Sounds like they used a Gigapad. It was designed for NASA Mars flights. I've got one and it's completely programable. Depending on how you set it up, it can take a few photos to hundreds. Then you use a stitching software to put it all together. The final image size depends on how many megapixels and photos taken. Processing this info can take a lot of time as well....about like processing a time lapse video. I usually try and limit mine to around a few dozens photos which generally comes out to a few gigabytes.