On December 11, 2017, US President Donald Trump signed a directive instructing NASA to prepare to return astronauts to the Moon "followed by human missions to Mars and other destinations."
The date set by the space agency is 2024 for the Moon and Mars in 2033, but according to experts and industry insiders, reaching the Red Planet at that time was very unlikely to hinder Hercules efforts on the scale of the Apollo program in the 1960s.
"The moon is a place of proof for our last mission to Mars," NASA administrator Jim Bridenstine said at a conference this week.
"The moon is our way to get to Mars in the fastest and safest way possible. That is why we go to the Moon."
According to Robert Howard, who heads the lab developing future space habitats at the legendary Johnson Space Center in Houston, the obstacles are not so much technical or scientific as much as budgetary issues and political will.
"Many people want us to have the moment of Apollo, and have a president who stands like Kennedy and says, we have to do it and all the countries gather," he said.
"If that happens, I will actually say 2027. But I don't think that will happen. I think in our current approach, we will be lucky to do it on 2037."
But Howard said if he was pessimistic, and considered political innocence to be ahead, "maybe in the 2060s."
From design, manufacture and testing of rockets and spacecraft is needed to learn the best way to plant lettuce: all basic work remains to be done.
Just getting there will take at least six months, compared to three days to months.
All missions can take two years, because Mars and Earth are united every 26 months, a window must be taken.
The main tasks include finding ways to protect astronauts from prolonged exposure to solar and cosmic radiation, said Julie Robinson, NASA chief scientist for the International Space Station.
"The second is our food system," he added. The idea of the current installation system "cannot be packed, portable or small enough to be carried to Mars."
And then there are questions dealing with medical emergencies: astronauts must be able to treat themselves in the event of an accident.
"I really think the big problem is the jacket," added Jennifer Heldman, a NASA planetary scientist.
One of the main complaints of Apollo astronauts was their gloves, which were too swollen and prevented them from doing agile work.
NASA is developing new clothes, the first in forty years, called xEMU, but will not be ready for its first outing on the International Space Station for several more years.
On Mars, dust will be more of a problem than on the Moon. Apollo astronauts returned with large amounts of lunar dust in their modules. Avoiding it from habitat will be very important for missions that involve spending months on the Red Planet.
The technique for exploiting Mars resources to extract water, oxygen, and the fuel needed for humans to live there does not yet exist – and must be tested on the Moon at the end of this decade.
Finally, there is the most basic question: how can a group of people overcome psychological stress because it has been completely isolated for two years?
It will not be possible to communicate in real time with Houston's mission control: radio communication will take between four and 24 minutes between planets, one direction. NASA plans to test delayed communication practices on the ISS in the coming years.
Artificial intelligence must also be developed to help and guide astronauts.
A researcher commissioned by NASA to study the possibility of getting to Mars in 2033 concluded that the aim was "impossible."
"This is not just a budget," said Bhavya Lal from the Institute of Science and Technology Policy. "That's also the organization's bandwidth, how many things can NASA do at the same time?"
For Lal, a more realistic time frame is 2039.