Friday, March 3, 2017

South Pole Communication Satellites

I recently published a post on the three satellite tracking antenna systems that I work on. This post is about the satellites that we track for South Pole communications.

Amundsen-Scott South Pole Station uses communication satellites that serve as relay stations, receiving radio signals from one location and transmitting them to another.

Currently the following three satellites are utilized. Combined they provide about 12 hours per day of coverage:

SPTR (South Pole Transfer Data and Relay Satellite (TDRS) is controlled by NASA at White Sands, New Mexico. This satellite utilizes S-Band communications along with the higher data rate Ku-Band for all the science data that is sent from here. The TDRS system was utilized by the Space Shuttle.
SPTR tracking antenna.

Skynet is a retired NATO4B communications satellite and is controlled at Oakhanger, England through Intelsat in Georgia
Skynet tracking antenna.

DSCS Satellite

DSCS Tracking Antenna

The United States Antarctic Program utilizes these three satellites on a daily basis to transfer South Pole science, operational and weather data, as well as internet, telephone, and email services.

Because of their location on the southern-most point of the earth, the three satellite dishes are out of view of communications satellites that are in a equatorial geosynchronous orbit. Communications satellites are launched into a high geosynchronous orbit which is an orbit around the earth with an orbital period of one sidereal day (about 23 hours 56 minutes and 4 seconds).

The synchronization of rotation and orbital period means that, for an observer on the surface of the earth, an object in geosynchronous orbit returns exactly the same position in the sky after a period of one sidereal day. Over the course of a day, the object's position in the sky traces out a path, typically in the form of a stretched out figure 8.

 If the orbit is highly inclined then the satellite is visible at certain times when it drifts slightly above and below the equatorial plane as it orbits the earth. None of the three tracking antennas ever go above 5 degrees in elevation during a pass.

A geostationary satellite above a marked spot on the equator. An observer on the marked spot will see the satellite remain directly overhead unlike other celestial objects which sweep across the sky.
This illustration shows the GOES (no longer used) and TDRS satellites. The elongated figure 8 is the orbital path. Whenever a satellite dips below the horizon the South Pole antennas can see it. We utilize the TDRS about 4 hours a day, sometimes broken up into smaller periods. 
MARISAT and GOES are no longer used and we currently use TDRS 5&6. They are both seen at a high inclination on the orbit plane.
An illustration of the relay.

When the above satellites are out of view the South Pole has access to the Iridium Satellite System that allows 24 hour coverage for business phone calls and email. There are 66 Iridium satellites in polar orbits (travel north and south around the world) 485 miles above the earth. This constellation provides phone coverage 24 hours a day in most areas of the earth.

These satellites also provide us with a Iridium flare show in the dark sky. They are highly reflective and as they pass over the pole the sun reflects off of their large antenna and appear to be a shooting star. There are periods when these flares occur every 10 minutes. They are fun and interesting to watch.
Iridium satellite.

The Iridium satellite constellation provides us with 24 hour coverage.

Iridium flare. Photo credit: Dana Hrubes

Iridium flare. Photo credit: Robert Schwarz

The station is to the left of the middle and the RF radomes are to the far right. To the far left is the Dark Sector science labs and antennas.
3/4 mile out from the station are two radomes and an RF equipment building seen at the bottom. The large radome to the left houses the 9 meter GOES antenna that is no longer used along with the much smaller Skynet and DSCS antennas. The smaller radome houses the 4 meter SPTR antenna. The three comprise my remote work stations and take about 40 minutes to walk to - on a good day.

Post settings Labels Published on Permalink Location Options

1 comment:

  1. Hey Mike,
    This is very factual information and I am trying to understand the physics nature of the projections. Do you mean the plain as a feature of the incline orbit of satellites or plane as in the flatness? Not sure what that is really! I am still trying to teach the difference between rotation and revolving. Great pictures and nice to see the credits to the photographers! I hope some of my students read more about the work done on the South Pole. We all learn from the best! Take care, Andee