A Visit To The Most Important Survey Telescope Ever Built

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Riding through the northern Chilean Andes, an incredibly rugged swath of desert that I’m sure in times gone by has tried men’s souls —- no one would ever suspect they were about to enter a prime ground-based window onto the Universe. It’s hardly the kind of landscape that evokes oohs and aahs for its beauty. But this dust-ridden land is home to some of the world’s greatest observatories. And by night, it offers an aperture onto the center of our own Milky Way and far-flung galaxies that literally stretch back to the beginning of time. 

My driver and I, however, are headed to the $473 million Vera Rubin Observatory, formerly known as the Large Synoptic Survey Telescope (LSST), which has been under construction since 2014. This 8.4 meter extremely wide-field telescope is completely unprecedented, never before possible and never before attempted.

In just its first year of operation, the LSST organization says that the telescope will see more asteroids, stars, quasars, and galaxies and issue more alerts than all previous telescopes combined. 

Known as a single wide-deep-fast sky survey, from its mountaintop vista at Cerro Pachon, the LSST will probe dark energy, dark matter, and find new objects within our own solar system. The telescope is also ideally suited for mapping the structure and content of our own Milky Way in order to definitively answer basic questions about our galaxy’s structure and accretion history. 

Arriving at El Pachon’s base, the futuristic structure looks like it’s come from an alternate science fiction universe of exotic, barren planets around someone else’s star. But the grind and noise of the construction ensures it’s real alright.

As for addressing the big questions of what’s causing the Universe’s so-called dark matter and dark energy, the LSST will be able to go very much further and fainter and cover the entire southern sky. It will measure the motions of billions of galaxies over cosmic time to see how their acceleration has slowed, sped up and changed over the eons. 

I put on a hard hat and take an elevator up to the main office, where LSST Project Manager Victor Krabbendam is waiting to show me around for the better part of an afternoon.

At first glance, the interior of the telescope’s dome and its ancillary workshops quickly take on the air of heavy industry rather than pure science. But pure science is what this massive structure will facilitate and in a way that the professional astronomical community has never, ever experienced.  

But standing on a platform overlooking a massive room that could easily be mistaken for the inside of a plant that manufactures industrial turbines, Krabbendam adroitly tells me how and why the observatory’s structure was designed the way it is.

Our optical design has celestial light going to the primary mirror, then up to a secondary mirror, then down to a third mirror and then up to the camera, says Krabbendam. We’re looking at 3.5 degrees of sky in every image, taking two pictures every 30 seconds, he says.   

The telescope will track any changes in brightness or position from image to image over times scales that range from 10 seconds to 10 years. If anything has moved, or it’s a different brightness, alerts will go out within two minutes, says Krabbendam. So, there will be thousands of alerts per hour and they will go out worldwide, he says.

To take so many images so frequently over a ten year period means that the telescope’s mount has to be able to slew (or pivot) from one position to the next within five seconds. 

From shutter closed to shutter open, it’s very important that we don’t spend too much time at any given position, says Krabbendam.

As for the biggest technical challenge?

Surprisingly, Krabbendam doesn’t mention the complicated multilevel structure or the remote construction site, but rather the telescope’s jewel in the crown —- a $168 million dollar digital camera currently in the process of being constructed by crews at the U.S. Department of Energy’s SLAC National Accelerator Laboratory in California. It’s not due to be attached to the telescope until after it arrives sometime in late 2021.   

Just recently, SLAC tested the camera by taking the largest digital photo ever in a single shot —- a 3,200-megapixel image the likes of which no one has ever attempted. Once attached to the telescope, the camera’s 189 sensors will create panoramas of the whole southern sky every few nights over a ten-year period.

Question is, how will astronomers be able to process all that data?

Krabbendam points to the room next door in which several of they are at a bank of computer screens in what will be the telescope’s future control room. Krabbendam says the team is already working on developing new algorithms in order to ensure that astronomers who access the observatory’s data can effectively use it for their research. 

Which is further along, the needed computational astronomical data analysis, or the LSST’s team to take snapshots of these pics at an amazing wide angle?

I am pretty confident that when we go on the sky we will be able to handle the data coming off the camera, Robert Lupton, a Princeton University astrophysicist and LSST team member, told me. We will make sense of it and it will go into the catalogs and be meaningful, he says.

But there are two parts to the LSST data system; one is the legacy survey that in ten years time will go incredibly deep over the entire sky, says Lupton.  So, in some sense there’s no great urgency to analyze that data because it will take ten years to get to the sort of sensitivity that we need to really push the state of the art, he says.

For this type legacy data, Lupton says that he is much less confident that the algorithms will be good enough to make full use of the survey in ten years time. That’s because there are unsolved algorithmic problems, but such problems won’t stop us from being able to take the data, he says.

As for transient data of the sort that will generate global interest and immediate alerts to the astronomical community at large?

That kind of data is a byproduct of tracking newfound supernova explosions, colliding neutron stars, the visual and optical counterparts to gamma ray bursts, or even movements of potentially hazardous near-Earth asteroids (NEAs). All such transient events will need to be analyzed immediately, says Lupton. 

Ten percent of the telescope’s observing time will be allocated to special things like chasing an object or going deeper into one part of the field, says Krabbendam. We’ll see a thousand extragalactic supernovae in every image, he says. 

The observatory will detect as many as 90 percent of near-Earth objects (NEOs), as small as 140 meters in diameter and as far away as the Main Belt of asteroids.   In fact, the telescope will go a long way in helping NASA meet a congressional mandate that dictates that the space agency catalog 90 percent of all potentially hazardous asteroids larger than 140 meters in diameter.

As for how light pollution from this new generation of satellite constellations will impact the observatory?

Elon Musk and SpaceX have been very cooperative in discussing the impact of his constellations on our site, says Krabbendam. We are having a very productive conversation with him about things that they can do to lessen the impact on us, he says.

The other potential outside obstacle remains the interrupted construction timeline due to Covid-19. My own visit to the observatory took place just a month before construction was shut down.

We had to shut down the site on March 20th due to Covid-19 and we required everyone across the whole project work from home, Krabbendam told me recently.  Some work in labs and shops have started again in various parts of the world, but the summit remains closed, he says. “We’re hoping and expecting we can still get first light in 2022,” said Krabbendam.

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