NASA is building a jumbo rocket. It's called the Space Launch System, or simply the SLS. The core stage of the SLS is slowly materializing in a sprawling facility on the north bank of the Mississippi River. Technicians are welding up a storm and have completed the largest component - a liquid hydrogen fuel tank that's 133 feet from nose to tail and looks like a shiny metallic zeppelin.

"This is our big boy," said NASA engineer Stephen C. Doering, dwarfed by the tank resting on cradles in a high bay.

NASA has a complicated way of building rockets that funnels money to multiple states in the southeastern United States. The SLS program is based in Alabama, at the Marshall Space Flight Center. Engine tests will be done in Mississippi, at the Stennis Space Center. The final stacking of the rocket and the launch will be from Cape Canaveral, Florida, at the Kennedy Space Center.

Construction of the core stage is handled here in Louisiana, at the Michoud Assembly Facility, which covers the equivalent of 31 football fields. The vast structure survived Hurricane Katrina in 2005, and then a direct hit from a tornado earlier this year.

But the new rocket will have to survive the unpredictable crosswinds of Washington.

President Donald Trump is now in charge of the space program, and no one in Washington seems to have a clear idea what's going to happen next. Trump has expressed interest in President John F. Kennedy's vow in 1961 to put American astronauts on the moon by the end of the 1960s. Thus everyone expects Trump to try to create a "Kennedy moment."

The 50th anniversary of the Apollo 11 lunar landing is coming up in two years. For NASA, and the entire space industry, that's a huge anniversary - and suddenly everyone seems to be talking about moon missions.

President George W. Bush wanted U.S. boots on the moon by 2020. President Barack Obama killed the Bush program, saying we'd been there and done that. But with Republicans in control of both Congress and the White House, the moon looms larger in the sky.

Last month, in his address to Congress, Trump made a single, enigmatic comment about space: "American footprints on distant worlds are not too big a dream."

Did that mean the moon? Mars?

Trump hasn't nominated anyone yet to lead NASA, nor has he picked a science adviser. He is expected to issue an executive order re-forming the long-disbanded National Space Council, which would be headed by Vice President Mike Pence and oversee civilian and military space programs.

In the meantime, civil servants at NASA headquarters are re-examining the current human spaceflight schedule to see whether there's a way to do something dramatic before the end of Trump's term.

The first SLS launch, penciled in for late next year, will also be the first time it is paired with the new Orion crew capsule. No one will be aboard. It's a shakedown cruise to test the hardware and life support equipment. Instead of live astronauts, mannequins will serve as the crew.

But last month, NASA's acting administrator, Robert Lightfoot, asked his team to look at the feasibility of adding astronauts to the first test flight. The feasibility study should be complete within weeks.

And then there's Elon Musk.

Musk, the founder and chief engineer of SpaceX, has met at least four times with Trump or his aides recently. Last month, in what appeared to be a hastily called teleconference with reporters, Musk announced that he intends to send two tourists next year on a figure-eight joy ride past the moon and back to Earth.

He did not identify the tourists, saying only that they were wealthy people who know each other and have already put down deposits. Musk said that he could do the moon flyby with his own new rocket, still under development, called the Falcon Heavy.

Another wrinkle: Musk told reporters that SpaceX would be willing to bump the rich tourists from that first flight and let NASA astronauts take their place.

There are reasons to view such a scenario as extremely unlikely. Powerful people in the space world would be unhappy to see Musk and SpaceX steal any thunder from the SLS and Orion. Huge aerospace corporations, including Boeing and Lockheed Martin, have contracts for this hardware.

The Alabama factor comes into play. The SLS is based at NASA Marshall, in Huntsville, the historic center of American rocketry. The Trump administration has a number of influential Alabamians, starting with Attorney General Jeff Sessions. Two former Sessions senate staffers, Stephen Miller and Rick Dearborn, work in the White House.

There are practical issues, too: Musk has a reputation for overpromising on timelines. SpaceX has never launched anyone into space. The Falcon Heavy has never flown. Moreover, NASA officials would be unlikely to embrace a SpaceX moon flyby unless it clearly fit into the agency's long-term plans for deep-space exploration.

"What does Elon want to do with this - is it just a one-off tourist flight?" said NASA's top official for human spaceflight, William Gerstenmaier, in an interview with The Washington Post. "I don't see it as advancing human presence in the solar system."

At the annual Robert H. Goddard Memorial Symposium this week in Greenbelt, Maryland, a student from Purdue University asked a panel of space experts a pointed question: What's harder in spaceflight, the technical engineering or the political engineering?

Mary Lynne Dittmar, executive director of the Coalition for Deep Space Exploration, which represents aerospace companies such as Boeing and Lockheed Martin, found that one easy to answer:

"Political engineering is always more challenging."

