Apollo 11 astronauts planted a flag on the moon on July 20, 1969. NASA

Landing 12 people on the moon remains one of NASA’s greatest achievements, if not the greatest.

Astronauts collected rocks, took photos, performed experiments, planted flags, and then came home. But those stays during the Apollo program didn’t establish a lasting human presence on the moon.

More than 45 years after the most recent crewed moon landing — Apollo 17 in December 1972 — there are plenty of reasons to return people to Earth’s giant, dusty satellite and stay there.

Vice President Mike Pence has promised that we will see US astronauts on the moon by 2024 (including the first women to ever touch the lunar surface), in a program called Artemis.

But on a recent phone call with reporters, NASA Administrator Jim Bridenstine said that ambitious goal is going to require quite a lot more federal cash, something that’s historically been a political sticking point in Washington.

„If it wasn’t for the political risk, we would be on the moon right now,“ Bridenstine said. „In fact, we would probably be on Mars.“

So why haven’t astronauts been back to the moon in nearly 47 years?

„It was the political risks that prevented it from happening,“ Bridenstine said. „The program took too long and it costs too much money.“

Bridenstine said that’s a major part of why President Trump has requested an additional $1.6 billion in funding for the current plan to return to the moon, which is „largely focused on a lunar lander that at this point doesn’t exist.“

Apollo 9 astronaut Rusty Schweickart recently told Business Insider that he wishes Bridenstine „good luck“ with this goal.

„Accelerating something that ambitious is a real challenge, and it takes commitment and dollars, and that’s what’s going to be required,“ Schweickart said. „We’ve tried two other times — administrations have tried — and they’ve been stillborn.“

Researchers and entrepreneurs have long pushed for the creation of a crewed base on the moon — a lunar space station.

„A permanent human research station on the moon is the next logical step. It’s only three days away. We can afford to get it wrong and not kill everybody,“ Chris Hadfield, a former astronaut, previously told Business Insider. „And we have a whole bunch of stuff we have to invent and then test in order to learn before we can go deeper out.“

A lunar base could evolve into a fuel depot for deep-space missions, lead to the creation of unprecedented space telescopes, make it easier to live on Mars, and solve longstanding scientific mysteries about Earth and the moon’s creation. It could could even spur a thriving off-world economy, perhaps one built around lunar space tourism.

But many astronauts and other experts suggest the biggest impediments to making this (and moon missions in general) a reality are banal and somewhat depressing.

It’s really expensive to get to the moon — but not that expensive

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A tried-and-true hurdle for any spaceflight program, especially missions that involve people, is the steep cost.

NASA’s 2019 budget is $21.5 billion, and the Trump administration is asking Congress to boost that to $22.6 billion in the 2020 budget.

Those amounts may sound like a windfall, until you consider that the total gets split among all the agency’s divisions and ambitious projects: the James Webb Space Telescope, the giant rocket project called Space Launch System (SLS), and far-flung missions to the sun, Jupiter, Mars, the asteroid belt, the Kuiper belt, and the edge of the solar system. (By contrast, the US military gets a budget of about $680 billion a year.)

Plus, NASA’s budget is somewhat small relative to its past.

„NASA’s portion of the federal budget peaked at 4% in 1965,“ Apollo 7 astronaut Walter Cunningham said during congressional testimony in 2015. „For the past 40 years it has remained below 1%, and for the last 15 years it has been driving toward 0.4% of the federal budget.“

Trump’s budget calls for a return to the moon, and then later an orbital visit to Mars. But given the ballooning costs and snowballing delays related to NASA’s SLS rocket program, there may not be enough funding to make it to either destination, even if the International Space Station gets defunded early.

A 2005 report by NASA estimated that returning to the moon would cost about $104 billion ($133 billion today, with inflation) over about 13 years. The Apollo program cost about $120 billion in today’s dollars.

„Manned exploration is the most expensive space venture and, consequently, the most difficult for which to obtain political support,“ Cunningham said during his testimony.

