PDS_VERSION_ID = PDS3
RECORD_TYPE = FIXED_LENGTH
RECORD_BYTES = 62
FILE_RECORDS = 102
^TEXT = "GR_101.TXT"
DATA_SET_ID = "NEAR-A-NLR-5-EROS/SHAPE/GRAVITY-V1.0"
PRODUCT_ID = "NAV-GRAVITY-MODEL-TXT"
PRODUCT_NAME = "NAV GRAVITY MODEL, TEXT FORMAT"
PRODUCT_CREATION_TIME = 2001-09-01
TARGET_NAME = EROS
INSTRUMENT_HOST_NAME = "NEAR EARTH ASTEROID RENDEZVOUS"
INSTRUMENT_NAME = "NEAR LASER RANGEFINDER"
START_TIME = 2000-04-30
STOP_TIME = 2000-08-27
SPACECRAFT_CLOCK_START_COUNT = "UNK"
SPACECRAFT_CLOCK_STOP_COUNT = "UNK"
OBJECT = TEXT
PUBLICATION_DATE = 2001-10-09
NOTE = "This file contains the gravity model
parameters derived by numerical integration of the accompanying
shape model, 'sh_101.txt'. It contains basic parameters such as
mass and density, the intertia tensor, and the gravitation harmonic
coefficients. It is presented in the in-house format used by the
NAV team, as described below.
The shape model on which this gravity solution is based was derived
from approximately 100,000 measurements made by the NEAR Laser
Rangefinder during the period 30 April 2000 to 27 August 2000, from
orbits at 35 and 50 km. The center of gravity offset (i.e., the
vector from the shape model center to the true center of gravity)
for both files is the same, and is included in the 'sh_101.txt'
data table. That vector is:
(-0.965632900625E-02, 0.242943063605E-02, 0.325843327842E-01)
Where the (x,y,z) above are in kilometers.
The coefficients in this file are the normalized (Cnm,Snm) coefficients
of the standard spherical harmonic expansion of Lengendre polynomials
and related functions. For a complete discussion of the derivations of
the gravitational potential and related shape model, see Miller, et
al. (2002) and Kaula (1966).
The shape model files and descriptive information regarding the file
formats and contents were kindly supplied by J.K. Miller of the NEAR
navigation team, in response to user requests made at the NEAR
PDS archive review.
REFERENCES
Kaula, W.M., 1966. Theory of Satellite Geodesy, Blaisdell, Waltham, MA.
Miller, J.K., A.S. Konopliv, P.G. Antreasian, J.J. Bordi, S. Chesley,
C.E. Helfrich, W.M. Owen, D.J. Scheeres, T.C.Wang, B.G. Williams
and D.K. Yoemans, 2002. Determination of Shape, Gravity and Rotational
State of Asteroid 433 Eros, Icarus, in press.
File Format
===========
The file is formatted as a table with 1-3 numbers in each row. The
values in each row are as follows:
Row 1 Column 1 The degree of the harmonic solution, NDEGREE
(i.e., '16')
Column 2 A '1', indicating that the results have been
normalized
Column 3 A '1', an internal processing flag
Row 2 Column 1 Volume in km^3 of the model
Column 2 Density in kg/m^3 (assumed constant)
Column 3 Mass in kg
Row 3 Column 1 The gravitational potential, GM, in km^2/s^3
Column 2 R0. Mathematically, this is the average radius
used in the model. In this specific case it has
been selected to be the maximum radius.
Column 3 -blank-
The next two rows contain the coefficients for the inertia tensor.
Note that this is a symmetric matrix, so only the unique elements are
specified here:
Row 4 Column 1 Ixx in km^2
Column 2 Iyy in km^2
Column 3 Izz in km^2
Row 5 Column 1 Ixy in km^2
Column 2 Ixz in km^2
Column 3 Iyz in km^2
The subsequent rows contain the gravitational harmonic coefficients
Cij and Sij. All the Si0 are = 0, and are thus omitted from this file.
The remaining coefficients are stored three to a record, in this
logical sequence:
C00
C10 C11 S11
C20 C21 C22 S21 S22
C30 C31 C32 C33 S31 S32 S33
etc.
which becomes this physical sequence:
Row 6: C00 C10 C11
Row 7: S11 C20 C21
Row 8: C22 S21 S22
Row 9: C30 C31 C32
Row 10: C33 S31 S32
etc.
The total number of coefficients stored is (NDEGREE+1)^2.
The last record in the file contains only a single entry in the first
column.
"
END_OBJECT = TEXT
END