NASA uses sun and moon to snap shockwaves

NASA recently used the technique to photograph shock waves caused by a NASA F-18 jet as it flew faster than the speed of sound above the Mojave Desert in the U.S.

Supersonic shockwaves are invisible to the naked eye, but we can photograph the change in refractive index resulting from the gradient in air density.

NASA captured the unbelievable photos shown here using the schlieren technique.

The space agency hopes to use its findings to make supersonic flight quieter, and less disruptive for those of us on the ground. If you’ve ever heard a sonic boom from an aircraft, this wave is what caused it.

The images were then cleaned up to produce the incredible results, which were published on its website on Thursday.

Earlier this year, NASA released some schlieren imagery taken with a high-speed camera mounted on the underside of a NASA Beechcraft B200 King Air, which captured images at 109 frames per second while a supersonic aircraft passed several thousand feet underneath over a speckled dessert floor. These are made more visible using special mathematical image processing algorithms.

As NASA explains, “a bright light source and/or speckled background is necessary for visualizing aerodynamic flow phenomena generated by aircraft or other objects”. Traditionally, this method has required complex and precisely aligned optics as well as a bright light source.

Using a celestial object like the sun for a background has a lot of advantages when photographing a flying aircraft.

There’s a little bit of planning needed to make sure the jet will eclipse the sun at just the right time, relative to the camera’s position on the ground, but it’s much easier and less expensive than flying a second plane to do the experiment. “Capturing schlieren images of a full-scale aircraft in flight was even more challenging due to the need for precise alignment of the plane with the camera and the sun”.

But we’re in an era where background oriented schlieren is opening up a whole new vista of opportunity to capture real aircraft in flight. By using a calcium-K (CaK) optical filter, the granulated texture of the sun’s chromosphere is enough that engineers can capture the distorted shockwave as jets fly across the entire disc of the Sunday. But the clever folks at NASA have managed to use celestial objects as the flawless backdrop for photos of supersonic shock waves.