[LEAPSECS] presentations from AAS Future of Time sessions

[Warner Losh]

On Jan 12, 2014, at 2:01 AM, Brooks Harris wrote:

> I'm not sure if there is a connection either. When did LORAN-C adopt 1958?


I can't answer definitively on when, but can point the way to what I know.

LORAN-C is defined by COMDTINST M16562.4A. Quoting from chapter 2:

"This epoch is from 0 hr, 0 min, 0 sec , 1 January 1958. The expected Times-of-Coincidence (TOC) of master station's transmissions with the UTC second are publish in the Times of Coincidence, Null Ephemeris Tables, Section 9 developed by and available from USNO. The difference between the time of the master's transmission with respect to UTC is also published by the USNO in the Series 4 and Series 100 Bulletins. USNO Time Service Information Letter of 15 August 1973, provides guidelines for making time measurements." (from http://navcen.uscg.gov/pdf/loran/sigSpec/chapt2c.pdf)

so that puts at sometime before 1973 :).

Digging more, we see Series 4 and Series 100 Bulletins from USNO. Or at least references to them (I thought I'd seen them online at USNO but can't find them now). We have a 1983 publication at http://tycho.usno.navy.mil/ptti/1983papers/Vol%2015_05.pdf that states:

"Prior to the 1970s, data collected by the Observatory were all logged manually" and goes on to say that "initially only locally monitored time pulses from Loran-C... were available." And talks about 10 years prior (approx 1973) the decision was made to automate collection of this data. It also talks about until recently (1983), the only dissemination of this data was US Mail.

But it doesn't tell of when the manual collection of data started, but implies the automated collection started in 1973, give or take a year.

Digging into the PTTI archives, we find an article on LORAN-C time keeping that has a good history of LORAN-C starting in 1957, and the transfer of LORAN-C to the USCG in 1958 (see page 79 (page 90 in the pdf) and following).  It also talks about how measurements were gathered from 1955 to 1958 that ultimately lead to the standard second definition during LORAN-C development. http://www.dtic.mil/dtic/tr/fulltext/u2/a280955.pdf Perhaps these documents will prove useful in working out TAI's origin, but it seems that LORAN-C started in 1958, and so did TAI time's EPOCH, so there's a strong inference to be made at the connection between the two... In fact, I wish I'd known of this publication sooner, since I worked on the retooling of the LORAN-C timing system in the early 2000's and I love historical stuff like this.

I don't know if other PTTI publications are online, but intensive google searching for them might prove fruitful as well. http://tycho.usno.navy.mil/ptti/ looks to contain at least a summary of each of the conferences. It is only intermittently responding to me at the moment. Others might have better luck trolling through there to find additional references that may have somehow escaped the watchful eye of Steve Allen...

Warner