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How to calculate eclipse for geostationary satellites ?



 
 
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  #1  
Old September 30th 06, 06:49 PM posted to alt.astronomy,uk.sci.astronomy
HJK
external usenet poster
 
Posts: 2
Default How to calculate eclipse for geostationary satellites ?

I have tred to make an online calculator based on a pdf I found at
http://www.cdeagle.com/omnum/shadow1.pdf
The method described in the document can be used to find eclipse for
geostationary satellites
caused by the earth shadow.

I hope I got it right
http://www.satellite-calculations.co...te_eclipse.htm
although I have seen some information indicating that max. eclipse is 72
minutes and not 69m36sec as my
calculator calculates. The reason might be that the suns does not pass
trough the earths atmosphere.

I have used http://www.stjarnhimlen.se/comp/tutorial.html to calculate the
suns declination which I use in
the eclipse ed duration formula, t=
ARCCOS(SQRT(1-R*R)/COS(Sundeclination)*24/pi .


What I now want to do is to calculate when the moon is causing eclipse for
the geostationary satellite.
Does anybody know how to do this ?

I have got the following from some old papers I have:
(it might be from the book Satellite Communication Systems- Design
Principles- M. Richaria)

Solar eclipse caused by the Moon
""""""""""""""""""""""""""""""""""""""""""

The occurence of solar eclipse on a geostationary satellite caused by the
Moon is irregular. It may be recalled that Earth-induced
eclipses are predictable, occurring within +/- 21 days of equinoxes. It is
also necessary to predict the duration and the extent of
occurances of Moon-induced eclipses for spacecraft operations planning. The
technique given here (Siocos,1981) makes use of Sun and Moon
position data available from the Nautical Almanac.

An eclipse occurs when the azimuth/elevation coordinates of the Sun and the
Moon from the satellite position
are equal or close enough to cause the Moon disk to mask the Sun partially
or completely.

The effective elevation, H, of the Sun or Moon from the satellite location
can be obtained from the following equation set:

Cos(Beta)=Cos(d)*Cos(LHA)

Tan(H)= (Cos(beta) - (Ro/Ro+Rs))/Sin(beta)
where d=declination of the stellar object (Sun or Moon)
LHA= local horizon angle
LHA= HAg + Fi
HAg= Hourangle with repect to Greenwich, available from the
Nautical Almanac.

I'm not sure what to use as Ro and Rs. I guess for the sun the declination
of the Sun stellar object is
the same as can be found using the tutorial at
http://www.stjarnhimlen.se/comp/tutorial.html


Does somebody know a good tutorial on how to do such calculations ?

I have been considering using the methods on
http://www.stjarnhimlen.se/comp/tutorial.html and simply use radius of the
earth as
42164km. By using the latitude/longitude of the satellite I should be able
to calculate Suns azimuth/elevation as seen from the satellite.
I think I just need to find a way of calculating Moon azimuth/elevation.


(please dont reply to the e-mail adress as its not working- I dont want to
be spammed..)


  #2  
Old October 3rd 06, 09:36 AM
nytecam[_1_] nytecam[_1_] is offline
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First recorded activity by SpaceBanter: May 2005
Location: london-uk
Posts: 741
Default

Quote:
Originally Posted by HJK
I have tred to make an online calculator based on a pdf I found at
http://www.cdeagle.com/omnum/shadow1.pdf
The method described in the document can be used to find eclipse for
geostationary satellites caused by the earth shadow ...snip...
It should look like this http://www.astroman.fsnet.co.uk/sat.htm

As a matter of interest, as seen from UK, most Geosats are located ~7 degrees below the celestial equator and can transit the Sun at this time of year [check Sun's declination is ~-7 degrees!] but can ONLY BE OBSERVED WITH SAFE SOLAR FILTERS - you've been warned!

Nytecam 51N 0.1W
  #3  
Old October 3rd 06, 10:16 PM posted to uk.sci.astronomy
Jonathan Silverlight[_1_]
external usenet poster
 
Posts: 298
Default How to calculate eclipse for geostationary satellites ?

In message , nytecam
writes

HJK Wrote:
I have tred to make an online calculator based on a pdf I found at
http://www.cdeagle.com/omnum/shadow1.pdf
The method described in the document can be used to find eclipse for
geostationary satellites caused by the earth shadow ...snip...


It should look like this http://www.astroman.fsnet.co.uk/sat.htm

As a matter of interest, as seen from UK, most Geosats are located ~7
degrees below the celestial equator and can transit the Sun at this
time of year [check Sun's declination is ~-7 degrees!] but can ONLY BE
OBSERVED WITH SAFE SOLAR FILTERS - you've been warned!


Wow. I knew ISS has been imaged crossing the Sun but it never occurred
to me that geostationary satellites crossed it.
On the subject of filters, do you know of a supplier of metal-on-glass
filters that fit a long lens (67 mm filter for preference, but I'll take
what I can get)
My favourite filter was the black plastic one from Solar Products NCH,
but I don't think they are still in business.
  #4  
Old October 10th 06, 02:31 PM
nytecam[_1_] nytecam[_1_] is offline
Senior Member
 
First recorded activity by SpaceBanter: May 2005
Location: london-uk
Posts: 741
Default

Quote:
Originally Posted by Jonathan Silverlight
In message , nytecam
writes

HJK Wrote:
I have tred to make an online calculator based on a pdf I found at
http://www.cdeagle.com/omnum/shadow1.pdf
The method described in the document can be used to find eclipse for
geostationary satellites caused by the earth shadow ...snip...


It should look like this http://www.astroman.fsnet.co.uk/sat.htm

As a matter of interest, as seen from UK, most Geosats are located ~7
degrees below the celestial equator and can transit the Sun at this
time of year [check Sun's declination is ~-7 degrees!] but can ONLY BE
OBSERVED WITH SAFE SOLAR FILTERS - you've been warned!


Wow. I knew ISS has been imaged crossing the Sun but it never occurred
to me that geostationary satellites crossed it.
On the subject of filters, do you know of a supplier of metal-on-glass
filters that fit a long lens (67 mm filter for preference, but I'll take
what I can get)
My favourite filter was the black plastic one from Solar Products NCH,
but I don't think they are still in business.
Jonathan - I use the Baader plastic 'silver' film filter from TelescopeHouse.com @ ~£15 for A4 sheet.

Nytecam
 




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