He added, according to Scientific American: „Unless the country, which is Congress here, decided to put more money in it, this is just talk that we’re doing here.“

Referring to Mars missions and a return to the moon, Cunningham said, „NASA’s budget is way too low to do all the things that we’ve talked about.“

The problem with presidents

U.S. President Donald Trump holds a space astronaut toy as he participates in a signing ceremony for Space Policy Directive at the White House in Washington D.C. Reuters/Carlos Barria

If the Trump administration succeeds in landing astronauts back on to the moon in 2024, that would come at the tail end of what could be Trump’s second term, if he gets reelected.

And therein lies another major problem: partisan political whiplash.

„Why would you believe what any president said about a prediction of something that was going to happen two administrations in the future?“ Hadfield said. „That’s just talk.“

The process of designing, engineering, and testing a spacecraft that could get people to another world easily outlasts a two-term president. But incoming presidents and lawmakers often scrap the previous leader’s space-exploration priorities.

„I would like the next president to support a budget that allows us to accomplish the mission that we are asked to perform, whatever that mission may be,“ Scott Kelly, an astronaut who spent a year in space, wrote in a Reddit „Ask Me Anything“ thread in January 2016, before Trump took office.

But presidents and Congress don’t seem to care about staying the course.

In 2004, for example, the Bush administration tasked NASA with coming up with a way to replace the space shuttle, which was set to retire, and also return to the moon. The agency came up with the Constellation program to land astronauts on the moon using a rocket called Ares and a spaceship called Orion. NASA spent $9 billion over five years designing, building, and testing hardware for that human-spaceflight program.

Yet after President Barack Obama took office — and the Government Accountability Office released a report about NASA’s inability to estimate Constellation’s cost — Obama pushed to scrap the program and signed off on the SLS rocket instead.

Trump hasn’t scrapped SLS. But he did change Obama’s goal of launching astronauts to an asteroid, shifting priorities to moon and Mars missions.

Such frequent changes to NASA’s expensive priorities have led to cancellation after cancellation, a loss of about $20 billion, and years of wasted time and momentum.

„I’m disappointed that they’re so slow and trying to do something else,“ Apollo 8 astronaut Jim Lovell told Business Insider last year. „I’m not excited about anything in the near future. I’ll just see things as they come.“

Buzz Aldrin said in testimony to Congress in 2015 that he believes the will to return to the moon must come from Capitol Hill.

„American leadership is inspiring the world by consistently doing what no other nation is capable of doing. We demonstrated that for a brief time 45 years ago. I do not believe we have done it since,“ Aldrin wrote in a statement. „I believe it begins with a bipartisan congressional and administration commitment to sustained leadership.“

The real driving force behind that government commitment to return to the moon is the will of the American people, who vote for politicians and help shape their policy priorities. But public interest in lunar exploration has always been lukewarm.

Even at the height of the Apollo program, after Aldrin and Neil Armstrong stepped onto the lunar surface, only 53% of Americans said they thought the program was worth the cost. Most of the rest of the time, US approval of Apollo hovered below 50%.

Today, most Americans think NASA should make returning to the moon a priority. More than 57% of nationwide respondents to an INSIDER poll in December 2018 said returning to the moon is an important goal for NASA, but only about 38% said that living, breathing humans need to go back. (Others who want the US to land on the moon say robots could do the lunar exploring.) Samantha Lee/Business Insider

Support for crewed Mars exploration is stronger, with 63% of respondents to a 2018 Pew Research Center poll saying it should be a NASA priority. Meanwhile, 91% think that scanning the skies for killer asteroids is important.

The challenges beyond politics

Many space enthusiasts have long hoped to build a base on the moon, but the lunar surface\'s harsh environment wouldn\'t be an ideal place for humans to thrive. NASA

The political tug-of-war over NASA’s mission and budget isn’t the only reason people haven’t returned to the moon. The moon is also a 4.5-billion-year-old death trap for humans and must not be trifled with or underestimated.

Its surface is littered with craters and boulders that threaten safe landings. Leading up to the first moon landing in 1969, the US government spent what would be billions in today’s dollars to develop, launch, and deliver satellites to the moon to map its surface and help mission planners scout for possible Apollo landing sites.

But a bigger worry is what eons of meteorite impacts have created: regolith, also called moon dust.

