Out in Front: Rocky Road to Robustness

February 1, 2010  - By

The news arrived after this issue had gone to press, so I pulled back this column to write about it. By early February, it will be oldish news, and further details will have appeared on our website.

The crux: another pitfall for the GPS constellation.

The system’s command and control operational software update uploaded in late 2009 has started wreaking some havoc with installed military receivers across many fielded platforms, as well as with some civil receivers. Whether major or minor havoc, I don’t pretend to know yet. The concept of selective availability anti-spoofing module (SAASM) figures in it, though now I’m toeing classified turf.

Whatever the control features may be, they are designed to work with authorized military receivers that have successfully passed security tests prior to fielding. But actual live introduction of the new software has produced different results than those seen in testing: some receivers in question are intermittently not tracking Y-code.

Corrective action could encompass either the Air Force rolling back the update or revising its software, or manufacturers modifying software within the receivers — thousands or perhaps tens, hundreds of thousands already in the field.

The conscientious, hardworking engineers at the GPS Wing had barely recovered from the SVN49 debacle, or perhaps not even, as a work-around has yet to surface. Now this.

In the category of small comfort, they are not alone. Recently manufactured GLONASS satellites have significant signal-generation problems. A new Compass satellite on orbit may no longer be controllable. And while Galileo inches forward, European political and industrial bickering perseveres. Ah, the bickering . . . .

Despite these distractions in the sky and elsewhere, we should all keep our heads down, noses to the grindstone, fingers to the keyboard — and eyes on the prize. A radio-frequency signal in space, like Heinlein’s moon, is a harsh mistress. Very exacting, very demanding. Occasionally punishing. Ultimately rewarding.

This Just In. By the time you read these words, the Loran signal may be dead and gone from U.S. territories. Thanks to the Coast Guard Commandant, the Secretary of Homeland Security, and those in the administration — perhaps the president himself — who know or care nothing about secure PNT, and who braggadaciously proclaim, “Back-up? We don’t need no steenkeen back-up!”

Meanwhile the Air Force Chief of Staff has started saying it is critical for the military to “reduce its dependence on GPS-aided precision navigation and timing” because of its vulnerability, and supporting officers confirm that GPS has been jammed or interfered with recently.

Do these people talk to one another? Surely they must.

The PNT Key. More robustness will always be a good thing. Once I have two coded signals on widely spread frequencies, I’m well on my way there. This is not just within the narrow band allocated to GNSS, but across many radio frequencies, many technologies.

This article is tagged with , and posted in From the Magazine, Opinions

About the Author:

Alan Cameron is editor-in-chief and publisher of GPS World magazine, where he has worked since 2000. He also writes the monthly GNSS Design & Test e-Newsletter and the Wide Awake blog.

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