The Collaborative International Dictionary of English v.0.48:

Ascensional \As*cen"sion*al\, a.
   Relating to ascension; connected with ascent; ascensive;
   tending upward; as, the ascensional power of a balloon.
   [1913 Webster]

   Ascensional difference (Astron.), the difference between
      oblique and right ascension; -- used chiefly as expressing
      the difference between the time of the rising or setting
      of a body and six o'clock, or six hours from its meridian
      passage.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ascensional
    adj 1: tending to rise