April 23, 2021

This Week in Amateur Radio

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Via HACKADAY: Eulogy To Arecibo: With Demise of a Unique Scientific Facility, Who Will Carry The Torch?

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Few telescopes will get an emotional response from the general public when it is ultimately announced that they will be decommissioned. In the case of the Arecibo Observatory in Arecibo, Puerto Rico, the past months has seen not only astronomers but also countless people across the world wait with bated breath after initial reports of damage to the radio telescope’s gigantic dish.

When the National Science Foundation announced that they would be decommissioning the telescope, there was an understandable outpouring of grief and shock. Not only is Arecibo a landmark in Puerto Rico, it is the telescope from iconic movies such as GoldenEye (1995) and Contact (1997). Its data fed public programs such as the Seti@Home and Einstein@Home projects.

Was Arecibo’s demise truly unavoidable, and what does this mean for the scientific community?

What Defines Arecibo

The Green Bank Telescope.

The real question is, what have we lost? Are there successors to Arecibo that are able to fill the very large gap now facing the scientific community? Looking at the aspects of the telescope that made it unique helps us find those answers.

Telescopes are essentially highly sensitive instruments for observing remote sources of electromagnetic radiation. In the case of optical telescopes, this means the visible part of the EM spectrum. Radio telescopes work in a similar way but are tuned to receive radio frequencies. Arecibo was capable of capturing between 1-10 GHz with multiple receivers using an effective 221 meters of its 304 meter diameter. Much like how an optical telescope’s primary mirror largely determines how much light will ultimately reach the sensor, so too does the size and shape of a radio telescope’s primary mirror (dish).

Most telescopes can be adjusted to point the reflector at different parts of the sky. This is mostly a matter of what mechanics and engineering allow, with the Green Bank Telescope in West Virginia currently the largest fully steerable radio telescope with a dish diameter of 100 meters. Puerto Rico’s Arecibo and China’s FAST radio telescope have fixed reflectors that make use of natural depressions in the terrain left by a karst sinkhole. Within this bowl-shaped depression the elements that make up the dish are installed, largely following those contours, with a moveable receiver array to aim the telescope. While convenient, this limits the view of these telescopes to a fairly narrow part of the sky.

The illuminated area of the FAST telescope on the primary dish.

Both newer and physically larger, it would seem obvious that China’s FAST telescope is superior to Arecibo, this is not entirely true. Arecibo’s dish reflectors are mounted in place more rigidly than FAST’s. While the latter is more flexible with winches able to adjust the shape of the reflector mesh, this comes with trade-offs at these higher frequencies. Even with upgrades to FAST’s receivers similar to the upgrades which Arecibo received in 1997, FAST would only be able to cover frequencies up to about 5 GHz, only half of Arecibo’s performance.

In addition to these properties, there is also the question of radar astronomy, which requires the transmission of powerful radar signals. Arecibo has four radar transmitters, of 20 TW (continuous), 2.5 TW (pulsed), 300 MW and 6 MW. These take up a significant amount of space, and therefore cannot be mounted in FAST’s secondary platform alongside its receivers due to weight and space concerns. Arecibo is only one of two telescopes that have seen regular use in radar astronomy, the other being the 70 meter Goldstone Solar System Radar, with a 500 kW transmitter.

With the detection of asteroids and comets being an essential part of Arecibo’s radar astronomy duties (tracking & early warning system), this has left a major blind spot. Without Arecibo, we have to mostly rely on optical telescopes to track these objects as they hurtle through the solar system.

The Infrastructure Budget Dance

Perhaps not surprisingly, Arecibo is a Cold War artifact, envisioned as part of an anti-ballistic missile (ABM) shield. Installations like Arecibo would provide detection duties, being presumably sensitive enough to filter out the real warheads from the fake ones within a MIRV ICBM from their radar signature. Without a solid understanding of the exact physics of a re-entering ICBM, Arecibo was part of an ARPA-led effort to fill in the knowledge gaps here.

