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Celestrak Space Weather Files or custom ASCII files are the recommended formats for Jacchia-Roberts drag data, but FreeFlyer also supports the binary Jacchia-Roberts drag file format shown below. Examples of this type of file are provided in the FreeFlyer installation directory under "data\deprecated" as solar_flux_jacchia_10-2019.dat (data from 1996 to 2024) and solar_flux_jacchia_1986_to_2014.dat (data from 1986 to 2014). These files are not updated with new FreeFlyer releases.
References:
1."Revised Static Models of the Thermosphere and Exosphere with Empirical Temperature Profiles," Jacchia, L. G., Smithsonian Astrophysical Observatory Special Report No. 332 (1971)
2."An Analytical Model for Upper Atmosphere Densities Based Upon Jacchia's 1970 Models, Celestial Mechanics," Roberts, E. R. Jr., Volume 4, Issue 3-4, 368-377 (1971)
3."Goddard Trajectory Determination System (GTDS) Mathematical Theory", FDD/552-89/001 and CSC/TR-89/6001, July 1989 |
Note: FreeFlyer uses 0th order interpolation (last defined value) when querying an epoch that is not contained in the file.
Jacchia-Roberts Binary File Format
The format of the deprecated Jacchia-Roberts binary file format is described below.
Jacchia-Roberts Atmospheric Density (Jacchia) File Layout
Record 1 (Header) Size=252
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Byte | Description
-------------------------------------------------------------------------
1-4 | IDAYS: MJD of first data on file
5-8 | IDAYE: MJD of last data on file
9-12 | NREC: Number of records (=500)
13-16 | IDAYEM: MJD of last measured data on file
17-20 | IFLAG: Last maintenance operation indicator
| =1, create
| =2, add
| =3, modify
| =4, delete
21-28 | YMDHMS: Date of last maintenance operation
29-252 | spare
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Records 2-500 Size=252
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Byte | Description
-------------------------------------------------------------------------
1-4 | IST: MJD of first day in record
5-172 | KP(I,J): I=1,21 J=1,4 (I*2)
| 21 sets of packed geomagnetic indexes (x10), beginning with
| day IST-1. Geomagnetic indexes are packed 2 per J index
| (8 per day)
173-252| TC(I): I=1,20 (R*4)
| 20 exospheric temperatures (1 per day)
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