Engineering topics

Ward, S. C.

Publications and source records attributed to Ward, S. C..

6 records

NASA NTRS1984

Hydrogen Masers as Time and Frequency Standards

Track each other with 100 times more precision than cesium standards. Geographically separated hydrogen masers tracked each other for more than year to within few parts in 10 to the 15th power. Frequency offset of hydrogen-maser output from hyperfine line frequency is function of ambient magnetic field, cavity mistuning, thermal motion of atoms in cavity and collisions of atoms with walls of the cavity. If maser remains at one location some of small offsets in frequency will remain constant throughout life of maser.

Ward, S. C.↗

NASA NTRS1984

Using GPS and VLBI technology to maintain 14 digit synchronization

To facilitate the navigation of spacecraft to the outer planets, Jupiter and beyond, the JPL-NASA Deep Space Network (DSN) has implemented three ensembles of atomic clocks at widely separated locations. These clocks must be maintained, synchronized, to with a few parts in 10 to the 13th power of each other and, the entire group must be maintained, to a lesser degree, in synchronism with Coordinated Universal Time (UTC)NBS/USNO. Over the last 1 1/2 years the DSN has been using Global Positioning Satellites (GPS) and Very Long Baseline Interferometry (VLBI) technology to perform these critical Frequency and Time (F&T) synchronization tasks. A year of F&T synchronization data collected from the intercomparison of 3 sets of cesium and hydrogen maser driven clock ensembles through the use of GPS and VLBI techniques are covered. Also covered, are some of the problems met and limitations of these two techniques at their present level of technology.

Ward, S. C.↗

NASA NTRS1983

A two-year history of atomic frequency standards syntonization in the Deep Space Network

The frequency and timing system (FTS) of the Deep Space Network (DSN) consists of a collection of three sets of clocks driven by independent atomic oscillators. The synchronization of the output frequencies (syntonization) of these oscillators (reference frequency standards) is reported. There is an implied specification of a + or - 5.5 X 10 to the 12th power related to the DSN time synchronization specification of a + or - 100 microseconds. Both the syntonization within the three sets and the syntonization of the sets to the international standard (International Atomic Time) are considered.

Ward, S. C.↗

NASA NTRS1981

The operational performance of hydrogen masers in the Deep Space Network (the performance of laboratory reference frequency standards in an operational environment)

Spacecraft navigation to the outer planets (Jupiter and beyond) places very stringent demands upon the performance of frequency and time (F&T) reference standards. The Deep Space Network (DSN) makes use of hydrogen masers as an aid in meeting the routine F&T operational requirements within the 64 m antenna network. Results as of October 1980 indicate the hydrogen masers are performing within the required specifications. Two problem areas are discussed: insufficient control over the environment in which the reference standards reside; and frequency drift.

Ward, S. C.↗

NASA NTRS1981

The operational performance of hydrogen masers in the deep space network: The performance of laboratory reference frequency standards in an operational environment

Hydrogen masers used as aids in meeting the routine frequency and time operational requirements within the 64 m antenna Deep Space Network. Both the operational syntonation (frequency synchronization) and the the clock (epoch) synchronization requirements were established through the use of specifically calibrated H-P E215061A flying clock. The sync/synt to UTC was maintained using LORAN and TV in simultaneous reception mode. The sync/synt within the 64 m net was maintained through the use of very long base interferometry. Results indicate that the hydrogen masers perform well within the required specifications.

Ward, S. C.↗

NASA NTRS1973

Time-synchronized VLF phase-tracking receiver

Coded signals transmitted at very low frequencies by National Bureau of Standards via its radio facility WWVL contain both primary time and frequency information. Synchronization of local time with WWVL signal standard requires comparison of phase differences between transmitted signal and output of traveling atomic clock such as rubidium frequency standard.

Ward, S. C.↗