June 14 (UPI) -- Mankind's first steps on the moon a half-century ago were followed by three more years of lunar missions. And then, a standstill.
Neither the United States nor any nation on Earth has sent a manned mission to the moon since NASA's Apollo 17 mission left in late 1972. While the space administration has periodically made plans to return, none have reached the operational phase. A large part of the reason is a lack of money and support.
The Constellation Program, proposed by George W. Bush's administration, hoped to return to the moon no later than 2020. It, however, was canceled by the Obama administration after the financial crisis. President Donald Trump has pushed for a return since taking office, but has equivocated on whether travel to the moon or Mars should take priority.
"Any project as complex as Apollo requires three things: resources, technology and -- most important -- the will to do it," Apollo 7 astronaut Walt Cunningham said at a 2015 congressional hearing aimed at examining U.S. goals in human space exploration. He pointed out that NASA's portion of the federal budget peaked at 4 percent in 1965 and has remained minimal ever since.
"For the past 40 years, it has remained below 1 percent and for the last 15 years it has been driving toward 0.4 percent of the federal budget," he said. "Manned exploration is the most expensive space venture and consequently, the most difficult for which to obtain political support."
Howard McCurdy, professor of public affairs at American University, said last month cost is a major factor. He said the United States spent almost $21 billion to put Neil Armstrong on the moon in 1969 -- which would equal about $200 billion today.
Cunningham said NASA has tried to cut costs to free up money for exploration, like reducing operations at U.S. Space Centers, but lawmakers have keep them open.
"NASA is still burdened with the same 10 Space Centers and a half-dozen other facilities," he said. "This reduces the funds available for science and space applications."
Experts say another hurdle is a lack of public support. American support for NASA's lunar missions has hovered around 50 percent for decades, even going back to the Apollo program when the United States was trying to beat Russia to the moon. A recent Pew Research poll found 55 percent of Americans consider it essential that NASA continue to explore. Forty-five percent said, however, that private explorers like SpaceX will ensure adequate progress in space.
Last month, Amazon founder Jeff Bezos' space company Blue Origin unveiled a full-size model of its Blue Moon lander, which he said could support a human moon landing by 2024. SpaceX has primarily focused its efforts on landing humans on Mars, but has hinted at moon missions and signed up a tourist to ride one of its rockets to the moon.
One argument against using public money in space is that it's better spent on Earth. Ahead of the first moon landing, civil rights leader Ralph D. Abernathy protested near the Kennedy Space Center with 150 poor black families to argue the money would be better spent feeding the poor.
"I want you to hitch your wagon to our rocket and tell the people the NASA program is an example of what this country can do," then-NASA chief Thomas O. Paine told Abernathy at the time.
Despite some renewed enthusiasm from the Trump administration, many of those same hurdles remain.
In May, Trump called for an additional $1.6 billion in NASA funding for the return to the moon, and promised to "restore" NASA to "greatness." Most of that money would be used to develop commercial human lunar landing systems and $651 million would develop the Space Launch System and Orion spacecraft, which are critical mission pieces. The plan, however, sought to draw from a Pell Grant surplus, which prompted criticism from education advocates and some Democratic lawmakers.
"I support restoring funding to NASA, but that cannot come at the expense of low-income students," Tennessee Rep. Steve Cohen tweeted. "Raiding Pell Grant funds to boost NASA's budget is foolish. If we are going to the moon, NASA will need funding AND an educated workforce."
NASA Administrator Jim Bridenstine defended the budget request, saying Congress can consider whether to approve the funds -- which he said would entirely fulfill NASA's funding needs for 2020. He noted more money, however, will be needed in the years ahead.
NASA's "Moon to Mars" program, announced in November, seeks to establish a permanent human presence on the moon through work with private U.S. and international companies. The venture proposes a spacecraft called "the Gateway" -- basically a space station that orbits the moon.
"The Gateway will, for the first time, give NASA and its partners access to more of the lunar surface than ever before, supporting both human and robotic missions," NASA's website states.
NASA plans to conduct its first unmanned mission next year, to test the new spacecraft systems. A manned test flight, with astronauts, could follow within two years. The first component of the Gateway craft is planned to launch on a private rocket in 2022.