( ( ( A ( potential difficulty ) ) ( of ( an ( adaptive ( secondary mirror ) ) ) ) ) ( ( is ( the ( ability ( to ( verify ( ( the ( commanded ( mirror shapes ) ) ) ( of ( a ( large ( convex ( deformable surface ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT A) (JJ potential) (NN difficulty)) (PP (IN of) (NP (DT an) (JJ adaptive) (JJ secondary) (NN mirror)))) (VP (VBZ is) (NP (DT the) (NN ability) (S (VP (TO to) (VP (VB verify) (NP (NP (DT the) (JJ commanded) (NN mirror) (NNS shapes)) (PP (IN of) (NP (DT a) (JJ large) (NN convex) (NN deformable) (NN surface))))))))) (. .)))
A potential difficulty of an adaptive secondary mirror is the ability to verify the commanded mirror shapes of a large convex deformable surface.
(ROOT (S (NP (DT A) (NN convex) (NN mirror)) (VP (VBZ is) (VP (VBN shaped) (PP (IN like) (NP (NP (DT the) (NN outside)) (PP (IN of) (NP (DT a) (NN bowl))))))) (. .)))
A convex mirror is shaped like the outside of a bowl.