|Operator||US Air Force|
|Mission duration||7.5 years (planned)|
|Spacecraft type||GPS Block IIA|
|Launch mass||1,816 kilograms (4,004 lb)|
|Start of mission|
|Launch date||12 September 1996, 08:49:00UTC|
|Rocket||Delta II 7925-9.5, D238|
|Launch site||Cape Canaveral LC-17A|
|Perigee altitude||20,058 kilometres (12,463 mi)|
|Apogee altitude||20,305 kilometres (12,617 mi)|
USA-128, also known as GPS IIA-18, GPS II-27 and GPS SVN-30, is an American navigation satellite which forms part of the Global Positioning System. It was the eighteenth of nineteen Block IIA GPS satellites to be launched.
USA-128 was launched at 08:49:00 UTC on 12 September 1996, atop a Delta II carrier rocket, flight number D238, flying in the 7925-9.5 configuration. The launch took place from Launch Complex 17A at the Cape Canaveral Air Force Station, and placed USA-128 into a transfer orbit. The satellite raised itself into medium Earth orbit using a Star-37XFP apogee motor.
On 17 October 1996, USA-128 was in an orbit with a perigee of 20,058 kilometres (12,463 mi), an apogee of 20,305 kilometres (12,617 mi), a period of 717.94 minutes, and 54.7 degrees of inclination to the equator. It broadcasts the PRN 30 signal, and operates in slot 2 of plane B of the GPS constellation. The satellite has a mass of 1,816 kilograms (4,004 lb). It had a design life of 7.5 years, and was decommissioned on July 20, 2011.