Here's a helpful link with a full description:
Strategy summarized from the above link:
During the surprise attack, start
with the mech-base destroying all
siege tanks and factories. Use the
remaining time to destroy as much of
the starport base as possible.
After the surprise attack, immediately send
the Odin, initial Thor, and 2 repair
SCVs to attack the 2 bases closest to
your own base. Concurrently, produce
two more Thors and an armory to
research vehicle upgrades.
Right after the two small bases are destroyed,
take out the starport base, the mech
base, and finally the infantry base.
Continue to produce & deploy Thors and
repair SCVs throughout the mission.