Congress has given NASA a mandate to put a human on Mars. It hasn't, however, given the space agency enough money to do it.

Outside experts have been pointing out this absurdity for some time. On Wednesday, Congress heard it directly from NASA's Inspector General Paul Martin, the person charged with overseeing the space agency.

The problem is simple: NASA is currently developing a space capsule (called Orion) and rocket system (called SLS) that could theoretically take astronauts to Mars, as ordered by Congress. But as Martin explained in his testimony before the House, lawmakers haven't given NASA enough money to develop the technology needed to use these systems for a Mars mission:

Even after the SLS and Orion are fully developed and ready to transport crew NASA will continue to face significant challenges concerning the long-term sustainability of its human exploration program. For example, unless NASA begins a program to develop landers and surface systems its astronauts will be limited to orbital missions of Mars. Given the time and money necessary to develop these systems, it is unlikely that NASA would be able to conduct any manned surface exploration missions until the late 2030s at the earliest.

Budget limitations, Martin added, are forcing NASA to develop the plan to go to Mars piecemeal — building a rocket system now, and hoping it'll get the money to build a lander later. For an analogy, imagine building the foundation to a new house before knowing whether you'll get a mortgage to pay for the rest of it.

This approach, Martin notes, typically causes schedule and cost overruns. But it can also lead to an even more absurd scenario: it's entirely possible that NASA will complete SLS — the largest rocket ever — by 2018, but have no money to actually do anything with it for a decade.

"SLS and Orion, by themselves, cannot do very much," John Logsdon, former director of the Space Policy Institute, told me earlier this month. "And there's just not going to be enough money for an exploration program unless something changes drastically."

This analysis comes just a day after Ted Cruz, conducting his first hearing as chair of the Senate's Subcommittee on Science, Space and Competitiveness, stressed the importance of putting a person on Mars. But so far, neither he nor other politicians have given any indication of how that'd actually be possible.

Further reading: For NASA, sending a person to Mars is simple. Dealing with Congress is hard.