Steven Kahn Maps Out the Project that will Map the Dark Universe
While many scientists spend entire careers on one subject or even a single question, not every scientist has the countenance to develop an experiment for two decades before it officially begins. The long wait doesn’t faze AAAS Fellow Steven Kahn.
Kahn, a professor of physics at Stanford University and a professor of particle physics and astrophysics at SLAC National Accelerator Laboratory, is the director of the Large Synoptic Survey Telescope (LSST) Project, which plans to image the entire Southern Hemisphere night sky every few nights for 10 years. Initial ideas for the telescope emerged in the 1990s. Currently under construction in Chile, it is expected to begin its formal survey October 1, 2022.
“LSST is such a new capability. It’s guaranteed to make major discoveries and major contributions — I am confident of that,” said Kahn, who has been involved with LSST for more than 13 years. “To me, it’s worth the long time it takes to get it going and actually make it happen.”
By imaging the same area repeatedly, the LSST is expected to build a comprehensive map of the visible night sky, which will help identify stars, galaxies, and moving objects in the solar system, including potentially hazardous asteroids. It will detect and measure properties of about 20 billion galaxies — between 10 percent and 20 percent of all galaxies in the visible universe. This huge data set can help provide insight into dark matter and dark energy, possibly answering questions about the fundamental origin, growth, and structure of the universe.
The heart of the LSST is a 3.2 billion-pixel digital camera. It will take more than 800 huge panoramic images a night that will each be downloaded in exactly two seconds. Within 60 seconds, the pictures will be beamed from a mountaintop in Chile to a data center in Illinois and automatically analyzed for interesting changes, and then alerts will ping around the world notifying others who might want to take a closer look with their telescopes.
Before becoming director, Kahn was the lead LSST camera scientist. Building the largest astronomical camera on Earth presented many challenges. For example, the sensors are positioned inside a vacuum-sealed cryostat, which must remain at -100°C to preserve data quality. Some thought it would be impossible to build a large enough lens that could still hold the vacuum seal, but the team succeeded. The group also designed a novel refrigeration system to collect heat generated by electronics packaged inside the vacuum so it is not released to the ambient air where it would distort the images.
Growing up in Long Island, New York, Kahn was never a tinkerer or builder; he wasn’t even that fascinated by outer space. He was a philosophical child.
“I was interested in big questions and that drew me to physics,” he said.
But as a graduate student, he realized that to answer the physics questions he was interested in, new tools were required to collect the necessary data. Ever since, he has gravitated toward projects that combine new equipment with profound and challenging questions.
For example, he helped the European Space Agency design and develop a novel spectrometer for the XMM-Newton Mission, an X-ray space observatory that launched in 1999. Conception to launch took 15 years, a typical timescale for space-based projects, which conditioned Kahn to be comfortable with long-term projects.
Kahn first heard about LSST in the late 1990s, while serving on the steering committee for a National Academy of Sciences decadal survey, a panel of experts from a variety of astronomical fields who identify the top research priorities for the coming decade. While his focus had been X-ray spectroscopy, he was so excited by LSST, he made it his primary mission upon moving to Stanford and SLAC in 2003.
Kahn helped set up a meeting with the Department of Energy and other key labs to explain their idea for LSST. Kahn dubbed it a “stop sign” meeting, because it was the DOE’s opportunity to say “stop, no way will we support this.” When the agency didn’t shut it down, the initial team went to work pulling together the best minds from all over the United States and other countries to develop a proposal.
It took many years of engineering and project management before funding was secured. About 300 people have been involved, a team Kahn described as a wealth of creativity that built the project from the ground up.
“That takes dedication to work hard on something that you don’t even know is going to happen,” he said.
The DOE eventually agreed to fund the $168 million camera, while the National Science Foundation pledged up to $473 million for the telescope and data management system. However, it was only last year that the agencies gave the final green light to commence construction.
“We are in the thick of construction right now,” Kahn said. “When you are spending a lot of money and cutting metal, essentially everything that can go wrong, will go wrong.”
But that's to be expected when pushing the state of the art, building something that has never been attempted before.
“Part of the skill in doing these projects is to have the fortitude to not fall apart,” Kahn stressed. “Figure out what to do and move forward and keep the thing on track. Then these hiccups become humorous antidotes 15 years later.”
There are still years to go before the first images are taken, then another 10 years of data collection, and countless meetings and potential hiccups in between. But Kahn seems to take it all in stride, keeping his eye on what matters.
“Ultimately, the motivation for us who work on these big projects is the belief that eventually great science will come from this,” Kahn said, “and we’ll have played a crucial, enabling role in making it happen.”