The Exploration of Space

able acceleration actual already appear astronautics astronomers atmosphere become body build carry certainly Chapter close completely consider considerable course deal developed difficult direction discovered discuss distance Earth effect energy escape example exist exploration extremely fact fall field Figure fuel give given gravity greater heat human hundred idea imagine important increase interesting interplanetary involved journey known landing later least less light limit live look lunar Mars material matter means miles million minutes Moon motors moving necessary never observed once orbit oxygen perhaps period planets Plate possible practical present pressure probably problem produce radio range reach reason remain rocket round satellite seems seen ship shown simple Solar space spaceship speed stars stations structure surface telescope temperature thousand Universe velocity Venus weight whole