The gravitational parameter (symbol of a body (normally a planet, moon or star) is a value which represents the strength of its gravitational pull. This value is used in calculations involving other bodies which orbit it. For a body with mass and the universal gravitational constant ,
Experimental difficulties in determining makes it one of the most inaccurate of the fundamental constants. Since the mass of heavenly bodies is also calculated from according to the force equation for gravity (accurate to about 0.06%)
direct calculation of orbits using the force equation would be unacceptably inaccurate and prone to change whenever a better value for is found.
Because of this, it is better whenever possible to perform orbit calculations in terms of and the mass ratios of bodies. Astronomical observations can determine to very high precision.
Values of interest for a Mars mission
Note: While most of these values are known to high precision, measurements still vary between observations and the less significant digits can change as the science advances. The table below gives the gravitational parameters to six significant digits or their full available accuracy (if less) when the source was published (2011). Anyone planning an actual or paper mission should search the literature for the most accurate and recent values.
- J.R. Wertz - Orbits and astrodynamics in J.R. Wertz, D.F. Everett & J.J. Puschell Space mission engineering: The new SMAD 2011. ISBN 978-1-881883-15-9 pp. 200-201
- N. Sarzi-Amade - Physical and orbit properties of the sun, earth, moon, and planets in J.R. Wertz, D.F. Everett & J.J. Puschell eds. Space mission engineering: The new SMAD 2011. ISBN 978-1-881883-15-9 p. 955