The U.S. Naval Observatory’s Alternate Master Clock on Schriever Air Force Base received its second rubidium fountain clock February 4 to ensure it has the most precise time in the world.
Both the USNO’s Washington D.C.-based primary and its local Alternate Master Clock facility serve as the Department of Defense’s common time reference. Additionally, the USNO monitors the GPS constellation and provides time offsets to the 2nd Space Operations Squadron for its daily navigation uploads to each individual GPS satellite.
“With the new rubidium fountain clock, we are going from the time standard of 1 to 2 nanoseconds down to 300 picoseconds,” said Bill Bollwerk, Head of USNO Detachment Colorado.
One nanosecond is equivalent to one billionth of a second, while a picosecond is equal to one trillionth of a second. Though these small slices of time may not sound important, every nth of a second is significant, especially in GPS operations.
“A nanosecond matters because it is equivalent to a 1-foot of error for GPS,” Bollwerk said. “If the GPS satellite clocks were off by 3 nanoseconds, you have 1-meter of error introduced into GPS.”
Designed and produced by physicists at the USNO laboratory in Washington D.C., the powered rubidium fountain clock traveled by dedicated truck to Schriever. Once the fountain clock arrived at Colorado base, with the help of members of the 2nd Space Operations Squadron, the 50th Security Forces Squadron and 50th Civil Engineering Squadron, the USNO team moved it to a climate controlled chamber in the USNO’s laboratory via an airsled hover lifter.
“The 2 SOPS men and women are able to operate and provide accurate instantaneous reliable support to U.S. military forces around the world, thanks to our partnership with the U.S. Naval Observatory,” said Lt. Col. Thomas Ste. Marie, 2 SOPS commander. “We are happy to be able to work together to support their upgrade. Our relationship allows 2 SOPS to continually reach our goal of record breaking time-transfer performance and navigation accuracies.”
Although 2 SOPS was happy to support the move, it’s not as easy as one might think.
“The process of moving the rubidium fountain was very complicated,” said Ken Dreiling, USNO Detachment Colorado. “We had to ensure the fountain clock was not actually in contact with the floor or the walls as we moved it from the loading dock through the hallways and elevator into our facility.”
The careful transport of the fountain was essential to prevent damage that could affect the clock’s performance.
“The fountain clock collects billions of rubidium atoms, encased in a spherical vacuum chamber and laser-cooled to a millionth of a degree above absolute zero degrees Kelvin, approaching the coldest temperature anything can be,” Bollwerk said. “The reason we do that is because we want to observe and measure the atoms for long time in an environment that minimizes unwanted noise like the Doppler Shift.”
Though the Alternate Master Clock provides precise timing for several communication and space systems, Missile Defense Agency, DOD facilities and several civilian infrastructures around the world, the new system was installed primarily to support GPS operations.
“It is great to have the most precise time standard in the world but it is useless unless you can get it to the user, not everyone can come to the facility and set their watch,” said Bollwerk. “GPS is USNO’s primary means of providing global precise time to the warfighter. It is a great partnership between the Navy and the Air Force.”
Dreiling said the new fountain clock will help improve GPS operations.
“The new rubidium fountain clock is the next-generation new frequency standard,” Dreiling said. “This will boost the GPS’s timing by 10-fold.”