HGS
HGS may refer to
PAS-22
PAS-22, previously known as AsiaSat 3 and then HGS-1, was a geosynchronous communications satellite which was salvaged from an unusable geosynchronous transfer orbit by means of the Moon's gravity.
Launch
AsiaSat 3 was launched by AsiaSat Ltd of Hong Kong to provide communications and television services in Asia by a Proton booster on 24 December 1997, destined for an orbit slot at 105.5° E. However, a failure of the Blok DM3 fourth stage left it stranded in a highly inclined (51 degrees) and elliptical orbit, although still fully functional. It was declared a total loss by its insurers. The satellite was transferred to Hughes Global Services, Inc., with an agreement to share any profits with the insurers.
Edward Belbruno and Rex Ridenoure heard about the problem and proposed a 3-5 month low energy transfer trajectory that would swing past the moon and leave the satellite in geostationary orbit around the earth. Hughes had no ability to track the satellite at such a distance, and considered this trajectory concept unworkable. Instead, Hughes used an Apollo-style free return trajectory that required only a few days to complete, a trajectory designed and subsequently patented by Hughes Chief Technologist Jerry Salvatore. This maneuver removed only 40 degrees of orbital inclination and left the satellite in a geosynchronous orbit, whereas the Belbruno maneuver would have removed all 51 degrees of inclination and left it in geostationary orbit.
Mercury sulfide
Mercury sulfide, mercuric sulfide, mercury sulphide, or mercury(II) sulfide is a chemical compound composed of the chemical elements mercury and sulfur. It is represented by the chemical formula HgS. It is virtually insoluble in water.
Crystal structure
HgS is dimorphic with two crystal forms:
Crystals of red, α-HgS, are optically active. This is caused by the Hg-S helices in the structure.
Preparation and chemistry
β-HgS is precipitated as a black powder when H2S is bubbled through solutions of Hg(II) salts. β-HgS is unreactive to all but concentrated acids.
Mercury metal is produced from the cinnabar ore by roasting in air and condensing the vapour.
Uses
When α-HgS is used as a red pigment, it is known as vermilion. The tendency of vermilion to darken has been ascribed to conversion from red α-HgS to black β-HgS. However β-HgS was not detected at excavations in Pompeii, where originally red walls darkened, and was attributed to the formation of Hg-Cl compounds (e.g., corderoite, calomel, and terlinguaite) and calcium sulfate, gypsum.
