Russian technicians fit a cluster of three Glonass satellites to a booster rocket.
Sometime in the last few years of the 20th century, a new term was added to the everyday vocabulary of ordinary Americans: GPS moved from James Bond movies to the dashboards of cars and trucks, the handlebars of motorcycles, and the backpacks of hikers and hunters. But GPS has never been the only satellite-navigation system. The Soviets had their own version of it called Globalnaya Navigatsionnaya Sputnikovaya Sistema or GLONASS, way back in the ‘80s. GLONASS survived the collapse of the Soviet Union, but without adequate funding it gradually disintegrated into little more than a handful of battered old satellites that gave university space science departments something to talk about but provided only intermittent navigational coverage.
Then in 2001 the Russians started launching new satellites, and in 2007 they promised that GLONASS signals would be free to Russian and foreign consumers alike. In January the Russian news agency Itar-Tass reported, “The GLONASS satellite navigation signal is again constant throughout Russia.”
Compared with the 24/7 worldwide availability that GPS has been achieving for more than a decade, “constant throughout Russia” hardly seems like anything to brag about. But a look at the real-time coverage map on the Russian Space Agency’s website shows that it is also something of an understatement.
Like GPS, GLONASS needs 21 satellites to provide full-time worldwide coverage, with three in-orbit spares. It’s got 20 of them up there right now, and six more are scheduled for launch in September and December. GLONASS receivers are already in production, with several of the companies that produce high-end GPS units offering GLONASS as an add-on to their surveying units.
This pole-mounted Magellan Pro Mark 500 is a combined GPS/Glonass receiver for surveying.
GLONASS, by itself, isn’t quite as accurate as GPS. It’s difficult to be precise about how much less because the accuracy of both systems varies from minute by minute and from place to place. But if you say that GLONASS is roughly half as accurate as GPS, you won’t be far wrong.
Yet adding GLONASS to GPS isn’t like adding water to wine: It doesn’t dilute its accuracy. In effect, using both systems gives the receiver more choice. If the signal from a GPS satellite seems unreliable, a receiver can reject that one and substitute a GLONASS satellite. Or if its view of some of the GPS satellites is obscured, the receiver can use GLONASS satellites to make up the shortfall.
To professional users like surveyors who are spending something in the order of $10,000 for a GPS receiver such as the Magellan ProMark 500, an extra $3,000 for GLONASS capability may well be a worthwhile investment in faster, more accurate mapping. But it’s unlikely that many automobile or boat owners would share that view.
Imagine, though, what might happen if a brave or farsighted manufacturer offered a GLONASS option for $50 or $100 on a mass-market GPS receiver. Automobile drivers make up a far bigger slice of this market than boaters, and the first few users would soon realize that having more satellites means better performance from their in-car navigators, particularly in urban canyons where tall buildings often obstruct a receiver’s view of the sky.
As for boaters, GPS already provides all the accuracy we can use, so it’s hard to see GLONASS being a huge advantage unless it’s as a backup if the entire system goes down. But before long, we may not have the choice.
This article originally appeared in the May 2009 issue of Power & Motoryacht magazine.