Idea:

Sent back in time every ten minutes -- no knowledge of pervious trip.

Quantum computer's idea to find the right access code to shut down the
drive (there's an infinite number of possibilites).  Drive can cause
cataclysmic failure but has manual override due to embarrassing
incidents with insance AIs.

Has to pass on attempted code somehow?  Is there first as there's no
code.

The mechanism to forward on the code doesn't work.

The next one thinks they're the first...

THE CODE IS PASSED ON BY WRITING IT ON THE BACK OF THE HAND