Why aren’t photos from fast-moving spacecraft blurry?
Asked 5/17/2013
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Spacecraft and probes can travel very fast, yet they still return sharp images of planets, moons, asteroids, and other targets. Why doesn’t that motion cause blur in the image, and how do space cameras handle cases where the apparent motion is significant?
Originally by user19869. Source · Licensed CC BY-SA 4.0
user19869
13y ago
2 Answers
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Space is really REALLY big and that has an amazing impact on angular momentum. Think about the sun in the sky. We're on a ball of rock that is moving at 67,000 mph and spinning at around 1000 miles per hour, but yet the sun crawls across the sky.
The reason is because that while the speeds may be very high, the distance is even higher. At very long distances, the difference that a given amount of movement makes is insignificant in comparison to the distance. It moves a very small amount of angle (thus angular momentum) if you were to make a triangle going from where the object or camera is at the start of the shot compared to where it is at the end of the shot.
Additionally, even if the angular momentum was high enough to cause an issue with resolving the image clearly, you can actually use motion control to track the movement if it's a known type of movement. This is frequently used with start tracking land based telescopes for long exposure photography. (Try pointing a camera for 60+ seconds at the sky on a dark clear night and you'll see star trails.) A motion control rig can adjust for the movement and stay focused on the moving subject despite the fact it is moving.
Originally by user11392. Source · Licensed CC BY-SA 4.0
user11392
13y ago
0
Generated from our catalog & community — verify before relying on it.
High speed alone doesn’t necessarily cause blur—what matters is the target’s apparent motion across the camera’s view during the exposure. In space, distances are usually enormous, so even very large real speeds often translate into only a tiny angular movement on the sensor.
That’s why a spacecraft moving quickly can still make sharp images of distant objects: over the short exposure time, the target may shift very little in the frame.
When the apparent angular motion is large enough to matter—such as imaging a planet or moon from low orbit—spacecraft can use imaging methods designed for motion. One common approach is a line-scan camera, which reads out a narrow strip of sensor continuously as the spacecraft moves. The motion of the spacecraft helps build up the full image line by line rather than blurring it.
So the short answer is: blur depends on apparent angular motion and exposure time, not just raw speed, and spacecraft cameras are often designed around the expected motion of their targets.
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