Giotto Attitude Constraints
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Giotto Attitude Constraints

October 15, 2009
This is slide 15 of 20 from the first Giotto slide set. The following caption is the one originally provided with the slide set.

Throughout the mission the spacecraft attitude defined by the Sun aspect angle (0° -Sun above the tripod) must be kept inside an allowed corridor (light yellow) which is given by two constraints: The high gain antenna must permanently point at the Earth to maintain the telecommunications link (communications constraint, green line), and, secondly, the spacecraft must generate enough power without being heated up too much (thermal/power constraint, red line).

The 'hot phase' of the mission occurs at the end of December 1985 when Giotto is 0.72 AU away from the Sun. In the event that the telecommunications link to the Earth is lost the spacecraft will slowly drift out of the allowed corridor. If, however, the attitude is kept within a certain narrow part of the allowed corridor (dark yellow), its boundaries given by the 'sheared constraint', Giotto could be up to 12 days without contact and still remain in the allowed corridor. The nominal attitude strategy (blue line) is continuously in the dark yellow part of the corridor and is based on minimum hydrazine consumption during the cruise phase. In this sense it is an optimal strategy from which one must deviate during the last few days of the cruise to arrive at the comet with the required Sun aspect angle of 107°.

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