Eventuellt "First Through Time" av Stanley Bennet Hough, skrivande som Rex Gordon. Publicerad 1962, så det fungerar. Jag har bara Goodreads översikt men:
Manlig astronauts huvudperson.
Kvinnlig operatör av synkrotron i USA.
Framtidens apokalyps.
En av omslagsdesignerna visar en silhuett mot ett klockans ansikte.
The top secret synchrotron took accurate photos of the future - and what they showed was disaster, both for the girl who ran the machine and the world she worked for. Major Judgen, astronaut, had trained for a first flight through space. Now he was called on to put his ability into an untested flight across time. Was his girl friend's death a certainty - and did that same certainty also doom the rest of humanity? Or was there a way to snatch a double victory from the discoveries to be made on the day after the world came to an end?