Space station research contributes to navigation systems for lunar travel


Canadian Space Agency astronaut David Saint-Jacques holds the camera assembly for the lunar imagery survey in the cupola of the space station. Credit: NASA

On its mission to the Moon, NASA’s Orion spacecraft is designed to use NASA’s Near Space Network and Deep Space Network to navigate. But if the craft loses communication with the ground or networks, crews can use a backup autonomous navigation system called Optical Navigation (OpNav). This system analyzes the images of the Moon or the Earth taken from the spacecraft to determine its position relative to one or the other of these two bodies.

A survey currently underway aboard the International Space Station is helping OpNav developers fine-tune the system to ensure crews return home safely. The Moon Imagery survey uses photographs of the Moon taken from the space station to calibrate the system’s software.

“The space station gives us a platform to collect images of the Moon without interference from Earth’s atmosphere,” says Steve Lockhart, principal investigator at NASA’s Johnson Space Center in Houston. “We can get pretty decent images of the ground, especially when the Moon is almost full and high in the sky. The challenge is to get clear images of the Moon in its very fine phases. Because it is then close to the Sun, the sky is only dark enough to get images when the Moon is close to the horizon, and then you’re looking through a lot of atmosphere.”

The survey uses two cameras mounted on a plate and offset about 20 degrees from each other. The plate is installed in the station’s cupola, a seven-window observation module, and the cameras point to one of the windows which has pure glass for the clearest view. One camera captures images of the stars and the other takes photos of specific views of the Moon. Each specific view is only available once a month for a short four-minute window. The software then uses algorithms to analyze these images and determine the craft’s position in space.

“We know where the space station is at all times and where it was when a particular photo was taken based on the time it was taken,” Lockhart explains. “The algorithm tells us where it thinks the station is and we can compare it to the known real location to judge the accuracy of our system.”

The system is automated, he adds. The space station crew simply orders the camera to point at Earth or the Moon, whichever is more appropriate at the time, to take a series of photos for about an hour.

Space station research contributes to navigation systems for lunar travel

This image is a composite of many individual images captured during a lunar imaging session, with the Moon tracing an arc across the camera’s field of view. An overlay image taken as the sun began to illuminate the atmosphere shows Earth’s location relative to the Moon’s track, and an enlarged image of the Moon has also been added. Credit: NASA/Steve Lockhart

Crew members have now conducted four rounds of surveys, photographing a full 29-day cycle of the Moon’s phases.

Images from the latest series in May captured varying exposures, from very underexposed to very overexposed. The researchers plan to analyze these images to see if they can be used to determine the distance and bearing of the space station and, from there, the location of a spacecraft, such as Orion’s position between the Moon and Earth.

This run also captured a very thin crescent moon, one of the toughest conditions for the system’s image processing algorithms. The team may improve future versions of the algorithm based on how the system handles this difficult stage of the Moon, one of the many goals of the upcoming Artemis I mission.

During course correction maneuvers, the OpNav camera mounted on the outside of Orion will take repeated images of the Moon and Earth for about two hours. These multiple images should ensure accurate measurements of Orion’s location in case the backup navigation system is needed. Knowing the precise location of a spacecraft is essential to guide it safely towards its re-entry into the Earth’s atmosphere.

Communication and navigation capability is one of the key technologies humans need to explore further into space. Orion is NASA’s next-generation spacecraft, capable of carrying humans to low Earth orbit and beyond, including to the Moon. Lockhart says commercial space exploration companies have also shown interest in the autonomous navigation system.

The Moon Imagery survey is an example of how the space station provides researchers with a platform to lay the groundwork for technologies and demonstrations that bring humanity closer to deep space exploration.

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