12. The Pioneer Missions
Before we could send men to the Moon, we had to first learn to leave the pad. Largely unknown, the first several unmanned Pioneer launches failed prior to the semi-success of Pioneer 4 in 1959. These demonstrated just how tough space travel was and paved the way for the success of the Surveyor and Apollo programs. The Pioneer program itself was ultimately a success, sending probes past Jupiter and Venus.
11. Mercury-Atlas 6
On Feb. 20, 1962, astronaut John Glenn became the first American to orbit the Earth. The spacecraft was Friendship 7, a capsule so tiny that astronauts joked the Mercury spacecraft was to be worn, rather than piloted. Glenn orbited the planet a total of three times before splashing down in the Atlantic. The mission earned Glenn worldwide acclaim, and he was celebrated as a hero in the United States.
Glenn, one of NASA’s original class of seven astronauts introduced in 1959, retired from NASA in 1964 to pursue a career in politics. However, in 1998, 36 years after his record-setting orbital mission, Glenn returned to space at age 77 as a crewmember aboard Space Shuttle Discovery.
10. Gemini 8
Sandwiched between Mercury and Apollo were the crucial Gemini missions. These demonstrated skills such as extra-vehicular activity, or EVA, docking and duration capabilities that astronauts would need to master to journey to the Moon. Gemini 8 highlighted this, when an emergency during docking with the Agena rocket forced early undocking and re-entry. The quick thinking and response by Neil Armstrong contributed to his selection for the first lunar landing.
9. Viking Missions to Mars
Mars is a tough place to operate. Few landings have been successful; the Russians, for example, have never made a successful landing on the Red Planet in 13 tries. The first successful U.S. soft landing on another planet occurred in 1976 with the Viking 1 lander. It and its sister mission, Viking 2 and their companion orbiters, studied Mars until 1980.
STS-1 was the first flight of the US Space Shuttle program, the STS standing for Space Transportation System. STS-1’s primary objective was to test and certify the system. This was also the first time humans were aboard a launch vehicle on its maiden flight. (The first Saturn V launches were unmanned). Launched April 12, 1981, STS-1 and Shuttle orbiter Columbia ushered in an era of reusable spaceflight technology and a return of the United States to manned spaceflight.
7. New Horizons
Launched in 2006 into a solar system escape trajectory, with a record speed of 36,373 mph, New Horizons will pass Pluto in 2015. The only mission that made this list that has yet to reach its objective, New Horizons has already returned stunning images of Jupiter during its 2007 flyby and gravity assist maneuver. After reconnoitering the Pluto-Charon system, New Horizons will continue on to any Kuiper Belt objects of opportunity.
This final repair mission in 2009 to the Hubble Space Telescope was originally cancelled after the Columbia disaster. After Columbia, it was deemed mandatory that final shuttle missions be dedicated to completing the International Space Station as a safe harbor in the event of damage similar to what doomed Columbia. The ground swell of support from both the public and the scientific community was so great, however, that one final mission to the aging space telescope was planned, with a backup rescue shuttle on the pad as a contingency. Astronauts from the Space Shuttle Atlantis replaced and repaired instruments aboard Hubble during five EVAs, extending the life of the orbiting telescope at least through 2014.
A joint mission between NASA and the European Space Agency, Cassini-Huygens was launched in 1997. The Cassini spacecraft became the first spacecraft to orbit the planet Saturn, in 2004. Cassini then released the ESA’s Huygens probe, which achieved the most distant landing of a spacecraft to date when it landed on Saturn’s moon Titan. Cassini has discovered seven new moons and sent back stunning pictures of both Saturn and its retinue of worldlets.
4. Apollo 8
In late 1968, astronauts Frank Borman, James Lovell and William Anders became the first humans to leave Earth orbit. The mission was largely a surprise to the public, and came months ahead of schedule in response to a feared Soviet manned launch the same year. The lunar module was not yet ready for flight, so the crew of Apollo 8 conducted their flight with the Command Module only. The famous Earthrise photo (shown above) was taken by the Apollo 8 crew. The biggest risk, of course, was lunar insertion; failure of an engine burn at the correct time for a precise length would have left the astronauts stranded in space. In some ways, Apollo 8 was the most dramatic of all the flights to the Moon.
3. Apollo 11
On July 20, 1969, the crowning achievement of United States spaceflight occurred when Neil Armstrong set foot on the Moon. Armstrong and Aldrin stayed on the lunar surface for 21 hours and 31 minutes, and returned to Earth with 47.5 pounds of moon rocks. But the most hair-raising portion of the mission was the landing; the crew made the surface with only 25 seconds of fuel remaining.
2. The Voyager Grand Tour Missions
Launched in 1977, the Voyager 1 and 2 spacecraft were arguably the most successful missions ever, completing flybys of Jupiter, Saturn, Uranus, and Neptune. This mission exploited an alignment of the outer planets that will not happen again in our lifetimes. Both Voyagers are still transmitting from the outer solar system, Voyager 2 at 95 Astronomical Units (A.U.), and Voyager as the most distant man-made object ever launched, at 116.7 A.U.
1. Apollo 13
Dubbed a “successful failure,” trouble started for the crew of Apollo 13 when an oxygen tank ruptured on their way to the Moon. Quick thinking by ground controllers (shown above discussing the crisis) and the crew resulted in a slingshot maneuver around the Moon and a return to Earth. The mission’s plight captivated the nation’s attention as the crew struggled to get their wounded spacecraft home safely. If Apollo 11 proved NASA’s ability to set a lofty goal and achieve it, Apollo 13 demonstrated the space agency’s resourcefulness and flexibility to confront a tough situation and ultimately triumph when things went wrong.