How to Tune Up Atomic Clocks in Space

Electronic equipment generates frequency tuning commands to syntonize two atomic clocks. (Photo: Elisa Haber)

A team comprising Dr. Henry Wang, Dylan Caponi, and Gebriel Iyanu is developing an effective, in-lab testing facility for the syntonization of AEHF/Milstar rubidium atomic clocks. Syntonization is the process by which clocks are calibrated to an equal frequency in order to remain synchronized as time-keeping devices.

Aerospace often receives questions from satellite operators regarding the performance of these clocks while in space. As a complex facilitator of global communication, it is simply impossible for AEHF/Milstar to be shut down in any way for testing or research purposes. As a result, there arises an essential need for a reliable simulation program. The test facility allows Wang and his team the ability to innovatively troubleshoot by simulating space environments. The research that they conduct will serve as an invaluable resource to all those who utilize the AEHF/Milstar constellation.

The AEHF/Milstar constellation is a collection of satellites orbiting the Earth whose purpose is to provide global communication for the United States military. Over time, the atomic clocks that reside within the satellites begin to diverge from one another in terms of their timekeeping abilities. These individual variations can result from temperature changes, radiation, and simply, lengthy spans of time. For precise communication activity, it is essential that each satellite’s atomic clock keep the exact same time as every other clock.

As part of the Photonics Technology Department, Wang, Caponi and Iyanu have built a fully functioning simulation of the atomic clocks’ environment and communicative computer systems.

From left to right, Dylan Caponi, Gebriel Iyanu, and Dr. Henry Wang, with their in-lab syntonization equipment. (Photo: Elisa Haber)

From left to right, Dylan Caponi, Gebriel Iyanu, and Dr. Henry Wang, with their in-lab syntonization equipment. (Photo: Elisa Haber)

The team utilizes two computers for two different purposes. One computer simulates the on-orbit computers that are found aboard the actual satellites while the other simulates the AEHF/Milstar satellite ground control timekeeping system. These two computers and other supporting instruments are connected to two atomic clocks sealed in a vacuum that simulates the space environment. One of the clocks represents the ground-controlled master clock in the constellation while the other simulates the clocks that will be syntonized to the master clock by the on-orbit computer.

The initial work of the project has been to simulate, discover, and analyze the various ways in which the clocks can deviate from one another as a result of variations in space vehicle temperature. By experimenting with the simulator, the team has learned a great deal about the nature of the clocks and how they react to these various environmental changes. In terms of applicable technology, the team is developing a software program that recognizes the frequency deviations of the clocks, generating a corrective command when the clocks pass a certain threshold of frequency discord — thus remedying the timekeeping imperfections.

“With this unique experimental capability, we can provide technical information from our testing labs to the satellite operators,” said Wang. He sees the project as an active resource designed not only to address problems as they occur, but before they occur. “Operational technicians will have questions and they come to Aerospace,” he said. “We can simulate and test and provide answers to the satellite operators. We will also actively provide technical suggestions and technical information to the operational personnel.”



—Matthew Kivel