Humans on Mars: how will we get there?
HUMAN ON MARS: HOW WILL WE GET THERE?
THE CURRENT STUDIES OF NASA
Why is it so difficult to go to Mars? Basically, because of the endurance of the human body, because of the reliability of the equipment and because of the incredibly high costs. These difficulties have to do with the distance, the force of gravity on Mars and the amount of matériel to be carried there.
Considering a crew of between 3 to 8 people, the same living quarters to be used on the surface of Mars could be used to transport the astronauts, starting from an orbit around the Earth. Current experience with space stations shows that the maximum time that the human body endures the lack of weight is 6 months. Beyond that, a long period of rehabilitation is needed after being subjected to weight again, rehabilitation that is very complicated to do on Mars.
Another problem is that of radiations. Without the protection of a magnetic field and an atmosphere, astronauts could receive high doses on the trip between Earth and Mars. There are two types of radiation: cosmic rays from deep within the Galaxy, and solar storms. In a period of 6 months (plus 6 months for the return trip) the cosmic-ray dose would be tolerable, whereas in the case of a solar storms special booths inside the module could be reserved for protecting the crew. In addition, water supplies, fuel, and the very walls of the module, made of plastic, would function as a shield. However, the adaptation of the human body to the conditions of the martian environment is unknown.
When studying a human mission to Mars we must think first in its ending, in the return trip. Mars has a considerable gravity, almost half the force of gravity on Earth. This means that to get out of Mars we must have a rocket of considerable size, that must be carried up there and placed on the surface. The task is made easier if the ship that has to take off from the surface is as small as possible, unable to travel for 6 months to Earth but just enough to jump to an orbit around the planet Mars, where the crew could be picked up by another, larger ship more able to bring them to Earth. This means that for the return of the crew we would have to take two modules to Mars: a rocket to take them out of the surface, and a ship to pick them up in space and bring them to Earth. Since most of the required fuel corresponds to the rocket, and as the mass of a rocket can be 90% fuels, the task of transporting the rocket over there is facilitated if fuels can be produced on Mars. By a well-known process called Sabatier reaction, natural gas and oxygen can be produced from the CO2 of the martian air and a small amount of hydrogen carried from here. Ideally, these equipment should go before the crew, and the rocket should be ready, with its fuel already stored, and the return ship already parked in orbit, before a third module leaves Earth carrying the astronauts.
Because the distance between the planets varies, the transit between the Earth and Mars is possible only every 26 months. This means that the drama shall be performed in three acts: in the first year the delivery of the equipment required to return, in the third year the delivery of the astronauts, and the ending by the fifth year, with the return home.
That is, a mission of an unprecedented duration.
The current idea is to thrust, from an orbit around Earth, each of the three modules required for a single manned mission separately. Each module will be accelerated towards Mars by a nuclear propulsor mated to them: current estimates show that the rocket to get out of the martian surface plus its fuel plant would have a total mass of 68,6 ton; its attachable nuclear propulsor to exit Earth would be 66 ton. The orbiter for the return trip would be 74,1 ton, and for its departure out of Earth, would be coupled to a nuclear propulsor of 73,4 ton. And the habitation module with astronauts inside would be of 60,8 ton and its starting nuclear propulsor 76,6 ton.
These nuclear propulsor, never tested in space even though they were on the ground and since the 60's, use nuclear reactors to heat hydrogen and expel it at high speeds backward through a nozzle. The performance is two times higher than conventional chemical rockets and is the only way to reach Mars in 6 months, the limit of tolerance of the human body in weightlessness.
Because each nuclear propulsor with its cargo is more massive than what can be raised from the Earth's surface with current technologies, the nuclear propulsor and the module which should be accelerated by it should be mated in space, in orbit around Earth. As there are three propulsors and three modules, we have six components to be launched from the ground for a single manned mission, with a total mass exceeding 400 ton, equivalent to the complete International Space Station. But each component would be less than 80 ton, which would allow a rocket derived from the Space Shuttle (basically, the external tank attached to the engines) to lift them from the ground.
So, 10 years after the project's approval, two large rockets would be launched from Cape Canaveral, Florida, amid thunderous roars and giant flares. Both payloads, a nuclear propulsor and a rocket module / fuel plant, would be mated in orbit around Earth. Days later two launches would raise another nuclear propulsor and a return ship, empty, that would also be mated in space. Once both propulsors with their mated cargo are ready, the nuclear engines would be activated. About ten months later these cargo would be arriving at Mars, and will be hitting the martian atmosphere with their heat shields, slowing down. The empty return ship would be captured into an orbit around Mars, as the empty rocket / fuel plant would fall to the surface, with the final descent cushioned by parachutes and engines. Once on the ground, a small, wheeled nuclear reactor will separate and move away to a safe distance. Its connecting lines will provide electricity to patiently turn the martian air into fuels.
Two years later, when the planets come close again, a third nuclear propulsor would accelerate a manned spacecraft from Earth to Mars. Within 6 months it would be arriving, and once again a ceramic shield would do its job, burning like an artificial meteorite while protecting the human beings inside. Parachutes, and engines when those are no longer sufficient, would gently place on the surface the first humans adventurers at Mars. After a short period of adaptation to the martian gravity, they would come outside, to install more, inflatable modules and start the experiments and explorations.
They would prepare the spots for the arrival, months later, of more equipment, to be used by the second crew within two years, or by themselves in an emergency.
A year and eight months later, with the first mission completed and with the planets close again, astronauts and samples would raise from the martian surface with the small rocket which fuels have been made on site even before the crew had departed from Earth. They would transfer to the empty return ship that had been waiting for them in orbit around Mars for four years. Once there, chemical engines would be enough to send them back to Earth. Six months later, a large rectangular parachute would open over Florida, and the astronauts would steer their little capsule to a safe landing back at Kennedy Space Center. A quarantine period to them and their samples would follow. Meanwhile, another crew would already be on their way to the planet Mars, where their respective equipment necessary for their stay and return would already be awaiting for them. And two years after this a third crew would depart.
THE STUDIES CONTINUE
This hypothetical "Mars Reference Mission" could have alternatives. For example, more inflatable modules, greater use of nuclear engines, reduction of 50% of the launched mass (by using new technologies and a different strategy), an orbital platform orbiting faster and faster to act as a catapult, electromagnetic motors, etc..
WHAT MAKES A ROCKET LIFT OFF?
It is not the fuel, no. It is money! The most expensive part of this story would be raising the 400 ton of equipment per crew from the earthly surface (26% of total costs), hence the importance of reducing the masses to a minimum. The total money is estimated today at about 100-thousand-million dollars. This is enough to feed 20 millions poor children for the duration of the program, or seen in another way, just 1 month of the global military budget. The money is there; the question is priorities.
So far, all the major space programs of the United States of America, like the Mercury program, which put its first astronauts into orbit, Apollo, which put the first humans on the Moon, or the International Space Station, whose main partners are the U.S.A. and Russia, were authorized by the United States Congress in the context of the geopolitics of the time. With a budget so high, it is likely that the only way a manned mission to Mars would lift off will be with U.S. tax dollars. So we will have to wait for the right geopolitical motivations. What would they be? All that can be inferred is that if a manned mission to Mars does not exist is because the final motivations do not exist either. For the time being.
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Based on a lecture given at the USP, on 30 June 2001. Originally published in ABC Color, on 29 October 2006. Illustration: At the beginning of the mission to Mars, two nuclear propulsors would carry the equipment necessary for the return to Earth. Two years later, when the planets are again close to each other, a third nuclear propulsor would carry the astronauts. Credit: John Frassanito and Associates, courtesy NASA.