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The end of the line for the Arecibo radio telescope

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schmitt trigger:
One of the side effects of the Cold War was that “big science” projects, if they even provided the remotest opportunity of enhancing “the National Security”, whatever that meant, would be funded. Large scale funding, no buts or ifs.

Neither the USA nor Russia have the political will to commit to such projects nowadays.  In this instance the baton is solidly in China’s hands.

Ian.M:
Its worth looking at https://history.nasa.gov/SP-4218/ch4.htm which covers the earlier history of the Arecibo dish.

The only comparable dish for long range deep space radar is in southern China: https://en.wikipedia.org/wiki/Five-hundred-meter_Aperture_Spherical_Telescope
Its only been online since 2017 and wasn't fully operational till the beginning of this year.  We are lucky not to have had a critical gap in Earth's planetary radar capabilty.

Can the Western world really afford to leave accurate orbit characterization of Earth crossing asteroid threats to the Chinese?   There aren't that many near equatorial suitable sites in countries that are firmly under Western world control, so IMHO rebuilding at Arecebo is well worth considering - its already got most of the ancillary infrastructure required and a prepared depression that just needs the scrap cleared out.

The dish was originally wire mesh (literally chicken wire) and was upgraded to aluminum panels in the early '70s to extend its capability to S band operation.  A wire mesh dish (or partially wire mesh with a high quality aluminum reflector in the center, elongated on its north-south axis) might be a cheap way of getting reasonable capability back into operation on the site.   Its possible that significant areas of the reflector panels could be salvaged safely for reuse.

The Arecibo feed platform needed to be as massive as it was because it was built with 1960's technology.    Modern composites would permit a much lighter structure, and modern electronics would permit a significantly smaller structure, so it could reasonably be lowered onto composite pylons protruding through the reflector to 'dock' it for maintenance and to withstand hurricanes.  Initially it could be lofted by a commercially available tower crane with its base located in the eastern or western quadrants of the reflector.  As funds allow, it could be upgraded to a suspension system similar to the previous one, but built with corrosion resistant materials.

David Hess:

--- Quote from: Ian.M on December 02, 2020, 08:40:23 pm ---The only comparable dish for long range deep space radar is in southern China: https://en.wikipedia.org/wiki/Five-hundred-meter_Aperture_Spherical_Telescope
Its only been online since 2017 and wasn't fully operational till the beginning of this year.  We are lucky not to have had a critical gap in Earth's planetary radar capabilty.
--- End quote ---

The Chinese dish lacks radar capability.  The article you linked even says so and I have heard the same from other sources:

Fifth, Arecibo's larger secondary platform also housed several transmitters, making it one of only two instruments in the world capable of radar astronomy.

Ian.M:
Thanks, David.

For effective radar, it isn't essential to transmit from the same antenna - one can use a phased array of much smaller remote dishes to form the transmit beam.  The downside is more wasted power and bigger side-lobes.  OTOH you *DO* need real dish surface area to improve the signal to noise ratio of the radar receiver. 

Whether or not that capability could easily and quickly be added to FAST would depend on what high bandwidth comms links they have to sync large steerable transmit capable dishes in the region.   Before Arecibo's failure there wasn't a great incentive to do so.

However I really shouldn't complain about your correction as it makes the case for an improved Arecibo rebuild with a fully movable feed platform (at least on a North/South axis) even stronger.

David Hess:

--- Quote from: Ian.M on December 02, 2020, 10:16:24 pm ---For effective radar, it isn't essential to transmit from the same antenna - one can use a phased array of much smaller remote dishes to form the transmit beam.  The downside is more wasted power and bigger side-lobes. 
--- End quote ---

You could have just said "bistatic radar".  :)

https://en.wikipedia.org/wiki/Bistatic_radar


--- Quote ---OTOH you *DO* need real dish surface area to improve the signal to noise ratio of the radar receiver.
--- End quote ---

The antenna aperture is just as important on transmit as receive.  If they had suitable transmitting dishes with enough aperture, then they would not need the larger dish.  I suspect in the case of radar it is more cost effective to use a larger dish with one large transmitter than to replicate the transmitters for many separate dishes.


--- Quote ---Whether or not that capability could easily and quickly be added to FAST would depend on what high bandwidth comms links they have to sync large steerable transmit capable dishes in the region.   Before Arecibo's failure there wasn't a great incentive to do so.

However I really shouldn't complain about your correction as it makes the case for an improved Arecibo rebuild with a fully movable feed platform (at least on a North/South axis) even stronger.
--- End quote ---

Or China will add that capability to their dish, although I get the feeling after reading various discussions that that will not be easy because it was not designed for it.

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