Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization

First Edition

© 1975-1979, 2008 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, First Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm


17.7  Generation Ships and Suspended Animation

Citing the tremendous difficulties involved in high speed interstellar journeying, many writers have turned in desperation to the concept of the "generation ship" or "interstellar ark." (See especially Bernal,2820 Clarke,2789 Gelula,2790 Haldeman,2839 Heinlein,2854 Macvey,732 Panshin,2579 and Strong.50) These mammoth vessels would contain self-sufficient communities of the sentient spacefaring species and their offspring.2759 Farfetched, sophisticated space drives would be unnecessary, since the revolving crew could tolerate trips lasting hundreds of years to the nearer stars. While the original explorer-colonists might never live to see the New World, their great-grandchildren and successive generations would survive to carry the great mission on to its conclusion.

Science fiction authors have described the social and genetic backsliding that could occur in such closed ecologies.2794 The degree of discipline that each individual would have to accept would be more demanding than that of any present totalitarian regime here on Earth. Birthrates must be strictly controlled, psychological interactions skillfully managed, epidemiological and eugenics rules absolutely enforced, and all aberrant ship-threatening behavior severely punished. From the human point of view the restrictions on personal freedom would be well-nigh intolerable. Still, as Dyson points out, "we have no right to impose our tastes on others."2792

The generation ship would provide a pathway to the stars for any patient extraterrestrial species that either could not or would not build relativistic propulsion systems. Speeds from 1-5%c should be ample to commute between neighboring star groups in periods of only a few centuries. This can be done using relatively primitive space hardware. Our own Pioneer 10 probe, which departed the solar system a few years ago, is now heading out into the interstellar void at 0.004%c -- a respectable velocity, considering that the craft was designed solely for interplanetary travel.

Of course, during the long journey the technology of the home planet will not stand still. In more than one science fiction story, the crew of the first interstellar ark arrives at their destination only to find that they had been passed many times en route by superior starcraft of more modern design, and that the target system had long since been colonized by others.2791 James G. Strong suggests that "such action will only arouse bitterness among the pioneers, and it would be kinder to avoid their destination -- certainly never to come within hailing distance of their ship."50

Note that there is no absolute requirement that the full complement of consumables be carried on board the Ark at launch. According to C.A. Cross, "its materials balance could be sustained by the return to it of unmanned vehicles carrying raw materials on long stern chase trajectories."2793 Like the interstellar ramjet that picks up its fuel along the way, an "Ark runway" would enable a generation ship to pick up supplies positioned earlier across its flight path by unmanned cargo vessels dispatched from the home planet.

There are several other alternatives to the generation ship. As Freeman Dyson once remarked: "Interstellar travel is essentially not a problem in physics or engineering but a problem in biology."

For instance, if medical science can learn how to prolong life indefinitely and create immortal astronauts, then the crew which began a lengthy voyage would live to see the end of it. The perspective of immortal beings would doubtless be quite farsighted, and it is not unreasonable to suppose that such creatures would have a leisurely, relaxed outlook on life. A century or two spent out of a 2000 year lifespan would seem no more painful than a 3-7 year voyage would to a human. Sea voyages of this length were common among sailors and traders of centuries past: Magellan’s global circumnavigation required 2 years, Sir Francis Drake’s 3 years, and Marco Polo’s excursion to China totaled 24 years.

Another possibility is the "sleeper ship," a well-worn science fiction theme during the last half-century. There are basically three classes of sleepers: Ectogenetic astronauts (discussed in the previous chapter), hibernauts, and cryonauts.

Hibernauts are starship crew members whose metabolisms have been greatly slowed. Like bears, woodchucks, bats and many rodents, these interstellar travelers would "hibernate" for most of the trip. For starfaring hibernauts, objective centuries would melt into subjective hours, creating a delightful illusion of near-instantaneous travel. Experiments with small mammals here on Earth indicate that it may be possible to induce artificial hibernation in humans using a variety of specific metabolic inhibitors such as the antabolone found in aestivating lungfish.2785 The addition of antabolone to other anti-metabolic ingredients should permit metabolism to be reduced to 1% of normal at temperatures near 0 °C. Hibernation for extended periods should be possible, although as in natural hibernation it will probably be necessary to periodically raise the temperature to normal for a few hours each month to allow certain cellular restorative functions to take place.67

Cryonauts are interstellar travelers whose bodily functions have been entirely shut down. Placed in "suspended animation" at cryogenic temperatures, these starfaring passengers cross the Galaxy in compact, refrigerated vessels equipped with ultrareliable supercomputers designed to patiently wait out the lonely centuries and then automatically reanimate the frozen travelers when the target star system is reached. Robert Prehoda, a science writer and technology forecaster, speculates that:

Cryonauts may travel for many centuries between the stars in fully automatic self-repairing spacecraft controlled by immortal super-computers -- descendants of "HAL" in 2001, A Space Odyssey. When they are revived, the journey will seem to have been only one night long. perhaps they will stay alert for a few years to explore new planets and transmit information about them back to Earth. Then they could be frozen again for another mission to a more distant star, repeating the freeze-revive-freeze cycle several times before circling back to Earth after an odyssey of many millenia.67

Suspended animation will require only a modest-level biotechnology, in all probability. The main problem with freezing organic tissues is the extracellular formation of ice crystals which cause tissue damage, making reanimation impossible. Nevertheless almost every kind of mammalian tissue has already successfully been frozen and thawed under appropriate conditions.3697 For instance, rabbit skin has been frozen to -196 °C in liquid nitrogen for 7½ months and is still viable when thawed.2786 Successful freezing and thawing of rat pancreas cells down to -196 °C has been shown,2788 and rat heart tissue can be reanimated after indefinite storage in liquid nitrogen.1687 And low temperature preservation of human blood cells, sperm and ova is now routine.

