The "new and improved" LDR-4 payload, delivered to Lockheed Martin Missiles & Space Co., reflects payload and manufacturing process improvements that TRW has introduced to the program since the late 1980s. It includes a new digital signal processor that's less than half the size and weight of the analog unit it replaces, enhanced memory management capabilities and a new, lighter-weight antenna steering assembly.

The Milstar communications payload is the hardware that performs the satellites' unique onboard processing and signal routing functions. LDR-4 is the fourth of six payloads that TRW is producing under contract to Lockheed Martin, the Milstar satellite prime contractor. It will be integrated by Lockheed Martin into the fourth Milstar satellite, which is scheduled for launch in 2000.

"This new payload is a good example of our commitment to using technology advancements to increase the operational utility and reliability of the Milstar satellites," said Dave Vandervoet, vice president and general manager of TRW's Telecommunication Programs Division. "We're proud of our record for increasing the payload's capabilities while decreasing the program's overall schedule and cost risk."

In addition to smaller, lighter hardware, the LDR-4 payload also takes advantage of a new initiative developed by TRW to streamline the process used to integrate and test the payload's three spot beam antennas.

Paul Borzcik, TRW's Milstar program manager, explained: "Up through LDR-3, we would integrate and test (I&T) the payload's three spot beam antennas piece by piece on the actual payload. Since the antennas attach to the outside of equipment panels, we couldn't do this work until we'd integrated and tested all the hardware inside the spacecraft and closed up the equipment panels for the last time."

To save time and to simplify future testing of the payload, a team of TRW mechanical engineers developed a new process that allowed the company to integrate and test the antennas separately from the payload.

"This simple change allowed us to perform several key I&T tasks in parallel, rather than in series," said Borzcik. "This new way of building the payloads will streamline both the payload integration process at TRW and the satellite integration process at Lockheed Martin."

Under current Pentagon planning, the Air Force will launch a total of six Milstar satellites. The first two satellites, launched in February 1994 and November 1995, respectively, are known as Block I satellites. They carry the TRW-built LDR payload.

Milstar satellites 3 through 6, which are designated Block II satellites, carry both the LDR payload and a new medium data rate (MDR) payload that expands Milstar's tactical communications capabilities. TRW provides the digital subsystem and antenna subsystems for that new payload, which is being integrated for Lockheed Martin by Hughes Space & Communications Co.

The Department of Defense's Milstar system includes a constellation of ultra-secure communications satellites in geosynchronous orbit, and a family of fixed-site, mobile and man-portable terminals.

Operating primarily in the extremely high frequency (EHF) and super high frequency (SHF) bands, Milstar provides secure, survivable communications among the National Command Authority and Army, Navy and Air Force users anywhere in the world, day or night, under any level of conflict.