The National Bureau of Standards Atomic Time Scale: Generation, Stability Accuracy, and Accessibility

Several changes have recently been made to improve the real time physical approximation of UTC(USNO), the coordinated time scale generated by the U. S. Naval Observatory. A provisional UTC(USNO) is generated in real time, and a physical clock is steered to this time scale by a phase microstepper. When final values for UTC(USNO) are available, a method has been devised to steer the real time UTC(USNO) to match the final UTC(USNO). Further improvement will involve the adoption of an algorithm to generate UTC(USNO) on a real-time basis. Details of this new algorithm are presented.

The U. S. Naval Observatory Clock Time Scales

Publisher Summary This chapter describes that the flow of time is a basic experience of every observer of nature. If one postulates that one can always say which of the two local events are earlier, then one has arranged the events at a given location in an ordered sequence. Any absolute objective reality of time, as opposed to the claimed subjective ideality, would have to imply that time by itself could produce effects. It discusses that a time scale uses equal intervals for its successive scale intervals and is called a uniform time scale. The chapter highlights that time can also be used as a substitute quantity to be measured instead of some other systems parameter. An important example is the possibility of expressing distance as light time, such as the possibility of having a unified standard for time and length with the velocity of light. It also explores that the most demanding applications of timekeeping, however, still exist in astronomy. Very long baseline radio interferometry (VLBI) requires independent clocks at intercontinental distances to stay within parts in 1014 over several hours. Pulsar research needs a reference time scale to be uniform to, within fractions of a microsecond over several months.

Timekeeping and its Applications

NBS Adminis t ra t ive Manual 2 3 1.01.04 1.01.05 L e g i s l a t i v e Authori ty 4 11-28-72 (Trans. 181) 1.01.06 APPOINTMENT OF OFFICERS AND EMPLOYEES (15 U.S.C. 275) "The o f f i c e r s and employees of t h e bureau, except t h e d i r e c t o r , s h a l l be appointed by t h e Sec re t a ry o f Commerce a t such time a s t h e i r r e s p e c t i v e s e r v i c e s may become necessary . I t 1.01.07 SERVICE CHARGES (15 U.S.C. 275a) "The Sec re t a ry s h a l l charge f o r s e r v i c e s performed under t h e a u t h o r i t y o f s e c t i o n 273 o f t h i s t i t l e , [15 U.S.C.] except i n cases where he determines t h a t t h e i n t e r e s t o f t h e Government would be b e s t served by waiving t h e charge. Such charges may be based upon f ixed p r i c e s o r c o s t s . The appropr i a t ion o r fund bear ing t h e c o s t of t h e s e r v i c e s may be reimbursed, o r che Sec re t a ry may r e q u i r e advance payment sub jec t t o such adjustment on completion of t h e work a s may be agreed upon." 1.01.08 OWNERSHIP O F FACILITIES (15 U.S.C. 276) " I n the absence o f s p e c i f i c agreement t o t h e con t r a ry , a d d i t i o n a l f a c i l i t i e s , including equipment, purchased pursuant t o t h e performance of s e r v i c e s au tho r i zed by s e c t i o n 273 o f t h i s t i t l e [15 U.S.C.] s h a l l be come t h e property of t h e Department of Commerce . I t 1.01.09 REGULATIONS (15 U.S.C. 277) "The Sec re t a ry of Commerce s h a l l , from t i m e t o t i m e , make r e g u l a t i o n s regarding t h e payment of f e e s , t h e l i m i t s of t o l e rance t o be a t t a i n e d i n s t anda rds submitted f o r v e r i f i c a t i o n , t he s e a l i n g of s t anda rds , t h e disbursement and r e c e i p t o f moneys, and such o t h e r m a t t e r s a s he may deem necessary f o r ca r ry ing i n t o e f f e c t s e c t i o n s 271-278b of t h i s t i t l e [15 U.S.C.]." 1.01.10 VISITING COMMITTEE (15 U.S.C. 278) "There s h a l l be a v i s i t i n g committee of f i v e members t o be appointed by t h e Sec re t a ry o f Commerce, t o c o n s i s t o f men prominent i n t h e va r ious i n t e r e s t s involved, and not i n t h e employ o f t h e Government. This committee s h a l l v i s i t t h e bureau a t l e a s t once a y e a r , and r epor t t o t h e Sec re t a ry o f Commerce upon t h e e f f i c i e n c y o f i t s s c i e n t i f i c work and t h e cond i t ion of i t s equipment. The membe r s of t h i s c o m i t t e e s h a l l s e rve without compensation, but s h a l l be pa id t h e a c t u a l expenses incu r red i n a t t e n d i n g i t s meetings. The pe r iod o f s e r v i c e o f t h e members of t h e committee s h a l l be so arranged t h a t one member s h a l l r e t i r e each yea r , and t h e appointments t o be f o r a pe r iod of f i v e years . Appointments made t o f i l l vacanc ie s occur r ing o t h e r than i n t h e r e g u l a r manner a r e t o be made of t h e remainder o f t h e per iod i n which t h e vacancy ex i s t s . ' ' NBS Adminis t ra t ive Manual 2 4 1.01.06 1.01.11 TRANSMITTAL 126 I United States of America DEPARTMENT OF COMMERCE

The Standards of Time and Frequency in the USA

Initial test results indicated that the Global Positioning System/Time Transfer Unit (GPS/TTU) performed well within the + or - 100 nanosecond range required by the original system specification Subsequent testing involved the verification of GPS time at the master control site via portable clocks and the acquisition and tracking of as many passes of the space vehicles currently in operation as possible A description and discussion of the testing, system modifications, test results obtained, and an evaluation of both GPS and the GPS/TTU are presented

USNO GPS program

An automated data collection and processing system designed to maintain and control the U. S. Naval Observatory (USNO) master clock system is described. Phase difference and time interval measurements (better than 0.1-ns resolution and 1.0-ns precision) from an ensemble of atomic clocks are used to construct a master clock time scale with a stability of parts in 10-14 on a near real time basis. Physical realization and dissemination of the time scale is achieved through program-controlied subsystems. The control and automatic data processing (ADP) systems are discussed and an analysis of system performance is made.

http://ieeexplore.ieee.org/iel5/19/4314025/04314054.pdf

Automated Timekeeping

An automated system presently used by the U. S. Naval Observatory (USNO) for determining, maintaining, and disseminating Precise Time and Time Interval (PTTI) to a worldwide community of scientific and military users is described and evaluated on the basis of present capabilities and future requirements. The objective of the system is to provide near-real-time dissemination of PTTI information from a Master Clock time scale with a stability in excess of a few parts in 10-14.

/pdf/automated-timekeeping-ii-2492a1bcjw.pdf

Kenneth Putkovich

Papers

Automated Timekeeping

Automated Timekeeping II