Aegis’s key ability


All psionic classes has own key ability except Aegis. I searched through many manuals but I found nothing to help me. I ve found "Table: Ability Modifiers and Bonus Power Points" but Aegis can’t use and "A saving throw against your power has a DC 10 + the level of the power + your key ability modifier (Intelligence for a psion, Wisdom for a psychic warrior, or Charisma for a wilder)." Nothing for Aegis. Can you help me understand?