| DATA_SET_DESCRIPTION |
Data Set Overview
=================
The Near Earth Asteroid Rendevous (NEAR) Eros Radio Science
(RS) Data Set is a time-ordered collection of raw and partially
processed data collected during the NEAR flyby of minor planet
433 Eros. For more information on the investigation conducted,
including mass determinations results, see [YEOMANSETAL1999].
Only data collected in the span after the engine abort anomaly,
(with resumption of two-way lock-up Dec 21, 1998) and prior to
DSM-2 burn January 3, 1999 was used for the mass estimation.
The radio data also supported NEAR Navigation.
The data set includes:
Directory Description
--------- -----------
ODF Orbit Data Files containing closed-loop (two-way)
Doppler and sequential range measurements.
EOP Earth-Orientation Parameter file
ION Ionosphere calibration file
TRO Troposphere calibration file
TXT Text files describing physical model inputs
and estimated solution parameters
Typical users of these data might analyze range and Doppler
measurements in the ODF to derive the NEAR trajectory during
the flyby.
Parameters
==========
The ODF contains the most important information (range and
Doppler) needed by spacecraft navigators and those interested
in determining gravitational parameters of Eros. Each ODF
is accompanied by a full PDS label which describes both the
content and format of the associated file. ODF data types
can include those listed below. Only those marked below with an
asterisk are present in this data set ODF.
Narrowband spacecraft VLBI, Doppler mode (cycles)
Narrowband spacecraft VLBI, phase mode (cycles)
Narrowband quasar VLBI, Doppler mode (cycles)
Narrowband quasar VLBI, phase mode (cycles)
Wideband spacecraft VLBI (nanoseconds)
Wideband quasar VLBI (nanoseconds)
* One-way Doppler (Hertz)
* Two-way Doppler (Hertz)
* Three-way Doppler (Hertz)
One-way total count phase (cycles)
Two-way total count phase (cycles)
Three-way total count phase (cycles)
PRA planetary operational discrete spectrum range (range
units)
* SRA planetary operational discrete spectrum range (range
units)
RE[GSTDN] range (nanoseconds)
Azimuth angle (degrees)
Elevation angle (degrees)
Hour angle (degrees)
Declination angle (degrees)
X angle (where +X is east) (degrees)
Y angle (where +X is east) (degrees)
X angle (where +X is south) (degrees)
Y angle (where +X is south) (degrees)
Processing
==========
ODF's are screened for 'bad' data points, which are removed
prior to analysis by the navigation or radio science teams.
Data
====
ODFs were issued approximately daily prior to the NEAR Eros
flyby, more often after the engine abort recovery.
These ODFs are stored in the ODF directory. File name is of the
form ydddeeeC.ODF where y is the one-digit year (1990s
implicit) of the first data, ddd is the three-digit day-of-year
of the first data, eee is the three-digit day-of-year of the
last data. Symbol C denotes an alphabetic character
distinguishing separate files issued during the same day.
Ancillary Data
==============
Ancillary files are needed for proper analysis and
interpretation of the radio data (file type ODF). These are
organized in parallel directories and stored approximately
chronologically.
Earth Orientation Parameter Files (EOP Directory)
---------------------------------------------------
Earth Orientation Parameter files are produced by the Time
and Earth Motion Precision Observation (TEMPO) Group at JPL.
These are ASCII files of variable length records. Each
record is delimited by an ASCII line-feed (ASCII 10).
File names have the form ydddzeee.EOP where y is
the one-digit year of the first data in the file, ddd is
the day-of-year of the first data in the file, z is the
one-digit year of the last data, and eee is the day-of-year
of the last data in the file. The file covers the most recent
nine months of past motion and a prediction for three months
into the future; these files are typically 30 KB. Each EOP
file is accompanied by a PDS minimal label with file name
ydddzeee.LBL.
Ionosphere Calibration Files (ION Directory)
---------------------------------------------------
Ionosphere Calibration files are produced by the
Tracking System Analytic Calibration (TSAC) Group at JPL.
