To take many exposures of the same scene and average the pixel values with the corresponding pixels from all the exposures. This increases the SNR and dynamic range, but naturally doesn't work very well if your subject isn't static. It doesn't increase the resolution of the image though.
For the 16mm movie cameras in this case, they probably selected frames from rigidly mounted cameras with little subject motion to get a good result out of it. Glenn strapped in tight in his tiny cockpit probably provided them with a decent number of frames they could stack without introducing much motion blur. In fact, you can see a bit of blurring at the end of one of the white straps center frame in that shot: https://cdn.arstechnica.net/wp-content/uploads/2025/09/03b-G...
For the 16mm movie cameras in this case, they probably selected frames from rigidly mounted cameras with little subject motion to get a good result out of it. Glenn strapped in tight in his tiny cockpit probably provided them with a decent number of frames they could stack without introducing much motion blur. In fact, you can see a bit of blurring at the end of one of the white straps center frame in that shot: https://cdn.arstechnica.net/wp-content/uploads/2025/09/03b-G...
It's a pretty common technique in astrophotography. Here's a page that goes into some more detail in that context: https://clarkvision.com/articles/image-stacking-methods/