NASA's mission to land on an asteroid and its Earth Science division drew criticism from members of Congress, as administrator Charles Bolden defended the agency on Capitol Hill.

At a House hearing on NASAs 2016 budget, space subcommittee chairman Lamar Smith criticized what he called "the disproportionate increase" in funding for the Earth science research, saying that over eight years almost $2 billion has been added to its budget. Smith and other Republicans argue that NASA should be focusing its resources on exploration in space instead of studying the climate here on Earth.

"There are 13 other agencies involved in climate-change research, but only one that is responsible for space exploration," Smith said. "The administration continues to starve NASA's exploration programs to fund a partisan environmental agenda. NASA simply deserves better."

Bolden, a retired marine corps general and former astronaut defended the division, saying, ""Nasa since its inception has responsibility for exploring the universe and also taking care of Earth, my favorite planet."

When asked if he would support moving Earth science research under the Environmental Protection Agency, Bolden balked.

"There's no 's' in NASA for 'science' and some think we shouldn't do science, but that's absurd," Bolden said.

Republicans have made an effort to drain funding from government research into climate change. While most Republicans support NASA, they have recently taken aim at its Earth science program that studies rising ocean temperatures, pollution and carbon dioxide levels in the atmosphere, amonth other areas.

Ted Cruz, chair of the Senate committee that overseas NASA, sparred with Bolden over the program. "I am concerned that NASA in the current environment has lost its full focus on that core mission."

"It is absolutely critical that we understand Earth's environment, because this is the only place we have to live," Bolden retorted.

The first objective of NASA's charter, as laid out by Congress, is "the expansion of human knowledge of the Earth and of phenomena in the atmosphere and space."

House Republicans also criticized the space agency for its planned "asteroid redirect mission," which has the objective of cutting off a boulder from an asteroid and placing it in orbit around the moon for study, calling the mission "uninspiring."

Bolden defended the asteroid mission by saying it was both a step on the path to Mars and an opportunity to "inform our ability to deflect asteroids". Asked why he had ignored recommendations about the program, he said: "I believe in constancy of purpose."

A final point of tension was NASA's reliance on Russian space shuttles to send astronauts to the International Space Station. Brooks said that since the American shuttle program was canceled, "the US hitches rides from Russia, we are no longer the preeminant space program."

Bolden argued that as long as Congress provides the funding, the missions will resume from US soil again in 2017, and NASA will "stop writing checks to the Russian space agency."

Representative Dana Rohrabacher suggested that the US should outsource its Mars mission to a private contractor such as SpaceX.

Bolden countered that "no commercial company is going to independently go to Mars without support of government," and said that he believes that relying on a private company would only slow the mission.