The bold bet that built a telescope

First look images from the NSF–DOE Vera C. Rubin Observatory

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NSF–DOE Vera C. Rubin Observatory

Today, Rubin is an $800 million observatory backed by the National Science Foundation (NSF) and the Department of Energy (DOE). But two decades ago, it was little more than a vision without funding, a home, or agency support.

That changed in 2003, when Stanford University and SLAC National Accelerator Laboratory jointly launched the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), setting in motion a chain of events that helped bring the LSST to life.

“Stanford and the Kavli Institute, joint with SLAC, were the critical incubators throughout the first decade of the 21st century to turn the dream into reality,” said Persis Drell, former SLAC director and former Stanford provost.

Roger Blandford and Steve Kahn were recruited as KIPAC’s founding director and deputy director, respectively, and both saw enormous potential in a then-nascent telescope concept called the Large-aperture Synoptic Survey Telescope – now officially known as the NSF–DOE Vera C. Rubin Observatory. Blandford first learned about the idea in the mid-1990s, when it was known as the Dark Matter Telescope, from University of Arizona astronomer Roger Angel.

“Both Roger [Blandford] and I had the same idea,” said Kahn, who now serves as dean of physical sciences at UC Berkeley but remains emeritus at Stanford. “We came to Stanford thinking LSST was a direction worth going in, and I started conversations about SLAC leading the camera project before I even officially started.”

Blandford was captivated by LSST’s potential to reshape astrophysics. The proposed observatory would capture a wide-field image of the southern sky every few nights for 10 years, creating the most detailed time-lapse of the universe ever assembled.

“It seemed to me a very different way of doing [astrophysics],” Blandford, a professor of physics at Stanford and of particle physics and astrophysics at SLAC, recalled. “It was going to be a discovery engine that generated this enormous data set that researchers from across fields could use to find new cosmic phenomena.”

A new challenge

Meanwhile, SLAC was ready for a new challenge. The lab had played a key role in developing the Fermi Gamma-ray Space Telescope (then called GLAST) and was looking for an ambitious follow-on project to help define the mission of the newly formed institute. “When I first started talking to SLAC leadership, they were thinking about gamma-ray astronomy follow-ons,” Kahn said. “But I saw LSST as the perfect project to anchor the institute.”

Steve Kahn, director of the Legacy Survey of Space and Time (LSST) project, addresses SLAC scientists and engineers as they celebrated the completion of a new clean room, where the lab will assemble and test the LSST Camera. | Andy Freeberg / SLAC National Accelerator Laboratory

Kahn, a former X-ray astronomer, had encountered the LSST concept in 2000 while serving on the Astronomy Decadal Survey and was struck by the project’s potential to advance both astrophysics and fundamental cosmology. Soon after, he and Blandford began traveling the country with Tony Tyson, the project’s original visionary, giving talks to scientists and donors and building momentum around the telescope.

A risky bet

Turning LSST from concept to reality would require a major institutional leap. At the time, Stanford had no traditional astronomy department, and despite decades of technical expertise in detector development, SLAC had yet to build an instrument for astrophysics of this scale. The camera design also pushed the limits of existing technology, and its proposed mirror configuration had never been attempted before. All of this made early buy-in from funders risky and uncertain.

Still, Kahn recognized its potential and approached SLAC director Jonathan Dorfan with a proposal for SLAC to take the lead on the LSST camera. Dorfan appreciated the scientific opportunity represented by LSST, and urged Kahn to assemble a team of SLAC scientists and engineers to develop it as a SLAC project. That early green light set in motion a determined, multi-year effort: drafting technical proposals, building partnerships, engaging DOE and other agencies, and forging alliances with university collaborators across the country.

Members of the team building the LSST, a large survey telescope being built in Northern Chile, gather to celebrate the successful casting of the telescope’s 27.5-foot-diameter mirror blank, August 2008. Steven Kahn, a KIPAC member, is now director of the LSST project. | Howard Lester / LSST Corporation

“SLAC had an outstanding technical and scientific staff used to tackling hard problems,” said Kahn. “The camera we proposed was massive and complex, but its design had more in common with particle detectors than with traditional astronomical instruments. That played to SLAC’s strengths.”

The hoped-for camera was, in fact, going to be the largest digital camera ever used for astrophysics – one with a 3.2-gigapixel focal plane that had to be flat to within five microns, or less than a tenth the thickness of a sheet of paper. “We did meet that,” said Aaron Roodman, head of the camera project at SLAC. “It’s flat to four microns. And we had to do that with no ability to adjust anything. Every piece had to be fabricated perfectly from the start.”

That precision enabled the camera’s most essential feature: its enormous field of view. “That’s the really key thing,” said Roodman, who is also deputy director of Rubin Observatory construction and a professor of particle physics and of astrophysics at SLAC. “Every time we point the telescope in a new direction, how much of the sky do we see in any one image?”

