From Concept to Cosmos: Vera Rubin Observatory’s 20-Year Journey with Hexagon

Conceptually started in 2000, the Vera C. Rubin Observatory is a groundbreaking astronomical experiment in Chile. It houses the Simonyi Survey Telescope, an automated 8.4-meter telescope designed to conduct a 10-year survey of the visible sky. The observatory aims to provide unprecedented insights into dark energy, dark matter, the solar system, and the Milky Way through its Legacy Survey of Space and Time (LSST). With its unique capability to photograph the entire Southern sky every few nights, the LSST will produce the largest astronomical database, enabling scientists to create “movies” of how astronomical objects move and interact.

In astronomy, the precise alignment of optical components is crucial as it directly impacts the quality of observations and scientific discoveries. Hexagon’s portable metrology software and automated alignment capabilities provide a comprehensive solution for ensuring optimal telescope performance. This is especially important for the Simonyi Telescope, which features the largest camera ever built for astronomy and astrophysics.

Scientists at the Vera Rubin Observatory recognized the need for advanced technology to achieve and maintain the highest alignment standards for its telescope. To enhance its alignment, operation, and maintenance processes, the observatory uses Hexagon’s SpatialAnalyzer (SA) software with a custom API application called T2SA (Telescope2SA).

This solution — which resulted from a collaboration that began in 2005 — demonstrates the long-term commitment required for such a complex project.

Challenge: Precision at a cosmic scale

Scientists at the observatory face significant challenges when aligning and maintaining the position of multiple large optical components. The observatory optical design incorporates an 8.4-meter diameter primary mirror, a 3.5-meter diameter secondary mirror, and a 1.65-meter diameter camera with multiple lenses, all of which have to be aligned with micron-level precision.

“We absolutely need all the mirrors with the right shape and in the right place to achieve a crisp image. We wanted to ensure that we could perform the alignment quickly and efficiently by simply pressing a button on the computer,” said Dr. Sandrine Thomas, Deputy Director of Rubin Observatory Construction.

Traditional alignment methods are time-consuming, require specialized expertise, and must be rigorously maintained to achieve the performance as the telescope moves and experiences temperature fluctuations throughout its mission. These conventional methods limit scientists’ ability to achieve their scientific goals. For example, the telescope must be close to focused before wavefront focusing algorithms can quickly refine the focus across the field of view to gather the best images. Achieving an accurate focus for the range of angles the telescope plans to observe and the range of temperature can be challenging, and the traditional methods are often time-consuming and/or require on-sky observations, reducing the telescope’s efficiency.

Solution: SpatialAnalyzer with T2SA brings automation to astronomical alignment

Observatory staff worked with Scott Sandwith, Hexagon’s Custom Projects Manager for SpatialAnalyzer software to define a custom T2SA application, interfacing it with the telescope control system. This solution enabled the team to perform automated, high-precision alignments of the telescope’s optical components.

SpatialAnalyzer offers Vera Rubin staff a wide range of metrology capabilities, including automated measurements, real-time adjustments, and compensation
for gravitational effects. Scott Sandwith used the software’s SDK (software development kit) automation interface to develop T2SA. T2SA adapts and responds to the telescope’s alignment commands. This key feature makes SpatialAnalyzer uniquely qualified for this application, enabling it to support the full range of measurement criteria and sampling strategies needed for rapid and precise alignment.

Additionally, the solution uses an AT930 Absolute Tracker positioned at the center of the primary mirror to take precise measurements. This setup — combined with SA’s advanced features — means the observatory can align optical components within 5-10 microns, with further refinement possible during observations. “SA lets us align our mirrors and instruments within the five microns, at which point we will adjust further in real time, every 45 seconds, with on-sky images,” Dr. Thomas noted.

SpatialAnalyzer with T2SA provides:

• Corrections for the position of the telescope’s secondary mirror (M2) and camera relative to the primary mirror
• Measurement of the impact of gravity on the telescope’s optical components alignment across the full range of motion
• Measurement and correction of the M2 and camera systems through the range of telescope azimuth and elevation angles, and camera rotator position

Results: Enhanced telescope performance and efficiency

By implementing SpatialAnalyzer with T2SA, scientists at the Vera Rubin Observatory have significantly improved the telescope’s alignment processes, their understanding of gravity induced misalignments and overall performance.

The team can quickly measure and correct the positions of optical components as the telescope moves, accounting for gravitational effects. This will significantly cut alignment time making the nightly observations more efficient. The alignment process that previously could take hours now occurs in minutes, maximizing valuable observation time.

Over the past few years, the solution has been extensively tested and refined. For example, the team’s onsite work with T2SA successfully completed a major test. It confirmed the telescope system can converge the optical components in their goal positions and orientations — in one move — within the optical performance tolerances. T2SA’s improved alignment process has also contributed to the Vera Rubin Observatory’s position as a cutting-edge astronomical facility. SA’s advanced features have helped the observatory overcome the limitations of traditional methods and gain more precise control over its complex
optical system.

Vera Rubin staff credit the system’s versatility with helping the observatory beyond performing nightly alignments, demonstrating Hexagon’s broader impact on the organization’s operations. For example, scientists also use Hexagon’s laser tracker to perform metrology tasks and plan to use T2SA to align its calibration device to the telescope.

Many large-scale measurement processes require more than a single measurement instrument. SA’s ability to handle multiple measurement devices or the relocation of a single instrument throughout the measurement volume is crucial for acquiring the necessary data in complex applications like the Simonyi Telescope.

Using SpatialAnalyzer enabled the Vera Rubin Observatory to accelerate its preparation for full operations while improving its overall telescope performance. Observatory staff believe this will ultimately benefit the global scientific community, which will rely on the observatory’s groundbreaking observations to further human understanding of our universe.

Looking forward

Looking ahead, as the Rubin Observatory prepares to install its primary mirror in September 2024, the SpatialAnalyzer T2SA solution will play a crucial role in the final alignment and commissioning of the telescope.

Additionally, this project’s success opens doors for similar applications in other large-scale observatories.

Scientists believe that the output of the Vera Rubin system will help other telescopes worldwide identify and drive even deeper scientific understanding. Hexagon is demonstrating its domain expertise as a key player in advancing astronomical research capabilities, potentially revolutionizing how next-generation telescopes are aligned and maintained.