Bradford Parkinson, the former US military engineer that invented GPS, admits that when America’s satellite systems work in tandem with Russia’s, they can achieve coverage that one system alone can’t.
“That little watch on your wrist is listening, and it’s probably listening to more than four satellites,” Parkinson, who helped launch some of America’s first GPS satellites into the Upper Van Allen Radiation Belt in 1978, tells Inverse. Most GPS systems require signals from at least four satellites to be accurate, but sometimes, as in Light’s case, getting four signals from the usual constellation of US satellites just isn’t possible. The satellites shot into space by ROSCOSMOS can be a lifesaver in these situations, though Parkinson’s vast knowledge of their history makes him wary of trusting GLONASS completely.
A satellite knows four things about itself: its x, y and z coordinates on a three-dimensional map, and the exact time — down to one billionth of a second — it was at that position. It combines all this data, sending it to Earth with a light-based “shout.” Back on the ground, the tracker uses that signal to calculate a range of distances estimating the position of the satellite that sent it. If it can hear signals from multiple satellites, it can calculate where the ranges overlap to give a pretty good sense of where it is.
Amid the sounds of the trees, her dog, and the nearby freeway, Light’s watch listened for American satellites but didn’t hear enough “shouting.” Fortunately, Russian satellites were well-positioned to be vocal. Tuning into GLONASS, says Parkinson, “gives you additional measurements that you can average into your solution, if you handle it right.”
But GLONASS is not a perfect system, he warns. That’s partially because the Russians actually have a slightly different way of mathematically describing the Earth, and their time system onboard GLONASS satellites differs slightly from ours. But largely, it’s because Russia’s satellites have a long history of falling out of the sky.
In the early days, says Parkinson, the Russian scientists were “closed” and didn’t like to talk about shortcomings in their system. That GPS and GLONASS satellites can now cooperate peacefully on a variety of devices is a relatively new phenomenon. While GPS has been available for civilian use since its inception, GLONASS has struggled to provide that consistent signal that trail runners have come to rely upon today because its satellites have struggled to withstand the treacherous Outer Van Allen Radiation Belt, 11,000 nautical miles above the Earth.
To this day, no satellite can survive indefinitely in this radiation hellstorm, a flurry of charged particles generated by the solar wind. “Our current technology is ever more susceptible to these accelerated particles because even a single hit from a particle can upset our ever smaller instruments and electronics,” said David Sibeck, a Van Allen Probes mission scientist at NASA. Figuring out how to build a GPS satellite that could withstand these rogue particles in the 1970s was, to Parkinson, a “great engineering feat.”
Doing so proved much more difficult for Russian scientists, who at the time were entering “the era of stagnation.” As the value of the ruble crashed, scientists at the Soviet Space Agency had increasingly fewer resources to get satellites into orbit.
In October 1982, they finally succeeded in launching the first GLONASS satellite; by 1995, their full constellation of 24 satellites had been deployed. But these machines, too weak to withstand the Outer Van Allen, lasted an average of two to three years before they literally crumbled to pieces in the sky. Satellites in the GPS system generally last about 12 years before they need to be replaced.
“We [GPS] hardened our satellites so they survived, and we’ve have a few last more than twenty years, Parkinson says. “GLONASS absolutely failed that. They were having to launch eight to twelve a year. They couldn’t build the darn satellites fast enough.”
GLONASS’ official history reports that, by 2002, “the GLONASS constellation consisted of 7 satellites” — not nearly enough to help Russians, let alone American trail runners, find their way home.