CoAuthors

Alexandre COUHERT (CNES, France); Clément COURDE (Observatoire de la Côte d'Azur, France); Pierre EXERTIER (GET, France); Jean-Michel LEMOINE (CNES, France); Flavien MERCIER (CNES, France); Eléonore SAQUET (CLS, France)

For the past fifty years, geodetic satellites have contributed to the measurement of numerous geophysical parameters. They thus enabled us to improve our knowledge on several Earth's physical parameters and behaviors, through their refined observation. In particular, the geocentric gravitational coefficient is a key contributor to Satellite Laser Ranging (SLR) validation of the stringent accuracy requirement on the radial positioning of altimeter satellites, defining sea level relative to the Earth’s center of mass. Indeed, SLR range biases estimated for the upcoming ITRF2020, derived from Medium Earth Orbit (MEO) Lageos and Etalon satellites, may not be applicable for Low Earth Orbit (LEO) altimeter satellites given the relatively large uncertainty of 2.0 ppb in the geocentric gravitational constant.
The purpose of this paper is to reassess the value of the Earth’s GM from SLR measurements. This constant is defined by the product of the Earth's universal gravitational constant G and its mass M. The analysis is based on its simultaneous estimation with laser station and satellite biases, taking the most of eight well-chosen geodetic satellites. At first we focused on two specific spherical geodetic satellites, said to be without signature effects, Blits and Larets. We were able to revise estimates of the GM constant using CNES’ ZOOM precise orbit determination software. Additionally, by combining MEO and LEO satellites, a consistent value of GM has been reassessed, being GM = 398600.4419 ± 0.0002 km3/sec² (TT-compatible). This value is higher than the reference value estimated previously in 1992. Also, some problems related to the design and center-of-mass corrections of the targets used have been raised and would need to be further investigated.