ESA to Give New Life to Old Satellites

JPNews writes "The European Space Agency is designing a program (www.esa.int) to re-configure dying television transmission satellites to be used as a XM Radio-like satellite radio network. 'Once in position, 35,000 km away in space, TV satellites will remain in orbit forever, but their useful life amounts to 15 years or less... further life can be squeezed from a low-propellant TV satellite switched over to mobile digital radio broadcasting where precision position control is less important.'"

Comments

A Primer on the ESA

[use_compress]

from: http://www.space.com/news/spaceagencies/esa_25year s_000602.html
However, ESA's biggest achievement of all, explained Bonacina, lies not in any one particular space project. Rather, it's the fact that 15 European nations have successfully worked together, and in cooperation with other non-European space programs, to reach a common goal.

It's amazing how little a program this wide in scope accomplishes :)

To summarize

[mlyle]

Most older communications satelites have what are called "transponders"-- they take everything that comes in on a certain band of frequencies and plays it out on another set.

Because usually relatively high-bandwidth analog signals with high quality requirements are sent through these transponders, and the satelites have a relatively small amount of output power, high gain antennas (big satelite dishes) are required to recover the signal, which must be very precisely pointed.

By using digital signals and audio compression technology, suddenly the signals can be narrower bandwidth. Noise is proportional to bandwidth, and since the signal is narrower, signal/noise ratio is improved. This means high-gain antennas may no longer be strictly necessary, and thus the position of the satelite becomes less critical as the orbit decays.

Note that this does not lock us in to a proprietary standard-- if the spectrum is allocated for this purpose, smarter digital transmitters can be put into space for the same purpose later.

Still important is attitude control-- the satelite's antenna must be pointed down and the solar panels pointed in a useful direction. But this often uses gyroscopes, reaction wheels, and magnetic systems-- which do not use propellant.

Finally, battery life is a question. No communications satelite is constantly receiving solar power, so if the satelite is operated while not in view of the sun, batteries on the satelite discharge. Satelites can withstand a limited number of charge cycles before they fail, and this is likely to form the true upper bound on satelite lifetime.

In all, it's a good idea. I imagine we'll see lots of clever ways to emerge on how to use legacy hardware we've put in space, as launch costs remain so expensive.

Re:To summarize

[Captain Nitpick]

One thing: when the battery dies, could you just use the bird when it's in sunlight? what's the orbit period like up there? would you have the content dropping out in the middle of the transmission, or could you hand it off to another old bird that just passed the daylight terminator?

Since they're talking about old tv satellites out at 35000km, it looks like these are geosynchronous orbits. This means that an orbit takes 24 hours. A geosynchronous satellite should only be in Earth's shadow for a brief time each day (too lazy to look it up/do the math).

Re:To summarize

[mlyle]

When we're talking about geosynchronous satellites, or near-geosynchronous satellites, the orbital period is going to be remarkably close to 24 hours.

The answer: Maybe, but probably not. Usually the satellites have control computers and bringing them back up after they've been powered off can be difficult. It also depends on how the satellite's power system is arranged.

It's also important to note that the closer it gets to midnight, the closer to the horizon (and thus, the harder to listen to) a satellite has to be to be in sunlight-- and there's not likely to be as many geosynchronous satellites over unpopulated latitudes.

The fact that stabilization coils and reaction wheels go offline when the satellite's battery discharges means the satellite might very well begin tumbling and thus not get so much useful power when it returns to daylight-- and also not know its exact attitude to begin to recover.

Finally, the failure mode of the battery is important. If the battery fails "closed", or shorted, it might connect the negative sides of the power bus to the positive and not allow the panel to generate any useful power.

Basically, when power systems start to fail on a satellite, even when it's a temporary problem (e.g. an accidental discharge of the batteries because of an orientation problem), it can be pretty hard to recover from-- if it's possible at all.

Re:False. They won't stay in "permanent" orbit.

[Anonymous Coward]

You're talking about satellites in geostationary orbit, 35,000km out. For reference the ISS is at 400km. They're as close to "permanent" as makes no odds. The moon isn't strictly in "permanent" orbit either, but no one gets too worked up about it.

Re:Amateur Radio

[Student_Tech]

Not sure if this is what you meant but try http://www.amsat.org/ .

Re:Excuse me?

[jovlinger]

Never used a TV satelite dish have ya sonny? You have to aim the dish fairly accurately at the satelite, which kinda requires that it be where it should. Since you never get perfect geosynch (IANAOrbitalEngineer, but stands to reason), you need to use little spurts of attitude jets to keep in place. You'll also need these to despin the gyros that maintain attitude from time to time.

The punchline is that these XM radio receivers, like GPS, don't require a dish to be pointed at the satelite, so it's free to stray further from it's assigned station. This allows you to use less fuel in staying in place.

But then, you're probably a troll, so I just wasted my breath.

Re:Forever?

[mlyle]

Things in geosynchronous orbit effectively stay up there forever. This isn't a small low-earth orbit satelite 150 miles up- this is 22000 miles up.

No orbits are "permenant" in the real world-- but some are close enough. The earth isn't gonna fall into the sun tomorrow.

Re:Just when you thought it was safe

[Beebos]

You can build one from the instructions here;

http://zapatopi.net/afdb.html

But, hurry, it won't be long to til the satelittes turn your brain into jelly!!!!!

_

Re:Excuse me?

[tanveer1979]

I would like to add here that many times communications satellites used for TV also are used for VSAT communications. On TV if the satellite has wobble booters in the receiver can compensate, but such satellites are pretty much useless for internet(VSAT).

We has a 128kbps VSAT terminal at college supplied by aging ernet satellite. Data rates used to come down to 2kbps yes kilo BITS. Such satellites are normally space junk, however this may allow us to sqeeze the last bit of life from the satellite, and this will result in cost of cummunications to come down pretty much. I wonder why didnt they think of it before!

Re:Excuse me?

[Animats]

There's a definite fuel penalty associated with holding geosynch position tightly. Some comsats have only 20Kg or so of on-orbit maneuvering fuel. There's a trick called a "COMSAT orbit" (because it was invented by somebody at COMSAT Corporation) to allow more of the deviation caused by the moon to be tolerated. The satellite moves around a few degrees relative to the earth, instead of holding geosynch position tightly, but long-term error isn't allowed to accumulate.

I'm not really up on this, but I used to work at a place that made the Intelsat satellites, and some of the people around me were working on this stuff.