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 Vesta. 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 Sami Asmar produced spherical harmonic models and maps. At Vesta, the mission was divided into three science orbits. All the orbits were polar. The Survey orbit was performed at a nominal altitude of 2735 km. The High Altitude Mapping Orbit, or HAMO, was performed at a nominal altitude of 685 km. The Low Altitude Mapping Orbit, or LAMO, was performed at a nominal altitude of 200 km. The spacecraft spent 20 days in Survey orbit, 34 days in HAMO-1, 141 days in LAMO, and another 40 days in HAMO-2. Between these science orbits, the spacecraft was in a transfer phase using the electric ion engines [RUSSELL&RAYMOND2011]. 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 Vesta, for example. ASCII (data type SHA) formatted spherical harmonics are defined. Because of the low degree field, no binary files (data type SHB) are provided. 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. Provided in this data set is a map of radial acceleration using the VESTA20H field with the J2 coefficient removed. 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 Vesta Raw Data Archive. Useful references which describe the procedures applied in general to processing Vesta orbiter tracking data include [KONOPLIVETAL2014B].  [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 will be produced for the Ceres phase. 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. 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 Vesta centered body-fixed coordinate system similar to the IAU coordinate system. The values differ slightly because the the orientation of Vesta is estimated in the orbit determination process. See 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.

Overview : Data in this archive have been reduced as part of mission data analysis activities of the Dawn Gravity Team. Review : This archival data set was reviewed by the Dawn Gravity Team prior to submission to the Planetary Data System (PDS). Data set design, documentation, and sample products have passed a PDS peer review. Data Coverage and Quality : This volume contains gravity models and maps generated from Dawn data collected between July 2011 and July 2012. JGDWN_VES20H_SHA.TAB is an ASCII file of coefficients and related data for a 20th degree and order Vesta gravity field produced at the Jet Propulsion Laboratory. The name of this gravity model is VESTA20H. The model used is described in the file's detached label. JGDWN_VES20H_RADIAL_0020.IMG is a digital map of the Vesta radial acceleration due to gravity with the J2 coefficient removed. The radial accelerations are computed with the VESTA20H field described in the JGDWN_VES20H_SHA.TAB file. This Vesta gravity field was produced at the Jet Propulsion Laboratory. The model used is described in the file's detached label. Limitations : The limitations in this data set follow from the quality of the execution, which is described above under Data Coverage and Quality.