GPS, Flying Clocks and Fun with – genius clockmaker – marine chronometer, accurate • Longitude

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  • November 2018 SCPNT/Stanford 1

    GPS, Flying Clocks and Fun with Relativity

    Tom Van Baak (tvb) www.LeapSecond.com

    “Time Nut”

  • November 2018 SCPNT/Stanford 2

    Outline

    • Part 1 – Navigation and traveling clocks • clocks, timing, the ‘T’ in PNT

    • Part 2 – GPS and relativity (time dilation) • so good it needs clock corrections

    • Part 3 – Atomic clock collecting hobby • going to extremes at home

    • Part 4 – Project GREAT • a DIY gravitational time dilation experiment

  • November 2018 SCPNT/Stanford 3

    Chronometers at sea

    • Who is this? – John Harrison

    • Why all the clocks? – genius clockmaker – marine chronometer, accurate

    • Longitude prize winner – 1759 (250+ years ago) – he put the “T” in PNT

    • Read.the.book – by Dava Sobel

  • November 2018 SCPNT/Stanford 4

    Chronometers at sea

    • Who is this? – John Harrison

    • Why all the clocks? – genius clockmaker – marine chronometer, accurate

    • Longitude prize winner – 1759 (250+ years ago) – he put the “T” in PNT

    • Read.the.book – by Dava Sobel

  • November 2018 SCPNT/Stanford 5

    Chronometers at sea

    • Who is this? – John Harrison

    • Why all the clocks? – genius clockmaker – marine chronometer, accurate

    • Longitude prize winner – 1759 (250+ years ago) – he put the “T” in PNT

    • Read.the.book – by Dava Sobel

  • November 2018 SCPNT/Stanford 6

    Chronometers at sea

    • Who is this? – John Harrison

    • Why all the clocks? – genius clockmaker – marine chronometer, accurate

    • Longitude prize winner – 1759 (250+ years ago) – he put the “T” in PNT

    • Read.the.book – by Dava Sobel

  • November 2018 SCPNT/Stanford 7

    Cesium “chronometers” by air

    • Who is this? – Len Cutler, hp clockmaker

    • See the clock? – hp 5060A cesium atomic – batteries & “digital” clock

    • Mission? – time synchronization – cross-country – round-the-world – 1960’s “flying clock” era

  • November 2018 SCPNT/Stanford 8

    Cesium “chronometers” by land

    • Who is this? – hp field engineer

    • See the clock? – hp 5061A cesium – atomic clock

    • Marketing ad – year 1967 – self-contained – portable, rugged – accurate 1μs/month

  • November 2018 SCPNT/Stanford 9

    Flying clocks around-the-world

    • Who is this? – J.Hafele & R.Keating

    • See the clocks? – 4 @ hp 5061A – backup DC power – time interval counter

    • Relativity experiment – year 1971 – commercial flights – RTW, twice! (6 days)

  • November 2018 SCPNT/Stanford 10

    Outline

    • Part 1 – Navigation and traveling clocks • clocks, timing, the ‘T’ in PNT

    • Part 2 – GPS and relativity (time dilation) • so good it needs clock corrections

    • Part 3 – Atomic clock collecting hobby • going to extremes at home

    • Part 4 – Project GREAT • a DIY gravitational time dilation experiment

  • November 2018 SCPNT/Stanford 11

    Ultimate “flying” clocks: spacecraft

    • GP-A • NTS-2 • NAVSTAR / GPS

  • November 2018 SCPNT/Stanford 12

    First space test was GP-A

    • Gravity Probe “A” • 1976, first H-maser in space

    – Robert Vessot, clockmaker • Successful test of relativity

    – science mission – launched to 10,000 km – 2 hour flight up / down – 60 ppm accuracy

  • November 2018 SCPNT/Stanford 13

    First orbital test was NTS-2

    • “Navigation Technology Satellite” • 1977, first cesium in orbit

    – Robert Kern, clockmaker • Successful test of relativity

    – pre-NAVSTAR (GPS) – 12 hour orbit – similar relativity as GPS – cesium clocks, synthesizer

  • November 2018 SCPNT/Stanford 14

    Relativity in NTS-2

    • Plots for NTS-2 • 4.425×10-10 = 38 μs/day

  • November 2018 SCPNT/Stanford 15

    32 atomic clocks in space: GPS

    • What’s this? – GPS IIR-M – present era

    • 250 year evolution – from Harrison

    to GPS – now many GNSS

    • Clock accuracy – from seconds/day

    to nanoseconds/day

  • November 2018 SCPNT/Stanford 16

    Relativity in GPS

    • GPS orbits are extreme: speed 14,000 kph, 8,700 mph (Mach 12) altitude 20,000 km, 12,500 miles (~3× Re) N.B. GPS speed is only 0.000013 c, “13 μc”

    • Large relativistic effects occur: Δf/f is −8.4×10-11, or −7.3 μs/day (kinematic) Δf/f is +5.3×10-10, or +45.6 μs/day (gravitational) Δf/f is +4.4×10-10, or +38.3 μs/day (net effect) 1.023 MHz set to 10.2299999954326 MHz

  • November 2018 SCPNT/Stanford 17

    How small is 4×10-10 ?

