Atlas 5 Rocket Launches Twin SES Communications Satellites

A United Launch Alliance Atlas 5 rocket boosted two SES C-band communications satellites into orbit Tuesday from Cape Canaveral, Florida. 

They are the second and third of a series of five that will provide TV and radio to millions of American households.

Atlas 5's Russian-built RD-180 first-stage engine and three Northrop Grumman solid-propellant strap-on boosters ignited at 5:36 p.m. EDT, lifting the 196-foot-tall rocket away from pad 41.

The Atlas 5 arced to the east over the Atlantic Ocean 40 seconds after liftoff, gently accelerating as it used fuel and lost weight.

Two minutes after launch, the three strap-on boosters burnt out and dropped away. Two and a half minutes later, the RD-180 shut down, the first stage fell away, and the Centaur second stage took over.

The flight plan called for three Centaur engine firings spread out over five and a half hours to place the SES-20 and 21 satellites in a circular geosynchronous orbit 22,300 miles above the equator.

At that height, satellites complete one orbit in 24 hours and so seem motionless in the sky – perfect for communications stations.

The SES-20 and SES-21 satellites were made by Boeing. They will join the SES-22 relay station, which was made by Thales Alenia Space and launched by SpaceX last June.

The satellites are the result of an FCC directive to free up the lower part of  C-band spectrum, normally used by radio and TV relay stations, for 5G internet networks.

To create place for 5G communications, SES-20, 21 and comparable satellites will operate in the higher area of the C-band spectrum.

Companies competing for slices of the 5G spectrum are paying SES and other existing C-band satellite operators back for the expense of developing and launching new satellites.