Lockheed Martin has received the first medium-data-rate (MDR) payload from Hughes for the next series of upgraded Milstar military-communications satellites. These are scheduled to begin launches aboard Titan 4/Centaur boosters in 1999.

The Block 2 spacecraft will have enhanced communications capabilities for all the US military services, including added security and faster data-rate transmissions (Flight International, 1-7 November, 1995).

The two original Milstar satellites, which were launched in February 1994 and November 1995, are Block 1 designs which include only the low-data-rate (LDR) payload supplied by TRW.

Because the MDR transmissions require more bandwidth, less room is available to build anti-jamming devices into the system, so the payload carries two specially designed nulling antennas which can pinpoint the jammer's direction and temporarily null the signals.

Other unique features common to the Block 1 and 2 Milstars are on-board signal processing, signal routing, resource control, crossbanding, and satellite crosslinking.

These remove the need for ground stations and allow ground- based commanders to establish and control their own customised communications networks from a single location using one or more satellites as a processing hub.

Source: Flight International