The days of big government funding of the space program are gone. At the end of World War II, a new era of competition between the United States and the Soviet Union began. Out of this Cold War came the Space Race. Each side was eager to prove its technological dominance by being the first to put a man on the moon. On July 20, 1969, Apollo 11 successfully placed two astronauts on the moon, giving the United States the edge in the Space Race.

Winning the Space Race wasn't cheap. The year of 1966 marked the largest space expenditure in government history with nearly 4.5% of U.S. government spending committed to NASA. From 1964 to 1967, more than 3% was committed to winning the Space Race.

Since the days of the Cold War, government funding of NASA has slowly declined. The 2012 projections call for only 0.5% of spending to go to NASA. Numerous missions were canceled because of the falling budget since the Cold War:

Pluto Kuiper ExpressThe Pluto Kuiper Express was a spacecraft that was planned for launch in 2004. It was slated to arrive at Pluto in 2012. The goal of the mission was to study the Kuiper Belt that sat beyond Neptune. The price tag in 2000 was $350 million. This cost was too steep for Congress to stomach. In 2006, plans to explore Pluto were again impacted when its status as a planet was removed. However, later that year NASA launched a spacecraft that will reach Pluto in 2015.

Mars Telecommunication OrbiterIn 2009, to service its growing population of rovers and other planned science vehicles, NASA was to launch an orbiter to arrive in 2010 called the Mars Telecommunication Orbiter. Its primary duty was to provide a better means of communication between Mars and Earth. Think of it as an upgrade to the planet's Wi-Fi system at a cost of $500 million. This project was canceled in 2005 because NASA shifted priorities. No longer was the anticipated volume of data enough to justify the high cost.

Comet Rendezvous and Asteroid FlybyThis project had big goals. This spacecraft, set to launch in 1995, was going to perform an asteroid flyby, but it had the loftier goal of piggybacking on an asteroid and firing a sensor into its core. The project was canceled in 1992 as a result of congressional funding cuts. Later, NASA realized some of the goals of this mission with its Stardust and Deep Impact missions.

ExoMars MissionThe ExoMars Mission was to be a collaboration between NASA and the European Space Agency that would have landed a mobile scientific platform on Mars. The craft was supposed to then drill deep into the subsurface of Mars and analyze those samples. Scientists know that because of the hostile environment of the planet, proving that life once existed on Mars would require drilling into the planet where erosion hasn't had an effect. The platform was to land on Mars between 2016 and 2018. According to Space.com, the United States will likely tell the ESA that it can no longer provide a launch vehicle for this mission due to budget cuts.

The MoonIn 2003, President George W. Bush laid out a vision to return human beings to the moon by 2020. In 2010, President Obama shifted the vision from landing astronauts on the moon to developing lower-cost vehicles that could act as space taxis. This vision included provisions to incentivize NASA and private companies to develop lower-cost vehicles to reach space. This emphasis came in the wake of the high-dollar space shuttle program that proved to be more costly and less versatile than originally planned.

The Bottom LineThe biggest of NASA's accomplishments and its failures are well known. Who could forget the "one small step for man" event or the Challenger and Columbia disasters? Opponents of the nation's space policy argue that the space program has gone backwards. Michio Kaku, professor of theoretical physics at the City University of New York, argues that NASA's priorities are in desperate need of a new vision.

Priorities are often dictated by money. In a global economy where there is little room for discretionary spending, funding for space exploration has been put on hold around the world.

Excerpt from:

5 NASA Missions You Didn't Know Were Canceled