Space travellers are people who explore outer space. They can be divided into three categories: comets, astronauts and cosmonauts. Comets are celestial bodies made up of ice, dust and rock that orbit the sun. Astronauts are people who are trained to travel in space and work on spacecrafts. Cosmonauts are people from Russia and other former Soviet Union countries who are trained to travel in space and work on spacecrafts.