TDRSS Space VLBI Jim Ulvestad

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TDRSS Space VLBIJim Ulvestad
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DSN Engineering Experts

• Gerry Levy was Captain of TDRSS
• Key technical and scientific contributions from
  JPL
• Roger Linfield Ph.D. in radio astronomy in 1981,
  started first real job at JPL in 1983
• Chad Edwards Ph.D. in particle physics in 1984,
  started first real job at JPL in 1984
• Jim Ulvestad Ph.D. in 1981, started first real
  job at JPL in 1984 (same day as Edwards)
• Lesson Get two smart people and one stubborn one
  to make difficult experiments work

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TDRS Satellite Sketch

• TDRSS was used exclusively for communication with
  Space Shuttle
• Only one TDRSS in orbit in 1986
• Challenger accident made TDRSS more available

eA 0.4 Tsys 320 K ?? 14 MHz
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TDRSS Observing Geometry

• Geostationary orbit above Atlantic Ocean,
  downlink to White Sands, New Mexico
• Downlooking satellite required telescopes on
  opposite side of Earth

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TDRSS Block Diagram
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TDRSS Classification Agreements

• White Sands is a classified facility
• TDRSS tapes classified as sensitive
• Northern Hemisphere was classifiedobserving
  sources in Northern Hemisphere was not allowed

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Allowed Observing Window 1986

• North not allowed
• Software limit prevented observing more than 14
  degrees from Earth center
• Earth subtends 9 deg. radius

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First Fringes TDRSS-DSS43

• One dark and stormy Friday night!
• Fringe rate 0.3 Hz (window 1 Hz)

• Found TDRSS-Usuda later in the weekend

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TDRSS Coherence Measurements
Link
Cs-H
Orbit only
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Second 2.3 GHz Experiment 1987

• Still limited to Southern Hemisphere, but
  observed up to 31 degrees from Earth center
• Detected 23/24 sources with baselines up to 2.15
  Earth diameters

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Best (u,v) Coverage

• (u,v) coverage and amplitude plots for 0727-115

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Important Japanese Contributions to TDRSS
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Hiracelli Congratulated by Pope

• VSOP-2 approved as science mission by JAXA

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TDRSS 15 GHz Experiment

• Experiment cooked up at MIT faculty club in
  1987 (IAU 129)
• Copies of VLBA 15 GHz receivers constructed by
  MIT and installed at DSS 43 and Nobeyama
• Northern Hemisphere opened up
• Detected 11/22 sources

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What Did TDRSS Demonstrate?

• Clocks can be transmitted to the spacecraft and
  corrected using a two-way link
• Coherence can be reasonably high even with a
  system not designed to do VLBI
• VLBI correlation is practical using a spacecraft
  orbit
• Many sources are detectable on baselines longer
  than an Earth diameter, even with an insensitive
  telescope
• References Levy et al. Science, 234, 187 (1986)
  ApJ, 336, 1098 (1989) Linfield et al. ApJ,
  336, 1105 (1989) ApJ, 358, 350 (1990)

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The TDRSS Captain Gerry Levy
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A Second TDRSS Leader Morimoto
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Two Lessons to Remember

• If you want to give a history talk in 20 years,
  make sure you publish the papers now!
• One thing that tells me a company is in trouble
  is when they tell me how good they were in the
  past. When memories exceed dreams, the end is
  near.
• Michael Hammer, quoted in The World is Flat,
  by Thomas Friedman

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A Third TDRSS Leader Hirax

• Hirax leads by example, and with humility rather
  than with arrogance
• Congratulations on retirement