Artist's rendering of the GPS IIR satellite. Image courtesy of Lockheed Martin.

Aerospace Continues
Mission Support with Delta II
GPS Launch

CAPE CANAVERAL AIR FORCE STATION, Fla. (9/25/06) — One year to the day after the modernization effort began for the Global Positioning System (GPS), the next stage in modernization occurred with the launch of the GPS IIR-15(M) aboard a Delta II rocket from Cape Canaveral Air Force Station Sept. 25. The launch marked another stage in the The Aerospace Corporation’s involvement with GPS.

Aerospace has been integral to the GPS program from its inception, providing end-to-end program support, from launch vehicle readiness to satellite development and testing to management of the the 29 operational satellites that make up the GPS constellation.

Delta II Rocket

Aerospace’s Delta II Operations team performed extensive launch verification to assess flight worthiness and launch readiness for the Delta II vehicle in preparation for the Sept. 25 launch. This process included a review of all build records and tests as well as independent verification of mission analyses and software. Analysis and monitoring continued during launch site processing, countdown, and post-launch operations.

According to Art Falconer, principal director of The Aerospace Corporation's Delta II Operations, particular attention was given during the readiness process to assess new designs and evaluate significant anomalies.

“This Delta II vehicle had some unique technical challenges that had to be resolved prior to launch," Falconer said. "Due to metal fatigue induced during ground firing tests, the structural integrity of a band around the first stage engine nozzle was suspect. This issue was a fleet-wide concern but this engine was the first that required a rework of the band to reinforce the structural capability at critical welds.”
Aerospace performed extensive analysis and testing and concluded that the engine band was flight worthy.

It was also discovered that the solid rocket motor nozzles had experienced substantial debonding between an internal liner and the nozzle’s steel shell. Although the structural integrity was not compromised, lack of a good bond could provide a potential path for exhaust gas leakage.
The sealing modes were re-evaluated by the Delta II team to assess the overall risk of leakage. The decision was made that the risk level for gas leakage was low, said Falconer. The team gave approval for vehicle launch.

"Cradle to Grave"
According to John Clark, principal director of The Aerospace Corporation's Space Systems group within our Navigation Division, the corporation’s involvement with GPS satellites is “cradle to grave.”

“We were part of formulating the original GPS IIR specifications. After contract award, we closely tracked the design, development, and factory test of the satellite,” Clark said. “At Cape Canaveral, Aerospace was part of the team conducting the final satellite checks, overseeing its integration with the Delta II booster and participating in its launch.”

Aerospace team members, along with Air Force Space Command’s 50th Space Wing, will continue their involvement in post-launch analysis, on-orbit tests, and satellite operations.

This work is part of the corporation’s larger mission with the program, to monitor the performance of the GPS constellation in space and identify when and how to replace aging satellites.

GPS IIR-15(M) mission preparation was fairly normal – mainly ensuring that the satellite did not share any problems that arose with other satellites. In contrast, last year’s IIR-14(M) launch, as the first modernized Block IIR satellite, required the team to deal with multiple design issues.

One key issue involved field reprogrammable gate arrays (FPGA), Clark said. The payload subcontractor relied heavily on FPGAs to reduce its development schedule. “The Aerospace team was aware of failures involving these gate arrays on other programs. We worked with the Aerospace laboratories and Engineering and Technology Group to study and test the contractor’s design and were able to establish the reliability of this new FPGA design,” Clark said.

Modernizing the GPS System
The GPS satellite constellation is in the process of being upgraded and the GPS IIR-15(M) represents the second launch of a modernized (M) Block IIR satellite. Modernized Block IIR satellites have a second civil signal to supplement the coarse acquisition signal used since 1978. The new signal means GPS horizontal accuracy is improved from 23 to 11 meters, Clark said.

According to Clark, the modernized satellite also adds a new military signal to improve GPS accuracy and availability, remedy shortcomings of the older system, and enable emerging uses. The GPS modernization program allows the government to retrofit a total of eight Block IIR satellites with the new signals.

Clark added, as the GPS constellation is modernized, military and civilian users will notice significant improvements in GPS functionality.

The Aerospace Corporation, based in El Segundo, Calif., is an independent, nonprofit company that provides objective technical analyses and assessments for national security space programs and selected civil and commercial space programs in the national interest.

Media Inquiries: Contact Dave Jonta, 310-336-5041, david.l.jonta@aero.org