U.S. planetary radar could get a boost from Green Bank Observatory


It was by chance that scientists were already playing with a demonstration of a new planetary radar system just as Earth was losing its most powerful instrument.

Well, serendipity and a fervent desire for more radar sightings of everything from asteroids hang out close to Earth to the frozen moons around the most distant planets. And the facility behind the experiment, the Green Bank Observatory in West Virginia, has enough history with planetary radar systems to want to play a new role in the field. The result is a tantalizing new image of a historic location on the most familiar solar system object of all, the moon. Scientists hope the image justifies the permanent installation of a much more powerful radar transmitter on the observatory’s main telescope, the Robert C. Byrd Green Bank Telescope.

“We have had absolutely fantastic results,” Karen O’Neil, Director of Green Bank Observatory site, said of the demonstration project at a panel discussion on Jan.21. small objects in the solar system like asteroids and which will inform the committee of the national academies which prepares the document which will shape the priorities of planetary science for the next decade.

Related: Loss of giant Arecibo dish makes humans more vulnerable to space rocks, scientists say

The recent radar experiment had been in preparation for a decade. And the installation is lighthouse radio telescope, the 300-foot (100-meter) satellite dish has partnered with radar transmitters in Puerto Rico and California over the years. So why not go further and create the signals themselves?

“It’s kind of a part of radio science that we’ve been involved in at some level for a very, very long time,” Tony Beasley, director of the National Radio Astronomical Observatory, who built the telescope. “About 10 years ago, there was growing interest in thinking about other roles and areas of radio science that Green Bank could get involved in, and so radar was an obvious candidate.”

The case of radars

Radar astronomy takes place in two parts: scientists must first create the radio beam to bounce off the mysterious object, then study the relatively weak echo that returns, deciphering the surface, shape and location of the object. the object.

The stages can occur on the same satellite dish as it converts quickly between send and receive modes, or two radio installations can team up, one producing the radar beam and the other ready to collect the return signal. . When Green Bank began planning its demonstration project, it had never sent radar signals itself, but had functioned as a receiver for America’s two major planetary radar transmitters.

At the time, there were two such transmitters: one at the Arecibo Observatory in Puerto Rico and one at NASA’s Goldstone Deep Space Communications Complex in California. But in December, Arecibo’s radio telescope science platform – including its transmitter – crashed after cable failures in the facility, ending its tenure.

Planetologists will continue to feel this loss, even if the Green Bank project turns into a full-fledged emitter. The Green Bank Interim System is not designed to replace Arecibo, since no one realized that the Puerto Rican installation was coming to an end; instead, it was designed to collaborate with Arecibo and Goldstone.

A photograph of the Green Bank Telescope taken in July 2020. (Image credit: NSF / GBO 20)

“The program that we developed was really built and designed in a way to complement the existing US radar infrastructure,” Beasley said. “Certainly the thing we’re talking about producing has some relevance for a post-Arecibo world, but in no case will it replace Arecibo. “

And it is not known whether the loss of Arecibo will influence the fate of the Green Bank project. The National Science Foundation (NSF), which owns both the Green Bank and Arecibo sites, plans to assess the project, acknowledging the recent loss but not scrambling to bolster its radar capability.

“If some abilities are lost, there is always the question of where would those abilities come from? Is there anything else that can continue something like this? Harshal Gupta, NSF program director for the Green Bank Observatory, told Space.com. “It is independent of what was happening in Arecibo. Now, considering what has happened, when fully developed, it might offer some of the capabilities that the planetary community might be able to use. But again, these two are two separate things. ”

A new image created using a demonstration radar transmitter at the Green Bank Telescope in West Virginia and receivers from the Very Long Baseline Array, captured in November 2020. (Image credit: Sophia Dagnello / NRAO / GBO / Raytheon / AUI / NSF / USGS)

Demo and design

The years of interest were here and the numbers looked promising. But before Green Bank embarked on a full-fledged planetary radar project, astronomers wanted to test the waters. To do this, scientists built a miniature transmitter, powered at less than a kilowatt and the size of a refrigerator, Beasley said, and transported it in November for a brief stint at the main focus of Green’s telescope. Bank, suspended above the large plate.

Then, the team took advantage of the telescope’s superlative: it is the largest fully steerable radio telescope in the world, capable of studying objects over 85% of the sky. So the team pointed the telescope and shot the radar system at the moon – more specifically, at the Apollo 15 mission landing site in the Hadley-Apennines region. The team used antennas from NRAO’s Very Long Baseline Array (VLBA) to pick up the bounced signal.

The image, with its sloping hills, austere crater, and stealthy groove, offers a glimpse of what could happen. But the moon is our old companion. Scientists would much rather use a shiny new planetary radar system to study more mysterious objects, like the asteroids that pass through our solar system neighborhood, most of which are blurs and specks, or the strange moons of the outer planets that have received few visitor spaceships.

“Now we’re just thinking about the next step,” Beasley said.

The Green Bank Telescope is the world’s largest fully steerable radio telescope. (Image credit: R. Creager / NRAO / AUI / NSF)

There are several options to consider when deciding what a system would look like, Beasley and O’Neil pointed out. Scientists believe they will continue to use a separate radio network to pick up the return signal, rather than housing that also operates at the Green Bank Observatory. For now it would be VLBA, but if a new generation Very large painting happens to be, the antennas for this system would be even more promising receivers, O’Neil said.

Two key factors that influence precisely what a radar system can do are the power of the transmitter and the specific frequency of the radio waves that produces. Green Bank is studying a transmitter that would use tens or hundreds of times more power than the demonstration instrument and operate at one of two frequencies. He’s also looking to use new transmitter technology, which would be more compact and, scientists hope, less finicky to operate.

Given the design parameters scientists are currently considering, the system would be able to study objects in a much larger swath of the solar system than existing systems, including on bizarre icy moons. “You’re increasing the volume you’re looking for in the solar system by an order of magnitude,” Beasley said. “It’s a substantial increase, so we’re very excited about the possibility there.”

There are of course logistical issues, and these could be a key issue for Green Bank, which is an extremely popular instrument and already does not have the time to do whatever scientific researchers would like. Typically, the telescope has observed two or three objects per year through its radar partnerships with Arecibo and Goldstone; Beasley said if the transmitter project came to fruition, the facility could spend about a third of its time on the radar.

All in all, a full-fledged project would reshape planetary radar, the scientists said.

“The capabilities we’re talking about are something that will surpass anything we’ve been able to do in the past with planetary radar astronomy,” O’Neil said. “We’re talking about something that has pretty amazing potential for planetary radar and really a system that has the ability to take us forward, I would say, into the planetary radar capability of the United States. It’s fun. to think about and pretty amazing to talk about. “

If the project continues and Green Bank installs a full-power radar transmitter, it will likely go live no earlier than perhaps 2024, depending on how quickly the funding – likely “in the tens of millions of dollars. “said O’Neil – meets. .

Gupta of the NSF said he was happy to see the protest’s success and can’t wait to see what happens next at Green Bank.

“All indications are that there are great promises. The first tests are excellent and there is great potential,” he said. “The big picture becomes clearer as science is done, as technology is developed. So I will simply say that there are unforeseen advances, unforeseen opportunities. Ultimately that would be exciting and we’ll see how it plays out. “

Email Meghan Bartels at mbartels@space.com or follow her on Twitter @meghanbartels. Follow us on Twitter @Spacedotcom and on Facebook.

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