Donn Liddle and Edward Oshel are the leading photogrammetrists in NASA Johnson Space Center’s Astromaterials Research and Exploration Science (ARES) Division. Both Liddle and Oshel are pioneers in the analysis of spaceflight imagery, using the science of photogrammetry to solve engineering problems encountered during missions.
Shortly after the Space Shuttle Challenger
tragedy in 1986, NASA realized they were lacking the capability for image analysis to study spaceflight anomalies. As a result, the agency formed the Image Science and Analysis Group (IS&AG), whose main task would be to screen and analyze space exploration imagery.
“Photogrammetry is the art and science of reconstructing the world that a camera saw,” Oshel said of their unique expertise.
Liddle and Oshel have been working together since the mid ’90s, when they met at Ohio State University while studying digital photogrammetry. Though both have master’s degrees in photogrammetry, Liddle also has a bachelor’s degree in surveying, and Oshel has a bachelor’s degree in physics and a master’s degree in astrophysics.
The fundamental principles of photogrammetry are the convergent nature of imagery and triangulation from multiple cameras.
“Most drawings you see are orthographic, meaning you have parallel projections,” Liddle said. “But in a photo, you have projections that come to a central perspective point. Using this realistic geometry, we can mathematically reconstruct the image at the moment of exposure. Combining the geometry of two photos taken from different locations allows lines of sight to be mathematically intersected to produce 3-D coordinates. When you start putting multiple images together, you can basically reconstruct a high-quality 3-D replica—often of a spaceflight event to provide meaningful data to ground teams. It’s kind of like having a time machine. You can measure how multiple objects relate to each other even though they may have since moved.”
“Our purpose is to provide the center and different programs with a way to have qualitative and quantitative data of things that are seen in imagery, primarily on orbit but [also] on launch tests, so they can use them for decision making,” Liddle said.
Johnson’s IS&AG were the first to identify the foam that broke off the external tank on Columbia,
and the only team that had the capability to make a quantitative analysis. By the next morning, they were already trying to decipher the size, shape, location and impact speed of the foam.
Their ability to work with suite of mismatched cameras and dynamic mission situations led to a key role in shuttle inspections implemented after Columbia
. And, that skillset is now applied to operations and sustaining engineering for the International Space Station, which represents a large segment of their current workload.
“We [look] for anything that basically could threaten [a] mission … Anything that looks anomalous [is] of interest to us,” Liddle said.
“The station has many parts that rotate, and some of these parts rotate in close proximity to other structures,” Oshel said. “So, the first time it’s rotated, the engineers on the ground want to know what the clearance is really going to be [in] orbit.”
Likewise, if an astronaut were to accidentally let go of a tool during a spacewalk, Liddle and Oshel would use photo measurements to inform program management of the objects trajectory to assess concern for re-contacting the object during a later orbit.
As part of ARES, the IS&AG is tasked with efficiently inspecting spacecraft to find and measure damage that might endanger astronauts. They’ve examined damage on the exterior of the space station from micrometeoroid orbital debris strikes, on its solar radiators and used imagery to determine the length, width and depth of the damage done.
“We have looked at strikes on windows from the space station and [evaluated] how big the [craters] in the glass [are], because if the crater is too big, the window might fail,” Oshel said.
Occasionally, work leads Liddle and Oshel to photogrammetry of astronauts themselves.
“Periodically, the crew puts little reflective balls at various key points on their bodies and then pose for photographs,” Oshel said. “We do a stereo image analysis and measure the dimensions of the astronaut. The measurements are sent to a crew health group, which looks for physiological changes from being in zero-G. The spine expands when [it’s not being compressed on] Earth. NASA wants to see how much the astronaut has grown.”
Measurements derived from imagery are also used to understand spacecraft performance during all phases of spaceflight, including future missions with the Orion spacecraft and corresponding Space Launch System (SLS) rocket.
Members of the IS&AG are working with the Orion crew module to study how the parachutes deploy and perform to ensure they don’t come into contact with any hardware. They are conducting tests on how Orion windows will affect imaging.
They are also partners in the design of camera systems on Orion and SLS so that they can provide flight controllers with mission measurements, such as command module separation from the service module to verify that there is no re-contact.
Nothing excites engineers quite like data, but sensors on spacecraft only tell some
of the story. Thanks to this groundbreaking ARES team, everyone from flight controllers to mission managers have a complete suite of information from which to make educated decisions.
The job is serious business, as protecting the crew and hardware is always at the forefront of each analysis. But for the IS&AG team, no matter the dimension, it’s a puzzle to be solved.
To learn more about the Astromaterials Research and Exploration Science Division, visit: http://www.nasa.gov/centers/johnson/astromaterials
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NASA Johnson Space Center
Donn Liddle, a photogrammetrist in NASA Johnson Space Center’s Astromaterials Research and Exploration Science Division, along with parachute designer Dr. Anita Sengupta, test a scale model of the Orion spacecraft and its parachute system in the low-speed wind tunnel at Texas A&M University. Image Credit: NASA/James Blair
Edward Oshel, a photogrammetrist at Johnson in the ARES Division, performs analysis on imagery of Orion test hardware. Image Credit: NASA