In the current state of science, only a crew that will have offspring during space flight for several hundred years has a chance to reach their destination.
In 1995, astrophysicists Michel Mayor and Didier Quelozm discovered the very first exoplanet, 51 Pegasi b (51 Pegasi b), orbiting a star other than our Sun. This discovery of the alien world marked the beginning of the search for habitable worlds.
23 years later, the number of exoplanets in existence is over 3,700. The likelihood of finding a world like ours is approaching.
Appointment of Proxima b
The recent discovery of Proxima Centauri b, the closest exoplanet orbiting the closest star to our Sun, gives the inhabitants of planet Earth another interesting opportunity.
It is very likely that this celestial body has a rocky surface and a mass close to that of our planet and is of great interest, since its equilibrium temperature suggests that water on its surface may be in liquid form.
Located 40,000 billion kilometers from Earth, Proxima b is an ideal destination. Theoretically, a short interstellar journey with a reconnaissance goal and the possibility of colonization is possible: we could thus settle people on another planet.
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But even if the rocket could reach a speed equal to one percent of the speed of light, which is much faster than that of a modern manned spacecraft, the flight to Proxima b would last over 423 years.
Giant autonomous ships
With such initial data, one human life is not enough to reach an exoplanet. Researchers must find a solution for the crew so that they can survive for hundreds of years in deep space.
You can, for example, freeze bodies. Despite advances in this area, cryogenic technologies have not yet reached the desired level: when cells are frozen, ice crystals form on their walls (vitrification), which will lead to the destruction of the body after rewarming.
Hibernation? All options for waking up from sleep, in which the physiological functions of the crew members are slowed down before the ship arrives at its destination, have yet to be explored.
Another hypothesis is a flying maternity hospital, in which human embryos, under the supervision of robots, quietly develop until they arrive at their destination. The main problem is the lack of human parents to raise children. In addition, there has never been a population fully born in vitro: and under these conditions it may not be desirable for the mission to rely on this method.
The best option might be to use giant autonomous ships that will travel in space while their populations are active. People will live and die on board until they reach their destination.
Several design concepts for such ships were featured in Islands in the Sky: Daring Ideas for Colonizing Space in 1996, but their mathematical and statistical calculations no longer fit our current technology.
Crew from 150 to 44,000 people
American anthropologist John Moore was the first to use the ethnographic tool Ethnopop to quantify the minimum number of people for a multi-generational flight.
Ethnopop simulates the marital and demographic situations of small settlers and uses external modules to create episodic epidemics and disasters. But these modules have never been applied in the context of space flight, since this program was developed to calculate and analyze the historical migrations of the first groups of people.
Considering that in space travel the processes of immigration and emigration are impossible, Moore came to the conclusion that for a 200-year mission, the initial crew should include between 150 and 180 people.
In his opinion, the crew should be composed of young people and produce offspring as late as possible in order to delay the appearance of the first generation as long as possible. These conditions will help to avoid overpopulation and a high proportion of consanguinity.
More recent calculations by anthropologist Cameron Smith foresee an increase in crew size. According to him, the initial crew should be between 14,000 and 44,000 people. This is the optimal figure to ensure healthy transmission of human genetic heritage.
According to his research, the crew of 150 will always be on the verge of extinction in the event of a major disaster. Smith recommends having more initial genetic samples on board, and this requires a large crew.
This significant increase in the number of people on board is due to the basic hypotheses of the scientist, who calculated the number of settlers arriving at their destination using a simple statistical approach.
It seems that there are difficulties in estimating the optimal number of starting personnel, and this without taking into account the psychological effects that may have an impact on the crew when parting with Earth forever.
Heritage Project
This is why I created the Heritage Project in 2017, a new statistical modeling tool like Monte Carlo. The project involves physicist Camille Beluffi, astrophysicist Rhys Taylor and research and development engineer Loïc Grau to provide realistic simulations of future space exploration.
Our project is multidisciplinary: physicists, astronomers, anthropologists, aeronautical engineers, sociologists and doctors take part in it.
Legacy is the first program entirely dedicated to calculating the probabilistic evolution of the crew aboard an interstellar craft. It must, among other things, determine whether a group of people of this size can provide life for several generations without any artificial supply of additional genetic material.
It has already become clear that determining the minimum number of crew members is an important step in the preparation of any mission involving the participation of several generations, it will involve not only the resources and budget necessary for such an enterprise, but also have sociological, ethical, social and political consequences. All of these elements are necessary to study the creation of a self-sustaining colony so that humans can settle on other planets.
The first results of our collaboration were published in the Journal of the British Interplanetary Society, and another article in the regular press. A public presentation of our research took place in Strasbourg as part of the Transmission Symposium, during which we demonstrated that the crew data provided by Moore and Smith is not viable on very long journeys.
Now we are talking about defining the principles and rules of life necessary for the crew with the minimum possible number of people to ensure the viability of the mission and be resilient in the face of disasters and serious diseases.
At the moment, a program is being developed that can predict the nutritional needs of the crew and determine the space required for space farming inside the ship itself. At the moment, hydroponic greenhouses are the best solution. Our calculations will soon establish the minimum vessel size requirements.
The first in-depth works on space exploration are just beginning to appear. The topic is still vast, and many human, spatial, cultural, psychological and social factors need to be incorporated into a computer program. Painstaking work is essential if we want people to be able to reach new worlds.
Frédéric Marin