    • Relativity correction: 4.4647×10-10 (fractional frequency offset) 38.575 μs / day (time interval ratio units) ~1 ms / month 1 s / ~71 years

    • In “newspaper” units: ~6 inches / distance to Moon ~1 atom / 1 meter ~1.4 m2 / area of Rhode Island ~1 cm3 / volume of Olympic swimming pool

  • November 2018 SCPNT/Stanford 18

    Relativity at human scale: SR

    • GPS velocity 14,000 kph, 8,700 mph (Mach 12) Δf/f is −8.4×10-11, or −7.3 μs/day (kinematic)

    • Human-scale velocity −3×10-13, 0.02 μs/day – flying (500 mph) −4×10-15, 0.0003 μs/day – driving (60 mph) −1×10-17, 0.0000008 μs/day – walking (3 mph)

  • November 2018 SCPNT/Stanford 19

    Relativity at human scale: GR

    • GPS altitude 20,000 km, 12,500 miles (~3× Re) Δf/f is +5.3×10-10, or +45.6 μs/day (gravitational)

    • Human-scale altitude +9.6×10-13, 0.083 μs/day – Mt. Everest (8848 m) +1.7×10-13, 0.015 μs/day – Denver, CO (1 mile) +9.5×10-15, 0.00082 μs/day – Hoover tower (285 ft)

    • “down to earth” relativity – Denver 3000× less than GPS

  • November 2018 SCPNT/Stanford 20

    Outline

    • Part 1 – Navigation and traveling clocks • clocks, timing, the ‘T’ in PNT

    • Part 2 – GPS and relativity (time dilation) • so good it needs clock corrections

    • Part 3 – Atomic clock collecting hobby • going to extremes at home

    • Part 4 – Project GREAT • a DIY gravitational time dilation experiment

  • November 2018 SCPNT/Stanford 21

    Precise time as a hobby (1994)

  • November 2018 SCPNT/Stanford 22

    How to keep time?

    • “Timebase” required (quartz oscillator) – how accurate is it? – how to measure it?

    • Use frequency counter – how accurate is it? – how to measure it?

    • Use a reference standard – how accurate …

  • November 2018 SCPNT/Stanford 23

    Timebase accuracy

    • 0.01 / 10.00 MHz = 0.1% (90 sec/day) • 0.0001 / 10 MHz = 10 ppm (1 sec/day)

  • November 2018 SCPNT/Stanford 24

    The quest for better oscillators

  • November 2018 SCPNT/Stanford 25

    The quest for more digits

  • November 2018 SCPNT/Stanford 26

    The quest for larger time lab

  • November 2018 SCPNT/Stanford 27

    Slippery slope!

    • I started www.LeapSecond.com – to share photos, data, software, lab reports, manuals

    • Then created the “time-nuts” mailing list – now 1800 ‘nuts interested in amateur precise time – like amateur astronomy, seismology, etc.

    • Relatively inexpensive, time-consuming hobby – measurement concepts work at $1 as well as $1000 – easy to buy, repair, trade, collect interesting gear – massive trove of military and telecom surplus (eBay)

  • November 2018 SCPNT/Stanford 28

    Vintage hp 5061A (eBay)

  • November 2018 SCPNT/Stanford 29

    Extremely wide range of precision

    • 10-2 = 1% ≈ 15 min / day • 10-4 = 0.01% ≈ 1 min / week • 10-6 = 1 ppm ≈ 0.1 s / day • 10-8 ≈ 1 ms / day • 10-10 ≈ 10 μs / day • 10-12 = 1 ppt ≈ 100 ns / day • 10-14 ≈ ~1 ns / day ≈ 1 s / 3,000,000 years • 10-16 ≈ ~3 ns / year ≈ 3 s / billion years

  • November 2018 SCPNT/Stanford 30

    10-2 heart beat

    • The original ‘1 PPS’ • 10% stability at night, long-term • 1% stability possible, short-term

  • November 2018 SCPNT/Stanford 31

    10-4 tuning fork, mains

    • Mechanical oscillator transistorized • “Four 9’s”

  • November 2018 SCPNT/Stanford 32

    10-4 tuning fork, mains

    • Power line frequency: 60± Hz

  • November 2018 SCPNT/Stanford 33

    10-6 quartz watch, chronometer

    • +160 ms/d = +1.85 ppm

  • November 2018 SCPNT/Stanford 34

    10-6 quartz watch, chronometer

    • Conservatively rated ¼ sec/day deviation

  • November 2018 SCPNT/Stanford 35

    10-8 pendulum clock, earth

    • Shortt-Synchronome • 1 second / year

  • November 2018 SCPNT/Stanford 36

    10-8 pendulum clock, earth

    • ~1 second / year, irregular

  • November 2018 SCPNT/Stanford 37

    10-10 ovenized qua