GIOTTO Radio-Science Experiment: Drag Deceleration and Spacecraft Attitude Perturbations Expected During the Encounter with Comet P/Grigg-Skjellerup in July 1992

Abstract

The GIOTTO Radio-Science Experiment will repeat its observations performed during the GIOTTO-Halley flyby at the next encounter with Comet P/Grigg-Skjellerup in July 1992. The change in velocity due to the influx of cometary gas and dust will be determined by X-band ranging and Doppler measurements. Due to the lower flyby velocity (five times smaller) and the lower dust generation rate compared to Halley (ten times smaller), the change in velocity is estimated to be between 4 mm/s and 4 cm/s for a closest approach between 1000 km and 100 km, respectively. Large dust particle impacts (masses greater than 10 mg) on the spacecraft body may change the spin rate, resulting in a degradation of the real-time data link to Earth or, in the worst case, loss of data. Nutation is not considered a problem for this encounter.