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Things were so much simpler in the 1960s. The United States and the Soviet Union were locked in a Cold War and racing to the moon in government-owned rockets. The United States won that race, planted a flag, left bootprints.

NASA today is faced with basic questions of destination, hardware and motivation. China has a growing space program but does not seem in a hurry to put astronauts on the moon, so there's no indication that a space race is heating up. NASA and Russia work shoulder to shoulder on the International Space Station.

Six years after NASA retired the space shuttle, the agency relies on Russian spacecraft to ferry American astronauts to and from orbit. SpaceX and Boeing have contracts to take astronauts to the International Space Station, but the first flights are probably a couple years away. In the meantime, NASA is building the SLS and Orion for "deep space exploration."

In the 2020s, that would mean astronauts orbiting the moon but not going to the lunar surface. The most ambitious such mission would last a full year and function as a trial run for the much more daunting trip to Mars. Gerstenmaier, questioned this week by an audience member at the Goddard Symposium, said he would not rule out a landing on the moon but did not think it was necessary for NASA's long-term Mars ambitions.

Gerstenmaier is a civil servant who has survived many strategic pivots at NASA. In his brief remarks at the rostrum this week, he said the SLS will only launch about once a year, which he said is not often enough for a compelling space program. He showed a graphic with government-owned rockets like the SLS lined up next to private rockets like SpaceX's Falcon Heavy and Blue Origin's New Glenn. "I love every one of these rockets," he said.

But NASA's steady-as-she-goes, methodical way of operating has been criticized by outsiders as overly slow and cautious. The current manifest for the SLS envisions several years between the first two flights.

Newt Gingrich, for one, has seen enough. Gingrich is a space buff who has consulted with Trump in an unofficial capacity. When Gingrich ran for president in 2012, he spoke of his dream of a moon base. He even cited one of his old ideas: that Americans in a moon colony could achieve statehood.

"The answer is to open the system up to competition, establish prizes, take risk, and dream big," Gingrich said in an email to The Post.

He added, "The key is to liberate space from government monopoly and maximize the inventive entrepreneurial spirit of the Wright brothers, Edison, Ford and other classic Americans."

The SLS is an old-fashioned rocket in many ways. NASA fully owns the rocket. It oversees every aspect of the rocket's design and operation. It's being built by the prime contractor, Boeing, under a traditional cost-plus contract that offers little incentive to do hold down the cost. The booster is also disposable.

All that exquisitely welded metal in the giant tank at Michoud will wind up at the bottom of the ocean. That's an expensive way to do business. The cost of a single launch of the SLS could be in the vicinity of $1 billion.

SpaceX and Blue Origin - the space start-up owned by Jeffrey P. Bezos (who also owns The Post) - have emphasized reusability. The two companies have built boosters that can land softly back on land or on a platform at sea.

Musk has said he wants to launch the first humans to the surface of Mars in 2024. He envisions gigantic spaceships that could carry 100 people at a time. The goal is to create cities on Mars so that the Martian civilization can be independent and self-sustaining, and humanity will be a multi-planet species.

Humans are Earthlings, however: Any mission to Mars would take many months and human bones deteriorate in weightless environments. Space is shot through with radiation, particularly beyond the Earth's protective magnetic field. No country has ever landed anything on Mars heavier than a rover. The atmosphere is too thin to be of much help in slowing down a vehicle deploying parachutes, but it's thick enough to cause turbulence and overheating.

Bezos is less focused on Mars, but he has repeatedly said he wants to see millions of people living and working in space. He would like industrial activity moved off-planet to help protect Earth's natural environment. Blue Origin has circulated a white paper describing how it would like to provide cargo delivery service as soon as 2020 for a (still hypothetical) NASA lunar base.

"We should make American Space Great Again," Gingrich said in the email to The Post. "Done properly we can be on the moon in President Trump's first term and orbiting Mars by the end of his second term."

Gerstenmaier is preaching cooperation: "None of us can do it alone," he said at the Greenbelt symposium.

"It is not a race to the moon" between NASA and the private sector, said Dittmar, whose coalition is funded by the big aerospace companies.

But it feels like a race, somehow. At the very least, everyone is suddenly in a hurry. Gerstenmaier talked about "an urgency" to NASA's activities. That's because, even without Trump channeling Kennedy, NASA has a serious plan to blast people back to the vicinity of the moon - "sometime in 2021, 2022," Gerstenmaier said. "That's not that far away."

If the plan holds, the big fuel tank at Michoud, plus another, smaller tank for liquid oxygen, and some other Michoud-created hardware, will wind up in Florida, at the Cape, as part of a stack of components forming a complete, full-fledged rocket that's taller than the Statue of Liberty.

At that point it will simply need a destination.