The BBC Blogs - Spaceman
« Previous | Main | Next »

'Zombie-sat' and the clever orbital dance

Jonathan Amos | 11:45 UK time, Tuesday, 25 May 2010

The "dead-but-alive" telecommunications satellite, Galaxy-15, has begun to enter the space of neighbouring craft, and their operators are planning evasive action.

Galaxy 15"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 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, another TV services spacecraft operated by SES World Skies.

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.

SES World Skies plan to evade Galaxy-15 interference

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 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; 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, but Patrick Wood, the chief technical officer for EADS Astrium satellites, 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. Galaxy-15 will likely end its days in one of the two great "garbage patches" in the sky.

These 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].

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].

We may all love our satellite TV, but we're starting to build a problem for ourselves.

Watch this space.


or register to comment.

  • 1. At 12:55pm on 25 May 2010, calmandhope wrote:

    Facinating piece, I'd missed this story somehow, but I'd presumed this sort of thing was happening more frequently than it appears to be. Did you have to have such a cheesy sign off though?

    Complain about this comment

  • 2. At 2:27pm on 25 May 2010, BobRocket wrote:

    Presumably the original customers of Galaxy 15 will no longer be able to 'see' the satellite when it drifts too far into AMC-11 space, why doesn't SES just turn off AMC-11 for a bit and use Galaxy until it has passed through and then go back to AMC-11, I don't see the need for the third satellite.

    Complain about this comment

  • 3. At 07:52am on 26 May 2010, Jonathan Amos wrote:

    @calmandhope: The Wensleydale reference should indicate to you that I don't take myself very seriously. @BobRocket: You don't play games with a zombie; you run ;-)

    Complain about this comment

  • 4. At 11:45am on 26 May 2010, Terry Gush wrote:

    The Zombie-sat malfunction and subsequent scattering of a flock of expensive neighbouring satellites and shortening their operating lives as they burn through limited reserves of propellant, is potentially fortuitous. The advantage being that a representative body such the IADC is given fresh impetus to campaign among satellite operators and investors to fund a space tug program to de-orbit this and future Zombie-sats and finally each of the 1238 locatable objects so far assembled in geosynchronous orbit.

    It seems unlikely that adverse space weather would “wing” one satellite while leaving neighbouring satellites unharmed, so the outcome of the investigations is keenly awaited, if they come to hand thank you.

    Please keep the cheerful sign off and other user friendly features that guarantee this pre-moderated space forum to an ad hominem free zone.

    Complain about this comment

  • 5. At 2:39pm on 26 May 2010, freddawlanen wrote:

    Why are any organisations, governments included, allowed to send things into space without plans in place to remove them when they become defunct?

    Surely if things like this and the "garbage patches" are allowed to continue it won't be long before something major happens like numerous satellites being knocked out of commission, or god forbid, astronauts lives being in danger from 'rogue' satellites, or like everything else, does it simply come down to greed over sensible long-term thinking?

    Complain about this comment

  • 6. At 01:09am on 27 May 2010, Keith B wrote:

    Why not get the Chinese to shoot down Galaxy 15? They've shown they're very good at that sort of thing. :-)

    Complain about this comment

  • 7. At 01:27am on 27 May 2010, jr4412 wrote:

    Jonathan Amos.

    "The two libration points now contain more than 150 defunct satellites."

    rather than getting someone "to shoot down" satellites, as Keith B (#6) suggests, why not get all future satellites fitted with some autonomous system which drives them into the atmosphere for burn-up, to kick in when communications or core systems fail.

    there has to be a way of reducing space 'junk'.

    Complain about this comment

  • 8. At 3:54pm on 27 May 2010, Jonathan Amos wrote:

    @Keith B: We need fewer bits, not more. @jr4412: Debris mitigation/de-orbit approaches are certainly the way forward, and we'll no doubt see a number of ideas suggested, from space tugs (as mentioned by @Terry) to drag sails.

    Complain about this comment

  • 9. At 3:12pm on 02 Jun 2010, Rephl3x wrote:

    This comment was removed because the moderators found it broke the House Rules.

  • 10. At 12:08pm on 11 Mar 2011, probiaph wrote:

    Why are any organisations, governments included, allowed to send things into space without plans in place to remove them when they become defunct?

    Surely if things like this and the "garbage patches" are allowed to continue it won't be long before something major happens like numerous satellites being knocked out of commission, or god forbid, astronauts lives being in danger from 'rogue' satellites, or like everything else, does it simply come down to greed over sensible long-term thinking?

    Felicio komardo - [Unsuitable/Broken URL removed by Moderator]

    Complain about this comment

  • 11. At 8:04pm on 12 Mar 2011, pharmas wrote:

    Its truly amazing how we manage to keep so many satellites in orbit. I can't imagine how it must have been in the past without the many benefits they provide. Even more ridiculous is how there are still many improvements to satellite technology still on their way.

    Satellite TV may be difficult to maintain but it sure helps keep the entertainment coming.

    Complain about this comment

  • 12. At 7:58pm on 17 Apr 2011, wczasy wrote:

    Further research leads me to the proper solution, which is to have the Russian on board the space shuttle use his pistol while on a space walk that will see him shoot the zombie-sat in the brain.[Unsuitable/Broken URL removed by Moderator]

    Complain about this comment

  • 13. At 6:01pm on 14 May 2011, Sam Denton wrote:

    Makes you think about how the sky will look like in 200 at night

    Will be full of Sat`s and space ships

    Now it`s exciting, in 200 it will make our stars disappear.

    But for now, anything that can increase TV quality is just fine.

    Complain about this comment

View these comments in RSS


Sign in

BBC navigation

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.