Where U U And C


Fig. 11-11. Notation Used for Attitude Uncertainty Computations

As an example of the application of Table 11-2, we compute attitude uncertainty for the IUE spacccraft with its spin axis attitude oriented toward the north ecliptic pole [Boughton and Chen, 1978]. Figure 11-12 shows the IUE

Vat borth ecliptic pou

Vat borth ecliptic pou

mission attitude geometry on the spacecraft-centered celestial sphere. A is the attitude at the north ecliptic pole, S is the direction of the Sun for a January 15 launch, E is the direction of the Earth as seen by the panoramic scanner, and N = S X E is the direction of the null. E is 90 deg from 5.

In this example, 0=^=90°, tj = 119°, £=29°, and «=90°. From Table 11-2 or Fig. 11-18 in the next section, we obtain

and d = sin^sini = _sin292_=055 * sin^sinTj sin 119°

Assuming that 0.1°, 1^=0.7°, and U9=4.9° with no correlated components, we get

The weighted mean of the attitudes obtained from the three methods will thus have an uncertainty of (see, for example, Bevington [1969])

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