Milstar Block I spacecraft, or Milstar Developmental Flight Satellite (DFS)-1 and -2, were designed with a Low Data Rate (LDR) payload in the +X wing of the satellite that broadcast in the Super High Frequency (SHF) and Extremely High Frequency (EHF) ranges, and also a classified communication payload in the -X wing.

DFS-2 was similar to DFS-1, but the classified payload was replaced by ballast in the form of a precision machined aluminum block to maintain the weight and balance characteristics of the satellite.

Due to a database error affecting the attitude control system of the Centaur upper stage of its carrier rocket, it was placed into a lower orbit than had been planned, and damaged by deployment at excessive rates.

The Electronic Systems Center at Hanscom AFB is responsible for the US Air Force portion of the terminal segment development and acquisition.

In August 2010 control of the Milstar system was transferred to the Advanced Extremely High Frequency program, in preparation for the launch of the first AEHF satellite, USA-214.

[citation needed] Milstar satellites provide secure, jam resistant, worldwide communications to meet the requirements of the United States military.