As the Cold War dragged on and priorities shifted before the final dissolution of the Soviet Union, Arecibo saw itself placed in a situation not dissimilar to the rust and flaking paint-covered marvels of the Soviet Union. Unneeded as a military asset, it saw its operational budget reduced year over year. Even with asteroid research as one of its unique mission profiles, in 2001 NASA announced that they would cut funding by 27% and ‘encouraged’ the National Science Foundation (NSF) to fund the $11 million budget of the whole program.

In 2007, the NSF announced that due to their own budget being reduced, they would have to close Arecibo unless other sources of funding could be found. Of note here is that Puerto Rico itself is rather poor, with its government not having the financial means to support even such an iconic telescope, and no senators in Washington DC to lobby on its behalf due to Puerto Rico not being a US state.

NASA funding for the telescope was restored in 2010, with an increase in 2012 to $3.5M/year. Despite this, the NSF made changes to the way Arecibo Observatory was run during this period, seeking commercial and other partners and removing Cornell University from the project. By 2015, the NSF was signalling that it was looking at decommissioning the facility.

When hurricane Maria damaged the 430 MHz feed line and part of the primary dish in 2017, a consortium led by the University of Central Florida (UCF) managed to stave off the observatory’s decommissioning through financial support, but then on August 10th, 2020, one of the secondary platform support cables broke, damaging the primary dish and the receiver platform.

As the decades of limping on with a minimal operating budget caught up with reality, November 7th saw a second cable snap, further damaging the primary dish. After engineers examined the facility following this second accident the statement to the press said that:

Preliminary analysis indicates the main cable, which failed on November 6, should have easily handled the extra load based on design capacity. Engineers suspect it is likely that the second cable failed because it has degraded over time and has been carrying extra load since August.

All of this seems to point towards the lack of a maintenance budget leading to the situation where the many cables of the Arecibo Observatory were not regularly inspected, maintained, or replaced. Especially in a fairly humid and warm climate like that of Puerto Rico where the corrosion of steel cables would be accelerated, a lack of maintenance would have caused reductions in carrying capacity.

What Could Have Been

Arecibo Observatory from the air in happier days.

A major problem with scientific installations like Arecibo is that they are not flashy or cool enough to warrant a constant flow of funding, with some Administrations worse than others. The main reason is that a lot of science involves mostly waiting, digging through years worth of data, more waiting and crunching more numbers and running models in the hope that you see a theorem confirmed.

When a politician or the average person on the street is asked what their thoughts on Arecibo’s demise are, it’s unlikely that many could sum up what the facility was used for, and why its loss is felt far beyond the astronomy community.

The Ángel Ramos Foundation Visitor Center located near the observatory was opened in 1997. It serves as an educational center with exhibits and displays not only about the Arecibo Observatory, but also astronomy and the atmospheric sciences. With the loss of the observatory the future of this center and the role of Puerto Rico in astronomy is put very much into doubt.

For the Future

In a world where some individuals count their worth in billions and Wall Street marks is progress in trillions, the operation and maintenance budget for a facility such as Arecibo is microscopically small. Despite that, there seems to be no indication that the decision to decommission Arecibo will be reverted. Whether or not a replacement facility will be built in Puerto Rico or anywhere in the US is still left up in the air at this point.

All that we know for certain right now is that despite its different geographical location and lack of radar transmitting capacity, the FAST telescope along with a host of smaller radio telescopes will be able to pick up most of the slack there. Due to China’s treatment of large scientific projects as a sign of prestige, in addition to building FAST, they are also scheduled to bring the country’s fully steerable 110 meter Qitai Radio Telescope online in 2023, which would make it the largest of its kind in the world.

One can only hope that the US and others take the bait and begin a friendly competition with China on building the best, most useful telescopes and other scientific projects to further humankind’s reach to the stars. Because in the end, having only crumbling sites like Arecibo to show for one’s economic prowess isn’t worth much at all when that one large asteroid manages to not avoid Earth.

Read more – via Blog – Hackaday https://hackaday.com/2020/11/24/eulogy-to-arecibo-with-demise-of-a-unique-scientific-facility-who-will-carry-the-torch/

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