NASA Moves Closer to Ultrastable Telescope

Babak Saif and Lee Feinberg at NASA's Goddard Space Flight Center have shown that they can dynamically detect subatomic distortions across a 5-ft segmented telescope mirror in their mission of building an ultrastable telescope that locates and images dozens of Earth-like planets beyond the solar system and then scrutinizes their atmospheres for signs of life.

Goddard optics experts Babak Saif (left) and Lee Feinberg (right), with help from Eli Griff-McMahon (center), an engineer at Genesis Engineering Solutions Inc., have created an Ultra-Stable Thermal Vacuum system that they will use to make picometer-level measurements. Courtesy of NASA/W. Hrybyk.

Collaborating with Perry Greenfield at the Space Telescope Science Institute in Baltimore, the team now plans to use a next-generation tool and thermal test chamber to further refine its measurements.

To find life, observatories would have to gather and focus enough light to distinguish the planet's light from that of its much brighter parent star and then be able to dissect that light to discern different atmospheric chemical signatures, such as oxygen and methane. This would require a superstable observatory whose optical components move or distort no more than 12 picometers. To date, NASA has not built an observatory with such demanding stability requirements.

Scientists say that even nearly imperceptible, atomic-size movements would affect a future observatory's ability to gather and focus enough light to image and analyze the planet's light. Consequently, mission planners must design telescopes to picometer accuracies and then test it at the same level across the entire structure, not just between the telescope's reflective mirrors. Movement occurring at any particular position might not accurately reflect what's actually happening in other locations.

"These future missions will require an incredibly stable observatory," said Azita Valinia, deputy astrophysics projects division program manager at NASA. "This is one of the highest technology tall poles that future observatories of this caliber must overcome. The team's success has shown that we are steadily whittling away at that particular obstacle."

To carry out the test, Saif and Feinberg used the High-Speed Interferometer (HSI), an instrument that Arizona-based 4D Technology developed to measure nanometer-size dynamic changes in the James Webb Space Telescope's (JWST) optical components during thermal, vibration and other types of environmental testing.

Like all interferometers, the instrument splits light and then recombines it to measure tiny changes, including motion. The HSI can quickly measure dynamic changes across the mirror and other structural components, giving scientists insights into what is happening all across the telescope, not just in one particular spot.

Even though the HSI was designed to measure nanometer- or molecule-size distortions, the team wanted to see it could use the same instrument, coupled with specially developed algorithms, to detect even smaller changes over the surface of a spare 5-ft JWST mirror segment and its support hardware. The test proved it could by measuring dynamic movement as small as 25 picometers — about twice the desired target.