Imagine you’re a collection of sensors, flying in formation in one of 31 US Air Force satellites in medium earth orbit above the Earth.

The satellite itself is part of the Air Force’s global positioning system (GPS) that lets truckers, hunters, and lost city drivers know exactly where they are.

But from your point of view, as a collection of sensors, the satellites are perfect platforms to detect and triangulate in on airborne or space-based nuclear explosions anywhere they may occur.

On the one hand, of course, detection has been no problem: There haven’t been any air-based explosions for decades.

On the other hand, there could be one anytime. And the country that did it might deny doing it if its leaders didn’t believe the US could track it.

So sensors have to be ready to detect a real explosion and do so through a jungle of potential false positives: Lightning bolts that occur more frequently than one per second (as well as unpredictably occurring super-lightning bolts), energetic particles from the Van Allen radiation belt that collide with electronics on the satellite, the welter of cell phone communication “noise,” and bolides entering Earth’s atmosphere at terrific speeds, flaring and sometimes exploding.

“What was tricky,” says project chief engineer Steve Yearout (5733) of the early

sensor placements, “is that we did not have a good idea what our observations of the environment would look like from the standpoint of space. Looking at Earth with sensors was new and not well understood — the background noise, the clutter.”

Steve should know. No matter which GPS satellite the sensors fly on, Steve has been there to turn them on and test their responses in the sky.

“We started launching our part of the payloads in 1983,” he says. “We’ve done 50 payloads so far. I’ve been involved in turning on all 50.”

That would be an average of two payload launches a year for the past 25 years, the most recent in March. His team packages them in what resemble several small suitcases.

The sensors include X-ray and particle detectors from Los Alamos National Laboratory. Sandia provides optical and electromagnetic pulse (EMP) sensors, radio frequency equipment, and the main processors that coordinate all commands from the ground, as well as return sensor output back to ground.

“We also have a state-of-health telemetry system that allows us to see how our system is functioning,” says Steve.

The sensors are delivered to an Air Force contractor (in the past, either Boeing or Lockheed Martin), which integrates the boxes into the satellite package. The satellite is launched from Cape Canaveral (the Air Force side of Kennedy Space Center), and then, once in orbit, switched on remotely by Steve and his teammates from Sandia, LANL, and the USAF.

Perfectly synchronized atomic clocks on all satellites mean that telemetry, geometry, and computer programs working together can accurately define the position of any point of interest.

Difficult as it is to test equipment in advance of the environment in which it will be used, the Sandia group’s sensor packages have performed exceptionally well over the years.

This includes surviving one faulty rocket that exploded on takeoff in the 1980s. A number of the boxed Sandia boards survived and were still operable. “We build pretty good stuff,” says Steve. He doesn’t count this launch as one of his 50.

Steve, ready for new career challenges, envisions “way down the road” moving into an arena just slightly downstream: analyzing data produced by the sensors he helped design, oversaw in production, watched launch, and keyed into action.

But for now, Steve is looking forward to turning on many more space-based sensor systems.