These are ASCII files of variable length records. Each
record is delimited by an ASCII line-feed (ASCII 10).
File names have the form ydddeeeC.ION where y is
the one-digit year of the first data in the file, ddd is
the day-of-year of the first data in the file, eee is the
day-of-year of the last data in the file, and C is a
character denoting sequence when more than one file with the
same ydddeee is handled. C starts from 'A' and progresses
to 'B', 'C', etc. with increasing numbers of similar coverage
files. Frequently, ION files are released at one week
intervals to cover a single month; ydddeeeA.ION would be
the file released during the first week, ydddeeeB.ION would
be the file released during the second week, etc. The files
archived here are monthly files that contain actuals for the
previous month. Each ION file is accompanied by a PDS minimal
label with file name ydddeeeC.LBL. Typical file sizes are
less than 50 kB.
Troposphere Calibration Files (TRO Directory)
---------------------------------------------------
Troposphere Calibration files are produced by the
Tracking System Analytic Calibration (TSAC) Group at JPL.
These are ASCII files of variable length records. Each
record is delimited by an ASCII line-feed (ASCII 10).
File names have the form ydddeeeC.TRO where y is
the one-digit year of the first data in the file, ddd is
the day-of-year of the first data in the file, eee is the
day-of-year of the last data in the file, and C is a
character denoting sequence when more than one file with the
same ydddeee is handled. C starts from 'A' and progresses
to 'B', 'C', etc. with increasing numbers of similar coverage
files. TRO files are typically released at the beginning of
a month and cover the previous. Each TRO file is accompanied
by a PDS minimal label with file name ydddeeeC.LBL. Typical
file sizes are less than 50 kB.
Text Files (TXT Directory)
--------------------------
Two file types are included in the TXT directory. The first
type is NMLMODL.TXT and is accompanied by a minimal PDS label
NMLMODL.LBL. It is the nominal set of namelist parameters
used to define physical characteristics of the spacecraft's
motion and tracking observables used by the JPL orbit
determination software suite. The second file is
PARAMSUM.TXT, accompanied by minimal PDS label PARAMSUM.LBL,
which is a summary of the estimated (solved-for) parameter
set. GM9 is the solved-for Eros GM in units of km^3/s^2.
Coordinate System
=================
Analysis was conducted in the frame of the DE-403 solar system
model, aligned with the 1993 ICRF/J2000 reference frame.
Software
========
Software for parsing, reducing, and analyzing data such as
these has been developed at several institutions and elsewhere.
Because such software must usually operate at the bit-level and
is written for a narrow range of platforms, it is not suitable
for general distribution. No software is included with this
archival data set.
|
| CONFIDENCE_LEVEL_NOTE |
Overview
========
Data in this archival data set have been processed as part of
the activities of the NEAR Radio Science Team. In general, this
is a weak to fair data set. The principal limitation is the
small amount of data prior to the flyby and immediately after a
large, unknown delta-v thrust anomaly.
Review
======
This archival data set was reviewed by the NEAR Radio Science
Team prior to submission to the Planetary Data System (PDS).
Prior to creation of the final version of the archival data
set, key elements of the archive were distributed for
preliminary review. These included electronic versions of
example PDS labels, CATALOG files, and Software Interface
Specifications. These materials were distributed to PDS
personnel, the experiment investigator, and others,
as appropriate.
Data Coverage and Quality
=========================
Significant events for Radio Science during Eros Flyby are
as follows:
START STOP
YY/DDD UTC Time YY/DDD UTC Time Comments
------ -------- ------ -------- ----------------
98/354 22:00:00 98/354 22:03:20 Rendevous-1 settling burn
98/354 22:03:20 98/355 06:40:00 Anomaly; unknown thrust vector(s)
98/356 08:06:00 Resume two-way Doppler (ERT)
98/357 19:43:00 Eros close-approach
98/359 02:54:00 Resumption of SRA data (ERT)
99/003 17:00:00 DSM-2 maneuver
Limitations
===========
The limitations in this data set derive from tracking geometry
and measurement data types. There are no known defects in the
data.
|
.png)
.png)
