Two Dishes at Jamesburg?

FAX Coversheet Tells of an Unknown Future – by Robert Brand

Look carefully at the facsimile cover sheet below and you will see two dishes at Jamesburg. One is in front of the other slightly obscuring it, but two dishes are certainly shown. There was only one that was ever constructed. Why? An artist’s whim? No!

It goes back to the time that the station was being planned. Pure and simple, they did not know whether a geostationary satellite was going to work and this was the alternative. A series (constellation) of low earth orbit satellites in polar orbit.

The fax  sheet above refers to BER tests between Hong Kong and Jamesburg conducted via the Pacific Ocean Intelsat on 19th Sept 1989. They still used the cover sheet that was designed in the early days.

The fall back position for a polar orbit constellation of satellites was simply that one dish would track a satellite from north to south and before it disappeared another would appear over the horizon and the second dish would acquire the signal and track it. Meanwhile the other dish would disengage from its track and return to the north ready to acquire the next satellite.

This game would need to be played at all sites around the pacific and there would be a point where all stations in range would switch to the new craft. This also meant that the Jamesburg dish is a very high speed large dish capable of tracking low earth orbits – unusual for a dish of this size (97 feet in diameter – 30 m). One benefit would be that the constellation would also be used over other oceans and land masses as they orbited.

Intelsat was launched in a stable geosynchronous orbit and the second dish was never installed otherwise Moree and other satellite stations would have also needed 2 dishes. I expect the planning for Jamesburg well and truly preceeded that of the Australian Moree earth station. I have had long conversations with Jack Ramey (listed on the fax). about the dish’s capabilities. Jack has been amazingly helpful and I expect that Jack is hoping that it may someday go back into service.

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4 thoughts on “Two Dishes at Jamesburg?

  1. It is the dish at the forefront of the fax sheet that was not installed. The rear dish is the one that is installed and on site. You can click on the images to see in large format.

  2. I wonder if the 100ft Ceduna 1 dish was also specified for this capability?
    It had a tracking speed of an incredible 0.3 degrees per second in both Az & El, although I only ever once saw it run in “full flight”, and then quite by accident. I always understood this was to enable the dish to track launches coming over the eastern horizon, as back when it was built, Ceduna was the first ground station to be able to communicate with the launch vehicles as they came back into radio contact having passed through the atmosphere.
    Harking back to my “accidental” full speed operation of the duoble drive motors, – during my early days at Ceduna, as a TO1 and still quite fresh out of training, – Ceduna 1 had a very rare “out of service period” just after the 30m Ceduna 2 facility was brought online. I was given the task of the full “service book” maintenance routine on the Ceduna 1 Synchro Resolver Manual Control Panel, which I diligently set about at the start of my maintenance day shift. Unfortunately I forgot to manually lock the brakes on.. End result, with a gently breeze running throughout the day, the dish was gently “blown around towards the POR”, in stark contrast to where it should have been – on the IOR. Towards the end of my shift I was initially quite pleased with myself, having got through the massive task of dismantling, cleaning and re-assembling all the “clockwork” components of the synchro resolvers and the manual control wheels, getting everything back together in the precise “pointing” position, – ready to put the large synchro resolver chassis back into the rack and “plug it back in”. Going around the end of the control room rack suite however to reconnect the myriad of massive Cannon connectors, I glanced out the window where, – to my horror I saw the 100ft dish “pointing” the other direction. Now I had a problem! What was going to happen if I plugged the syncro resolver antenna position controller back in?
    I figured one of 3 things.
    1) Emmission of “Grey electrons”, – hmmm quite possible.
    2) A screaming rotation of the syncho resolvers in the controller to bring it back into alignment with the actual position of the dish, or
    3) Maybe, just maybe, the antenna would drive back to align with the controller.
    End of shift! What to do? Nothing ventured, nothing gained! Plug it in!
    Every-one stood around to watch me suffer under utter humiliation. No-one breathed while I plugged it in and swithed the power back on, – but to everyone’s amazement, None the least my own, the dish motors arced up to full speed and literally screamed. Much to my relief, – the Ceduna 1 antenna drove back to its IOR pointing location, only slowing momentarily as it converged with the synchro resolver positions and the Nixi Tube display positions in the controller.
    I had lived to learn another day!
    Thanks to my many mentors and “associates in crime” including: “JG”, “ERW”, “BLA”, “PWB”, “PM”, “CE”, just to name a few.
    Those were good times indeed.

  3. The Jamesburg antenna had an acceleration rate of 1° per second per second and a tracking velocity of 1° per second when it was originally built using a five horn multipulse tracking system. Each axis had two 20 hp 5000 rpm DC motors driving it. When they put in the step tracking system the motors were replaced with 20 hp 3600 rpm AC motors. This slowed the antenna down to approximately 0.7° per second.

    • Hi Jack – for those that do not know, Jack is one of the Jamesburg staff that has been there from the start. He can tell you about the plans for two dishes. Good to see you mention the speed here!

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