Centre of mass values for LAGEOS, LAGEOS-2, Starlette/Stella, Ajisai, 
Etalon-1/2, and LARES, computed for most known system configurations.

Please use the following reference if you employ these values in your 
analysis of SLR data:

Rodriguez J., Otsubo T., Appleby G. Upgraded Modelling for the 
Determination of Centre of Mass Corrections of Geodetic SLR 
Satellites: Impact on Key Parameters of the Terrestrial Reference
Frame. Journal of Geodesy, 2019. doi: 10.1007/s00190-019-01315-0

Note that the corrections do not include several temporary stations with very 
low data contribution, or some engineering and experimental stations. Also, a 
few entries from very early systems for which non-sensical CoM values were 
obtained have been removed and will be investigated in the future.

CoM values are rounded to 1 decimal place to preserve fully the difference 
between LAGEOS and LAGEOS-2 arising from the model. In no way does this 
mean that the accuracy with which any of these values is known approaches 
the level of 0.1 mm.

The file systems.dat details the system configurations for the stations 
for which CoM values have been computed. Changes in the CoM values in the 
tables correspond to documented changes in the stations that appear in this 
file.

Code is provided to interrogate the tables and obtain CoM values for the 
specified station, epoch, satellite and laser wavelength (com_6multi.for). 
An example program demonstrating the use of the relevant subroutine is also 
provided (com_6multi_test.for).

In cases of stations with multiple hardware system configurations, we do not
presently have a mechanism to identify the specific hardware setup from the 
information provided in the normal point data. Ad hoc hacks could be added 
to deal with this situation, but this would not be clean, sustainable, or 
something I wish to have anything to do with. The problem has been described 
to the ILRS Central Bureau and Data Formats & Procedures Standing Committee:

https://lists.nasa.gov/pipermail/ilrs-dfpwg/2018/000139.html

The practical workaround I use is to order the entries in the tables so that 
for any given epoch the last entry corresponds to the most often employed one 
(in cases where more than one system configuration is present). The example code 
provided returns all possible values and indicates the number of entries. 
Users should simply use the last value returned, which will be the correct 
one most of the time.

Default values
---------------
Computed as the average of all the available entries, these should be used when 
no suitable entry in the table is found. The code provided returns them if the 
variable RETURN_DEFAULT is set to .TRUE. in com_6multi.for

LAGEOS    : 245.4
LAGEOS-2  : 244.8
ETALON    : 572.9
Ajisai    : 986.2
Starlette : 76.1 
Stella    : 76.1
LARES     : 130.2


José Rodríguez (jc.rodriguez@oan.es) 2022-09-15