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Comment by Wololooo | Hacker News Reader

Even if I am not a radio astronomer, this instrument was unique in nature and still in use for very specific observations and until the very end of its operation was able to deliver data. It is disheartening to learn that it was indeed due to gross maintenance negligence (as assumed originally by many) that the final fatal failure occurred, when potentially the structure could have been salvaged.

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Losing Arecibo was, as I understand it, a big blow to the NANOGrav experiment, which is looking for very low frequency gravitational waves by measuring pulsar timing variations[1].

Albeit having limited field of view the Arecibo Telescope was very sensitive[2], and so could see pulsars that the other telescopes they used could not. And the longer they could collect data from a set of pulsars the lower frequency waves they could probe.

[1]: https://nanograv.org/news/15yrRelease

[2]: https://pirsa.org/20100068 Moving Closer to a Detection of nHz-frequency Gravitational Waves with NANOGrav (Arecibo details at around 10:20)

My uninformed recollection from when the warning signs were raised, is there was not even budget to perform emergency maintenance, and they were resigned to the inevitable collapse.

I worked and did research atobservatory for my PhD - you are exactly correct. It was well known to the scientists and onsite engineers that a collapse was imminent, for years. Ironically, prior to the collapse the agency responsible for funding performed a study to see would need to do to stop supplying money to the observatory, and found that due to environmental impact, it would actually be more expensive to stop funding. After that study we all suspected that the agency was just waiting for decay or a natural disaster to do the dirty work for them

Would you link the study you are referring to?

Sure - https://www.nsf.gov/mps/ast/env_impact_reviews/arecibo/eis/F...

That's not what the report says. There was ~$14 million allocated for repairs in 2-18 after Hurricane Maria, but the cable sockets weren't identified as needing repairs until the first one failed. The problem wasn't the money, it was the failure to identify the problem. See page 28/29.

What was unique about it compared to this one for example?

https://en.wikipedia.org/wiki/Five-hundred-meter_Aperture_Sp...

Arecibo did high power transmit for radar imaging of asteroids/comets/the sun/etc and ionosphere studies, among other things. FAST is not capable of transmit (it was not designed for it and the suspended receiver mass is much lower). Also, FAST has a RF-noise emitting theme park built just outside of it's grounds.

The uniqueness of Arecibo was this transmit coupled with such a large aperture (so small pattern on sky).

> Arecibo did high power transmit for radar imaging of

the Sun? that's something I never thought about, and now that I'm thinking about it, still seems very interesting. It seems like there would be so much noise radiating from the burning ball of fusion that radar signals would just get absorbed/lost. And now I've sat here for 5 minutes doing nothing but imagining this.

The sun is bright, but it's not bright all over in the lower VHF/UHF ranges. The quiet sun has a mimimum radio emission at about 50 MHz and then linearly (mostly) increases up to 10 GHz (and more). So at the lower frequencies radar echos can be detected as long as there are no active flares/etc going on. http://a.superkuh.com/radio-sources.jpg

Although it's emission (due to the transparence of it) is not just a disk but sometimes increases on the limb depending on frequency, http://a.superkuh.com/solar-disk_relative-brightness_vs_sola...

Here's a diagram of how the ray paths from an Earth based radar reflect from the soft target that is the sun, http://a.superkuh.com/what-solar-radio-looks-like.jpg

Thanks! To a layman it seemed like they were really similar devices.

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