What Flies Beneath: Space Station Spied From Above!
The International Space Station was caught on camera as it passed between eastern India and a Landsat satellite.
It's not terribly unusual to spot the International Space Station. At around 250 miles (400 km) high, the football field-sized ISS is traveling over 17,000 mph (27,350 km/h) and circles the globe 16 times a day, and when the lighting is right it's easy to find in a clear sky if it's passing near your location (especially if you know when and where to look!) But recently the ISS was identified in images taken from a surprisingly different viewpoint: far above in an orbit nearly twice as high.
On June 19, 2016, the Landsat 8 Earth-observing spacecraft captured a sequence of images with its Operational Land Imager instrument from its altitude of 438 miles (705 km). In eight of the images the ISS can be seen passing in front of cloud cover over the eastern Indian state of Odisha. Seen above, the images are separated by just fractions of a second and each is in a different spectral wavelength which accounts for the changes in exposure and tone.
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Although it's not the first time such an event -- called an underflight -- has been captured on camera, it doesn't occur very often.
"On average ISS underflights seem to happen a few times a year," Michael Gartley, a scientist at Rochester Institute of Technology, explained in an post by Adam Voiland on NASA's Earth Observatory blog. Two previous such underflights most recently occurred for Landsat 8 on April 17 and Feb. 23 of 2016, and before that once in 2015 and three times in 2013.
Because of how Landsat 8's imager works the original data had to be adjusted to make the shape of the ISS apparent, at the expense of losing resolution in the cloud and surface details. (Learn more here.)
It's not just the space station that Landsat and other spacecraft have identified passing below; communication, weather, and other Earth-observing satellites have also been spotted -- as have larger pieces of "space junk," tens of thousands of which are currently in orbit around our planet.
"(Earth-observing satellites) present an unlikely tool for aiding the space situational awareness community in their task of monitoring the growing population of low-Earth orbit space objects," said Gartley, who processed the Landsat 8 images. "Although the frequency of underflights of space objects is low, the resulting signatures can provide well-calibrated location information."
Launched Feb. 11, 2013, Landsat 8 orbits Earth collecting valuable data and images used in agriculture, education, business, science, and government. Started in 1972 Landsat has provided the longest continuous record of changes in our planet's surface seen from space. Learn more about Landsat science here.