| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains Raw data taken by New Horizons
Radio Science Experiment
instrument during the PLUTOCRUISE mission phase.
The REX instrument measures the amplitude and phase of radio signals captured
by the New Horizons high-gain antenna. The main investigation is an
occultation experiment which uses radio signals transmitted from Earth to
probe the atmosphere and ionosphere of Pluto and Charon. Ancillary
investigations include measurements of the 4 cm wavelength radiothermal
emission from planets or other radio sources. Phase data may also be combined
with Pluto encounter tracking data, derived from the Radio Science Subsystem
separately from REX and to be archived in separate non-REX data set(s), to
infer the influence of gravitational fields on the spacecraft as it moves
through the Pluto system.
The main investigation requires coordinated use of the Earth-based
transmitters and the spacecraft receiver as the two physical elements of the
REX instrument. The 'Ground Element' comprises DSN (Deep Space Network)
hardware and operations facilities on Earth, and the 'Flight Element' includes
signal processing hardware and software onboard the spacecraft.
Unless inclusion of tuning profiles for one-way uplink transmissions is noted
below, this data set includes only samples taken and measurements made by the
REX system hardware on-board the New Horizons spacecraft -- either of one-way
uplink signals or of 4cm-wavelength thermal emission.
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REQUIRED UNDERSTANDING: THE REX AND THE NEW HORIZONS (NH) REGENERATIVE
RANGING TRACKER [DEBOLTETAL2005] ARE
*****SEPARATE***** AND *****INDEPENDENT*****
SUBSYSTEMS THAT BOTH USE THE RADIO FREQUENCY (RF) AND TELECOMMUNICATIONS
SUBSYSTEMS. TWO-WAY RANGING DATA WILL NOT BE ARCHIVED IN REX DATA SETS.
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During the Pluto Cruise mission phase, the New Horizons project performed a
series of Annual CheckOuts (ACOs), designed to determine basic functionality
and performance of the instrument complement. For REX these tests included
the exercise of calibration test patterns, the reception of a ground-based DSN
uplink signal for evaluating inflight REX system gain, linearity, stability of
the composite uplink, USO, and REX receiver chain, characterizing the REX
bandpass frequency response, and searching for any spurious signals in the REX
passband. In addition, occultations of the Earth's moon were performed in May
2011 and January 2012 (ACO-5 and ACO-6) to provide example data and experience
in performing occultation inversion in preparation for the encounter at
Pluto/Charon.
Although one-way uplink data signals were sent from the Ground Element to REX,
the characteristics of those signals are not needed to analyze these REX
observations comprising instrument checkout, characterization and calibration
activities. However, for the two Lunar Occultations, uplink data tuning
profiles are included in this data set.
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_REX_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.
Known issues in REX data
========================
The following item assumes familiarity with the REX, REX terminology
and the required reading and other documentation provided with this
data set.
Time tag anomalies in ROF sequences
-----------------------------------
REX places ten incrementing time tags in each REX Output Frame (ROF).
The time tags can be used both to identify any breaks in a sequence of
ROFs, and to determine the time between any two ROFs within a
sequence.
The normal sequence for time tags is to start at zero in the first ROF
and increment ten times per ROF, so the first time tag of the second
ROF is 10, that of the third ROF is 20, etc. In practice, the first
and last ROFs in a sequence do not always show simple zero starts and
clean finishes, respectively, indicating data corruption in just those
ROFs. There is no indication of corruption elsewhere in ROF streams,
and REX commanding ensures there are always adequate ROFs before and
after any observation, so discarding starting and ending ROFs in a
sequence based on simple inspection of time tags is the way to handle
this issue.
Refer to the REX documentation for more detail.
Version
=======
This is VERSION 1.0 of this data set.
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 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_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
=========== ================================== =============
REX REX 0X7B0 - 0X7B3 *
* Not all values in this range are in this data set
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)
===== ===================================
0x7b0 - REX Lossless Compressed Data (CDH 1)/REX
0x7b1 - REX Packetized Data (CDH 1)/REX
0x7b2 - REX Lossless Compressed Data (CDH 2)/REX
0x7b3 - REX Packetized Data (CDH 2)/REX
Instrument description
----------------------
Refer to the following files for a description of this instrument.
CATALOG
REX.CAT
DOCUMENTS
REX_SSR.*
SOC_INST_ICD.*
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
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.
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_REX_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; that is,
some sequences may have failed to execute due to spacecraft events
(e.g. safing) and there will be observations associated with those
sequences. No attempt has been made during the preparation of this
data set to identify if any, or how many, such empty sequences there
are, so it is up to the user to compare the times of the sequences
to the times of the available observations from the INDEX/INDEX.TAB
table 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) 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.
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 REX Principal Investigator:
Len Tyler, Stanford University
Len Tyler
350 Serra Mall, David Packard #372
Stanford University
Stanford, CA 94305-9515
USA
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