Complex sentence: This rocket was the first man-made device reaching "space" with a height of 84.5 kilometres, for which reason the October 3rd, 1942 is said to be the "day of birth of space travel".
Split into simpler sentences: This rocket was the first man-made device reaching "space" with a height of 84.5 kilometres. For this reason the October 3,1942 is said to be the "day of birth of space travel".