This past August the U.S. landed a one-ton spacecraft on the surface of Mars. Sending a spacecraft to Mars is not unique in itself, since we have sent several exploration vehicles to the Red Planet over the past five decades.

The latest such mission placed Curiosity Rover on Aeolis Palus in Gale Crater.

This very advanced rover system carries instruments that will look for conditions relevant to the past or present habitability of the planet. Over the next few years, Curiosity will explore its landing site while searching for evidence that Mars was once capable of supporting life. Of course, the other question is whether Mars could support life in the future.

About two weeks after Curiosity arrived at Mars, NASA selected InSight as its 12th mission in its Discovery Program. InSight (Interior exploration using Seismic Investigations, Geodesy and Heat Transport) will carry out a unique geophysical investigation of Mars, looking into its deep interior to see why the Red Planet evolved so differently from Earth.

The mission involves placing instruments on the Martian surface to investigate whether the core of Mars is solid or liquid, and why Mars' crust is not divided into tectonic plates that drift like those of Earth.

Knowledge gained about the interior of Mars in comparison to Earth will help scientists better understand how terrestrial planets form and evolve.

However, Curiosity is certainly far and away the most complex vehicle to reach Mars, and it may be the last of the rovers for decades to come. Given the trend in space exploration budgets and the economy in general, it is unlikely NASA will be able to afford any future missions of this scale until such time that astronauts are sent to the planet. Since there is no urgency to do this, it will be at least decades before the U.S. will mount a human expedition to Mars.

NASA does have one other Mars mission planned to occur between Curiosity and InSight. It is a modest orbiter called MAVEN, slated for launch next year to study the planet's atmosphere.

Other modest missions may be funded in the interim decades ahead, but budget cuts and ongoing indecision at NASA regarding future missions suggests it could be a decade or more before any NASA mission touches down on the Red Planet's surface beyond InSight.

NASA had agreed to work with the European Space Agency (ESA) on a joint series of missions called ExoMars. However, when the Obama administration released its fiscal year 2013 budget proposal last February, there were no funds for NASA participation in ExoMars. That decision also included a proposed 20-percent cut in NASA's overall planetary sciences program.

Surely, part of the reason for the proposed cuts is the fact that the Curiosity Rover mission saw its costs increase from initial estimates of about $1.6 billion in 2006 to $2.5 billion by 2012.

In addition the original 2009 launch slipped to 2011. NASA's science program has also been squeezed by the increasing costs of other complex missions, such as the James Webb Space Telescope (JWST), which now has an estimated cost of $8 billion.

So, who is killing the space program? The answer seems to be: everyone involved. Program managers and contractors underestimate program costs. Politicians don't have a mandate to spend large amounts of money on space exploration in the current budget environment.

NASA is not creating enough public excitement and interest in these programs to demand that congress fund them. The space community is not innovating new, low-cost missions of importance. There seems to be a general malaise among the space "movers and shakers."

The simple truth seems to be that space exploration has matured to the point where public interest levels have fallen while costs have risen to extreme heights.