The first of three international missions to Mars gets underway Tuesday when a Japanese H-2A rocket boosts a United Arab Emirates spacecraft known as "Hope" into space for a seven-month voyage to the red planet. It will be the first interplanetary mission ever attempted by an Arab nation.

A little more than a week later, China plans to launch its Tianwen 1 mission, sending its first orbiter and a surface rover to Mars while NASA presses ahead with launch of the agency's $2.4 billion Perseverance Mars rover, equipped with a small drone-like helicopter, on July 30. All three will reach their target in 2021.

The three missions are taking advantage of a planetary launch window that only comes around once every 26 months when Earth and Mars are in favorable positions in their orbits around the sun. This year's launch window closes in mid August, and any spacecraft delayed past then will face two years of expensive storage.

The European Space Agency had planned to join Emirates, the United States and China, sending a powerful rover to Mars during the current window. But ESA recently was forced to stand down until the next window, primarily because of problems with the parachutes needed to help lower the rover to the martian surface.

And so, the UAE will lead the way this year with the Emirates Mars Mission, and if all goes well, Hope will brake into orbit around Mars next February to kick off a complex mission to shed new light on the physics and chemistry of the martian atmosphere.