Get ORA-01157 when startup database

I created a datafile /tmp/encrypted_ts.dbf. When the machine started again, the datafile was gone. When I started it I got ORA-01157, the details are:

ORA-01157: cannot identify/lock data file 54 - see DBWR trace file
ORA-01110: data file 54: '/tmp/encrypted_ts.dbf'

So I ran alter database datafile 54 offline drop;, and I got ORA-01516. How can I startup the database again?