Lockheed Martin [LMT] said recently it received the core structure for the Air Force’s fourth Space-Based Infrared Systems (SBIRS) geosynchronous satellite (GEO-4).

The structure was delivered to Lockheed Martin’s Mississippi Space and Technology Center where engineers and technicians will integrate the spacecraft’s propulsion subsystem, according to a statement.

Lockheed Martin engineers and technicians will now integrate the propulsion subsystem with the core structure, which is essential for maneuvering the satellite during transfer orbit to its final location, as well as conducting on-orbit repositioning maneuvers throughout its mission life. The integrated core propulsion module will then be shipped to Sunnyvale, Calif., for final assembly, integration and test.

Jeff Smith, vice president of Lockheed Martin’s overhead persistent infrared mission area, said recently in a phone interview this is important because it’s the first big step other than payload activity.

“This is the last core,” Smith said. “Now, we put on the tanks and we get the core structure built with all the propulsion systems. Then that is shipped back to (Lockheed Martin’s) Sunnyvale (location).”

SBIRS GEO-4 is on schedule to be available for launch in 2015. Smith said the GEO-3 payload will be delivered in Oct. 2013 and the GEO-4 payload will be roughly mid-2014.

Featuring a mix of GEO satellites, hosted payloads in highly elliptical earth orbit and associated ground hardware and software, SBIRS delivers resilient and improved missile warning capabilities while contributing to the military’s missile defense, technical intelligence and battlespace awareness mission areas.

Smith said Lockheed Martin is undergoing a number of affordability initiatives to help keep the cost of the satellites down, including reducing personnel working on the satellites and making sure requirements don’t change.

“GEO-3 and GEO-4 are almost identical to GEO-2,” Smith said. “They’re effectively clones, except for obsolescence. (There’s) no new costs in developing and verifying new design (and) we also have a tight governance process to ensure the requirements don’t change. We also have reduced head count significantly, almost 300 people since we launched the first satellite last year. We have a combination of head count and initiatives here making sure requirements don’t change, and that is true for GEO 5 and GEO 6 too. The idea is to build near clones.”

Smith also said Lockheed Martin expects to receive $75 million in funding to begin long lead parts procurement for GEO-5 and GEO-6 by June.

“Hoping to get GEO-5 and GEO-6, (the) first part of that, $75 million for the truly long lead stuff: Computers, detectors, readout chips, we’d like to get that by June,” Smith said. “Next phase toward end of year, early next year, will be the rest of the long lead stuff and the full production phase (in) 2014, roughly.”

Lockheed Martin’s SBIRS contracts include four highly elliptical orbiting (HEO) payloads, four GEO satellite and ground assets to receive, process and disseminate the infrared mission data. The company expects to receive funding to begin long lead parts procurement for the fifth and sixth GEO satellite by the end of 2012.

Lockheed Martin is the prime contractor for SBIRS while Northrop Grumman [NOC] is the payload integrator.