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DAWN CERES GRAVITY SCIENCE DERIVED SCIENCE DATA V3.0 (PDS)

NSSDCA ID: PSSB-00682

Availability: At NSSDC, Ready for Offline Distribution (or Staging if Digital)

Description

This description was generated automatically using input from the Planetary Data System.

Data Set Overview

The Dawn Gravity Archive Data Collection of Science Data Products (SDP) includes data products generated from gravity investigations conducted by members of the Dawn Gravity Team while the spacecraft was in orbit around the asteroid Ceres. Gravity SDPs include spherical harmonic models, maps or images of those models, and possibly line-of-sight acceleration profiles. A group at the Jet Propulsion Laboratory JPL under the direction of Ryan Park produced spherical harmonic models and maps. At Ceres, the mission was divided into different science orbits. All the orbits were polar. The RC3 orbit was conducted at an alitutde of 13500 km, The Survey orbit was performed at a nominal altitude of 4400 km. The High Altitude Mapping Orbit, or HAMO, was performed at a nominal altitude of 1450 km. The Low Altitude Mapping Orbit, or LAMO, was performed at a nominal altitude of 375 km. An extended mission phase XMO1 was conducted at the same altitude as LAMO. Additional extended mission phases of XMO2, XMO3 and XMO4 were conducted at altitudes of 1480 km, 7520-9350 km, and 20000 km. Between these science orbits, the spacecraft as in a transfer phase using the electric ion engines [RUSSELL&RAYMOND2011].

Modification History

Version 3 of the gravity field is consistent with the final SPC shape model of Ceres (Park et al. High resolution shape model of Ceres from stereophotoclinometry using Dawn imaging data, Icarus, 2018). Additionally, data are weighted differently in this delivery resulting in small changes to the uncertainty values of the gravitational field parameters. Version 3 includes all updates to the V2.0 dataset, plus these changes, i.e. fixing CENTER_LONGITUDE in the data labels, adding an updated coordinate system document and modification of the data products consistent with this coordinate system. Version 2 of the gravity field corrected the location of the Kait crater. During the development of higher-level data products for Dawn, the Gravity team discovered that the Gravity team and the imaging team were using different craters to define the coordinate system. Under concurrence from the Dawn project, the gravity team corrected the gravity field products to align with data products used by other teams. The corrected location of the Kait crater is a rotation of -0.064074 deg about the z-axis. The corresponding version 2 of the gravity field re-estimates the gravity field parameters, pole right ascension, declination, prime meridian, and rotation rate. The version 2 gravity field fixes the y-axis coordinate to align exactly with the Kait landmark crater. Details of the coordinate system are described in the corresponding labels for the DATA/SHADR and DATA/SHBDR data products. Because the gravity field was re-estimated in this new frame, the gravitational field parameters and pole frame are slightly different from the previous version. The change is large enough to affect the DATA/SHADR and DATA/SHBDR data products, which have been updated in the version 2 dataset but not large enough to affect the 1-degree resolution of the DATA/RSDMAP products, which remain unchanged.

Parameters

Spherical harmonic models are tables of coefficients GM, Cmn, and Smn -- as in equation (1) of [TYLERETAL1992]. These can be used to represent gravitational potential of Ceres, for example. ASCII (data type SHA) formatted spherical harmonics are defined. Each file contains up to four tables: a header table containing general parameters for the model (gravitational constant, its uncertainty, degree and order of the field, normalization state, reference longitude, and reference latitude); a names table, giving the order in which coefficients appear; a coefficients table (degree m, order n, coefficients Cmn and Smn, and their uncertainties). Radio Science Digital Map files are image representations of gravity and other parameters. Free air gravity, geoid, Bouguer anomaly, isostatic anomaly, and topographic values may be displayed using this data type. Data are formatted as PDS image objects.

Processing

Spherical harmonic models, maps, and line-of-sight acceleration profiles are derived from raw radio tracking data in several steps. The tracking data are processed in large orbit determination programs that integrate the equations of motion (DPODP at JPL [MOYER1971]), and model mathematically the radio science observables (ramped Doppler and range data). The observations are related to the geophysical parameters through the numerical integration and the detailed mathematical modeling of the radio science observables, and of all forces acting on the spacecraft trajectory, including planetary and third body gravity, solar radiation pressure, planetary radiation pressure, atmospheric drag, solid body tides, and relativity, where applicable. The gravity field coefficients are obtained by accumulating normal equations from often hundreds of data arcs, and solving these systems of linear equations with thousands of unknowns. The unknowns include arc parameters, particular to one data arc (such as the spacecraft state, radiation pressure scale factors, atmospheric drag scale factors, etc.) and common parameters (such as the gravity coefficients, the planetary gravitational constant or GM). Radio tracking data are processed in arcs delimited by propulsive maneuvers, occultations, etc. The spacecraft periodically performed angular momentum desaturation maneuvers. These maneuvers allowed the reaction wheels to spin down to avoid damage, but they had be countered the use of thrusters. Arcs may be delimited by these maneuvers. The details of each of these maneuvers specified in the small forces file of the Dawn Ceres Raw Data Archive. Useful references which describe the procedures applied in general to processing Ceres orbiter tracking data include [PARKETAL2016]. [THORNTON&BORDER2003] is a general reference for Orbit Determination.

