While the FAA’s current WAAS network offers equipped users with improved GPS performance across the continental U.S. and Alaska, it still does not provide the redundancy and reliability required from an aviation navigation service. So the FAA has now contracted to obtain additional geostationary satellites (GEOs) to rectify this shortcoming.
WAAS signals are currently beamed down from FAA transponders aboard two very-high-altitude commercial GEOs located over the western Atlantic and central Pacific. Should the WAAS downlink transponder fail in either of them, particularly the unit aboard the western Atlantic GEO, then a significant part of North America would lose GPS accuracy enhancement and satellite failure alerts, along with potential degradation in the user’s position calculations.
This lack of redundancy in WAAS has been acknowledged as the system’s Achilles’ Heel since its original design in the early 1990s–a fact underscored by a panel of independent experts called in by the FAA after WAAS suffered serious integrity failures during acceptance testing in 2000, delaying its introduction by almost three years.
Now the FAA has bitten the bullet and, under a contract potentially worth $597 million, has committed to place WAAS transponders aboard two future GEOs with an option for a third. The first of these GEOs, a PanAmSat Galaxy XV, is scheduled to be launched in March next year and aimed for a geostationary position above the equator at 125 degrees West, where it is expected to become operational in June next year. Launch of the second GEO, a Telesat Anik F1, is scheduled for October next year, and is due to become operational at 107 degrees West in January 2006.
In preparation for the two new GEOs reaching operational status, the current nationwide WAAS surface network will also be expanded by adding more GPS ground-monitoring stations and associated ground uplink stations. The latter analyze the monitor’s data and then send accuracy corrections, failure alerts and warnings of hazardously misleading information (HMI) up to the GEO for rebroadcasting to users.
Along with the two present GEOs, the two new satellites will provide a high degree of redundancy and much greater reliability for WAAS. The additional GEOs will also allow the system to advance from its current initial operational capability to full operational capability, currently forecast for 2007.
No timeline has been announced for the optional third launch, but it is understood that it might occur during 2006, with its optimum location around 85 degrees West. Further in the future the FAA is looking at the need for fourth and fifth GEOs to replace the current Atlantic and Pacific satellites, called Atlantic Ocean Region-West (AOR-W) and Pacific Ocean Region (POR), owned by Inmarsat, which are expected to be removed from service after 2007.
The FAA’s contract for its new GEOs also underlines the international flavor of satellite operations, and the intricate mating rituals performed by industry giants to become involved in them. PanAmSat’s Galaxy XV is American but will be launched by a French Ariane booster rocket, while Intelsat’s Anik F1 is Canadian and will be sent aloft aboard a Russian Proton.
And when the contract was originally proposed by the FAA to be a sole-source award to Lockheed Martin, WAAS developer Raytheon promptly filed a strong protest about the agency’s noncompetitive intentions. In turn, Lockheed Martin filed a counter protest. But after the smoke of battle cleared, Lockheed Martin announced how pleased it was to have a fine company like Raytheon become a partner in its program. In return, Raytheon stated how pleased it was that an experienced organization like Lockheed Martin would henceforth become a team member on its multimillion dollar FAA Stars ATC automation program.
Satellite Transponders 101
Commercial geostationary satellites (GEOs) carry up to 200 or more transponders, supplied by TV networks, telephone companies, financial institutions and other organizations. However, the failure of any one transponder does not call for the replacement of the GEO. It simply means that the transponder’s owner must then obtain a new unit and find space for it aboard another GEO scheduled for launch in the near future.
The choice, however, is sometimes limited–the GEO’s intended orbital location above the equator has to meet the requirements for signal coverage over the customer’s region and, equally important, the ownership and control of the GEO must be acceptable to the customer. Many GEOs, particularly those serving the third world, are owned by government bodies whose interests may be inimical to those of the U.S. And in the FAA’s case, securing congressional funding to cover the high costs of leasing transponder space aboard commercial GEOs has always been a stumbling block.