Are You Sure You Want to Donate This?

Posted on Fri, October 5 2012
SINS Typewriter

“Are you sure you want to donate this?” I asked the intern. “This” was a slightly-used Smartphone, in perfect working condition. The intern, Rebecca Bacheller, was, indeed, willing to donate it. She heard that the Time and Navigation team wanted to disassemble one and showcase the current state of geolocation devices, enabled by the Global Positioning System and other advanced electronics. Our plan was to label the phone’s circuits, and show how they correspond to classical methods of navigation that had been practiced for centuries. Becky was excited that she would be credited in the label; she also had another motive: namely a reason to trade up to the newest version of the popular phone. This is a never-ending treadmill: once you get on, it is impossible to get off. I prepared myself for the transfer by going on-line and special-ordering tools to disassemble it: a “pentalobe” screwdriver, a plastic pry-bar, and a tiny Phillips-head screwdriver. I also downloaded instructions on how to disassemble the phone, and I borrowed a head-mounted magnifier. When the day arrived, fellow curator Andy Johnston and I got to work, surrounded by a few sidewalk superintendants from the Space History Division.

USS Alabama

 The USS Alabama was launched in 1984, carried up to 24 Trident ballistic missiles armed with nuclear warheads, and is still in the fleet.


Before describing what we found, I want to mention an important part of the new gallery. One of the centerpieces of Time and Navigation is a “SINS” guidance system, removed from the nuclear-powered submarine USS Alabama. “SINS” stands for “Submarine Inertial Navigation System,” and it was responsible for telling the sub where it was without having to surface to take a fix on stars or otherwise reveal its location. Hence the “inertial” components: a set of gyroscopes and accelerometers that, as its developer Charles Stark Draper called it, was like practicing “astronomy in a closet.”  It was not perfect: the gyros had a tendency to drift, so periodically the sub would come near the surface to receive navigation signals from a Transit satellite orbiting overhead.  (An engineering backup of a Transit will also be on display in the gallery.)  A refrigerator-sized digital computer combined data from these inputs, corrected the gyros’ drift, and computed the sub’s position. The whole ensemble is rather bulky and heavy, and as Heidi Eitel mentioned in an earlier blog post, getting everything to fit in the gallery is quite a challenge.

SINS Typewriter

 This modified IBM Selectric typewriter, connected to a special computer system, output data about the operation of two SINS (Submarine Inertial Navigation System) units aboard the nuclear-powered submarine USS Alabama. It could also provide input to the computer in emergencies.


So what does this have to do with the cell phone? As we disassembled it, Andy and I realized that almost every component of the SINS was present, even if you need a high-power magnifier to see it. A three-axis accelerometer? Check.  Gyroscopes? Yes. A radio to receive satellite navigation signals? Yes, although the phone receives signals from GPS, not Transit satellites. A computer? Of course—the phone uses an “A4” processor supplied by the company ARM. It has more processing power than the CRAY-1 that used to be on display in the Beyond the Limits gallery. A keyboard and display to give and receive commands? Yes--the phone’s touch screen even replicates the old-fashioned “QWERTY” keyboard of the electric typewriter used on the submarine. A radio to communicate with the rest of the world?  The phone has several, covering the major cellular frequencies in the UHF region. (The sub communicated by trailing a long wire behind it and receiving “Very-Low-Frequency” (VLF) radio signals—far below the standard AM broadcast band-- chosen because they could penetrate water.)  The Smartphone even has a magnetic compass.


 This disassembled smartphone showcases the current state of geolocation devices (as of 2012), enabled by the Global Positioning System and other advanced electronics. The phone's circuits correspond to classical methods of navigation that have been practiced for centuries.


The difference in size between the two systems is breathtaking, but there is another difference that may be even more significant. The SINS was designed to allow the submarine to navigate without anyone, other than the crew, knowing where it was. By contrast, a Smartphone has all kinds of circuits and software on board to let the world know where its owner is, and what he or she is doing. Submariners might be uncomfortable carrying one of these around. It is going to be a challenge to show this disassembled object to our visitors and convey the magnitude of what they are looking at. Many visitors carry these devices with them and hardly give them a second thought. The gallery opens next spring, and we’ll see how this exhibit works.