[amsat-bb] Re: 'Zombie-sat' and the clever orbital dance

Trevor . m5aka at yahoo.co.uk
Tue May 25 11:44:47 PDT 2010

The BBC are running the video on their website 


73 Trevor M5AKA

--- On Tue, 25/5/10, David - KG4ZLB <kg4zlb at 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-----
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