NASA's Constellation program did include such steps, but President Barack Obama cancelled it in 2010 with approval from many scientists, who wanted a more ambitious goal.

Among those who now think that was a mistake is the director of the Hayden Planetarium in New York, Neil deGrasse Tyson.

“I understand the rhetoric that we have been to the moon, so why go back? But the real answer is that we have not been to the moon in 40 years,” Tyson said.

Tyson says the current Mars plan is too vague.

“I think we have lost our way, in the real world. What works on paper does not always work in the real world and, in the real world, we have lost our way,” Tyson said.

David Alexander, director of the Space Institute at Rice University, puts the blame for NASA's current predicament on the politicians who tightly control the funding.

“A lot of people blame NASA for not having a plan or not having this and that, but, actually, they have lots of plans based on what they have been told to do by Congress and by various Congresses over the years,” Alexander said.

But Congress has many enthusiastic supporters of space exploration, says NASA Deputy Administrator Lori Garver.

“We work closely with appropriators and authorizers and we believe there is broad support for a stable NASA budget,” said Garver.

And Garver believes Congress will fund the new launch system and other technology NASA needs to get humans to Mars, fulfilling a goal that she says NASA has had in mind for decades.