Whole organs have also been reanimated, though this is more difficult Marshal Shlafer and Armand M. Karow, Jr. successfully restored isolated rat hearts cooled to -30 °C and perfused with a commonly-used biological antifreeze called "dimethylsulfoxide," or DMSO.1685,1692 Dr. Isamu Suda of Kobe University in Japan froze a whole cat brain to -20 °C for more than 6 months using a DMSO cryoprotectant perfusate. After thawing, the brain was shown to have nearly normal electroencephalic wave tracings.3694,3695

What about whole-body freezing? Many experiments during the past few decades have demonstrated that laboratory rats can be cooled to -10 °C and later restored to life in apparently normal condition. However, the period of "cold sleep" must not exceed a few hours and no more than 50% of the body fluids may be solidified.2787 Lower lifeforms are much easier to freeze. Nematode worms, for example, survive suspended animation at liquid nitrogen temperatures indefinitely when subjected to a specific DMSO perfusion treatment.1689

What about whole humans? The well-known mammalian diving reflex, together with the body’s lowered oxygen needs at temperatures close to freezing, have permitted people to survive drownings in icy river waters during literally hours of submersion. Dr. Ivan W. Brown, Jr. of Duke University Medical Center has successfully revived a human child whose body-temperature was reduced to 5 °C.67 Following the successful cryopreservation experiments on dog kidneys performed by Dr. M.D. Persidsky at the Institute of Medical Science in San Francisco and Ronald Dietzman of the University of Minnesota, Robert Prehoda has tentatively suggested a hypothetical medical procedure for placing human beings into a state of reversible suspended animation:

The body temperature is lowered to 0° C and a heavy water (D2O) perfusate now circulates through the body. Soon most of the H2O molecules have been replaced with D2O. A 5%-by-volume addition of fluorinated DMSO is now added to the perfusate. This chemical will partially protect the cells during freezing, but its main function is to act as a biological carrier, insuring that the powerful metabolic inhibitors will reach adequate levels within all the cells. Salt-free albumin and ATP are added to the perfusate, allowing the level of dissolved salts within the cells to be reduced. The pressure is greatly increased, and large quantities of dissolved xenon gas begin to be circulated through the body. The fluid-filled cavities around the brain, spinal cord and in the eyes are properly protected by separate perfusion systems.

The heavy-water-based perfusate is replaced with a liquid fluorocarbon which can hold large quantities of dissolved xenon. The pressure is slowly raised as the temperature is reduced. At 5000 psi, an optimum quantity of xenon can be perfused through the body, thoroughly penetrating every cell. No more xenon is needed. The pressure is slowly increased to 30,062 psi. The perfusate pump is shut off. The body temperature is -24 °C. The pressure is then lowered to 5000 psi and rapid solidification begins to take place through the body. Cooling continues as the pressure is again increased to 30,062 psi, allowing the heat of fusion energy to be dissipated. The up-and-down pressure cycle is repeated four more times during continuous cooling, permitting the body to be uniformly frozen. Xenon hydrate protects every cell against freezing damage. The body temperature continues to be lowered at a controlled rate until it is only 4.2 degrees above absolute zero -- the temperature of liquid helium. You are now in a state of complete suspended animation.67

These steps may be followed in reverse order to achieve reanimation.*

Cryonauts may not be immortal. Every minute 106 atoms of radioactive K-40 and 2 x 105 atoms of C-14 decay in a human body, spraying bones and organs with beta particles and other low-level radiation. Accumulation of trace amounts of radionuclides is virtually inevitable for any carbon-based lifeform, and these minute natural emissions may produce genetic mutations and other irreversible cellular damage over millennia of cold storage.

Prehoda estimates that the natural decay of radioactive isotopes in body tissues will cause a lethal accumulation of radiation damage in human cryonauts in roughly 35,000 years. This difficulty can perhaps be avoided by raising potential astronauts from birth in a carefully controlled radiation-free environment. Food, water, and air must be purified and made free of the harmful isotopes. This accomplished, cryonauts should last for millions of years in suspended animation (assuming adequate shielding from the cosmic ray background) and would be prime candidates for long-term low-velocity galactic exploratory and colonization missions.


* Already about fifty people have been frozen, using somewhat more primitive perfusal techniques, by several Cryonics Societies around the country. These methods may not prove successful, but we won’t know for sure until reanimation is attempted on one of the many frozen patients, perhaps a century from today.


Last updated on 6 December 2008