The UNSC Andraste is UNSC Frigate shown in the art novel Art of Halo 3. The UNSC Andraste was the therd frigate attacking the Ark in the level, 'The Storm' 's ending cutscene. After the failed attack the Andraste took off to an unknown location and did not go though the portal, but stayed on Earth
Triviathe UNSC Andraste is still unknown, only showing its self in the attack, its rummored it took part in the space battle above Reach and was one of the 3 ships that servived the attack. master sargant Haseo served on this ship as an ODST, but was KIA back on Reach, his wife Ayana is the UNSC Andraste's piolet.
PS i looked in to it in the halo history there were only 3 or 4 ships that servived the battle, piller of auttom as one of them!