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Building the Geodetic VLBI Network

Some Rememberances

at 50 Years----------Tom Clark

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Based on original presentations at

IVS 10th Anniversary Ceremony, Bordeaux

March 2009and

IAA Medal CeremonySt. Petersburg

VLBI ≡ Very Long Baseline Interferometry

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• Microwave noise signals from extra-galactic radio sources (quasars) are acquired simultaneously at radio telescopes around the world.

• At each station, the noise signals are referenced to a very stable (~1:1014) atomic clock (H-Maser).

• A small fraction of the noise comes a small (<10-3 arcsec) region in the core of the quasar and is coherent at the distant telescopes (Θ < λ/D).

• Radio Astronomy studies structure & variability of the quasars.

• Geodesy uses the quasars as highly “stable” reference points to determine vector baselines.

In the current generation Mark-6 system, tape recorders have been replaced with COTS disk drives.Near-real-time eVLBI replaces tape/ disk with Gb/s Internet connections.

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50 years ago in 1967 VLBI Began

Tape Recording -- 3 groups:USA Quasars --- Digital Computer Tape

[NRAO (KIK, IP-T, BGC ...) + CalTech (MHC) + Cornell]Canada Quasars --- Video Tape

[Alan Yen et al]

USA Spectral lines --- Quasars, Relativity, Geodesy[MIT+ HAYS (I2S, AE2R, ARW ...) + SAO (JM2) + Onsala][NASA + UMD(TAC et al) added in 1968]

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NASA/Goddard gets involved in VLBI:Goddard had an R&D program with Harry Peters developing Hydrogen Maser frequency standards.Goddard was “home base” for satellite tracking networks (Manned & Unmanned, but not the DSN).Bob Coates (later CDP Project Manager) was the key to both these resources.Goddard management encouraged its scientific staff to work on independent projects of interest.Goddard had many large general-purpose IBM-360 computers which we used as VLBI correlators!My U.MD Graduate Students provided a source of “slave labor”.

Getting Bob Coates interested

Correlators!

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I’m amazed how good my predictions were !

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When Bob Coates agreed to support VLBI, little did he know that, in just a few years, these

requests would blossom into a major part of “his” Crustal Dynamics Project (CDP) !!!

It was this “Oktoberfest 1969” that was the “marriage” of the Haystack/MIT/Goddard VLBI Group

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Mark-1 used MANY Tapes!10,000+ during “Oktoberfest 1972”

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Student Activities during months spent at NRAO

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Mark-3 VLBI Gets it own Tee Shirt, courtesy of Kate Hutton.

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1975–81: Starting PPME & CDPPPME = The Pacific Plate Motion Experiment: A joint program between NASA & Japanese CRL.CDP = NASA’s Crustal Dynamics Project– Techniques = VLBI + Satellite Laser Ranging, later GPS + DORIS– Experimental Test of Plate Tectonics and the 1978 Minster-Jordan

Plate Motion Model– Regional Deformation along San Andreas Fault– UT1, Polar Motion, Precession, Nutation

Provided significant funding for development of Mark-3 Data Terminal and many VLBI stations.

$ $ $ $

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1970's: Bob Coates “creates” CDPBob knew the “NASA system” the driving force who generated the CDP Project Plan which at its peak was funded at a level ~25M$/yr.

Bob passed away in 2016. His passing was a major loss to what is now named the Space Geodesy

Program

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NASA’s Crustal Dynamics ProjectNASA’s CDP & NGS’s Polaris projects served as the focus for Space Geodesy (VLBI, SLR, GPS,

Doris) measurement programs & technical developments for the entire decade of the 80’s

September, 1981

New Telescopes, New Receivers, New Friends in the 1980s

In 1985, Rich Strand signed on as Station Manager and Chief Operator to make the 26m Gilmore Creek facility be the CDP's most productive station.

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Fairbanks, AlaskaSummer 1984

As project $$upport dried up in the new millenium, Rich (KL7RA) retired to the Kenai peninsula to build his “perfect” dream ham station.

Rich passed away in 2016.

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VLBI as seen by the public

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VLBI as seen by the public

Jim RyanMr. Data Analysis

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At Goddard, starting in the early 1970's, Jim Ryan and Chopo Ma

developed an efficient “machine” to analyze and catalog the large

volumes of data rolling out of the global network of VLBI stations.

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Some of the Significant VLBI Results: 1985 - 1990

Confirmed most features of 1978 Minster-Jordan Tectonic model, but with ~10% discrepancy in the Pacific – North America velocityAgreement with NUVEL global model very close.Earthquakes “measured” in Alaska and California.VLBI LOD shows close agreement with integrated wind field derived from global climate models.Free-core nutation of the Earth’s core detected with annual period and amplitude of ~ 2 mas.Etcetera . . . .

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The 25+ year history of US – Germany Plate Motion

Measured Rate = 16.85 mm/yr±34 μ/yr FSE

Jim RyanMr. Data Analysis

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Last summer Jim sent a message to his friends telling us that he had just been

diagnosed with Stage 4 Pancreatic Cancer.

Jim passed away a month later. We held a traditional Irish wake

and nourned his passing.

Remembering Departed Friends1993: Alan Yen – Inventor of the Canadian S2 System1998: Nick Renzetti – “Boss Man” of JPL/DSN 1999: Klemens Nottarp – Builder of Wettzell & O’Higgins2001: George Resch – VLBI Developer in DSN/JPL2006: Harold Hahn – Union chief & friend at Fairbanks2009: Bill Hudson – Mojave Crew Chief1988: NRAO 91M Telescope – Collapsed from old age1992: Richmond 18M Telescope – Hurricane Andrew1993: Hat Creek 26M Telescope – Wind damage2007: Hartbesthoek 26M Telescope – Bearing Damage

2015: Rich Strand

2016: Jim Ryan

2016: Bob Coates