sequence that includes code
and parameters refresh.
ACO-3 (Jul-Aug 2009)
Executed standard WakeUp sequence that includes memory/code checks, aperture
door performance test and pixelhack issue verification followed by 48 hour of
decontamination.
Adjusted HV limit parameters. Performed a spinning 'dark' observation (in some
cases the Sun strobes through the slit).
Concluded activities with the standard Button-Up sequence that includes code
and parameters refresh.
ACO-4 (Jun-Jul 2010)
Executed standard WakeUp sequence that includes memory/code checks, aperture
door performance test and pixelhack issue verification followed by 48 hour of
decontamination and three one hour dark observations.
Performed Pointing, Flux and HV optimization observations on rho-Leo,
histogram and pixellist Flat-Field scan on rho-Leo, 93 frame histogram IPM
scan, 24 hour MeV Solar Wind (HEET) baseline observation, held histogram test
with LEISA and Lorri, SOCC pointing and flux verification on Sun (including
box scan perpendicular to the slit) and SOCC Flat-Field scan on Sun (box scan
along the slit).
Concluded activities with the standard Button-Up sequence that includes code
and parameters refresh.
ACO-5 (May 2011)
Executed standard WakeUp sequence; adjusted HV limit parameters; performed a
spinning 'dark' observation.
ACO-6 (May-Jun 2012)
Executed standard WakeUp sequence; adjusted HV limit parameters; performed a
spinning 'dark' observation; performed Pluto encounter rehearsal; performed
Pointing, Flux and HV optimization observations on rho-Leo and HD93521, and on
the Sun through the Solar OCcultation Channel (SOCC).
ACO-7 (Jun-Jul 2013)
Executed standard WakeUp sequence; adjusted HV limit parameters; performed a
spinning 'dark' observation; performed Pluto encounter rehearsal; performed
Pointing, Flux and HV optimization observations on rho-Leo; performed dual
target pointing verification on 10 Lac and 8 Lac (HD214680 and HD214168).
ACO-8 (Jul 2014)
Executed standard WakeUp sequence; adjusted HV limit parameters; performed a
spinning 'dark' observation; performed an IPM scan, which failed.
Every observation provided in this data set was taken as a part of a
particular sequence. A list of these sequences has been provided in
file DOCUMENT/SEQ_ALICE_PLUTOCRUISE.TAB.
N.B. Some sequences provided may have no corresponding observations.
For a list of observations, refer to the data set index table. This
is typically INDEX.TAB initially in the INDEX/ area of the data set.
There is also a file SLIMINDX.TAB in INDEX/ that summarizes key
information relevant to each observation, including which sequence
was in effect and what target was likely intended for the
observation.
Version
=======
This is VERSION 2.0 of this data set.
The pipeline (see Processing below) was re-run on these data for each
version since the first (V1.0). As a result, ancillary information,
such as observational geometry and time (SPICE), may be updated.
This will affect, for example, the calibration of the data if parameters
such as the velocity or orientation of the target relative to the
instrument, or the recorded target itself, have changed.
See the following sections for details of what has changed over each
version since the first (V1.0). Note that even if this is not a
calibrated data set, the calibration changes are listed as the data
will have been re-run and there will be updates to the calibration
files, to the documentation (Science Operations Center - Instrument
Interface Control Document: SOC_INST_ICD) and to the steps required
to calibrate the data.
ALICE updates for PLUTOCRUISE
Data Sets V2.0
==============
The previous Pluto Cruise data sets' deliveries (V1.0) went
through peer review in December, 2014. When subsequent versions
of those data sets were being delivered, some with additional data
(from August, 2014 through January, 2015) before all of those
previous liens were resolved, the previous data sets were left as
is, with those liens folded into the newer data sets.
New observations added with this version (V2.0) include IPM
histogram scans in December, 2014, which failed.
Other changes for this version were re-running of the ancillary
data in the data product, updated geometry from newer SPICE
kernels, minor editing of the documentation, catalogs, etc., and
resolution of liens from the December, 2014 review, plus those
from the May, 2016 review of the Pluto Encounter data sets.i
Processing
==========
The data in this data set were created by a software data
processing pipeline on the Science Operations Center (SOC) at
the Southwest Research Institute (SwRI), Department of Space Operations.
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 System (FITS) format. Each FITS
file has a corresponding detached PDS label file, named according
to a common convention. The FITS files may 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
- Instrument description
- Other sources of information useful in interpreting these Data
- Visit Description, Visit Number, and Target in the Data Labels
Filename/Product IDs
--------------------
The filenames and product IDs of observations adhere to a
common convention e.g.
