Envisat center-of-mass information since launch (from ftp://ftp.cls.fr/pub/ids/satellites/macromodels/en1mod.pdf) (values define COM in spacecraft coordinate system):

		X(m)	Y(m)	Z(m)
CGMASS	2009001 20301 0.	-4.365	-0.002	-0.039
CGMASS	2009001 20308 0.	-3.856	-0.008	+0.003
CGMASS	2009001 20509 0.	-3.857	-0.008	+0.003
CGMASS	2009001 20706 0.	-3.857	-0.008	+0.003
CGMASS	2009001 20828 0.	-3.857	-0.008	+0.003
CGMASS	2009001 20911 0.	-3.858	-0.008	+0.003
CGMASS	2009001 20912 0.	-3.858	-0.008	+0.003
CGMASS	2009001 20927 0.	-3.858	-0.008	+0.003
CGMASS	2009001 30930 0.	-3.862	-0.009	+0.003
CGMASS	2009001 60930 0.	-3.862	-0.009	+0.003

SLR array offset from the satellite coordinate origin:

				X(m)	Y(m)	Z(m)
OFFSET	5	2009001	563909774.4	-4.920	+1.350	-1.180

Envisat observation correction values:

			(m)
OBSCOR	512009001	51	-0.0512

From ftp://ftp.cls.fr/pub/ids/satellites/macromodels/en1mod.txt: Base of each reflector is not at the LLR reference point. The distance is 53.7 mm. Therefore, the correction to add to the measurements is azimuth dependent, between 48.7 and 53.7 mm.

Other CoM references:

Envisat center-of-mass information since launch (IDS): ftp://ftp.cls.fr/pub/ids/satellites/macromodels/en1mod.pdf
Envisat nominal attitude law (IDS): ftp://ftp.cls.fr/pub/ids/satellites/en1att.txt
Envisat mass history: http://fdsa.esoc.esa.de/envisat/mass.env
Envisat mass history (IDS): ftp://ftp.cls.fr/pub/ids/satellites/en1mass.txt
Envisat maneuver history: http://fdsa.esoc.esa.de/envisat/ENVmano.html
Envisat maneuver history (IDS): ftp://ftp.cls.fr/pub/ids/satellites/en1man.txt