1. Satellites and Space Probes

2. Viking Mission to Mars

3. Stardust In the early 1990s, NASA established a program called Discovery to competitively select proposals for low-cost solar system exploration missions with highly focused science goals. Stardust, the fourth Discovery mission, sent a spacecraft to fly through the cloud of dust that surrounds the nucleus of a comet. For the first time ever, the mission brought cometary material back to Earth. Stardust was the first U.S. mission dedicated solely to a comet and was the first to return extraterrestrial material from outside the orbit of the moon. Stardust's main objective was to capture a sample from a well-preserved comet called Wild-2 (pronounced "Vilt-2"). Launched February 7, 1999, from Cape Canaveral, Florida, on a Delta II rocket, Stardust collected interstellar dust as it flew through the solar system in spring 2000. On January 15, 2001, the spacecraft executed a flyby of Earth. In summer and fall 2002, the spacecraft again collected interstellar dust. On January 2, 2004, Stardust flew close to comet Wild-2 and collected cometary particles for analysis. On January 15, 2006, samples of comet and interstellar dust were delivered in a return capsule that will landed in the Utah desert. Through the course of the entire mission, Stardust flew a total of 5.2 billion kilometers (3.2 billion miles).

5. America's first experimental space station, Skylab, was designed for long durations. Skylab program objectives were twofold: To prove that humans could live and work in space for extended periods, and to expand our knowledge of solar astronomy well beyond Earth-based observations. The program was successful in all respects despite early mechanical difficulties. Skylab was launched into Earth orbit by a Saturn V rocket on May 14, 1973. Through the use of a "dry" third stage of the Saturn V rocket, the station was completely outfitted as a workshop area before launch. Crews visited Skylab and returned to Earth in Apollo spacecraft. Three, three-man crews occupied the Skylab workshop for a total of 171 days and 13 hours. It was the site of nearly 300 scientific and technical experiments, including medical experiments on humans' adaptability to zero gravity, solar experiments and detailed Earth resources experiments. The empty Skylab spacecraft returned to Earth on July 11, 1979, scattering debris over the Indian Ocean and the sparsely settled region of Western Australia.

7. The Pioneer Venus Project The Pioneer Venus Project's main objective was to investigate the solar wind in the Venusian environment, map the planet's surface through a radar imaging system and study the characteristics of the upper atmosphere and ionosphere. Pioneer Venus consisted of two spacecraft: the Orbiter and the Multiprobe. The Orbiter carried an assortment of instruments for investigating plasma in upper Venusian atmosphere, observing reflected sunlight from the cloud layers at a variety of wavelengths, in addition to a surface radar mapper, and was launched on the May 20, 1978. It reached orbit around Venus on Dec. 4, 1978. Although originally intended to operate for one Venusian year, most of the Orbiter's instruments were still operating when the spacecraft entered the atmosphere on Oct. 8, 1992. The Pioneer Venus Multiprobe, which was launched on Aug. 8, 1978 and reached Venus on Dec. 9, 1978, was made of 5 separate probes: the probe transporter (referred to as the Bus), a large atmospheric entry probe (called Sounder), and three small probes. The Sounder released from the Bus on Nov. 15, 1978. The three smaller probes released on Nov. 19, 1978. The probes sent data to Earth as they descended toward the surface.

9. Pioneer The Pioneer series of spacecraft performed first-of-their-kind explorations of the Sun, Jupiter, Saturn and Venus. The different missions had little in common except that they all paved the way for later in-depth investigations, and were all spin stabilized.

10. Goals: NASA and the European Space Agency joined forces to send Ulysses to study the heliosphere - the region of space influenced by the Sun and its magnetic field - from a unique polar orbit. The spacecraft's 10 instruments on board measured the Sun's fields and particles, ultraviolet, X-rays and gamma rays. Accomplishments: Ulysses was the first mission to survey the space environment above and below the poles of our Sun. The spacecraft used an unprecedented gravity assist maneuver at Jupiter to hurl itself out of the plane of the ecliptic and into its solar polar orbit. During its 18-year mission, Ulysses made nearly three complete orbits of the Sun. The probe revealed for the first time the three-dimensional character of galactic cosmic radiation, energetic particles produced in solar storms and the solar wind. Not only has Ulysses allowed scientists to map constituents of the heliosphere in space, its longevity enabled them to observe the Sun over a longer period of time than ever before. The spacecraft's six-year orbits over the Sun's poles allowed scientists to observe our star from an unprecedented angle during both calm and turbulent periods. Ulysses also made the first direct measurements of interstellar dust particles and interstellar helium atoms in the solar system and the discovery that the magnetic field leaving the Sun is balanced across latitudes.

12. Galileo plunged into Jupiter's crushing atmosphere on Sept. 21, 2003. The spacecraft was deliberately destroyed to protect one of its own discoveries - a possible ocean beneath the icy crust of the moon Europa. Galileo changed the way we look at our solar system. The spacecraft was the first to fly past an asteroid and the first to discover a moon of an asteroid. It provided the only direct observations of a comet colliding with a planet. Galileo was the first to measure Jupiter's atmosphere with a descent probe and the first to conduct long-term observations of the Jovian system from orbit. It found evidence of subsurface saltwater on Europa, Ganymede and Callisto and revealed the intensity of volcanic activity on Io.