L5 at Risk from Malfunctioning Fuses

For want of a nail the shoe was lost.
For want of a shoe the horse was lost.
For want of a horse the rider was lost.
For want of a rider the battle was lost.
For want of a battle the kingdom was lost.
— Proverb dating to the 14th century

Three new GLONASS satellites launched successfully on September 25 and are now working their way into that system’s orbital plane 3. At press time for this issue, one had started broadcasting. Meanwhile, the GNSS community awaits pending modernization efforts from the U.S. GPS — specifically, the first satellite to carry the new L5 civil signal, aloft, and the first satellite of the next generation, IIF. Unless IIR-20(M) with the L5 demo payload transmits the L5 signal by August 26, 2009, the U.S. government may lose its International Telecommunications Union allocation for that frequency.

Ironically, the IIR-M satellite was retrofitted with L5 capability and rushed into the lineup to compensate for anticipated difficutlies with the IIF. Now it appears that both will remain grounded until at least spring 2009. While IIR-20(M) has been ready since at least May, the IIF satellite has yet to pass its full battery of tests at the Boeing manufacturing facility in Southern California.

GPS World’s Military and Government editor Don Jewell (DJ) spoke with experts at the Launch and Range Space Wing (LRSW), Space and Missile Systems Center, Los Angles Air Force Base, regarding the problem with the Delta II rocket. Malfunctions with this launcher have repeatedly caused postponements for GPS IIR(20)-M.

DJ: What exactly is the problem that is causing the launch delay?

LRSW: GPS IIR-M missions require a three-stage Delta II launch vehicle. This version of the Delta II uses timers as part of the ordnance system that controls timing of the third-stage events, including rocket motor ignition and spacecraft separation. These ordnance timers essentially operate like a burning length of fuse over a [specific] period of time. The launch delay occurred after a functional test failure in the existing supply of 40-second timers.

DJ: What is being done to address the fuse problem?

LRSW: As part of the root cause investigation, multiple engineering tests have been conducted to understand the failure mechanism. We are working closely with the ULA [United Launch Alliance, a joint Boeing-Lockheed venture] to produce a replacement lot of hardware to support the last two GPS IIR-M launches.

DJ: Why is the problem just showing up now, at the end of life of the military Delta II program?

LRSW: The problem occurred during a lot re-qualification test of the remaining inventory of 40-second timers.Crimped Fuses. Until recently, the Delta II had been one of the most successful rockets in the history of the space launch program. The ordnance timers or fuses are designed nominally to burn for 40 seconds exactly, and in the past they have always performed according to spec. But sources told Jewell that recently the machine that crimped these fuses for decades ceased to function and could not be repaired. A new machine using pneumatic crimpers instead of hydraulics was put in place to produce the fuses. Since installation of the pneumatic machine, the test fuses have been burning erratically.

As a senior vice president from a related rocket program told Jewell, “When you make a major change in producing a critical subsystem in even the most successful program, your risk factor goes through the roof, and you are asking for trouble. And trouble is exactly what the Delta II program has right now.”

GPS Performance Standard Document Updated

The National Executive Committee for Space-Based Positioning, Navigation, and Timing (PNT) released an updated GPS Standard Positioning Service Performance Standard, committing the United States Department of Defense (DoD) to an improved level of GPS accuracy for civilian signals.

It is the fourth revision of the standard positioning service (SPS) performance standards document, and the first update since October 2001. In addition to specifying GPS minimum performance commitments, the standard serves as a technical document complementing the GPS Signal in Space (SIS) Interface Specification.

The most significant change in the updated standard is a 33 percent improvement in the minimum level of SIS range accuracy, from 6 meters root mean square (rms) accuracy to 4 meters rms (7.8 meters, 95 percent). Other notable changes include the addition of minimum levels of SIS range velocity accuracy and range acceleration accuracy, which were unspecified in the previous version.

The updated document introduces a definition for an “expandable 24-slot” GPS constellation with more than 24 satellites, although the baseline 24-slot GPS constellation definition remains unchanged from the previous version of the SPS performance document.While the stated dedication to improvement is notable, it has a built-in conservative margin for minimum performance. The executive summary notes: “with current (2007) SIS accuracy, well designed GPS receivers have been achieving horizontal accuracy of 3 meters or better and vertical accuracy of 5 meters or better, 95 percent of the time.”

One item noticeably missing from the updated document is a commitment to semicodeless GPS access. This comes as no surprise, as the DoD published a notice in the Federal Register on September 23, stating that it will cease to support codeless/semi-codeless GPS access as of December 31, 2020.

The SPS document only addresses the L1 GPS signal, because this is the only civil GPS signal that is currently fully operational.

The full SPS document can be found on the National Executive Committee for Space-Based Positioning, Navigation, and Timing website.

JAMFEST in January

The 746th Test Squadron at Holloman Air Force Base has rescheduled its sixth JAMFEST at White Sands Missile Range, New Mexico, to mid-January, 2009; it had originally been slated to take place in October.

The 746th, which serves as the Central Inertial and GPS Test Facility (CIGTF), is the U.S. DoD’s designated lead test organization tasked with testing and evaluating GPS user equipment and integrated GPS-based guidance and navigation systems. JAMFEST programs provide GPS jamming scenarios for testing, as well as training in GPS-denied environments.

Through partnership with the GPS Wing and the Joint Navigation Warfare Center, the 746th is able to provide this diverse testing and training opportunity at a significantly reduced cost to JAMFEST participants. Contact 746ts.info@46tg.af.mil.

NOAA Adds CORS, WAAS Tracking Sites

The National Oceanic and Atmospheric Administration’s (NOAA) National Geodetic Survey has incorporated 43 new GPS tracking sites into the Continuously Operating Reference Station (CORS) network, including 13 sites established by the Federal Aviation Administration as part of their Wide Area Augmentation System (WAAS).

Four of the new WAAS sites are located in Alaska, four in Canada, and five in Mexico. WAAS provides differential GPS correctors for airline navigation across North America. The WAAS network now contains 38 GPS tracking sites.

“The CORS network is a critical NOAA product that helps ensure the consistency and accuracy of the nation’s spatial reference system,” said John H. Dunnigan, assistant administrator of NOAA’s National Ocean Service. “These additional stations are part of a continuing effort by NOAA to improve the accuracy of the spatial reference system and to be on the cutting edge of positioning technology.”

The addition of the new sites significantly improves both the geographic coverage of the CORS network as well as the accuracy with which CORS users can position property boundaries, transportation arteries, buildings and other map-worthy objects, and more. The data is also used in weather prediction.

The NOAA CORS network now contains more than 1,200 sites spanning the United States, its territories, and several foreign countries. Surveyors, GIS users, and others can combine their own GPS data with data from the CORS network to determine three-dimensional positional coordinates that approach a few centimeters in accuracy.

Alternatively, users can submit their GPS data to the web-based Online Positioning User Service (OPUS) utility to have NOAA compute such coordinates automatically.