[IGSMAIL-7258] igs08_1886.atx: Update including GLONASS-M satellite R851

[Ralf Schmid]

Dear IGS colleagues!

The absolute IGS antenna correction file (igs08_wwww.atx) has been 
updated. The new release is called 'igs08_1886.atx' (Please note that 
'1886' corresponds to the number of the upcoming GPS week!). It contains 
the following changes:

1) According to the Information Analytical Centre (IAC), GLONASS-M 
satellite R851 (2016-008A) launched on 7 February 2016 replaced 
GLONASS-M satellite R714 in almanac slot 17. Therefore, the following 
satellite has been added:

R17 (R851)

The following PRELIMINARY phase center offset (PCO) values were assigned:

PCO_X = -54.5 cm
PCO_Y =   0.0 cm
PCO_Z = 245.0 cm

According to the Center for Orbit Determination in Europe (CODE), R851 
is already active since 24 February 2016 (DOY 55).

source:
> |  751  | 2514 | 3/17 |  04  | 07.02.2016 | 24.02.2016 |  unusable | 24.02.2016 |
https://www.glonass-iac.ru/en/CUSGLONASS/index.php

2) A decommission date for the following satellite has been added:

R17 (R714): 23 February 2016

NAGU message 013-160225:
> NOTICE ADVISORY TO GLONASS USERS (NAGU) 013-160225
> SUBJ: TRANSFER TO THE RESERVE 17/04 (714) 24.02/0430-24.02/1206 MT
> 1.CONDITION: 17/04 (714) TRANSFERRED TO THE RESERVE
>  SINCE 24.02/0430 UNTIL 24.02/1206 MT (UTC+0300)
https://www.glonass-iac.ru/en/CUSGLONASS/index.php


The updated antenna correction model is available at
ftp://ftp.igs.org/pub/station/general/igs08_1886.atx
or
ftp://ftp.igs.org/pub/station/general/igs08.atx

Many thanks to Stefan Schaer for his help!

With best regards,
Ralf Schmid
on behalf of the IGS Antenna Working Group