Subject: [IGSMAIL-1653] Information ragarding Block IIR modeling
From: Yoaz Bar-Sever
Date: Wed, 30 Jul 1997 8:52:01 PDT

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IGS Electronic Mail      Wed Jul 30  8:52:01 PDT 1997      Message Number 1653
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Author: Yoaz Bar-Sever
Subject: Information ragarding Block IIR modeling

Information ragarding Block IIR modeling for precise orbit determination
========================================================================

The first block IIR satellite was launched on the night of July 23.
It was named SVN 43, PRN 13, and placed in plane F. As of todate it is
still undergoing BOL testing. The satellite is different from Block II/IIA
satellites in many areas. The following information should be helpful
in implementing a proper solar radiation model and measurement model
for this satellite. This information is based on several sources but
I assume full responsibility for it while, at the same time, not claiming 
that it is error free. I assume you have previous knowledge of GPS
Block II/IIA modeling.

Attitude:
========

Body-fixed coordinates are designated X, Y and Z, with origin at the
center of mass, Z along the navigation antenna, and Y along the solar
array boom. For beta angles larger that 1.6 degrees, the attitude algorithm 
is the same as that for Block II/IIA satellites, except that the +X axis 
faces away from the Sun. Unlike Block II/IIa satellites, this attitude
mode includes shadow crossing. For beta angles between 1.6 deg and -1.6 deg,
the satellite switches to a fixed yaw mode. This transition happens at
orbit dusk. During this mode the X and Z axes are in the orbital plane,
where +X points roughly in the direction of velocity.

Solar radiation:
===============
Use the T30 model (Fliegel and Gallini, Solar Force Modeling of Block IIR
Global Positioning System Satellites, Journal of Spacecraft and Rockets,
Vol. 33, No. 6, pp 863-866):

X = -11 sin B - 0.2 sin 3B + 0.2 sin 5B
Z = -11.3 cos B + 0.1 cos 3B + 0.2 cos 5B

where B is the angle between the Sun and the Z axis, positive if X forms
an accute angle with the Sun and negative otherwise (i.e., it is almost
always negative). The BOL mass in 1100 kg.

Center of gravity to phase center vector:
========================================
PC = CG + V,
where V is a vector given in meters, in the body-fixed coordinates.
There is conflicting information here (surprise,  surprise). One set of
numbers is: V=(0.0031, -0.0012, 1.72), and another set of numbers is:
V1=(0, 0, 1.6764) for L1 and V2=(0, 0, 1.9812) for L2.
An earlier set of numbers was V=(0, 0, 1.17).
We will probably attempt to estimate a Z-shift once data is avaliable.

I will try to find anwers to any questions you might have regarding Block IIR
modeling.

--
 Dr. Yoaz E. Bar-Sever
 [email-masked]                  MS 238-600
 voice: (818) 354-2665 office            Jet Propulsion Laboratory
        (626) 794-9243 home              4800 Oak Grove Dr.
 FAX:   (818) 393-4965                   Pasadena, California  91109

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