Time and Frequency Activities at the JHU Applied Physics Laboratory

摘要

The Johns Hopkins University Applied Physics Laboratory Time and Frequency Laboratory (JHU/APL TFL) provides support to multiple NASA missions operated at JHU/APL that span our solar system from the study of the Sun's coronal mass ejections (STEREO) to the examination of the outer planets and the Kuiper Belt objects (New Horizons). This space mission support includes providing precise time and frequency to the integration and testing of flight hardware, frequency reference for spacecraft ranging and communications via the JHU/APL satellite communications facility, and the time-stamping of ground-receipt telemetry packets from various spacecraft. The JHU/APL TFL's ensemble of three high performance cesium standards and three hydrogen masers are integrated to form the APL timescale that is the basis for estimating UTC-UTC(APL) and for evaluating the performance of the individual clocks. Traceability to the USNO, NIST, and UTC is maintained via GPS Common-View and Precise Point Positioning time transfer. The JHU/APL TFL's clocks are also incorporated into the formulation of International Atomic Time (TAI). The JHU/APL TFL Master Clock is a hydrogen maser and the frequency adjustments of UTC(APL) are performed with a high resolution offset generator. This combination of hydrogen maser and high resolution offset generator along with our UTC-UTC(APL) estimation algorithm has made it possible to maintain UTC(APL) within 10 nanoseconds of UTC 95% of the time. In January 2012, the JHU/APL TFL was moved to a new building on the south campus of JHU/APL. This new facility includes an environmentally controlled clock vault which will enable enhanced performance of our atomic clocks and improve the stability of our time and frequency output.