ALI_0123456789_0X4B0_ENG.FIT
^^^ ^^^^^^^^^^ ^^^^^ ^^^\__/
| | | | ^^
| | | | |
| | | | +--File type (includes dot)
| | | | - .FIT for FITS file
| | | | - .LBL for PDS label
| | | | - not part of product ID
| | | |
| | | +--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
| | N.B. ApIDs are case-insensitive
| |
| +--MET (Mission Event Time) i.e. Spacecraft Clock
|
+--Instrument designator
Note that, depending on the observation, the MET in the data filename
and in the Product ID may be similar to the Mission Event Time (MET)
of the actual observation acquisition, but should not be used as an
analog for the acquisition time. The MET is the time that the data are
transferred from the instrument to spacecraft memory and is therefore
not a reliable indicator of the actual observation time. The PDS label
and the index tables are better sources to use for the actual timing of
any observation. The specific keywords and index table column names for
which to look are
* START_TIME
* STOP_TIME
* SPACECRAFT_CLOCK_START_COUNT
* SPACECRAFT_CLOCK_STOP_COUNT
Instrument Instrument designators ApIDs **
=========== ================================== =============
ALICE ALI 0X4B0 - 0X4B7 *
* Not all values in this range are in this data set
** ApIDs are case insensitive
There are other ApIDs that contain housekeeping values and
other values. See SOC Instrument ICD (/DOCUMENT/SOC_INST_ICD.*)
for more details.
Here is a summary of the types of files generated by each ApID
(N.B. ApIDs are case-insensitive) along with the instrument
designator that go with each ApID:
ApIDs Data product description/Prefix(es)
===== ===================================
0x4b0 - ALICE Pixel List Lossless (CDH 1)/ALI
0x4b1 - ALICE Pixel List Packetized (CDH 1)/ALI
0x4b4 - ALICE Pixel List Lossless (CDH 2)/ALI
0x4b5 - ALICE Pixel List Packetized (CDH 2)/ALI
0x4b2 - ALICE Histogram Lossless (CDH 1)/ALI
0x4b3 - ALICE Histogram Packetized (CDH 1)/ALI
0x4b6 - ALICE Histogram Lossless (CDH 2)/ALI
0x4b7 - ALICE Histogram Packetized (CDH 2)/ALI
Notes:
------
1) CDH 1 and CDH 2 refer to the spacecraft redundant Command and Data
Handling systems in general, and here specifically to their
respective Solid State Recorders (SSRs) 1 and 2, where ALICE data
be stored and prepared for downlink. ALICE can send data to SSR
1 or to SSR 2, or, for mission-critical data, to both redundantly.
ALICE shares its channel to the SSRs with the Long-Range
Reconaissance Imager (LORRI), so both instruments cannot store
data simultaneously. ALICE has the capability to store histogram
data to instrument-internal storage, and to transfer it to the
SSR(s) later; such an operation is called a Held Histogram, and
it allows ALICE to take data at the same time that LORRI is taking
and writing data to the SSR(s).
2) Packetized and Lossless refer to the method used on-board to
convert raw, high-speed instrument data on the SSR to low-speed
data ready for downlink. The conversion process is generally
referred to as compression, even though Packetized conversion does
not reduce the data volume In practice, Pixel List data always
use Packetized compression. Histogram data may use Packetized or
Lossless compression. Depending on the actual data contents,
Lossless compression reduces data volume by 60 to 90% or more;
for nominal science data a factor of 3 or more is normal.
Lossless compression is used whenever possible to reduce downlink
data volume. There is no difference, between Packetized and
Lossless compression, in the resultant FITS files after processing
by the Science Operations Center (SOC) data pipeline.
Instrument description
----------------------
Refer to the following files for a description of this instrument.
CATALOG
ALICE.CAT
DOCUMENTS
ALICE_SSR.*
SOC_INST_ICD.*
NH_ALICE_V###_TI.TXT (### is a version number)
Other sources of information useful in interpreting these Data
--------------------------------------------------------------
Refer to the following files for more information about these data
NH Trajectory tables:
/DOCUMENT/NH_MISSION_TRAJECTORY.* - Heliocentric
ALICE Field Of View definitions:
/DOCUMENT/NH_FOV.*
/DOCUMENT/NH_ALICE_V###_TI.TXT
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. PDS-SBN
practices 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. TARGET_NAME may be N/A (Not Available or Not
Applicable) for a few observations in this data set; typically that
means the observation is a functional test so N/A is an appropriate
entry for those targets, but the PDS user should also check the
NEWHORIZONS:OBSERVATION_DESC and NEWHORIZONS:SEQUENCE_ID keywords in
the PDS label, plus the provided sequence list (see Ancillary Data
below) to assess the possibility that there was an intended target.
Specifically for ALICE observations, any observation that has an
observation description or sequence ID that includes the words dump
or held will usually have N/A as its target, but that indicates the
observation was actually taken as part of an earlier sequence and held
held locally in instrument memory (i.e. a Held Histogram; see the
Notes in the Data section below), and the Dump sequence represents the
commands that transferred the instrument data onto the spacecraft
Solid-State Recorders (SSRs). In the cases of Held Histograms, the
user should check the previous sequence in the sequence list. For
other cases note that if the characters _P_, _C_, or _PC_ are in the
sequence ID, then the intended target was likely Pluto, Charon, or
Pluto and Charon together, respectively.
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-PLUTOCRUISE-V1.0.
