Prospero is a small retrograde non-spherical moon of Uranus found on 1999-07-18 by the astrophysicist Matthew Holman and his team , and given designation S\/1999 U 3 . Prospero is a relatively small retrograde irregular satellite of Uranus discovered on 18 July 1999 by the astrophysicist Matthew Holman and his team , and given the provisional designation S\/1999 U 3 .