The opponent is now China, who this year put the world's first probe on the hidden side of the moon and proposes to build a lunar base, a concept also supported by the European Space Agency (ESA), which presents the " Moon Village "as a springboard for Mars.
According to Paulo Gil, the return of astronauts to the moon "may be a means" for the United States to "train" a trip to Mars, where "there may be microbial life" and resources to explore, the Chinese also want to go to the moon. "
Astrophysicist Pedro Machado, of the Institute of Astrophysics and Space Sciences, understands that "it is a matter of time" to have astronauts on Mars, but not in the time estimated by the Americans.
In its accounts, it will take 20 years for a base on the Moon and 30 to 50 years for the Man to reach Mars. The risks and challenges are many, but the Moon "will be a test balloon" for Mars.
"There is everything to do on the Moon," he says, giving as an example the creation of a "long-term life support" that includes energy, water, food and oxygen to breathe
Increased risks and impacts of irrigation rates 700 times higher than those of Earth
In addition, astronaut shelters and suits will have to be made to protect them from cosmic rays, extremely high thermal amplitudes, meteorites, dust storms and solar winds.
Luís Campos, a professor at the IST and a specialist in applied and aerospace mechanics, adds to the list the adaptation of the body to "long stays in space", noting that "muscles atrophy" and "blood goes less to the legs and more to the head".
"Despite all technical progress there are always risks," he warns. Not even a rocket, he illustrates, is totally reliable.
An astronaut on a Moon or Mars mission can receive doses of cosmic radiation up to 700 times higher than those on Earth, which have an atmosphere and magnetic field that protects living beings from the bombardment of cosmic rays, highly energetic particles that circulate around a speed close to light, and solar winds, unpredictable emissions of subatomic particles from the solar corona.
Injuries to the human body caused by cosmic radiation, which increases the risk of cancer, can spread to the brain, heart and central nervous system and lead to early onset of cardiac complications, neurodegenerative diseases, or cataracts.
Mars Challenge: A long journey with many unknowns
On Mars, the risks and challenges are heightened. According to IST researcher Paulo Gil, "there is still no safe method" to land humans on a planet with a "very thin atmosphere" and the "journey is very long", about two years back and forth, which is why "potentially deadly."
Because of the distance separating Mars from Earth, spacecraft take-off can only be done under favorable conditions every two years, so astronauts will have to stay on the "red planet" waiting for a new window of opportunity.
But as it was with the Moon in 1969, going to Mars will mean that humanity has challenged itself, according to astrobiologist Zita Martins.
"Discovering new worlds, challenging ourselves, developing new technologies …", enumerates the teacher of the Higher Technical Institute, for whom "there are no isolated missions" because "science is international".
Justifying interest in Mars, Zita Martins, who studies the origins and the quest for life, states that the planet "is relatively close to the Sun", a "source of energy and nutrients", and therefore may have had life in the past. There is also evidence of liquid water found on its surface.
In his autobiography "Magnificent Desolation," Buzz Aldrin, the second man to step on the moon, on July 21, 1969, advocates the construction of a lunar base and human exploration of Mars, in addition to commercial flights into space, and suggests a path: "Knowledge, faith and commitment".
In "Mission to Mars: My View on Space Exploration," a book he published in 2013, but not released in Portugal, as in 2009, the Apollo 11 astronaut presents a more daring alternative to Gateway: a station orbital spacecraft on Phobos, the largest and closest moon to Mars, from which robotic vehicles could be sent to the planet or where a laboratory could test technology for human missions.