Every observation provided in this data set was taken as a part of a
particular sequence. A list of these sequences has been provided in
file DOCUMENT/SEQ_ALICE_PLUTOCRUISE.TAB. In addition, the
sequence identifier (ID) and description are included in the PDS label
for every observation. N.B. While every observation has an associated
sequence, every sequence may not have associated observations. Some
sequences may have failed to execute due to spacecraft events (e.g.
safing). No attempt has been made during the preparation of this data
set to identify such empty sequences, so it is up to the user to
compare the times of the sequences to the times of the available
observations from INDEX/INDEX.TAB to identify such sequences.
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 Navigation and Ancillary Information
Facility (NAIF) SPICE toolkit from the PDS NAIF node, (see
http://naif.jpl.nasa.gov/).
The most common time unit associated with the data 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) was 65.184s at
NH launch, and the first three additional leapseconds occured
in at the ends of December, 2009, June, 2012 and June, 2015.
Refer to the NH SPICE data set, NH-J/P/SS-SPICE-6-V1.0, and the
SPICE toolkit docmentation, for more details about leapseconds.
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.
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
New Horizons ALICE Principal Investigator:
Alan Stern, Southwest Research Institute
S. Alan Stern
Southwest Research Institute
Department of Space Studies
1050 Walnut Street, Suite 400
Boulder, CO 80302
USA
|
| 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
may not be reduced to calibrated (Level 3) data. This issue is raised
here to explain why some data products in the raw data set,
NH-X-ALICE-2-PLUTOCRUISE-V2.0,
may not have corresponding data products in the calibrated data set,
NH-X-ALICE-3-PLUTOCRUISE-V2.0.
Data coverage and quality
=========================
Every observation provided in this data set was taken as a part of a
particular sequence. A list of these sequences has been provided in
file DOCUMENT/SEQ_ALICE_PLUTOCRUISE.TAB. N.B. Some sequences
provided may have zero corresponding observations.
Refer to the Confidence Level Overview section above for a summary
of steps taken to assure data quality.
The lollipop-shaped fuzz in images of some ALICE spectra, seen as high
signal levels at the box end of the slit around Hydrogen Lyman-alpha (H
Lya) wavelengths, is due to a characteristic of the detector and
aperture. To make the Micro Channel Plate (MCP) more sensitive to UV
light, it was coated with potassium bromide (KBr) photocathodes from
520 to 1180 Angstrom and with cesium iodide (CsI) photocathodes from
1250 to 1870 Angstrom. A vertical strip - a spectral band of 70
Angstrom centered at ~1216 Angstrom - of the MCP was masked and left
uncoated to reduce the sensitivity of the detector to H Lya
radiation. In the slit portion of the aperture (0.1deg wide x 4deg
high), the diffraction grating keeps the strong H Lya line within that
uncoated band. However, in the 2x2 degree box portion of the aperture
designed to capture the Sun during occultations, the H Lya spreads out
beyond the uncoated 70-Angstrom band over another ~55 Angstroms of more
sensitive photocathode-coated detector on either side. The quantum
efficiencies of the photocathode- coated surfaces are about an order of
magnitude more sensitive to sensitive to H Lya wavelengths than the
bare, uncoated MCP glass, which gives rise to high signal levels from
the box area of the slit i.e. the lollipop fuzz.
Observation descriptions in this data set catalog
=================================================
Some users will expect to find descriptions of the observations
in this data set here, in this Confidence Level Note. This data
set follows the more common convention of placing those
descriptions under the Data Set Description (above, if the user is
reading this in the DATASET.CAT file) of this data set catalog.
Caveat about TARGET_NAME in PDS labels and observational intent
===============================================================
A fundamental truth of managing data from some spacecraft missions
is that the intent of any observation is not suitable for insertion
into the command stream sent to the spacecraft to execute that
observation. As a result, re-attaching that intent to the data
that are later downlinked is problematic at best. For New Horizons
that task is made even more difficult as the only meta-data that
come down with the observation is the unpredictable time of the
observation. The task is made yet even more difficult because
uplink personnel, who generate the command sequences and initially
know the intent of each observation, are perpetually under
deadlines imposed by orbital mechanics and can rarely be spared for
the time-intensive task of resolving this issue.
To make a long story short, the downlink team on New Horizons has
created an automated system to take various uplink products, decode
things like Chebyshev polynomials in command sequences representing
celestial body ephemerides for use on the spacecraft to control
pointing, and infer from those data what the most likely intended
target was at any time during the mission. This works well during
flyby encounters and less so during cruise phases and hibernation.
The point to be made is that the user of these PDS data needs to
be cautious when using the TARGET_NAME and other target-related
parameters stored in this data set. This is less an issue for the
plasma and particle instruments, more so for pointing instruments.
To this end, the heliocentric ephemeris of the spacecraft, the
spacecraft-relative ephemeris of the inferred target, and the
inertial attitude of the instrument reference frame are provided
with all data, in the J2000 inertial reference frame, so the user
can check where that target is in the Field Of View (FOV) of the
instrument.
Review
======
This dataset was peer reviewed and certified for scientific use on
12-5-2016.
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