Because of popular science fiction television shows and movies—last year's blockbuster Interstellar comes to mind—many people are aware of the sleeper ship concept as a means of transporting human beings across the immense distances of interstellar space.
In recent years, the search for planets around stars other than the Sun has been amazingly successful. To date, more than one thousand planets have been confirmed orbiting nearby stars, most of them discovered by NASA’s Kepler space telescope. Some of these planets are Earthlike, including three that were discovered just in the last month, and this means that worlds that we'd want to colonize could be nearby.
But “nearby” means a few light years away.
Propelled by nuclear fusion engines, which we do not have yet, voyages on that scale would take several decades, and knowing this sci fi writers for a while now have imagined astronauts hibernating through the voyage. Sleeping with the aging process suspended or reduced to a fraction of the normal rate, human colonists could arrive young and full of vigor at a destination world.
Given current trends in biotechnology and medicine, it’s probably reasonable to suspect that we'll have a safe form of human hibernation–also called suspended animation–before we have nuclear fusion engines. Hibernation is a wonderful option for a small crew of explorers, but for a distant planet with an Earth Like environment, our goal will probably be colonization. To assure adequate genetic diversity for long-term survival, a starship would need to transport 10,000-40,000 colonists. That’s according to calculations by Portland State University anthropologist Cameron Smith, and it means we're talking about a ship the size of a city.
On the other hand, even on a fairly small ship, the numbers can be increased substantially by suspending humans in an immature state–as embryos, or even as gametes (egg and sperm cells). We already have the technology to keep embryos and gametes frozen for as long as we want; we do this on a regular basis today. Pack up a bunch of frozen embryos or gametes, put them in a freezer at -200°C, launch the freezer on a trip across space, and that’s an egg ship, or, using alternate terminology, a seed ship.
As for who, or what, goes along with the human seedlings, a few different strategies are possible, depending on available robotic and hibernation technology, the level of our ambition to spread humanity through the cosmos, and the direction that our sense of ethics evolves in connection with emerging biotechnology.
Hybrid sleeper-egg ships and world ships
This first strategy depends on human suspended animation being achieved and proven safe for those hibernating for many years or decades. A small crew of a hundred or so adult humans, mostly young women, would travel in suspended animation, along with many thousands of frozen embryos or gametes. Since it would be impractical for all of the adult colonists to be pregnant at the same time anyway, some men could be included, but too many would be a waste of valuable space, as one of the main functions of the adults would be carry out pregnancies. Also, the need for a female majority would prioritize gay women in the crew selection process. Given this idea, along with the thousands of frozen embryos, social conservatives may have some modest objections to the sleeper-egg ship concept.
After arrival at the destination world and establishment of a safe, first outpost, some of the embryos would be thawed (or some gametes thawed to make embryos through in vitro fertilization). Most of the women would be impregnated a few times over the next several years. The children would be raised and educated, and, to keep the gene pool diverse, the first generation of women born on the colony world would get pregnant, not from their colonial brothers and cousins, but from newly thawed batches of preserved embryos, or gametes. This would go on for a few generations as the population builds up.
A variation on the hybrid sleeper egg ship is an egg ship combined with a world ship. Instead of hibernating, adult colonists would spend the long travel time in a kind of moving space colony. It would need farms to maintain a food supply, and enough activities and space to keep everyone from getting bored. Therefore, it would have to be orders of magnitude larger than a sleeper ship, and carry many more than a hundred adults. Like the hybrid sleeper ship, it also would carry many thousands of frozen embryos or gametes, but also young children leaving Earth with the adults; that way, the embryos could be implanted in women of childbearing age upon arrival at the colony world.
The next strategy is to forget about sending adults and send just robots and computers to develop and raise the gametes or embryos into the colonial pioneers that they’d need to be. This idea eliminates the need for achieving long-duration suspended animation, and for the large volume inside the ship and payload mass that would be needed to support a hundred hibernating adults. But it requires other technological developments, beginning with the artificial uterus. As I’ve written previously on this blog, technology for developing an embryo from fertilization to birth, completely in a machine, instead of a woman’s body, is developing in increments. It’s a an easy bet to expect that we’ll have motherless birth by mid century, probably before we’re sending even tiny robot ships to the nearest star, possibly even before we send the first human mission to Mars. As with human hibernation, early forms of the artificial uterus will probably depend on the presence of medical staff overseeing the process and sometimes intervening. But given how rapid computer and artificial intelligence technology is advancing, even completely automated systems are not unreasonable to imagine.
Once the children are born, however, light years away from Earth, we have to consider their rearing and education. We're talking about doing this all with computers, robot or android nannies, videos, and maybe holographic projections. The first generation of colonists will grow up with no human parents, grandparents, uncles, or aunts. They won't even have any nearby sports teams to admire, although they could watch events transmitted from Earth (delayed by a few years, due to the distance).
Pondering this may evoke horrific images from William Golding’s novel Lord of the Flies, but this interstellar mission would employ technology and very good planning to make sure, not only that the children survive infancy, but grow up as civilized human beings. From birth, android nannies would cuddle them, and computers would educate them over the next quarter century, and help them form a government. In addition to technology and career training, the robots would have to teach the kids how to avoid the wrong kind of pregnancy–the natural kind that could harm genetic diversity of the budding colony– and help them in rearing the second generation.
No matter how advanced the technology for intelligence by that time, we wouldn’t know if the plan would work, unless we test it first on Earth. In other words, we’d have to experiment with babies raised by android nannies in an isolated environment with no other people. Ethics alert; our current society would not allow this, I agree with their reasons, and I hope you do too.
But, just for fun, let’s ponder this scenario, a little longer. While growing up, the colonists must be told about Earth history and their origins, and, hopefully, not too many out of hundreds will find that news so unsettling that they turn to violence. Thinking about the latter possibility reminds us that the robots and computers will also have to give out punishments. Eventually, they’ll have to serve as judges when things become more complex as the children mature. Will any machines capable of such a high level of mental function be willing to give up their positions of power when the first generation of human colonists is ready to take over the leadership? Should they give up their power? Having thirty years more experience in the new world than the first generation of humans, relinquishing leadership might not be in the best interest, either of the machines or the humans.
In that case, why bother sending humans at all? In a new book scheduled for publication this fall, Louis D. Friedman, Executive Director Emeritus of The Planetary Society suggests that machines will eventually render humans obsolete in space travel.
“Robotics, artificial intelligence, and bio-molecular engineering are evolving faster than humans,” says Friedman, who co-founded The Planetary Society with Carl Sagan and Bruce Murray in 1980. “We might make it to Mars, but from Mars to the stars human presence may be without humans present.”
It may be logical, but we may wish to send physical humans anyway. A main motivation for a colony could be human survival, making ourselves not only a multi-planet species, but also a multi-star system species.
Considering the unknowns regarding the android nanny idea, the two earlier strategies that include adults look much better to me. On the other hand, this does not mean that android nannies could not be used to assist the human parents on their mission to establish a human presence on a new world. The artificial uterus could be used as well to increase the number of children born in the first few generations, which also frees the adults of the burden of numerous pregnancies. It also means that we could send a more Earth-like female-to-male ratio of 50:50 for adult colonists, allowing the new generation to grow up with fathers, which is just as important as having mothers. All in all, if we're going to transplant ourselves, which is a smart thing to do if we want humanity to survive into the far future, keeping a more conventional biological environment is probably also wise.
David Warmflash is an astrobiologist, physician, and science writer. Follow @CosmicEvolution to read what he is saying on Twitter.