Inside GNSS: Engineering Solutions from the Global Navigation Satellite System Community
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Inside GNSS • April 2006

GPS Help Line

Inside the Master Control Station at the 2nd Space Operations Squadron (2SOPS), Schriever Air Force Base, Colorado, crews continuously monitor and control the GPS constellation’s navigation signals. By doing so, 2SOPS keeps the GPS signal as accurate as possible, making it a phenomenally successful global utility.

Yet, as GPS users know, other factors — such as differences in receivers, terrain, environment, and platforms — can affect navigational accuracy in the field.

Inside GNSS • September 2006

Player Pianos, Sex Appeal, and Patent #2,292,387

. . . It is simply too good to be true.

But by now we know that Hedy Lamarr and George Antheil were awarded U.S. Patent No. 2, 292,387 on August 11, 1942 for a "Secret Communication System."

And that, indeed, the two artists invented the "frequency hopping" method of radio signal transmission, later to be known as "spread spectrum."
As they explained in their patent application:

GNSS Solutions • September 2006

Atomic Clocks on Satellites and Mitigating Multipath

Q: GPS satellites used to carry two cesium and two rubidium atomic standards on board. Subsequently, GPS switched to all rubidium clocks. Galileo plans to use hydrogen masers instead. What are the relative merits of these clocks for use in navigation satellites?

A: It is well recognized that the space-qualified atomic clocks in the GPS satellites are an enabling technology, if not the enabling technology for the system. However, they are also one of the more difficult technologies to acquire.

Inside GNSS • September 2006

USAF Announces More IIF Delay

The GPS Block IIF program continues to lose ground, with first launch of a satellite now projected as no sooner than May 2008 and as late as January 2009 in a “worst case,” scenario, according to the U.S. Air Force. Program costs are also increasing.

Inside GNSS • September 2006

GPS . . . the Movie (You So Knew It Had to Happen)

This is what happens when the grandchildren of Mickey Rooney and Judy Garland go out and “rent the old barn and put on a show!”

First, there was an independent Seattle, Washington–based filmmaker named Eric Colley and a screenwriter named Hallie Shepherd who knew about the 150,000 actual GPS-guided scavenger hunts now taking place in 200 countries.

Inside GNSS • September 2006

GPS Passes Artillery Tests

U.S. Department of Defense (DoD) contractors appear to be getting closer to fielding GPS-aided precision guidance systems that can withstand the arduous requirements of artillery shells and other fired munitions.

Inside GNSS • July/August 2006

Thales Navigation Sold

Shah Capital Partners, a private equity firm focusing on technology, will acquire GNSS receiver manufacturer Thales Navigation from the Thales Group, of Paris, France.

Inside GNSS • July/August 2006

Industry Sees Galileo Contract Outline in 2006

The consortium negotiating to build and operate Europe’s Galileo system now expects to sign an agreement with the Galileo Joint Undertaking (GJU) by the end of 2006.

Inside GNSS • July/August 2006

GPS III Contract Award Set Back

Okay, now it’s official: The GPS Block III contract award has been delayed from Fiscal Year 2006 (FY06) to Fiscal Year 2007 (FY07).

GNSS Solutions • July/August 2006

Orbital Precession, Optimal Dual-Frequency Techniques, and Galileo Receivers

Q: Is it true that the GPS satellite geometry repeats every day shifted by 4 minutes?

A: It is true that the GPS satellite orbits were selected to have a period of approximately one half a sidereal day to give them repeatable visibility. (One sidereal day is 23 hours, 56 minutes, and 4 seconds long or 236 seconds shorter than a solar day.) However, because of forces that perturb the orbits, the repeat period actually turns out to be 244 to 245 seconds (not 236 seconds) shorter than 24 hours, on average, and changes for each satellite.

Jammer Dectector
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