Houston (AP) - For the first time in the history of space travel, two women will perform an outdoor mission at the International Space Station today. The US astronauts Christina Koch and Jessica Meir are to replace a current regulator on the outer wall. The astronauts as well as Nasa explained that the mission was an important milestone for women in space travel. In the past, only 15 spacewalkers had completed field work so far - a women-only squad has never been there before.