Data

Data are available online through the Planetary Data System (http://pds.nasa.gov). A volume of reduced data was prepared for the Dawn mission at Vesta and a similar volume for Ceres. ASCII spherical harmonic models are stored in the DATA/SHA directory with file names of the form GTsss_nnnnvv_SHA.TAB where: 'G' denotes the generating institution 'J' for the Jet Propulsion Laboratory 'T' indicates the type of data represented 'G' for gravity field 'sss' is a 3-character modifier specified by the data producer. This modifier is used to indicate the source spacecraft or project, such as V for Vesta or C for Ceres. '_' the underscore character is used to delimit modifiers in the file name for clarity. 'nnnnvv' is a 4- to 6-character modifier specified by the data producer. Among other things, this modifier may be used to indicate the target body, whether the SHADR contains primary data values as specified by 'T' or uncertainties/errors, and/or the version number. For Dawn, this specifies the degree and version of the field. '_' the underscore character is used to delimit information in the file name for clarity. 'SHA' denotes that this is an ASCII file of Spherical Harmonic coefficients '.TAB' indicates the data is stored in tabular form. Each SHADR file is accompanied by a detached PDS label; that label is a file in its own right, having the name GTsss_nnnnvv_SHA.LBL. Binary spherical harmonic models are stored in the DATA/SHB directory with file names of the form GTsss_nnnnvv_SHB.DAT where: 'G' denotes the generating institution 'J' for the Jet Propulsion Laboratory 'T' indicates the type of data represented 'G' for gravity field 'sss' is a 3-character modifier specified by the data producer. This modifier is used to indicate the source spacecraft or project, such as V for Vesta or C for Ceres. '_' the underscore character is used to delimit modifiers in the file name for clarity. 'nnnnvv' is a 4- to 6-character modifier specified by the data producer. Among other things, this modifier may be used to indicate the target body, whether the SHBDR contains primary data values as specified by 'T' or uncertainties/errors, and/or the version number. For Dawn, this specifies the degree and version of the field. '_' the underscore character is used to delimit information in the file name for clarity. 'SHB' denotes that this is an Binary file of Spherical Harmonic coefficients and covariance '.DAT' indicates the data is stored in a binary data file. Each SHBDR file is accompanied by a detached PDS label; that label is a file in its own right, having the name GTsss_nnnnvv_SHB.LBL. Radio Science Digital Map products are stored in the DATA/RSDMAP directory with file names of the form GTsss_ffff_nnnn_cccc.IMG where: 'G' denotes the generating institution 'J' for the Jet Propulsion Laboratory 'T' indicates the type of mission data represented 'G' for gravity field 'sss' is a 3-character modifier specified by the data producer. This modifier is used to indicate the source spacecraft or project, such as V for Vesta or C for Ceres. '_' the underscore character is used to delimit information in the file name for clarity. 'ffff' is a 4- to 6-character modifier specified by the data producer to indicate the degree and order of the solution for the gravity field, topography or magnetic field. '_' the underscore character is used to delimit information in the file name for clarity. 'nnnn' is a 4- to 8-character modifier indicating the type of data represented 'ANOM' for free air gravity anomalies 'ANOMERR' for free air gravity anomaly errors (1) 'GEOID' for geoid 'GEOIDERR' for geoid errors (1) 'BOUG' for Bouguer anomaly 'ISOS' for isostatic anomaly 'TOPO' for topography 'MAGF' for magnetic field (1) Geoid and gravity anomaly errors are computed from a mapping of the error covariance matrix of the gravity field solution. '_' the underscore character is used to delimit information in the file name for clarity. 'cccc' is a 4-character modifier specified by the data producer to indicate the degree and order to which the potential solution (gravity, topography or magnetic field) has been evaluated. In the case of the error maps for the gravity anomalies or geoid error, this field indicates to which maximum degree and order the error covariance was used to propagate the spatial errors '.IMG' indicates the data is stored as an image. Each RSDMAP file is accompanied by a detached PDS label; that label is a file in its own right with name GTsss_ffff_nnnn_cccc.LBL.

Coordinate System

Dawn Gravity SDP files use a Ceres centered body-fixed coordinate system similar to the IAU coordinate system. The values differ slightly because the the orientation of Ceres is estimated in the orbit determination process. See the coordinate system document in the DOCUMENTS directory: DOCUMENT/CERES_COORD_SYS_180628.LBL and the labels of specific gravity products for details.

Software

None.

Media/Format

This data set is stored online at the Planetary Data System (http://pds.nasa.gov/) and may be downloaded using a web browser or FTP software. A copy may be requested on physical media if downloading is not possible. The Planetary Data System maintains backup copies of this data set on various media.

These data are available on-line from the Planetary Data System (PDS) at:

https://sbnarchive.psi.edu/pds3/dawn/grav/DWNCGRS_2_v3_181005/

Alternate Names

  • DAWN-A-RSS-5-CEGR-V3.0

Discipline

  • Planetary Science: Small Bodies

Additional Information

Spacecraft

Experiments

Questions and comments about this data collection can be directed to: Dr. David R. Williams

 

Personnel

NameRoleOriginal AffiliationE-mail
Dr. Alexander S. KonoplivData ProviderNASA Jet Propulsion Laboratoryask@krait.jpl.nasa.gov
Dr. Dustin R. BuccinoGeneral ContactNASA Jet Propulsion Laboratorydustin.r.buccino@jpl.nasa.gov
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