STScI’s Russell B. Makidon Optics Laboratory continues to advance state-of-the-art tools for future flagship missions.
How do we realize an ambitious concept: A space telescope with the power to image and characterize dozens of faint, potentially Earth-like planets outside our solar system? A telescope that can detect signs of life on an exoplanet orbiting a star more than 100 light-years away? A telescope designed to address the question: How common is life beyond the Solar System?
As anyone in STScI’s Russell B. Makidon Optics Lab will tell you, when it comes to designing groundbreaking technologies for transformational science, the path from vision to reality involves methodical, step-by-step development, building on existing knowledge and technology, continuous refinement, and close collaborations. In 2019, researchers in the Optics Lab made significant advances in the hardware and software used to manipulate starlight that illuminates distant worlds.
Capturing Light from Distant Planets
The high-contrast, high-resolution imaging needed to search for life outside our solar system involves meeting the seemingly contradictory requirements of gathering light from the planet while blocking light from the star. Collecting and analyzing starlight that reflects off the planet’s surface requires a mirror large enough to detect the extremely faint illumination of a small, distant planet, along with a coronagraph designed precisely enough to block 99.99999999 percent of the otherwise overwhelming light from the star—without also blocking the planet.
A mirror large enough for the job needs to be segmented to fold up and fit inside a launch vehicle. This makes the problem of blocking starlight more challenging. While the basic component of a coronagraph is very simple in concept—an opaque disk that prevents light from reaching the detectors—the full assembly is actually quite complicated, because light is diffracted and distorted by different components of the telescope. The more complex the mirror, the more difficult it is to cleanly block the starlight.
Addressing Complex Challenges
Since 2013, the institute’s Optics Lab has been at the forefront of advancing technologies for future generations of segmented space telescopes, in particular in the areas of optical mirror alignment, wavefront sensing and control, and coronagraphy needed to capture images of distant worlds. Staff carry out research and development of hardware and software by using a combination of simulations and physical experimental setups, including the High-Contrast Imager for Complex Aperture Telescopes (HiCAT) testbed.
In 2019, our staff continued to make important strides in high-contrast coronagraphy using HiCAT. Between 2018 and 2019, researchers were able to increase the level of starlight suppression enabled by the coronagraph from 10-6 (blocking all but 1 part in one million) to 10-7 (1 in 10 million), approaching the 10-8 level that the team believes is possible on the HiCAT testbed. To get a sense of this level of light suppression, think about a firefly circling a bright lighthouse. A coronagraph designed to reveal distant exoplanets could block the light from the lighthouse effectively enough to see the firefly—from a distance of 1,000 miles.
Building on a major accomplishment of 2018, the lab also succeeded in expanding the area of light suppression around the simulated star to a full 360 degrees for a segmented aperture. This so-called dark zone, which researchers succeeded in producing on one side of the image in 2018, now circles the entire star, effectively doubling the detection area and significantly expanding a future telescope’s planet-hunting capability.
With these advances—achieved through a combination of improvements to hardware and software used to sense and correct for light distortions, and improvements to modelling and simulations used to analyze and explain results—the coronagraph system is on track to reach Technology Readiness Level 4 at the component level by mid-2020. This is the first of three milestones in the lab’s three-year program to advance high-performance coronagraph systems technology readiness levels for direct imaging of exoplanets using segmented telescopes—a crucial step in answering the question: Are we alone?