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Out in Front: An SVN up for Grabs

November 1, 2009  - By
Image: GPS World

Wednesday evening, September 23, Savannah, Georgia, 5:30 to 7:00 p.m., Session P2b — a date that will live in GPS history. The 400 to 600 of us who were there to witness it will never forget it. The SVN-49 Review Panel.

Unprecedented puts it mildly.

The ION program read: “SVN49 (GPS IIR-M 20) was launched in March of 2009 to support GPS constellation sustainment as well as to bring into use the new third civil signal, the L5. During the early orbit check out of this satellite, out-of-family measurements were observed impacting the legacy GPS L1 and L2 signals. The panel will review the background, current status, issues, and options moving forward with SVN49.”

Col. David Goldstein, chief engineer, GPS Wing, gave a frank and open history and description of the situation. The panelists explained the options under consideration for partial fixes — a complete fix and eradication of the pseudorange error is not possible — and added a few remarks, but were mostly there to answer questions and provide perspective in response to opinions from the floor.

It reminded me — now this is a leap — of a climb I led in days of yore up Mt. Kilimanjaro. Or escorted, really; the Swahili-speaking Tanzanian porters did all the leading. About two days in and a third of the way up, we realized that because of a schedule change we had made earlier for longer safari in the Selous, we didn’t have quite enough time to climb the mountain in the accepted manner and still make it back down for the once-weekly flight out. So over muesli and mangos the next morning in the A-frame hut, I just threw it open to everyone and said, “It’s your trip. What do you want to do?”

Folks said later that in decades of group travel, they’d never seen the like.

Basically, that’s what Col. Goldstein, Col. Madden, and the GPS Wing did. Just threw it open. “It’s your signal. What do you want to do?”

The most likely solution may involve a partial adjustment to the signal, and then setting it useable with the caveat that it will not perform to the same degree of accuracy as other satellites, nor uniformly for all receivers.

Javad Ashjaee of JAVAD GNSS had an interesting suggestion, which basically amounted to what my teenagers sometimes tell me: “Deal.” That is, just turn it on, and away we go. Use the anomaly to study multipath phenomena. Of course, he is in the enviable postion of having, or producing, receivers that can separate out the so-called defined multipath element.

However it pans out, I commend the GPS Wing for taking such an open, public, and when you come right down to it, honest approach. I  heard a bit of grumbling behind the scenes that some protocols were not adhered to in going so public. But you know what? That’s how things get done, as opposed to bogging down under cover.

And that Kili thing. We did make it up the mountain. Some of us. Sick as all getout from the altitude. Glad to come down. But we made it. Same’s gonna happen with this SVN.

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