SATELLITE SYSTEMS - GPS Satellite Surveying - page 70

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[70

Figure 3.5 The satellite body-fixed coordinate system.

Lin
—
-3.
——
Nor
PgE

Th e symbol p denotes the SRP in the direction of the sun. With the sign convention
of Equation (3.79), p should be positive. The other parameter is called the Y bias.
Th e reasons for its existence could be structural misalignments, thermal phenomena,
or possibly misalignment of the solar panels with the direction of the solar photon
flu x. The fact that a Y bias exists demonstrates the complexity of accurate solar
ra diation pressure modeling. Table 3.2 shows the effects of the various perturbations
ov er the period of one day. The table shows the difference between two integrations,
on e containing the specific orbital perturbation and the others turned off. It is seen
th at SRP orbital disturbance reaches close to 100 m in a day. This is very significant
co nsidering that the goal is centimeter orbital accuracy. Over a period of 1-2 weeks
th e SRP disturbance can grow to over 1 km.

[70

3. 1.4.4 Eclipse Transits andYaw Maneuvers Orbital determination is fur-
th er complicated when satellites travel through the earth shadow region (eclipse). The

TABLE 3.2 Effect of Perturbations on GPS Satellites over One Day

Perturbation Radial Along Cross Total

Earth flattening 1335 12902 6101 14334

Moon 191 1317 361 1379

Sun 83 649 145 670

C 2 , 2 , S 2 , 2

32 175 9 178

SRP 29 87 3 92

C n,m , S n,m

6 46 4 46

( n, m = 3 ... 8)

Source: Springer et al., 1999.
Note: The units are in meters.