Squids Have Beaks and Other Mysteries of the Universe – Andy Rasmussen

Physicist Andy Rasmussen works with the SLAC-based Camera Team to develop and build the sensor array at the heart of the LSST camera, an instrument of unprecedented scale and scope. Rasmussen describes the scale of the camera’s focal plane as “mind boggling: three billion pixels, comprised of 189 science sensors, each segmented into 16 channels, all read out in two seconds – incredible!” The same enthusiasm evident in Rasmussen’s description of the LSST focal plane has been manifest in his lifelong love of research beginning as an amateur biologist.

“My (literal) first interest in research came at an early age, probably age 8 or so. I was fascinated by Nature. In Japan, where I grew up, there were many, many species of insects that defied imagination. In front of my eyes there was specialization of body parts, finite life cycles, metamorphoses. Once I decided to buy a fresh squid from the local fish shop, dissect it and carefully illustrate the structure of the body, internal organs, eye, the membranes, and so on. Imagine my surprise when I discovered that squids have beaks! I did have a copy of The Universe, a Time/Life science library book, with lots of pictures of galaxies and globular clusters – and that was pretty dull by comparison.”

Rasmussen joined the LSST team at SLAC in 2005 because of the ambitious project goals, the unique challenge of the work, and the opportunity to engage in a project that promises to have a huge impact in the field. Andy explains, “The survey data acquired using LSST will enable scientific fields that have historically been data-starved. It will provide multi-band photometric data with frequent coverage, which should yield many new discoveries in the time domain, including regular discoveries of distant supernovae, proper motions of many, many stars, and solar system objects. The plentiful, short exposures will enable routine stacking of deep images into even deeper images that won’t be compromised by the poor image quality that accompanies long exposure times.”

One of the more challenging demands of Rasmussen’s work is maintaining optimal imaging performance over the entire focal plane all at once. He described it as a complex, systems related task. “Achieving this will be a first; nothing like it has been achieved to date,” he said. “One detail I pay particular attention to is how we will position the 189 individual sensor surfaces to fall within a planar volume only 10 microns thick – one tenth the thickness of a typical human hair!”

In his off hours, Rasmussen continues to indulge his curiosity regarding how things work. Recently he repaired his “old, beloved Volvo.” What began as a simple DIY project to prolong the life of a car “loaded with sentimental value and engine problems” proved to be more complicated and challenging than he intended. “Having slogged through that,” he said, “I now understand the value of that shop class I missed in high school. I also know why I am not a mechanic!”

With the temper of a scientist, Rasmussen engages in what he considers the most satisfying aspect of his work: quantitatively simulating the LSST performance. The LSST Image Simulation group provides high fidelity end-to-end simulations of the sky that mimic conditions to be observed during the LSST survey. These simulated images and catalogs are used in designing and testing the LSST system, and they provide realistic LSST data to the science collaborations to evaluate the expected performance of LSST.

Beyond Rasmussen’s enthusiasm for LSST’s technical and engineering ability to reveal the wonders of the universe, he stresses the practical contribution to the scientific community by the project’s data. “The public nature of LSST data,” he said, particularly the short latency period, “is a different and new approach compared to almost every other field. In my experience with space-based astronomical data, there was a proprietary period giving advantage to the proposer or principal investigator – in some cases as much as 12 months following its capture. With LSST, there is no Time Allocation Committee or proposal review panel, so the data goes public almost immediately… The combination of LSST data will be high quality, with high availability. This promises to change the astronomical/research world considerably.”

By Robert McKercher and Andy Rasmussen