The Giotto encounter with Comet P/Grigg-Skjellerup - First results from the Giotto Radio-Science Experiment
Abstract
Drag-induced deceleration of the Giotto spacecraft was detected during its encounter with Comet P/Grigg-Skjellerup. Doppler measurements conducted before and after the flyby, performed in two-way coherent tracking mode, revealed a total decrease in the spacecraft's radial velocity of (0.4 +/- 0.1) mm/sec. Assuming inelastic momentum transfer, the total deceleration corresponds to a total effective cometary mass of 40 +/- 15 mg. Real-time Doppler measurements during the encounter on 10 July 1992, performed in one-way noncoherent tracking mode, show an abrupt frequency decrease at 15:30:42.78 UT by 138.4 Hz. This discontinuity cannot be attributed to a spacecraft deceleration or propagation effects along the line-of-sight. The most likely explanation is an instrumental effect of the spacecraft radio system. The spacecraft spin period decreased by 1 ms from 3.992 sec to 3.991 sec. A small, but detectable nutation, with nutation angle of 0.08 deg and period 3.292 sec, was generated after the frequency discontinuity. One large dust particle of at least 30 mg effective mass is required to explain the nutation.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- February 1993
- Bibcode:
- 1993A&A...268L..13P
- Keywords:
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- Giotto Mission;
- Grigg-Skjellerup Comet;
- Radio Astronomy;
- Cosmic Dust;
- Power Spectra;
- Red Shift;
- COMETS;
- GRIGG-SKJELLERUP;
- GIOTTO MISSION;
- SPACECRAFT OBSERVATIONS;
- MASS;
- DUST;
- COMA;
- GEM MISSION;
- DECELERATION;
- DOPPLER METHODS;
- PARTICLES;
- IMPACT EFFECTS;
- NUTATION;
- ORIGIN;
- SOURCE;
- GRE INSTRUMENT;
- VELOCITY;
- GEOMETRY;
- Astrophysics; Comets