A Tale of Two Satellites
An artifact returns to service after being on display for eight years.
- By Rebecca Maksel
- Air & Space magazine, February 2013
Opening at the National Air and Space Museum on April 12, the exhibit “Time and Navigation” tracks the progress of timekeeping over three centuries. One of the highlights of the exhibit, a Transit 5 navigation satellite used by the U.S. Navy to guide its nuclear-powered submarines, was added to the collection as a replacement for an artifact that got away. The swap began in 1984. That year, when the U.S. Air Force called Johns Hopkins’ Applied Physics Laboratory looking for a spare satellite to launch into polar orbit, APL program manager David Grant knew just where the service could find one: hanging from the ceiling of the National Air and Space Museum. Grant had recently taken his children for a visit, and remembered seeing an Oscar 17 satellite on display.
“I got a call from the folks at the Applied Physics Laboratory,” recalls Allan Needell, then-curator of the satellite collection. “They were pursuing a scientific program of launching satellites to study the aurora, and the satellite that they had given us was actually one in the production line for that type of work. When they donated it, they thought it was surplus, but then they developed plans for additional satellites, and realized that using the display unit we had would save them a lot of time and money.” More than $2 million, in fact.
“It’s a really cool story,” says Andy Johnston, a geographer in the Museum’s Center for Earth and Planetary Studies. “It’s the only example that we can find where something was on display at the Museum, pulled, and then sent into space.”
The satellite—briefly nicknamed “Museum Sat”—was used in the Polar BEAR (for Polar Beacon Experiments and Auroral Research) program, sponsored by the Defense Nuclear Agency. During the cold war, scientists realized that if a nuclear weapon was detonated in the atmosphere, its electromagnetic impulse would knock out communications satellites. So researchers decided to send a satellite into the aurora borealis to test its response to a plasma-rich environment. Knowing that the ions that produce the aurora affect the transmission of radio signals, the scientists believed that the area of sky around the displays would be a useful surrogate for learning more about the electromagnetic effects of a nuclear explosion in space.
But the APL didn’t just take the Oscar 17 and run; it replaced it with the Transit 5 navigational satellite— an artifact the Museum had wanted all along.
In the 1960s, the U.S. Navy needed a precise navigation system for its nuclear-powered ballistic missile submarines. Mechanical gyroscopes on submarines tend to drift, requiring a sub to surface periodically to take a reading on the stars—effectively giving away its position. Launching the Transit satellite series enabled subs to stay underwater; they would rise just to periscope depth to deploy an antenna, which would receive Transit’s signal as it passed overhead. Measuring the frequency of the satellite signal, sub crews could determine their position to within 660 feet.
Transit—an engineering backup—was an important addition to the Museum’s collection. “An engineering backup is where they build a satellite exactly like the one that’s going to fly,” says Needell, “and they put instruments in it and do tests to make sure that the connections are working properly. Once something on the engineering backup works, they install unstressed units on the flight article, and qualify that for flight. That way they can do all the adjustments and experiments on the engineering backup without having to put the flight unit through all of those contortions.”
The Transit system remained in use until 1996, when the Global Positioning System became fully operational. At that point, the remaining satellites became part of the Navy’s Ionospheric Monitoring System.