Seems to me that the actual signal levels that are arriving at your lnb
must be really small, and of course dependent on how the aerials are aimed
on the sat itself, ie footprint. Also one supposes the closer to the horizon it is for aiming the dish, the more atmosphere it needs to travel through to get to you. Ignoring for a second the that close to the horizon will mean
you need a higher dish to avoid things on the ground, , eventually these
Sats must go faulty. What on earth do they do with them then, to avoid collisions. There must be loads of old ones up there by now. Do they save a bit of rocket fuel to boost them well away? If they do and the fault is in the link, they are presumably stuffed and have to let it wander about for ever.
Brian
eventually these
Sats must go faulty. What on earth do they do with them then, to avoid >collisions.
Do they save a
bit of rocket fuel to boost them well away?
On Thu, 14 Apr 2022 10:03:56 +0100, "Brian Gaff \(Sofa\)" <bri...@blueyonder.co.uk> wrote:
eventually theseNothing, as far as I know. Space is just a lot more, well, spacious
Sats must go faulty. What on earth do they do with them then, to avoid >collisions.
than it's easy to imagine. Theoretically a point on the Clarke orbit
must be just that, a point, but in reality the tolerance is probably a
few tens of miles, and the satellites are only a few feet across.
Rod.
move out of the ecliptic, where live ones are maintained.
On 14/04/2022 16:16, R. Mark Clayton wrote:
move out of the ecliptic, where live ones are maintained.
Surely not the ecliptic. I think most satellite dishes have a beam width
a lot less than 46 degrees, and I haven't noticed them nodding up and down during the course of the year. I'd expect them to be aligned relative to
the earth's axis, not the earth's orbit, although I'd expect station
keeping to be easier for the latter.
On Thursday, 14 April 2022 at 10:28:21 UTC+1, Roderick Stewart wrote:
On Thu, 14 Apr 2022 10:03:56 +0100, "Brian Gaff \(Sofa\)"
<bri...@blueyonder.co.uk> wrote:
eventually theseNothing, as far as I know. Space is just a lot more, well, spacious
Sats must go faulty. What on earth do they do with them then, to avoid
collisions.
than it's easy to imagine. Theoretically a point on the Clarke orbit
must be just that, a point, but in reality the tolerance is probably a
few tens of miles, and the satellites are only a few feet across.
Rod.
They normally de-orbit geostationary ones to a different orbit, although normal decay will normally see them move out of the ecliptic, where live
ones are maintained.
Nobody seems to have thought this through then. After all, one assumes orbit decay has to be only via solar wind at those altitudes. That would possibly make them very unstable, since the largest areas will be the solar sells,
I'd imagine and station keeping by gyros can only continue while these are still working.
Brian
On 14/04/2022 10:03, Brian Gaff (Sofa) wrote:
Do they save a
bit of rocket fuel to boost them well away?
Yes. See <https://en.wikipedia.org/wiki/Graveyard_orbit>
No they should not be out of the ecliptic, at least not by very mush as this would produce a now you see it now you don't for those near the edge of the footprint north or south.
On 14/04/2022 16:16, R. Mark Clayton wrote:
move out of the ecliptic, where live ones are maintained.Surely not the ecliptic. I think most satellite dishes have a beam
width a lot less than 46 degrees, and I haven't noticed them nodding up
and down during the course of the year. I'd expect them to be aligned relative to the earth's axis, not the earth's orbit, although I'd expect station keeping to be easier for the latter.
Yes, these days there are international standards for end-of-life
satellites. The Astra ones hold enough fuel to move them to a parking
orbit a bit higher than the geostationary ones.
On 14/04/2022 10:03, Brian Gaff (Sofa) wrote:
Seems to me that the actual signal levels that are arriving at your lnb
must be really small, and of course dependent on how the aerials are
aimed
on the sat itself, ie footprint. Also one supposes the closer to the
horizon
it is for aiming the dish, the more atmosphere it needs to travel through
to
get to you. Ignoring for a second the that close to the horizon will mean
you need a higher dish to avoid things on the ground, , eventually these
Sats must go faulty. What on earth do they do with them then, to avoid
collisions. There must be loads of old ones up there by now. Do they save
a
bit of rocket fuel to boost them well away? If they do and the fault is
in
the link, they are presumably stuffed and have to let it wander about for
ever.
