Space-related activities that rely on the precision time scale known as Coordinated Universal Time (UTC) may soon experience Y2K déjà vu.

It’s been over a decade since the world collectively dealt with the “Y2K bug,” where software codes and data formats presumed that the 20th century was the only century. Two-digit-year formatting was expedient and seemed to make perfect sense from a cost-benefit perspective at the time. It saved memory bits. People were used to it. The year 2000 was still a long way off. Despite monumentally expensive efforts toward software patches, testing and analysis, the world may never learn just how many critical failures occurred New Year’s Day of ’00.

UTC is the atomic version of mean solar time, which has dutifully correlated International Atomic Time (TAI) — the average accumulation of SI seconds — with the measure of solar days known as Universal Time (UT). UTC does so by infrequently accepting leap seconds into its “atomic calendar” to keep the atomic standard synchronized within 0.9 seconds of astronomical time of day. This defining arrangement has been relied upon for many space-related activities, because if a system knows what time it is, then it also knows (to better than a second) how Earth’s longitudes are oriented.

The Radiocommunication Sector of the International Telecommunication Union (ITU R) now “owns” the definition of UTC because UTC began as a recommended practice for broadcasting timing signals by radio. In October, committees within the ITU R are preparing to conclude that traditional civil timekeeping tied to the sun and Earth has become inconvenient.

However, the astronomical basis of UTC has proved useful outside radiocommunications, where the technical and business impacts of changing UTC have not been considered sufficiently. If the ITU R proposal advances, the only way to know for sure how complex system architectures will be affected would be to launch comprehensive and potentially costly impact studies similar to those for Y2K. And if UTC is redefined, operations that employ UTC successfully will be forced to change unnecessarily.

While Y2K-bug expenditures were absolutely necessary, redefining UTC is not. Anything other than the status quo entails unknown costs in an economy already troubled by worldwide uncertainty. Because the impact on the space-operations community has not been studied in detail, and because those advancing a change have yet to demonstrate consequential and unavoidable faults with the status quo after years of consideration, we urge that the definition of UTC remain unchanged.


Dave Finkleman is a senior scientist in the Center for Space Standards and Innovation at Analytical Graphics Inc. The article was co-written by John Seago, also with Analytical Graphics, and Ken Seidelmann, a professor at the University of Virginia and former director of astrometry at the U.S. Naval Observatory.