Gravity Model Files

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By default, FreeFlyer uses the "EGM96.potential" data file for modeling the geopotential of Earth and point masses for modeling any other celestial objects included in a Spacecraft's Force Model, but custom files can be specified for Earth or any other celestial body using the approaches discussed on the Zonals and Tesserals page of the Setting up the Force Model section of the Spacecraft Propagation Guide.

 

The format used for FreeFlyer's gravity model files consists of a header and the body. The header of the potential file includes values for the physical properties of the celestial body (Gravity Constant (mu), Body Radius, Reciprocal Flattening). These values are used when propagating the Spacecraft using a gravitational potential field file (see Zonals and Tesserals). For other calculations that depend on the physical properties of a celestial body, such as Spacecraft.Height or propagation of a Spacecraft with a point mass gravitational model, the celestial body physical properties are accessed using syntax such as "Earth.Mu".

 

A sample header (from the EGM96 potential file included with the installation) is shown below, as well as the first line of the body. This sample can be used as a starting point when creating your own gravity model files using custom gravitational field data.

 

Model Name        Earth Gravity Model 96 (EGM96)

Body              Earth

Degree            360

Order             360

Gravity Const.    3.98600441500000E+05

Body Radius       6.37813630000000E+03

Rec. Flattening   2.98257000000000E+02

Normalized        Yes

Tide Model        Tide-Free

 

URL               http://cddisa.gsfc.nasa.gov/926/egm96/egm96.html

 

      Deg  Ord            C                    S

GCOEF    2    0  -0.484165371736E-03  0.000000000000E+00

 

 

The following gravity models are provided with FreeFlyer:

 

Filename

(*.potential)

Model Name

Central Body

Degree

Order

Gravity Constant

Body Radius

Reciprocal Flattening

Normalized

Tide Model

Reference URL

EGM96

Earth Gravity Model 96 (EGM96)

Earth

360

360

3.98600441500000E+05

6.37813630000000E+03

2.98257000000000E+02

Yes

Tide-Free

http://cddis.gsfc.nasa.gov/926/egm96/egm96.html

EGM2008

Earth Gravity Model 2008 (EGM2008 truncated to 200x200)

Earth

200

200

3.98600441800000E+05

6.37813700000000E+03

2.98257223500000E+02

Yes

Tide-Free

http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm2008/

GGM02C

Grace Gravity Model 02C (GGM02C)

Earth

200

200

3.98600441500000E+05

6.37813630000000E+03

2.98257000000000E+02

Yes

Zero-Tide

http://www.csr.utexas.edu/grace/gravity/

GGM03C

Grace Gravity Model 03C (GGM03C truncated to 200x200)

Earth

200

200

3.98600441500000E+05

6.37813630000000E+03

2.98257000000000E+02

Yes

Zero-Tide

http://www.csr.utexas.edu/grace/gravity/

GMM1025A

Mars Global Surveyor 1025 A (GMM1025A)

Mars

80

80

4.2828369773938997E+04

3.3970000000000000E+03

1.6877900000000000E+02

Yes

Tide-Free

http://icgem.gfz-potsdam.de/ICGEM/shms/mars/ggm1025a.gfc

GMM2B

Goddard Mars Model 2B (GMM2B)

Mars

80

80

4.2828371901284001E+04

3.3970000000000000E+03

1.6877900000000000E+02

Yes

Zero-Tide

http://bowie.gsfc.nasa.gov/926/MARS/GGM2BC80.SHA

GL0660B

GSFC GRAIL Gravity Model (truncated to 300x300)

Moon

300

300

4.90280030555540E+03

1.73800000000000E+03

1851.85185185189E+00

Yes

Tide-Free

http://pds-geosciences.wustl.edu/grail/grail-l-lgrs-5-rdr-v1/grail_1001/shadr/jggrx_0660b_sha.tab

GRGM660PRIM

GSFC Preliminary GRAIL Gravity Model (truncated to 300x300)

Moon

300

300

4.90279980693169E+03

1.73800000000000E+03

1851.85185185189E+00

Yes

Tide-Free

http://pds-geosciences.wustl.edu/grail/grail-l-lgrs-5-rdr-v1/grail_1001/shadr/gggrx_0660pm_sha.tab

JGM2

GSFC JGM-2 Geopotential Model

Earth

70

70

3.98600441500000E+05

6.37813630000000E+03

2.98257000000000E+02

Yes

Zero-Tide


JGM85F01

Mars Global Surveyor 85F (JGM85F01)

Mars

85

85

4.28283763830000E+04

3.39420000000000E+03

1.6877900000000000E+02

Yes

Tide-Free

http://pds-geosciences.wustl.edu/dataserv/gravity_models.htm

JGMRO110C

Mars Reconnaissance Orbiter (JGMRO110C)

Mars

110

110

4.2828375641000000E+04

3.3960000000000000E+03

1.6877900000000000E+02

Yes

Tide-Free

http://pds-geosciences.wustl.edu/mro/mro-m-rss-5-sdp-v1/mrors_1xxx/data/shadr/

JGM3

Joint Gravity Model 3 (JGM3)

Earth

70

70

3.98600441500000E+05

6.37813630000000E+03

2.98257000000000E+02

Yes

Zero-Tide


LP100j

GSFC LP-100j Lunar potential Model

Moon

100

100

4.9028004760000e+003

1.7380000000000e+003

1851.85185185189E+00

Yes

Tide-Free

http://pds-geosciences.wustl.edu/lunar/lp-l-rss-5-gravity-v1/lp_1001/sha/

LP100k

GSFC LP-100k Lunar potential Model

Moon

100

100

4.9028002380000e+003

1.7380000000000e+003

1851.85185185189E+00

Yes

Tide-Free

http://pds-geosciences.wustl.edu/lunar/lp-l-rss-5-gravity-v1/lp_1001/sha/

LP150q

Lunar Prospector 150q

Moon

150

150

4.90280107600000E+03

1.73800000000000E+03

1851.85185185189E+00

Yes

Tide-Free

http://pds-geosciences.wustl.edu/lunar/lp-l-rss-5-gravity-v1/lp_1001/sha/

LP165p

Lunar Prospector 165p

Moon

165

165

4.90280105600000E+03

1.73800000000000E+03

1851.85185185189E+00

Yes

Tide-Free

http://pds-geosciences.wustl.edu/lunar/lp-l-rss-5-gravity-v1/lp_1001/sha/

MGN120p

Magellan 120p

Venus

120

120

3.2485858972600e+005

6.0510000000000e+003

5.0000000000000e+003

Yes

Zero-Tide

http://pds-geosciences.wustl.edu/mgn/mgn-v-rss-5-gravity-l2-v1/mg_5201/gravity/

MGN180u

Magellan 180u

Venus

180

180

3.2485859207900e+005

6.0510000000000e+003

5.0000000000000e+003

Yes

Zero-Tide

http://pds-geosciences.wustl.edu/mgn/mgn-v-rss-5-gravity-l2-v1/mg_5201/gravity/