He wanted to make sure that the engine was working and could be used to return early to the Earth if necessary.
hiː wˈɔntᵻd tə mˌeɪk ʃˈʊɹ ðætðɪ ˈɛndʒɪn wʌz wˈɜːkɪŋ ænd kʊd biː jˈuːzd tə ɹᵻtˈɜːn ˈɜːli tə ðɪ ˈɜːθ ɪf nˈɛsᵻsɚɹi.