Nasa on Monday announced its latest plan to send astronauts back to the Moon in 2024 and estimated the cost of meeting that deadline at $28 billion (Dh108.23bn), $16bn of which would be spent on the lunar landing module.
US Congress, which faces elections on November 3, will have to sign off on the financing for a project, known as Artemis, that is a top priority for President Donald Trump.
The $28bn would cover the budgetary years of 2021 to 2025.
On Monday, Nasa administrator Jim Bridenstine said political risks were often the biggest threat to Nasa's work, especially before such a crucial election.
Former US president Barack Obama cancelled plans for a manned Mars mission, after his predecessor spent billions of dollars on the project.
If Congress approves the first tranche of $3.2bn by Christmas, Mr Bridenstine said Nasa was still on track for a 2024 Moon landing.
"To be clear, we're going to the South Pole," he said, ruling out the sites of the Apollo landings on the Moon's equator between 1969 and 1972.
"There's no discussion of anything other than that."
Three projects are in competition to build the lunar lander that will carry two astronauts to the Moon from their vessel Orion.
The first one is being developed by Blue Origin, founded by Amazon chief executive Jeff Bezos, in partnership with Lockheed Martin, Northrop Grumman and Draper.
The other projects are being undertaken by Elon Musk's SpaceX and US company Dynetics.
The first flight, Artemis I, scheduled for November 2021, will be unmanned: the new rocket SLS, currently in its test phase, will take off for the first time with the Orion capsule.
Artemis 2, in 2023, will take astronauts around the Moon but will not land.
Artemis 3 will be the equivalent of Apollo 11 in 1969, but the stay on the Moon will last longer for a week and will include two to five "extravehicular activities".
"The science that we would be doing is really very different from anything we've done before," Mr Bridenstine said.
"We have to remember during the Apollo era, we thought the Moon was bone dry. Now we know that there's lots of water ice and we know that it's at the South Pole."