In Rubin’s case, the answer is staggering: the camera can capture a patch of sky 3.5 degrees across – about seven times the width of the full moon. Each image spans an area 45 times larger than the moon’s disk.

NSF–DOE Vera C. Rubin Observatory and SLAC National Accelerator Laboratory team members prepare the LSST Camera – the world’s largest digital camera – for its move to the eighth level, where it will be installed on the Simonyi Survey Telescope. | RubinObs / NOIRLab / SLAC / NSF / DOE / AURA / A. Pizarro D.

“That is enormous,” Roodman said. “There’s no large telescope that has anything like that.”

With its wide-angle view, massive mirror, and rapid readout speed, Rubin will map the entire southern sky every few nights.

Delivering that performance required a tightly integrated system of optics, electronics, mechanics, and cryogenics – all operating in a vacuum. “Most instruments limit the electrical components placed inside a vacuum vessel,” Roodman explained. “We placed our electronics in the vacuum, to digitize the data right at the source and minimize noise – just like in a particle physics detector.”

A deep partnership

While DOE’s formal approval process for LSST unfolded over several years, Stanford and SLAC played a key role in keeping momentum alive by rallying community support for the camera and developing its early design.

A major turning point came in 2008, when Charles Simonyi and Bill Gates donated $30 million to fund the construction of LSST’s primary and tertiary mirrors – a technical risk, since both mirrors were cast from a single piece of glass, something that had never been done before. But the bet paid off, and crucially, it allowed work to begin years before the agencies had approved the project.

“That private funding was absolutely critical,” Drell said. “It let us take the long lead-time step of machining the mirrors before we had agency approval. That made everything else possible.”

The unique institutional structure of KIPAC, which bridged SLAC and Stanford’s physics department, helped enable the sustained push the LSST project required.

“From the beginning, the partnership between Stanford and SLAC wasn’t just administrative,” said Risa Wechsler, KIPAC’s current director. “It has always been a deep intellectual collaboration that helped shape the vision and technical roadmap for LSST.”

That momentum continued in more recent years under new SLAC leadership, including former lab director Chi-Chang Kao and former associate lab director for Fundamental Physics JoAnne Hewett, whose leadership helped guide the project through key stages of design, construction, and commissioning.

Support from Stanford physics faculty with expertise in fundamental cosmology – including Andre Linde, Leonard Susskind, Renata Kallosh, and Eva Silverstein – also helped ground the project intellectually. “It was a really nice mesh,” Kahn said. “SLAC had the technical expertise to do a project of this magnitude, and Stanford had the intellectual connection to think about how we would fully exploit the results.”

By 2010, LSST topped the Astronomy Decadal Survey’s list of ground-based telescope priorities. Because Blandford was chair of that survey, he intentionally recused himself when it came time to rank projects. “It was my colleagues who came to the conclusion that it was the number one priority in the survey,” he said. “I just tried to make sure the process worked.”

This milestone helped secure DOE and NSF buy-in. SLAC was formally chosen to lead the camera effort, and in 2013, Kahn became LSST Project Director, overseeing not just the camera but also the integration with the telescope being built in Chile. Over the next decade, SLAC scientists and engineers designed, built, and tested the 3.2-gigapixel camera, overcoming complex technical challenges along the way.

A lasting legacy

Stanford and SLAC’s influence extended beyond design and construction. Through KIPAC, they built a training ground for scientists who now lead major components of Rubin’s science efforts.

“There are people who were Stanford students or postdocs who are now playing leading roles in commissioning and science planning,” Wechsler said. “That legacy is really important.”

The roots of that legacy stretch back to KIPAC’s earliest years, when the institute recruited a cohort of young faculty – including Wechsler, Tom Abel, and Steve Allen – who helped shape the scientific direction LSST would ultimately follow. Together with Kahn and Blandford, they mentored a rising generation of researchers, including Phil Marshall, Masao Sako, and Chihway Chang, who played key roles in LSST’s early science planning and now help lead its core collaborations.

That outcome was no accident, Kahn said. “One of the things we were very intentional about when we started KIPAC,” he added, “was building an institute that trained people for the kind of large-scale, data-intensive science LSST would require.”

A deep satisfaction

For Roodman, watching the observatory approach first light has been very personal. “I feel deep satisfaction,” he said. “We’re not done, but it’s incredibly gratifying to see how far we’ve come and how well the camera and the whole observatory are working. There’s huge excitement about the science to come.”

Media gallery

Snapshots from LSST watch party to observe first images

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As the project reaches this milestone, Blandford finds himself thinking of Vera Rubin – the pioneering astronomer whose work confirmed the existence of dark matter and who died in 2016.

“In 2005, I chaired a committee for the NSF, and Vera was one of the members,” he recalled. “At one point, I asked her to take responsibility for the parts of our report that dealt with LSST. She didn’t know much about it at the time, but she became quite an enthusiast.”

The telescope now bears her name. “I’d like to think she would approve of where it’s gotten,” Blandford said. “And that’s a nice feeling.”

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