GPS III Alternative Payloads Canvassed

April 1, 2014  - By
Image: GPS World

GPS III prime contractor Lockheed Martin has heard from six companies concerning alternate designs for the GPS III satellite payload, according to reports. A company spokesperson said “constantly canvassing the industrial base to see what’s out there” is merely part of Lockheed’s standard business practice.

Lockheed Martin partner Exelis Geospatial Systems currently supplies the payload, as it has for all previous GPS generations. Earlier this year, Gen. William Shelton, Air Force Space Command, said the first GPS III launch date had slipped from late 2015 into 2016, and confessed to “patience wearing thin” at a press breakfast.

Part of the delay may have been due to signal crosstalk in the new, as yet unlaunched, payload. Crosstalk occurs when a signal broadcast on one circuit creates an undesired effect on another circuit.

The Story So Far. In December 2013, Lockheed Martin turned on power to the bus and network communications payload of the second GPS III satellite, SV-02, at its test facility in Denver. This demonstrated the satellite’s mechanical integration, validated its interfaces, and opened the way for electrical and integrated hardware-software testing. The first GPS III satellite (SV-01) was powered on in February 2013.

In October, the Lockheed Martin GPS III Nonflight Satellite Testbed (GNST), a full-sized, functional satellite prototype at Cape Canaveral Air Force Station, successfully communicated via cross-links to Air Force simulators of the current GPS constellation in orbit. Testing also demonstrated the ability of an Air Force receiver to track navigation signals transmitted by the GNST.

Exelis Advances. In mid-March, Exelis announced successful completion and full testing of six transmitter assemblies, which are integral payload components for the GPS III satellites. The test program includes random vibration, pyroshock, and thermal vacuum testing, replicating space-like conditions through deployment and on-orbit environments. In January, Exelis received three rubidium atomic frequency standard clocks from Excelitas Technologies specifically designed for GPS III.

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