Illustration of an explant near its star

Manipulating Starlight

STScI’s Russell B. Makidon Optics Laboratory continues to advance state-of-the-art tools for future flagship missions.


Conference attendees at a table for a demonstration
Testbed Demonstrations
In January 2019, a simplified tabletop model of HiCAT, affectionately known as BabyCAT, debuted at the 233rd meeting of the American Astronomical Society. BabyCAT was designed to explain high-contrast imaging and coronagraphy, demonstrate the experimental setup, and communicate the importance of this type of research and development to the astronomical community. BabyCAT has proven so useful that JPL commissioned its own version, which was delivered in December. In the summer of 2019, BabyCAT was the focus of a joint project between the Optics Lab and STScI’s Office of Public Outreach undertaken by an intern in STScI’s Space Astronomy Summer Program. The intern worked with optics researchers, outreach scientists, and educators to successfully design an even simpler model and explanation of coronagraphy for the public.

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.
 

Staff member in a white suite working with equipment on a table top
Ongoing Collaborations and Partnerships
STScI’s Makidon Optics Laboratory is home to three optical experimental setups: the High-Contrast Imaging Testbed (HiCAT), the James Webb Space Telescope Optical Simulation Testbed (JOST), and the Space Telescope Ultraviolet Facility (STUF). The space is temperature, humidity and pressure controlled, and includes a vibration isolation pad. The Optics Lab team collaborates with the Johns Hopkins University’s Department of Mechanical Engineering; ONERA (the French Aerospace Lab); Laboratoire d’Astrophysique de Marseille in France; the University of Rochester in New York; Observatoire de la Côte d’Azur in France; Princeton University in New Jersey; Leiden University in the Netherlands; NASA’s Goddard Space Flight Center in Maryland; NASA’s Exoplanet Exploration Program at the Jet Propulsion Lab in California; and Ball Aerospace in Colorado.

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?
 

blue and white image with a black circle at the center
The final output of the HiCAT is a processed image showing the effects of the coronagraph system on starlight. A coronagraph system is deemed successful when it can thoroughly block the light of a star, creating a dark zone large and dark enough to reveal orbiting planets. In 2019, researchers were able to significantly increase both the contrast and area of the dark zone.
A black and white pattern with a circular shape
An apodizer is a component of the coronagraph that helps cancel out distortions caused by the shape of the telescope opening and the mask that blocks the star’s light. In 2019, important incremental improvements were made in both design and manufacturing.