GEO Satellite question
Freddy posed the following question to Dr. Robert A. Nelson: Dear Dr. Nelson: I understand that GEO satellites are 2 degree appart in its orbital position. How is possible that some satellites ( Telstar 11N and NSS 10 located at 37.5W; Astra 2C and 1D at 31.5 E) occupied the same orbital position ?. Could […]
Freddy posed the following question to Dr. Robert A. Nelson:
Dear Dr. Nelson: I understand that GEO satellites are 2 degree appart in its orbital position. How is possible that some satellites ( Telstar 11N and NSS 10 located at 37.5W; Astra 2C and 1D at 31.5 E) occupied the same orbital position ?. Could you please, help me to understand this ?.
Thank you Dr. Nelson.
Dr. Nelson responded as follows:
The two-degree spacing requirement applies to satellites that use the same
frequencies at C-band or Ku-band. Interference is avoided through the use
of highly directional Earth Station antennas, although there is inevitably
some adjacent satellite interference, with a C/I typically around 22 dB.
Satellites that share the same orbital slot use different frequency bands
and sometimes also different polarizations. For example, at 101 degrees WL,
there are several satellites, including an SES Americom C/Ku-band satellite,
an MSAT L-band satellite, and three or four DirectTV satellites that use a
special portion of Ku-band for DBS and also use different polarizations.
These satellites are separated by only about 0.02 degrees, or about 15
kilometers. Very exact stationkeeping must be maintained.
Dr. Nelson’s Satellite Communication Systems Engieering course is next scheduled December 8-10, 2009 in Beltsville, MD.