Brian
--
Robin
reply-to address is (intended to be) valid
heoretically a point on the Clarke orbit must be just that, a point, but
in reality the tolerance is probably a few tens of miles, and the
satellites are only a few feet across.
Obviously when being first
positioned in the right place they use fuel, but often the stabilisation is then done by Gyros,
I wonder what the main causes of failure are? Obviously when being first positioned in the right place they use fuel, but often the
stabilisation is then done by Gyros, unless every so often the solar
wind has shifted them enough to need to use rockets to reposition.
These days, one assumes this is mostly automated. I also often hear of
some sats having spares already in orbit, but surely that would shorten
their operational life, if the temperature cycling, aging of solar
cells gyros etc, were taken into account.
Brian
Gyros are fine for attitude/orientation. But you need reaction thrust to correct for the unavoidable drifts away from the required orbit whilst in use. That tends to mean 'consumables' (fuel) that eventually becomes depleted. The sat then has to be moved off to a 'graveyard' parking orbit
to clear the way for a new sat. Which requires the last part of the consumables.
FWIW the Russians have developed quite impressive 'plasma' electronic
drives for space use that have a very high dV and fuel efficiency. NASA *has* been using these - but that now probably needs the past (very) tense now!
Overall, though, a problem of course is all the 'junk' sat launches
continue to leave in orbit somewhere. De-orbiting into the atmosphere is practical for some, but not all.
Jim
In article <t3gi2b$ec4$1...@dont-email.me>, Brian Gaff \(Sofa\) <bri...@blueyonder.co.uk> wrote:
I wonder what the main causes of failure are? Obviously when being first positioned in the right place they use fuel, but often the
stabilisation is then done by Gyros, unless every so often the solar
wind has shifted them enough to need to use rockets to reposition.
These days, one assumes this is mostly automated. I also often hear of some sats having spares already in orbit, but surely that would shorten their operational life, if the temperature cycling, aging of solar
cells gyros etc, were taken into account.
Brian
--
Please use the address on the audiomisc page if you wish to email me. Electronics https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
biog http://jcgl.orpheusweb.co.uk/history/ups_and_downs.html
Audio Misc http://www.audiomisc.co.uk/index.html
Micrometeorite strikes and high energy sub-atomic particle strikes, can
also cause sudden failures.
In article <t3goi7$nb7$1@dont-email.me>, David Woolley <david@ex.djwhome.demon.invalid> wrote:
Micrometeorite strikes and high energy sub-atomic particle strikes, can
also cause sudden failures.
Perhaps also worth mentioning given current 'events' that sats may also be vulnerable to being hit by objects from an exploded object. Curious
example
of this risk cropped up a while ago when bits from a Russian object caused people on the ISS to take shelter just in case some impacted.
Jim
--
Please use the address on the audiomisc page if you wish to email me. Electronics https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
biog http://jcgl.orpheusweb.co.uk/history/ups_and_downs.html
Audio Misc http://www.audiomisc.co.uk/index.html
The Iss and its controllers do have radar looking many miles ahead so they can make course changes to avoid this sort of thing, but its the bits
smaller than you can see that are the danger.
For a while old Long March rocket bodies had a tendency to explode several years after they had been used, and of course this spreads tiny bits through several orbits, however, at 22,400 miles out, its still relatively clear of this hazard. That is not to say of course that malicious intent might cause problems at that altitude if a weapon was sent there. It has been demonstrated that a relatively small laser weapon can disable a satellite at quite long ranges. They do not have to blow it up, just hit something important.
As we know several nations have misguidedly used fragmentation techniques to destroy various in orbit objects and thus create hazards for many other spacecraft. There is active research going on on cost effective ways to
clear such particles, but however you do it you are bound to miss some.
I remember when I could still see a bit seeing pictures of areas of the outside of the ISS where there were dings and dents and scrapes where tiny objects had hit it. Thus far no serious damage has been done but some handrails have had to be changed due to sharp edges of dings damaging the silicon on astranaughts gloves.
They are normally covered in RTV compound for better grip.
I think the only incident that was down to impact damage was an ammonia leak in a radiator, which had to be replaced.
Brian
The Iss and its controllers do have radar looking many miles ahead so
they can make course changes to avoid this sort of thing, but its the
bits smaller than you can see that are the danger.
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