Mars or bust? A daring mission to send NASA astronauts on a nearly 600-day mission to fly by Mars and Venus in the early 2020s has picked up some fans in the U.S. Congress. (See: "Future of Spaceflight.")

Even as NASA confirmed plans in its latest budget proposal Tuesday to develop a human mission to visit a nearby asteroid, members of the House Science Committee endorsed the alternative Mars mission.

"It is the least complex mission profile for reaching the Mars vicinity," said Doug Cooke, a former NASA associate administrator for exploration, during a committee hearing on February 27. "The mission provides an opportunity for an incredible first step that will make travel to Mars real to the people of the world."

Under the proposed mission, NASA's Space Launch System (SLS) heavy-lift rocket would launch an Orion spacecraft carrying two astronauts in November 2021. The spacecraft would fly past Venus in April 2022 and Mars in October of that year before returning to Earth in June 2023.

While NASA is already developing SLS and Orion, the mission would require the development of a more powerful upper stage for SLS and of a habitation module. (See: "Up on the Farm? Five Reasons NASA Needs Space Greenhouses.")

Mars Inspiration

The flyby mission is based on a concept called Inspiration Mars introduced a year ago by Dennis Tito, a multimillionaire who, in 2001, became the first tourist to visit the International Space Station. Tito's original proposal called for a privately financed 2018 mission to fly past Mars alone, returning 501 days later. By late last year, though, Tito said the mission required NASA's support, including SLS and Orion.

The mission proposal comes at a time when there is a lack of consensus about the next step in human spaceflight beyond Earth orbit. While most agree the long-term goal should be landing humans on Mars, there's less agreement about the path to take to get there.

Asteroid or Bust?

Last year, NASA unveiled plans for what it believes should be that next step, the Asteroid Redirect Mission. A robotic spacecraft would travel to a small near-Earth asteroid and shift its trajectory into an orbit around the moon. Astronauts would then visit it with an Orion spacecraft in the early 2020s.

NASA, though, has provided few additional details about the proposed mission, and many in Congress are skeptical that the mission makes sense.

"While consensus on Capitol Hill might be hard to find, there is general agreement that the president's asteroid retrieval mission inspires neither the scientific community nor the public who would foot the bill," said Lamar Smith, the Texas Republican who chairs the House Science Committee, at the hearing. "NASA, the White House, and Congress should consider this Mars flyby mission proposal."

Other members of the committee, though, were more skeptical of the proposed Mars flyby mission. Eddie Bernice Johnson, the top Democrat on the committee, noted that 2021 is the currently scheduled date of the first SLS/Orion mission to carry astronauts, after an uncrewed test flight in 2017.

"I doubt that a flyby of Mars will ultimately be considered an appropriate first shakedown flight for a new crewed spacecraft," she said.

Space Stepping-Stones

No NASA officials testified at last week's hearing, and NASA Administrator Charles Bolden didn't directly answer questions about the mission concept during a briefing with reporters Tuesday about the agency's 2015 budget proposal.

However, he emphasized that NASA did have a "stepping-stone approach" for sending humans to Mars, and that the planned asteroid mission—for which NASA is seeking $133 million in that budget request—was a key step toward that long-term goal.

"In order to carry out these pioneering missions, we have to develop technologies for our Asteroid Redirect Mission that will lead to the subsequent first crewed mission to Mars," Bolden said. However, he must convince members of Congress and others who have their minds set on a near-term Mars mission.

"I continue to believe, as do many Americans, that Mars is the logical destination to put human space exploration back on track and demonstrate the 'can do' spirit that seems to have faded over time," Tito said in a statement after last week's hearing.

"The window of opportunity in 2021 is challenging but achievable and waiting to be claimed."