G. A. Avanesov

Comet Halley: Nucleus and jets (results of the VEGA mission)

Abstract The VEGA-1 and VEGA-2 spacecraft made their closest approach to Comet Halley on 6 and 9 March, respectively. In this paper those results of the onboard imaging experiment which were obtained around closest approach are discussed. The nucleus of the comet was clearly identifiable as an irregularly shaped object, with overall dimensions of (16±1)×(8±1)×(8±1) km. The nucleus rotates in the prograde sense about an axis nearly perpendicular to the orbital plane with a period of 53±2 hours. Its albedo is only 0.04± 0.02 0.01 Many of the jet features observed during the second fly-by have been spatially reconstructed. Their sources form a quasi-linear structure on the surface. The dust above the surface is shown to be generally optically thin with the exception of certain specific dust jets. Brightness features on the surface are clearly seen. Correlating our data with other measurements, we conclude that the dirty snow-ball model will probably need to be revised.

Regatta-Astro Project: Astrometric Studies from Small Space Laboratory

The Regatta-Astro project provides a great set of astrometric and photometric measurements from Small Space Laboratory (SSL). SSL is a special spacecraft being designed at the Space Research Institute, USSR Academy of Sciences. The main feature of this spacecraft is the attitude control by solar light pressure. The main objective of the project is to compile precise global catalogues of star positions, parallaxes and proper motion containing stars with magnitude up to 8–9 and a position accuracy of 0.″01. The astrometric concept of the project is based on a highly deterministic spacecraft angular motion and numerous observations of each star using wide-angle TV cameras with CCD detectors. The SSL computer provides measurement data pre-processing, photometric referencing and data compression. Ground-based computers process the data statistically. The estimated vector includes star coordinates, SSL angular motion parameters and generalized distortion of the instruments used.