Apollo (1961): It was the NASA program that resulted in American astronauts' making a total of 11 spaceflights and walking on the moon.
Hubble (1990): It is the most productive science mission in the history of NASA. It has helped scientists understand how planets and galaxies form.
Viking (1976):The first spacecraft to successfully land on Mars, it 1 was part of a two-part mission to investigate the Red Planet and search for signs of life.
Chandra (1999):It is the most sophisticated X-ray observatory built to date. It is designed to observe X-rays from high-energy regions of the universe, such as the remnants of exploded stars.
Cassini-Huygens (1997):This spacecraft orbited Saturn, making an extensive survey of the ringed planet and its moons.