Texas Republican Senator and likely presidential hopeful Ted Cruz has had it with NASA researching our home planet, preferring that NASA devote its attention to sending humans to Mars and inspiring children with space exploration missions.

His vision collided with NASA's actual mission, which has been in place since its founding in 1958, and was represented at a Senate hearing on Thursday by NASA administrator Charles Bolden.

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Senator Cruz's critique of what he sees as an agency that has drifted off course was met with a strong response by the NASA chief, who forcefully defended the agency's mission.

"I'd like to start by asking a general question," said Cruz on Thursday during a subcommittee hearing on the Obama administration's $18.5 billion budget request for NASA for fiscal year 2016, which includes funding increases for Earth science research.

"In your judgment, what is the core mission of NASA?" Cruz asked.

"Our core mission from the very beginning has been to investigate, explore space and the Earth environment, and to help us make this place a better place," Bolden said. NASA studies everything from the depths of the oceans to the solar energy coming into the Earth's atmosphere.

Cruz pushed back against the "Earth" part of NASA's mission. "Almost any American would agree that the core function of NASA is to explore space," he said. "That's what inspires little boys and little girls across this country."

"I am concerned that NASA in the current environment has lost its full focus on that core mission."

Bolden defended spending more money on Earth science activities, saying he is "proud" of it since it's led to a greater understanding of the planet.

"We can't go anywhere if the Kennedy Space Center goes underwater and we don't know it — and that's understanding our environment," Bolden said, in a clear reference to global warming-related sea level rise.

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

"Science helps exploration, exploration helps science," Bolden said.

Climate activists were dismayed when Cruz was handed the subcommittee gavel at the start of the new Congress. NASA is one of the largest players in climate science research across the entire federal government, in terms of funding, since the agency operates the satellites and other equipment that are essential to keeping tabs on the changing climate.

Cruz, like many Republican lawmakers, denies that manmade emissions of greenhouse gases are the main cause of global warming and its many impacts.

Democratic Senator Bill Nelson of Florida, a former NASA astronaut, defended the agency's focus.

“Earth science directly relates to everything that we’re doing in exploration," he said.

NASA launched an unprecedented five Earth-observing satellites in the past year, studying everything from how carbon dioxide moves throughout the atmosphere to soil moisture content.