From Halopedia, the Halo wiki
Soundtrack:
Music of Halo: Nightfall
Composer(s):
Christopher Carmichael
Length:
1:38
Previous:
Red Sunrise
Next:
How Will You Die
Countdown is a piece of music made for Halo: Nightfall as part of the Music of Halo: Nightfall. It is composed by Christopher Carmichael. The track runs for 1 minute and 38 seconds.[1] It is heard in the fifth and last episode, when Randall Aiken detonates the HAVOK nuke, and Jameson Locke and Talitha Macer manage to escape Alpha Shard.