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^[5][6] by Hughes Chief Technologist Jerry Salvatore.^[7] 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.^[8]

Although Hughes did not end up using the low-energy transfer trajectory, the insight to use a lunar swingby was key to the spacecraft rescue. According to Cesar Ocampo, Hughes had not considered this option until it was contacted by Ridenoure,^[9] although the Hughes engineers involved in the lunar flyby operations have stated that they were already working on the lunar swingby mission design before being contacted by him.^[7]

Rescue of satellite

Using on-board propellant and lunar gravity, the orbit's apogee was gradually increased with several manoeuvres at perigee until it flew by the Moon^[9] at a distance of 6,200 km from its surface in May 1998, becoming in a sense the first commercial lunar spacecraft. Another lunar fly-by was performed later that month at a distance of 34,300 km to further improve the orbital inclination.

These operations consumed most of the satellite's propellant, but still much less than it would take to remove the inclination without the Moon assist manoeuvres. With the remaining fuel, the satellite could be controlled as a geosynchronous satellite, with half the life of a normal satellite – a huge gain, considering that it had been declared a total loss. The satellite was then maneuvered to geosynchronous orbit at 150–154° W.

Once the satellite was in a stable orbit, it was commanded to release its solar panels which had been stowed during takeoff and maneuvering. Of the satellite's two solar panels, only one released, and it became apparent that a tether was not operating correctly on board, which engineers attributed to heating and cooling cycles due to the satellite operating outside its design range while traveling to its final orbit. In 1999, HGS-1 was acquired by PanAmSat, renamed to PAS 22, and moved to 60° W. It was deactivated in July 2002, and moved to a graveyard orbit.^[3]

See also

• AMC-14

References

External links

• Krebs, Gunter (22 March 2013). "AsiaSat 3, 3S / HGS 1 / PAS 22". Gunter's Space Page. Retrieved May 14, 2013. 
• Ridenoure, Rex (13 May 2013). "Beyond GEO, commercially: 15 years… and counting". The Space Review. Retrieved May 14, 2013. 
• Salvatore, Jerry (15 July 2013). "The Chief Technologist’s view of the HGS-1 mission". The Space Review. Retrieved July 15, 2013. 
• Skidmore, Mark (8 July 2013). "An alternative view of the HGS-1 salvage mission". The Space Review. Retrieved July 8, 2013. 
• "AsiaSat 3:Collection of related press releases". Astronet. Retrieved May 14, 2013. 
• "Asiasat 3/HGS 1 Mission Profile". NASA. 19 December 2011. Retrieved May 14, 2013.