A. Fienga, J. Laskar, T. Morlay, H. Manche, P. Kuchynka, C. Leponcin-Lafitte, M. Gastineau and L. Somenzi, “INPOP08, a 4D planetary ephemeris: From asteroid modelisation and time-scale computations to ESA Mars Express and Venus Express contributions”, Astronomy & Astrophysics, 507, 2009, pp. 1675-1686.
The orbital solutions of the Sun, the eight planets, the dwarf planet Pluto and the Moon, the libration of the Moon and the time scale transformation TT‑TDB are available as binary or text data files.
The binary and text data files provide the rectangular coordinates (x,y,z) in kilometers of the bodies with respect to the International Celestial Reference Frame (ICRF). The librations are given in radians. The time scale transformation TT‑TDB is given in seconds for the files including it.
These INPOP08a ephemeris files are provided in four file formats:
- Binary files
- Text files
- Binary files compatible with the JPL DExxx ephemeris file format (without the time scale transformation TT‑TDB)
These INPOP08a ephemeris files extend the internal format of the binary JPL DExxx ephemeris files (http://ssd.jpl.nasa.gov/?ephemerides) by including the time scale transformation TT‑TDB. These binary files are encoded using the “INPOP binary ephemeris file format – version 1.0”. These files provide the orbital solution expressed in the TDB time scale. The coordinates in the data files are expressed as the coefficients of the Chebychev polynomials. These INPOP08a ephemeris files don’t include the coefficients for the nutation.
These files can’t be read using the older programs based on the “testeph.f” program. These files must be read with the CALCEPH Library which provides a compatible C and Fortran Application Programming Interface.
These INPOP08a ephemeris files are encoded as plain text files: the coordinates in the ascii data files are expressed as the coefficients of the Chebychev polynomials. These files provide the orbital solution expressed in the TDB time scale. These files don’t include the coefficients for the nutation but they include the time scale transformation TT‑TDB.
The file format of these files are described in the following document. The exponent letter of the real numbers is ‘D’ (instead of ‘E’).
Binary files compatible with the JPL file format
These INPOP08a ephemeris files use the same internal format as the binary JPL DExxx ephemeris files (http://ssd.jpl.nasa.gov/?ephemerides): the coordinates in the data files are expressed as the coefficients of the Chebychev polynomials. These files provide the orbital solution expressed in the TDB time scale. These files don’t include the coefficients for the nutation and the time scale transformation TT‑TDB. So these files could be read with the same programs (such as the JPL software package) which read the binary JPL ephemeris files.
The internal format is described in the paper:
David Hoffman: 1998, “A Set of C Utility Programs for Processing JPL Ephemeris Data”,
Due to the problem of the endianess in the computer (order in which integers are stored as bytes in computer memory), the binary files are available into two formats:
- Little-endian for Intel x86, IA64 or Alpha based processors (and their clones)
- Big-endian for Motorola PowerPC, IBM Power or Sparc based processors (and their clones)
The ascii header files are provided to show the content of the two first records of the binary ephemeris files. The file format of these ascii files is the same as described in (Hoffman, 1998).
The ascii testpo files are provided to check that your software is able to read the files and return the correct values. The testpo files is compliant with the format requested by the JPL program testeph.f and could be used with it.
To use these data files instead of the JPL ephemeris files, you only have to change the name of the files in your software program.
If you use a program based on the “testeph.f” program from the JPL, then you may have to set the variable NRECL (and KSIZE if you don’t use the subroutine FSIZER2). The prefered method is to read the beginning of the first record and then to compute the length of the records (same as KSIZE) with the libration’s triplet (which contains the location, order and time-coverage of Chebychev polynomial).
We provide the open-source CALCEPH Library, which provides a compatible C, Fortran and Python Application Programming Interface. This library avoids the problems with the variables (NRECL and KSIZE) and the endianess. It supports the access to the multiple ephemeris files at the same time.
For all comments concerning these pages, contact the authors: firstname.lastname@example.org.
Last update Wednesday 06 October 2021