For years we've been hearing that NASA plans to send a manned mission to Mars. The ideal time for this would be a period when Earth and Mars orbit close to each other for both the "to" and back" trips, and just such a period of "Mars Close Approach" will arrive in the 2033 to 2035 time frame. In preparation for this proximity, Boeing (BA -2.20%), one of the key contractors building NASA's new Mars-capable Space Launch System, laid out a six-step program in March 2016 describing how the trip will go -- and when.

But that was then, and this is now. Now, NASA's associate administrator for human exploration, William Gerstenmaier, admits that NASA might not have the money it needs to go to Mars by the 2030s -- or at all.

Mars sunrise

Destination: Mars. But it will cost NASA a bundle to get there. Image source: Getty Images.

Popular Mechanics covers a popular mission

This, in a nutshell, is the sad tale told in the latest issue of Popular Mechanics, which reports that NASA has two big problems with putting human footprints on Mars.

The first is technical. In PM's words, Gerstenmaier told a recent assembly of the American Institute of Aeronautics and Astronautics that "the agency just doesn't know how to land something as heavy as a crewed spacecraft on Mars." The problem is the air on Mars -- or rather the lack of it.

Mars' atmospheric pressure is less than 1% that of Earth's -- meaning there's less air for a parachute to grab onto to slow a spaceship's descent to the Martian surface. At the same time, there is some atmosphere -- enough that a spaceship must still carry a heavy heat shield along to protect it when entering the atmosphere.

NASA estimates that a crewed lander sent to Mars would probably weigh between 10 and 15 metric tons -- at least five times more massive than the Curiosity Rover (plus all its landing gear) that landed on Mars in 2012. But because of the parachute paradox, NASA currently lacks the technical know-how to put a spaceship so massive down on Mars safely.

That brings us to NASA's second big problem: money. Currently, NASA has a $19.3 billion annual budget, which must cover not just the bill for preparing a Mars mission, but the cost of running (and supplying) the International Space Station, launching research satellites, and a whole host of other programs besides. Assuming a roughly 2% annual rate of increases in NASA's budget, America's space agency lacks the funding it would need to develop "surface systems" adequate to land a manned mission on Mars, a mission which experts estimate would cost anywhere from $100 billion to $1 trillion

Adding to NASA's problems, President Donald Trump's most recent proposed federal budget called for NASA's funding not to rise 2% -- but to drop by $200 million instead.

Can SpaceX save the day?

Now, there is another option: NASA could outsource the Mars landing mission to SpaceX, which founder and CEO Elon Musk has boasted will be able to land men on Mars sooner than NASA, and at a lower cost. Musk says he can get the job done for as little as $10 billion per astronaut.

In recent years, SpaceX has boasted of plans to land an unmanned "Red Dragon" space capsule on Mars on its own, and "as soon as 2018," a date later walked back to 2020 (Musk's deadlines are notoriously malleable). Subsequent missions would drop more Dragons on Mars, each carrying supplies to be used by SpaceX astronauts targeting a 2025 manned landing on Mars. For this mission, SpaceX had been designing a crewed "Red Dragon" spaceship estimated to mass just six tons -- still three times bigger than the Curiosity mission, but perhaps half the mass of NASA's planned lander.

Problem is, Musk admitted last week that his original plan for putting astronauts on Mars -- landing them propulsively, firing "SuperDraco" retrorockets to brake a Red Dragon in a "powered" descent -- probably won't work after all. Speaking at the International Space Station Research & Development Conference in Washington, D.C., Musk admitted he is "pretty confident" that propulsive landing is in fact not "the right way" to land Red Dragon on Mars.

Good news, bad news

But that doesn't mean Musk has entirely given up on Mars. In fact, he says SpaceX has come up with a "far better approach" than its original plan. The bad news is that, so far, he hasn't told us what it is. The only hints he's dropped (via Twitter) are that "powered landings on Mars" can still be done "for sure," but that, to make the physics work, they will need to use "a vastly bigger ship." Not Dragon then, but something bigger.

This suggests that NASA's problem is Musk's, too. At six tons, Red Dragon may not be able to carry enough fuel, or big enough engines, to propulsively brake a six-ton lander for a Mars landing. On a bigger ship, though, the heat shield might comprise a smaller percentage of the vessel's total weight, while the overall lander would have more fuel capacity -- and perhaps enough to enable a safe, powered descent.

What it means for investors

Another hint Musk dropped may be of even more importance to investors. Describing his work on a powered descent for Dragon crew capsules, which will service the International Space Station under a NASA contract, Musk said he was confident that his newest solution will "be a system that NASA feels good about" -- for servicing ISS, and perhaps for landing a Mars mission as well.

My hunch is that SpaceX may now be thinking more along the lines of going to Mars as a NASA contractor, and not flying solo. If NASA is agreeable, that would mean far fewer internal development costs that SpaceX would need to incur to fund a mission to Mars. It would lessen SpaceX's need to "go public" in an IPO to raise funds (albeit probably to investors' dismay), while at the same time potentially costing NASA less than it would otherwise have to pay to develop its own Mars mission with contractors like Boeing and Lockheed Martin (LMT -0.42%)

That's actually the second significant development to watch: If SpaceX shifts gears and offers NASA a more affordable path to Mars, and if SpaceX can solve the problem of powered landings on Mars, then this would lessen NASA's need to spend the aforementioned "$100 billion to $1 trillion" hiring Boeing and Lockheed to help it reach the Red Planet.

The upshot: This would be good news for bringing a manned Mars mission within the range of what NASA's budget can afford -- but bad news for investors in Boeing and Lockheed.