Practical use of EPM and DE ephemeris

DOI: 10.34759/trd-2022-125-18

Аuthors

Kasmerchuk P. V.^*, Vernigora L. V.^**

Lavochkin Research and Production Association, NPO Lavochkin, 24, Leningradskay str., Khimki, Moscow region, 141400, Russia

*e-mail: pavel.kazmerchuk@gmail.com
**e-mail: vlv@laspace.ru

Abstract

The design of interplanetary space missions is impossible without knowledge of the position of solar system objects and their dynamics. To determine the position and speed of an astronomical object at a specific point in time (on a specific date), special tables called ephemeris are used. Modern ephemerides are built on the basis of integrating rather complex equations of motion that take into account the gravitation of many bodies in the solar system, including large asteroids and trans-Neptunian objects, relativistic effects, perturbations from the dynamic compression of the Sun, mutual perturbations of the planets, the Sun and the Moon, etc. When building dynamic models ephemeris, data from radar observations of planets, laser observations of the Moon, data on the parameters of the movement of spacecraft during their approach to large planets, the results of interferometry with very long bases, etc. are used.

To date, one of the most accurate are the Ephemeris of Planets and Moon (EPM) ephemerides developed by the Institute of Applied Astronomy of the Russian Academy of Sciences (IPA) and the Development Ephemeris (DE) ephemeris of the NASA Jet Propulsion Laboratory (JPL). Various variants of the DE series ephemeris appeared in the 60s of the XX century, the EPM ephemeris began to be created in 1974.

The coordinate system used in a particular version of the ephemeris must be specified in the documentation. In most versions, the coordinates are as close as possible to the International Celestial Reference System (ICRS — International Celestial Reference System). The origin is the barycenter of the solar system. The X axis is directed to the vernal equinox at the J2000 epoch, the Z axis is perpendicular to the plane of the Earth’s equator, the Y axis completes the system to the right. The resulting coordinate system is independent of the Earth’s rotation. Units of measurement of coordinates are kilometers, measurements of time are days of barycentric coordinate time (TDB). The Julian day is used. Algorithms for converting a calendar date to a Julian day and vice versa can be found in.

There are quite a few tools that allow you to calculate the ephemeris data of astronomical objects, for example, online ephemeris services, as well as offline libraries. However, if the task is to use ephemeris in your own software, in which for some reason the use of third-party libraries is impossible or there are high performance requirements for subroutines working with ephemeris, which require specific code optimizations, you can use the text representation of ephemeris in the DE format available for free download from the IPA and NASA servers.

Keywords:

ephemeris, C++, Ephemeris of Planets and Moon (EPM), Development Ephemeris (DE)

References

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