ICEINSPACE
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Moon Phase
CURRENT MOON
Waxing Crescent 1%
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25-01-2013, 12:30 AM
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Dazed and confused
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Join Date: May 2012
Location: Melbourne
Posts: 3,492
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What about an artificial star for the southern hemisphere?
We all know Polaris makes it easy for those in the northern hemisphere but what about a satellite that sits over the south celestial pole that is solar powered and acts like a large beacon?
How high would it have to be and how feasible would it be?
It would make polar alignment for the south a doddle.
If we all put in a few hundred to kick it off and then have sponsors or some benevolent person or organisation to launch it.
Imagine that a real artificial star
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25-01-2013, 12:58 AM
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Old Man Yells at Cloud
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Join Date: Jan 2007
Location: Rockingham WA
Posts: 3,435
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Nice idea and technologically possible, but I'm not sure a geostationary polar orbit is possible?
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25-01-2013, 07:42 AM
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Registered User
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Join Date: Apr 2012
Location: Sydney
Posts: 5,244
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Ahh! What a lovely thought!
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25-01-2013, 08:31 AM
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Registered User
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Join Date: Feb 2008
Location: Tungkillo, South Australia
Posts: 599
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Unless it is at a 'stellar' distance, parallax would make it useless except for someone at the South Pole.
Charles
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25-01-2013, 09:56 AM
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Astro Noob
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Join Date: Dec 2011
Location: Sydney
Posts: 1,982
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A satellite is either falling around Earth or falling to it, satellites don't just hover in one place. The best you could hope for would be a few satellites spaced out on an orbit that is inclined to line up with the SCP, maybe a highly elliptical ~24hr orbit with a low periapsis over the north pole and a very high apoapsis over the south pole so that they appear to pass through the SCP at exactly the same time each night. Then you could align using one of them for a split second at an exact time each night. Having the orbit highly elliptical would mean that maybe the satellite would be moving slowly enough as it passed through the SCP, at apoapsis, that it would be useable. I don't know the maths but an orbit with a period of 24hrs with a periapsis of about 500kms would surely have an apoapsis of around 80,000kms? Not sure about the parallax issues at that altitude? but I'm sure Charles is right.
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25-01-2013, 11:30 AM
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Astro Noob
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Join Date: Dec 2011
Location: Sydney
Posts: 1,982
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I'm having a slow day at work (waiting for renders) so I've done some maths!
My guess was pretty close as an orbit with a semi-major axis of about 42500kms (apoapsis of about 84500kms) would have a period of around 24hrs. From this I figure that an observer at the equator would see the satellite, at apoapsis, about 4.5 degrees from the SCP. This error would decrease as one got closer to the south pole. At around the latitude of Sydney I figure the error would be a bit over 2 degrees, still too high to use for alignment given Polaris's separation from the NCP is only about 0.7 degrees (I think).
Perhaps you could have 10 satellites in 10 day orbits so that one is visible at the SCP at a certain time of each night, this might reduce the error enough to make it useful, except that everyone would have to align at the same time or they miss out for that night!
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25-01-2013, 01:43 PM
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Seriously Amateur
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Join Date: Sep 2009
Location: Brisbane
Posts: 1,279
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Quote:
Originally Posted by pluto
A satellite is either falling around Earth or falling to it, satellites don't just hover in one place.
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I am pretty sure they can if they are at the correct distance. Satellite TV relies on having satellites that do not change their position, otherwise you would always be on the roof shifting your dish....
EDIT: here you go
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25-01-2013, 01:59 PM
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Astro Noob
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Join Date: Dec 2011
Location: Sydney
Posts: 1,982
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An object in a geosynchronous orbit is still falling around the Earth, it's just that at that altitude/speed it takes it 24hrs to complete an orbit. Obviously in the 24hrs it takes to complete it's orbit the Earth has rotated 360deg and therefore the satellite has stayed in the same position in the sky relative to the Earth. Also a geosync orbit like the one you described is only possible above the equator. Of course you could have orbits at other inclinations and eccentricities that take 24 hours but the objects on those orbits would not appear to stay in the same spot in the sky.
Quote:
Originally Posted by adman
I am pretty sure they can if they are at the correct distance. Satellite TV relies on having satellites that do not change their position, otherwise you would always be on the roof shifting your dish....
EDIT: here you go |
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25-01-2013, 02:30 PM
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Seriously Amateur
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Join Date: Sep 2009
Location: Brisbane
Posts: 1,279
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Quote:
Originally Posted by pluto
An object in a geosynchronous orbit is still falling around the Earth, it's just that at that altitude/speed it takes it 24hrs to complete an orbit. Obviously in the 24hrs it takes to complete it's orbit the Earth has rotated 360deg and therefore the satellite has stayed in the same position in the sky relative to the Earth. Also a geosync orbit like the one you described is only possible above the equator. Of course you could have orbits at other inclinations and eccentricities that take 24 hours but the objects on those orbits would not appear to stay in the same spot in the sky.
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my point was that they can appear to hover in one spot from the ground, not that they are actually hovering..
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25-01-2013, 02:42 PM
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Novichok test rabbit
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Join Date: Aug 2012
Location: Somewhere in the cosmos...
Posts: 10,388
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In this day and age, surely they could make a mount with inbuilt GPS that automatically adjusts the alt to the current position as well as the azimuth to point spot on true SCP.
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25-01-2013, 02:53 PM
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Astro Noob
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Join Date: Dec 2011
Location: Sydney
Posts: 1,982
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Quote:
Originally Posted by LewisM
In this day and age, surely they could make a mount with inbuilt GPS that automatically adjusts the alt to the current position as well as the azimuth to point spot on true SCP.
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I think the alt wouldn't be too hard but having an accurate compass with accurate deviation info might be...?
Maybe they could put a small camera in the polar scope to take 1-2 min exposures and work out, by the trailing, where the SCP is and adjust for it... ...hmmmm *runs off to buy a webcam and a rasberry pi*...
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25-01-2013, 03:29 PM
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PI cult recruiter
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Join Date: Apr 2010
Location: Brisbane
Posts: 10,584
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Quote:
Originally Posted by pluto
Maybe they could put a small camera in the polar scope to take 1-2 min exposures and work out, by the trailing, where the SCP is and adjust for it... ...hmmmm *runs off to buy a webcam and a rasberry pi*...
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PoleAlignMax figures out your alignment error by plate solving three images with short slews in between. It's like magic 
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25-01-2013, 03:37 PM
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Astro Noob
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Join Date: Dec 2011
Location: Sydney
Posts: 1,982
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Quote:
Originally Posted by RickS
PoleAlignMax figures out your alignment error by plate solving three images with short slews in between. It's like magic |
Awesome thanks Rick, I'll give it a go!
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25-01-2013, 04:53 PM
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Registered User
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Join Date: Mar 2011
Location: NSW Australia
Posts: 324
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25-01-2013, 05:07 PM
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Astro Noob
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Join Date: Dec 2011
Location: Sydney
Posts: 1,982
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Quote:
Originally Posted by mikerr
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I want one! 
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25-01-2013, 08:32 PM
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Dazed and confused
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Join Date: May 2012
Location: Melbourne
Posts: 3,492
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hmmm, a few of those placed around the country would be awesome!
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25-01-2013, 08:53 PM
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Life is looking up!
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Join Date: Sep 2010
Posts: 2,017
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What! More space junk.....I hope not!
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