In a bid to send astronauts to Mars, US space agency Nasa has invited applications for four people to live in a simulated Martian exploration habitat in order to prepare them for the real-life challenges of future missions to the red planet. Nasa started taking applications for participants to live for a year in Mars Dune Alpha, a 1,700-square-foot Martian habitat created by a 3D-printer that is inside a building at Johnson Space Center in Houston. Identify the macro environment factor which has influenced Nasa to develop Mars Dune Alpha.