wow, they still use analog film
A sheet of slow (fine grain) film at this size can capture detail way beyond what any digital sensor I know of - surely it can be scanned with the equivalent of multi-gigapixel resolution - and if one were to develop such a monster sensor, it would have a hard time competing with the film in all but a few edge cases. (Most notably the ability to transmit imagery to the ground immediately, provided the necessary bandwidth is available.)
You make a good point about the scanning. Any wet film product these days must generally be scanned to allow for further production in our "soft-copy" world.
My (attempted!) point was that fine-grain film* creates a negative which will be a challenge to match for most sensors out there - it is my understanding sensor yield drops drastically as it increases in size, so if you need a huge sensor, film is still the most cost-effective solution for a lot of applications. Then again, 'cost-effective' and 'national security' are two phrases which do not often come up in the same sentence!
*) My favourite - ADOX CMS20, has a resolving power which easily outperforms even a Summicron 50 at a sensible (not diffraction-restricted) aperture - more than 500lp/mm; the manufacturer claim up to 800lp/mm are resolvable (!)
That translates into some 12,500 line pairs/inch of film/sensor, as long as the optics are holding up their part of the bargain - or somewhere just short of 1 gigapixel from a 24x36mm frame, if scanned using -cough- sufficiently expensive equipment.