From Halopedia, the Halo wiki
Farthest Outpost is the thirteenth track (Disc 1 Track 13) included in Halo 3: Original Soundtrack, and plays during the Halo 3 campaign level The Ark. It is composed of Farthest Outpost (0:00-2:03), No Time for Sightseeing (2:03-2:49), and Make Them Pay (2:49-5:14).
Farthest Outpost (2:03) begins with the vocals singing gracefully, unaccompanied. Strings enter to echo the melody before muted percussion enter, leading into a section of bass line and percussive beats, the latter of which features the same snare drums and hi-hat parts from In Amber Clad (from Halo 2: Original Soundtrack). Low strings enter, playing a flowing melody as the vocals continue softly in the background. After the melody has repeated a few times, the percussion takes over while the the strings briefly plays the melody of Weight of Failure (from Prologue in Halo 2: Original Soundtrack). The piece plays in the opening cutscene, when the Fleet of Retribution arrives at Installation 00, and makes a reprise in the credits of Halo 3 in the form of Duty Bound (from the later track Roll Call). The opening strings were later featured in the track From the Vault from Halo: Reach Original Soundtrack.
No Time for Sightseeing
No Time for Sightseeing (0:46) is a short reprise of the digital notes and bass line from the track Out of Shadow, though using muted percussion, thus resembling a rearrangement of the second section of Broken Gates (from Mombasa Suite in Halo 2: Original Soundtrack), albeit without the male vocal. This section plays when John-117 launches the attack on the the Type-27 Mantis under construction.
No Time for Sightseeing is also played in The Ring Experience of Halo: Outpost Discovery, during the section in which the Honeybee drone crosses the desert landscape on the Halo with various wildlife, before proceeding to enter the ring's internal superstructure to encounter Sentinels. The section is followed by the gregorian chant of the Halo Theme.
Make Them Pay
Make Them Pay (2:25) is a full rearrangement of Perilous Journey (from Halo: Original Soundtrack), though the sounds of the strings sections are considerably crisper compared to the original rendition. A heavy bass drum is audible in the background playing seven beats before resting and then repeating. This section plays when John-117 commandeers the vehicles at the crashed D77H-TCI Pelican.