 The first selection round , consisted of a selection based on science qualifications in the field in question , which Van den Berg easily passed . The final four candidates were tested on physical and mental qualifications which he also passed , while two of the others failed due to possible heart issues . He was now part of the final two , and NASA always trains two astronauts , a prime and a back @-@ up . In 1983 he started to train as an astronaut and six months before the launch he was told that he would be the prime astronaut , much to his own surprise . When he went into space he was 53 years old , making him one of the oldest rookie astronauts . 
