The BBC are running the video on their website http://news.bbc.co.uk/1/hi/science_and_environment/10150614.stm
73 Trevor M5AKA --- On Tue, 25/5/10, David - KG4ZLB <kg4...@googlemail.com> wrote: > The "dead-but-alive" > telecommunications satellite, Galaxy-15 > <http://www.orbital.com/SatellitesSpace/Communications/PanAmSat/>, > has begun to enter the space of neighbouring craft, and > their operators are planning evasive action. > > "Zombie-sat" has captured the imagination of the internet > space forums these past few weeks. It's probably the > nickname that's done it. > > When we sit on the sofa skipping across the smorgasbord of > channels with our remote-controls, we don't usually give > much thought to the "bent pipes" that sit 36,000km above our > heads, delivering the televisual feast. > > Intelsat's Galaxy-15 > <http://www.intelsat.com/resources/galaxy-15/operational-status.asp> > satellite was put in geostationary orbit five years ago to > re-distribute TV services to cable companies across North > America, and also to send navigation data to aeroplanes to > improve the accuracy of their GPS receivers. > > But the "bird" experienced a major hiccup at the beginning > of April. > > It's not known precisely what happened. One possibility is > that it was damaged by high-speed particles billowing off > the Sun in a solar storm - an ever-present danger for > orbiting electronics. > > The satellite is still operational: it's still "on", but > Intelsat cannot control it. Any signal it receives, it > re-transmits at high power. It's a very unusual situation. > > What doesn't help is the fact that Galaxy-15, which is > supposed to sit at 133 degrees West (over the eastern > Pacific), is drifting slowing eastwards by about 0.05 > degrees a day. This will take it into the path of other > satellites, and first to have an issue is AMC-11 > <http://www.ses-worldskies.com/worldskies/satellites/01_amc-fleet/amc-11/index.php>, > another TV services spacecraft operated by SES World Skies > <http://www.ses-worldskies.com/worldskies/index.php>. > > If SES were to do nothing, Zombie-sat would soon start > picking up and retransmitting signals sent to AMC 11. To > users on the ground who depend on AMC 11 for their daily > dose of MTV, this could lead to a horrendous mash-up. > > It would be like trying to listen to two people who are > shouting the same conversation at you. > > So, SES World Skies will today begin a delicate orbital > dance, in which they will allow AMC 11 to drift in tandem > with Galaxy-15 while at the same time sneaking up another > satellite behind the pair. > > The plan is for the SES controllers to then leapfrog many > of the services on AMC-11 across to this other satellite, > known as SES-1, thereby minimising the disruption to > customers. > > The manoeuvres are unprecedented, says Alan Young, the > chief technology officer with SES World Skies. > > "The closest AMC-11 and Galaxy-15 will > come is measured in > kilometres, and in space terms that's > quite close. But the risk here > is not one of collision; we're not at all > concerned about that. The > problem is that they're so close when > viewed from Earth that it's > not easy to distinguish between the two > satellites and seeing as > they both operate in the same frequency > band, there will be > interference if we're not careful. > > "We've gone to a number of measures, > including moving customers on > AMC-11 on to a very large uplink antenna. > This means we can very > finely discriminate between the two > spacecraft so that we can direct > all of the energy into AMC-11 and as > little energy as possible into > Galaxy-15. If you don't put anything into > Galaxy-15, you won't get > anything out." > > AMC-11 will eventually be moved back to its orbital slot to > resume normal operations once the zombie has passed through, > which should be 7 June. > > All satellite operators and comms companies will have to > work out what Galaxy-15 means to them. Here at the BBC, > we've had to consider how some of our international services > like the BBC World News channel <http://www.bbcworldnews.com> might be > affected. > > This channel is fed through Intelsat's Galaxy-13 platform. > The most recent calculations suggest everything should be > fine. > > Anyone sitting on their sofa in North America should be > oblivious to the space waltz that is about to take place. > > There are some wider issues, however. For satellite > manufacturers, there will be keen interest in understanding > exactly what happened to Galaxy-15. > > Satellites have redundant, or back-up systems > <http://news.bbc.co.uk/1/hi/sci/tech/8458203.stm>; > and when they have major upsets, there are usually modes > that will completely re-boot the spacecraft automatically > after a period of time. > > Galaxy-15 was made by Orbital Sciences <http://www.orbital.com/>, but Patrick > Wood, the > chief technical officer for EADS Astrium satellites > <http://www.astrium.eads.net/>, told me the entire > industry had an interest in finding out what went wrong: > > "Part of our design review process is to > check through the > architecture to ensure there isn't a > single point that, were it to > fail, we'd lose complete control of the > spacecraft. Clearly > Galaxy-15 has had a major event and most > organisations will want to > understand what happened. From an > industrial point of view, the > surprising thing is that Galaxy-15 is > locked on full power. This > tends to suggest the control/tele-command > side of the spacecraft has > failed and left the spacecraft in > whatever mode it was in when it > was last commanded. It's a very unusual > case." > > And, of course, the whole episode raises once again the > issue of orbital space debris > <http://news.bbc.co.uk/1/hi/sci/tech/7916582.stm>. > Galaxy 15 will likely end its days in one of the two great > "garbage patches" in the sky. > > These libration points > <http://en.wikipedia.org/wiki/Geostationary_orbit#Earth_orbital_libration_points>, > as they are known, are located at roughly 105 degrees West > and 75 degrees East. They are gravitational "sweet-spots" > where drifting objects will naturally coalesce. > > The two libration points now contain more than 150 defunct > satellites [395Kb PDF] > <http://www.secureworldfoundation.org/siteadmin/images/files/file_460.pdf>. > > Satellite operators are urged to put their geostationary > spacecraft in a "graveyard orbit" once their missions are > complete. This usually means pushing the platforms even > higher into the sky. > > But of the 21 spacecraft which reached end of life in 2009, > only 11 were disposed of in accordance with the Inter-Agency > Space Debris Coordination Committee's (IADC) re-orbiting > guidelines [99 Kb PDF] > <http://www.iadc-online.org/Documents/Docu/IADC_Mitigation_Guidelines_Rev1_Sep07.pdf>. > > > We may all love our satellite TV, but we're starting to > build a problem for ourselves. > > Watch this space. > > > > -----Inline Attachment Follows----- > > _______________________________________________ > Sent via amsat...@amsat.org. > Opinions expressed are those of the author. > Not an AMSAT-NA member? Join now to support the amateur > satellite program! > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb > _______________________________________________ Sent via amsat...@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? 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