Madhu Thangavelu, an aeronautical engineer at the University of Southern California, wrote in 2014 that the moon is covered in „a fine, talc-like top layer of lunar dust, several inches deep in some regions, which is electrostatically charged through interaction with the solar wind and is very abrasive and clingy, fouling up spacesuits, vehicles and systems very quickly.“

Peggy Whitson, an astronaut who lived in space for a total of 665 days, previously told Business Insider that the Apollo missions „had a lot of problems with dust.“

„If we’re going to spend long durations and build permanent habitats, we have to figure out how to handle that,“ Whitson said.

There’s also a problem with sunlight. For about 14 days at a time, the lunar surface is a boiling hellscape that is exposed directly to the sun’s harsh rays; the moon has no protective atmosphere. The next 14 days are in total darkness, making the moon’s surface one of the colder places in the universe.

A small nuclear reactor being developed by NASA called Kilopower could supply astronauts with electricity during weeks-long lunar nights — and would be useful on other worlds, including Mars.

„There is not a more environmentally unforgiving or harsher place to live than the moon,“ Thangavelu wrote. „And yet, since it is so close to the Earth, there is not a better place to learn how to live, away from planet Earth.“

NASA has designed dust- and sun-resistant spacesuits and rovers, though it’s uncertain whether that equipment is anywhere near ready to launch.

A generation of billionaire ’space nuts‘ may get there

spacex starship steel moon landing space colonization elon musk twitter D5US3AeU8AAHxyV Elon Musk/SpaceX via Twitter

Another issue, astronauts say, is NASA’s graying workforce. Today, more American kids polled say they dream about becoming YouTube stars, rather than astronauts.

„You’ve got to realize young people are essential to this kind of an effort,“ Apollo 17 astronaut Harrison Schmitt recently told Business Insider. „The average age of the people in Mission Control for Apollo 13 was 26 years old, and they’d already been on a bunch of missions.“

Schweickart echoed that concern, noting that the average age of someone today at NASA’s Johnson Space Center is closer to 60 years old.

„That’s not where innovation and excitement comes from. Excitement comes from when you’ve got teenagers and 20-year-olds running programs,“ Schweickart said. „When Elon Musk lands a [rocket booster], his whole company is yelling and screaming and jumping up and down.“

Musk is part of what astronaut Jeffrey Hoffman has called a „generation of billionaires who are space nuts,“ developing a new, private suite of moon-capable rockets.

„The innovation that’s been going on over the last 10 years in spaceflight never would’ve happened if it was just NASA and Boeing and Lockheed,“ Hoffman told journalists during a roundtable earlier this year. „Because there was no motivation to reduce the cost or change the way we do it.“

The innovation Hoffman was referring to is work of Musk’s rocket company, SpaceX, as well as by Jeff Bezos, who runs aerospace company Blue Origin.

„There’s no question: If we’re going to go farther, especially if we’re going to go farther than the moon, we need new transportation,“ Hoffman added. „Right now we’re still in the horse-and-buggy days of spaceflight.“

Many astronauts‘ desire to return to the moon aligns with Bezos‘ long-term vision. Bezos has floated a plan to start building the first moon base using Blue Origin’s upcoming New Glenn rocket system.

„We will move all heavy industry off of Earth, and Earth will be zoned residential and light industry,“ he said in April 2018.

Musk has also spoken at length about how SpaceX’s forthcoming Starship launch system could pave the way for affordable, regular lunar visits. SpaceX might even visit the moon before NASA or Blue Origin.

„My dream would be that someday the moon would become part of the economic sphere of the Earth — just like geostationary orbit and low-Earth orbit,“ Hoffman said. „Space out as far as geostationary orbit is part of our everyday economy. Someday I think the moon will be, and that’s something to work for.“

Astronauts don’t doubt whether or not we’ll get back to the moon and onto Mars. It’s just a matter of when.

„I guess eventually things will come to pass where they will go back to the moon and eventually go to Mars — probably not in my lifetime,“ Lovell said. „Hopefully they’ll be successful.“

Update: This story was originally published on July 14, 2018. It has been updated with the Trump administration’s latest lunar plans.

Correction: A previous version of this story included an incorrect number of moonwalkers. During NASA’s Apollo program, 12 people landed on the moon.