(S (S (BASENP (DT The) (NN purpose)) (VP (VBZ is) (S (VP (ADVP (RB simply)) (VP (TO to) (VP (VB test) (NP (BASENP (DT the) (NN propulsion) (NN system)) (SBAR (WHNP (WDT that)) (S (VP (VP (VBZ uses) (NP (BASENP (DT the) (NN pressure)) (PP (IN from) (BASENP (JJ solar) (NN light) (NNS particles))))) (S (VP (TO to) (VP (VP (VP (VP (VB move) (BASENP (DT the) (NN ship))) (ADVP (RB outward) (PP (IN from) (BASENP (DT a) (NN starting) (NN orbit))))) (PP (IN around) (BASENP (DT the) (NN earth)))) (PP (IN at) (BASENP (NN 500) (NNS miles)))))))))))))))) (PERIOD .))