As with most things in life, NASA missions tend to gain the most attention when they either succeed fantastically or fail utterly.
When Apollo 11 touched down on the lunar surface in 1969, the New York Times ran with the headline "MEN WALK ON MOON." And when NASA's Orbiting Carbon Observatory took a nosedive into the Indian Ocean in 2009, newspaper editors and bloggers alike were quick to break out the "FAIL" headlines.
But what about the NASA programs that neither soared nor plummeted? In this article, we'll run through five space missions that wound up on the cutting room floor.
5. Mercury-Atlas 10
NASA's groundbreaking Project Mercury encompassed six manned launches between 1959 and 1963 -- the first of which saw Alan Shepard make history as the first American to fly in space.
Each subsequent solo mission allowed NASA to hone its space flight technology, leading to the second U.S. manned space flight program, Project Gemini.
NASA had originally planned to finish the project in style with a 10th Mercury launch, sending Alan Shepard up on an encore mission to perform re-entry experiments. But by 1963, NASA's attention was firmly set on getting the two-seater Gemini spacecraft into orbit. In June of that year, NASA canceled Mercury-Atlas 10.
Two years later, Gemini's debut manned flight soared up through the clouds to carry out the previously slated re-entry experiment, only without Shepard. The astronaut was diagnosed with an inner-ear condition called Meniere's disease and did not return to space until 1971's Apollo 14 Moon mission.
This, his second and final space mission, took place a full decade following his historic space flight.
4. Comet Rendezvous and Asteroid Flyby
NASA canceled Mercury-Atlas 10 in order to move on to bigger and better things. The Comet Rendezvous and Asteroid Flyby (CRAF) mission, however, failed to come to fruition in part because it was bigger and better.
The ambitious mission got the boot in 1992 when Congress rolled out funding cuts.
NASA scientists had big plans for CRAF's Mariner Mark II spacecraft, which would have launched in 1995 to not only perform an asteroid flyby, but also ride along with a comet and fire a sensor into its heart. As with many overly ambitious projects, it was also overbudget. So when the axe came down, NASA shuffled the remaining CRAF funds into the endangered Cassini-Huygens mission to Saturn.
Fortunately, CRAF's objectives weren't forgotten, as NASA's Stardust and Deep Impact missions, as well as the European Space Agency's Rosetta mission, would later follow up on these aims.
3. Jupiter Icy Moons Orbiter
Say what you will about NASA's Prometheus Jupiter Icy Moons Orbiter (JIMO) plan, but it certainly wasn't canceled for being boring.
Begun in 2004, the robotic mission would have seen a nuclear-powered, arrow-shaped vessel set out in 2015 for three frozen Jovian moons -- Europa, Ganymede and Callisto -- where beneath caps of ice, lightless oceans might just hide alien life.
Naturally, the mission came with a hefty price tag: $500 million. Given the funding cuts in President George W. Bush's 2006 budget request and the mission's highly ambitious engine design, NASA decided to go in another direction.
The agency allocated $320 million to continue work on the proposed spacecraft's nuclear thermal rocket propulsion system while scrapping the actual trip to Jupiter's frigid moons. Meanwhile, Europa, Ganymede and Callisto continue to keep their secrets.
2. Mars Telecommunication Orbiter
If you were to touch down on Mars today, you'd really have to rough it.
There's no breathable air, the temperature extremes are brutal and there's not a single Internet connection on the entire planet. Seriously, just try and stream your cute cat and Lady Gaga videos on the slopes of Olympus Mons. It's not going to happen.
Yet NASA actually planned to make the first step toward a YouTube-enabled Mars in 2009, when it would have launched the Mars Telecommunication Orbiter (MTO). The spacecraft would have arrived in 2010 to establish the first interplanetary Internet link. The connection would have streamed data between Mars' current population of robotic rovers and their creators on Earth.
NASA killed the $500 million mission in 2005 as part of a shift in priorities. The expected surge in Mars-to-Earth data transmissions just wasn't shaping up as anticipated and, without an immediate need for MTO, it made more sense to devote the precious funds to other missions.
While the orbiter itself was canceled, NASA hasn't given up on the idea. If Earth's involvement with Mars increases in the decades to come, an interplanetary Internet connection will likely come to pass.
1. Pluto Kuiper Express
As we saw with the Mars Telecommunications Orbiter, a canceled NASA mission is often just a little ahead of its time. The Pluto Kuiper Express (PKE) was a similar case.
This spacecraft was originally slated to launch in 2004 for a 2012 arrival at the dwarf planet Pluto, where it would study the far-flung Kuiper Belt of space beyond Neptune. With a year 2000 price tag of $350 million, can you guess why NASA canceled its first mission to Pluto? That's right: budgetary concerns.
When news spread that the PKE was destined for the scrap heap, the Planetary Society, the world's largest space interest group, launched a letter-writing campaign to try to save the project.
Naturally, efforts to win over members of U.S. Congress failed and, in 2006, Pluto fans suffered another blow as the International Astronomical Union took away its planet status. Yet, that same year, NASA successfully launched PKE's successor, the New Horizons Pluto Kuiper Belt Flyby.
In 2015, the spacecraft will indeed cross paths with the black sheep of our planet's solar family.