In space this is refered to as geostationary orbit .
The image below shows 15 such communications satellites positioned over Europe , including two main groups of spacecraft. The Astra group , operated by SES ( More commonly recognised for many years as the home of Sky analogue TV ) and the Hotbird group operated by Eutelsat.Italian military communications satelliteSicral 1 is also visible.
On March 16 2004 Eutelsat W3A was launched by Proton from Baikonur.
Three weeks later the satellite had attained geostationary orbit , 36,000 km above the equator.
Before going into service , the satellite underwent extensive tests which took place at
1.7 degrees east.
The reference star is mag 10.5
1 28187U 04008A 04094.03354412 .00000009 00000-0 00000+0 0 288
2 28187 0.0391 309.1091 0002210 325.8290 290.5045 1.00271618 256
3A will eventually be located at 7 degs east.
120 second exposure ( 8x15 second frames)
By May 4th , on orbit tests were completed and W3A started to drift towards its operational location at 7 degrees east. On the evening of May 6 the skies here cleared allowing me to try and locate the moving satellite.
Sure enough , an unidentified object was spotted at around 3.75 degrees east and a series of 7.5 second exposures were taken to evaluate the drift.
A total of 560 exposures were captured over a period of 82 minutes.The results show the satellite drifting east at a rate of approximately one degree every 24 hours.
A time lapse video ( 1.75mb) can be seen here
Time lapse video showing W3A drifting towards its final location at 7 degrees east
Field of view is 30 arc minutes east to west.
By the evening of May 16 W3A had arrived at 7 degrees east.Fortunately the clouds dispersed for a few hours and I was able to capture both W3 and 3A in position.
This image shows the two satellites co-located in orbitThe brighter spacecraft to the left is 3A , about 50 km east of W3.
A later press release described how Eutelsat's newest possession drifted into position the evening before , and whilst I was imaging it , the transfer of programming from one satellite to the other was actually taking place
Full details here
After leaving 7 degrees east in May 2004 , W3 spent some time at 48 east.
In November Eutelsat moved the bird back across the arc to 21.5 east to replace the highly inclined 2F3.
In this unique animation
W3 is seen steady at 21.5 E , whilst 2F3 moves quickly through the field of view at around 22 east.
The following data table was kindly prepared by Björn Gimle using Rob Matson's "Skymap"
It shows the times the satellites entered partial shadow (penumbra), full shadow (umbra), then finally the time they exited Earth shadow
Penumbra Umbra Exit Hot Bird 1 SGP 22:58:08 23:02:01 23:36:50 SGP4 23:01:48 23:37:07 Hot Bird 2 SGP 22:58:20 23:02:16 23:36:26 SGP4 23:02:21 23:36:26 Hot Bird 3 SGP 22:58:57 23:02:59 23:36:26 SGP4 23:02:44 23:36:44 Hot Bird 4 SGP 22:58:20 23:02:10 23:36:46 SGP4 23:01:59 23:37:00 Hot Bird 6 SGP 22:58:54 23:02:55 23:36:29 SGP4 23:02:48 23:36:36Björn has also extracted the information in order of shadow entry .From that we can determine which satellite is which in the fleet.The negative image below identifies the five birds and their relative positions in space.
Astra Group , 19 degrees east into eclipse This animation ( 2Mb) filmed over a three hour period on the evening of March 8 2004, shows the seven SES Astra spacecraft in orbit and entering shadow.Conditions were not good due to a bright Moon , which washed out detail in the latter frames.Shadow entry time was 08/03/2004 22:24:58; 12.48s
In the image above , a still taken just prior to eclipse , the positions of the individual birds are labelled according to the predicted shadow entry time , using up to date TLEs and Nova for Windows.However , SES Astra have kindly corrected the data , and provided information based upon their own positioning....which is as follows :
The animation below is made up of four 9.5 second frames with field of view approx 30 arc minutes. It shows the seven Astra satellites operated by SES located at 19.2 degrees east.The birds are in geostationary orbit 35,700 km above the equator.A background star can be seen tracking through the frames. The seventh satellite is in inclined orbit and well to the North of the main group.It has been identified by the Flight Dynamics Section , SES , as Astra 1C. Time of capture was 2013 GMT October 16 2003
These spacecraft are about the same length as a supermarket delivery truck..... 30-35 metres , and yet they can be seen using a modest telescope as the light from the sun plays on their solar panels.
There are now hundreds of communications satellites in geostationary orbit forming man made constellations in the night sky.
Although satellites in geostationary orbit appear to stand still when viewed from earth , if we could travel out into space and get quite close to the spacecraft we would in fact see that they were continually drifting within an imaginary box about 100 km on each side.As the satellites get older , the rate of drift tends to increase as onboard fuel runs low.The position of each bird is closely monitored by ground stations , and when required , correcting burns are made to adjust the orbit.Eventually when the fuel state becomes critical a decision may be made to place the satellite into inclined orbit.Sometimes refered to as the "Comsat Manoeuvre" this series of commands places the spacecraft in an ever increasing figure of "8" orbit above and below the equatorial plane.
As the inclination increases over time , the satellite will become unusable for direct to home services , but can still be utilised by commercial ground stations to accommodate data , video and telephony communications.
In the following animation , which spans a period of about 40 minutes , the movement of two Eutelsat birds , thought to be Hotbird 1 and Hotbird 3 , are tracked.
This time lapse animation from October 24 2003 shows the movement of the five Hotbirds at 13 degs east over a period of about 80 minutes.
When the sun tracks behind the geostationary arc ,satellite signals can be disrupted for some minutes .It would be great to image a group of satellites sihouetted against the solar disc , however each geostationary bird is just 1/10th of an arc second in size when viewed from Earth , and as far as I know , this type of picture has never been produced.
To simulate what it might look like , I have taken two actual photgraphs , and combined them.The result can be seen below.(The Astra group were imaged at night )
What surprises me is the "spread" of the birds across the solar disc , in this instance about 9 arc minutes (Sun is approximately 32 arc minutes across)
So far there has been no positive identification , but thanks to some sterling work by SeeSat-L members it looks very much as if this is an old communications satellite , which has been de-commssioned and placed in a "Graveyard " orbit.
The other possibility (unlikely) is that it could be an asteroid.
To view the video (1.5mb) ,click .. here
The sequence is made up of eleven nine second frames (three frames were dropped ) covering a period of about two minutes.Estimated magnitude of the fainter object plus 12-14.
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