revision preference src: By December 1963, the parachute was already to undergo full-scale deployment testing. By December 1963 the paraglider spaceplane concept was running into technical difficulties and subsequently became replaced by the parachute splashdown concept. <SEP> tgt: By December 1963, the parachute was already to undergo full-scale deployment testing. On the other hand, by December 1963 the paraglider spaceplane concept was running into technical difficulties and subsequently became replaced by the parachute splashdown concept.