It was discovered early in the Diaspora that the maximum practical safe speed for a sublight ship was approximately .8 c, as radiation and particle shields can not protect the vessel above that velocity.

The generation ships were built as complete, life-sustaining habitats oriented around the smallest practical self-sustaining population and designed to boost to that velocity at one gravity. In the long term, onboard gravity was provided through centrifugal force. In addition to their human passengers, the generation ships also had to provide for all terrestrial livestock and plants which would be required to terraform the colonists' new home for their survival. Even aboard these huge ships, space was severely limited, and many early colonial expeditions reached their destinations only to come to grief through the lack of some essential commodity the settlers had not known to bring along. This sort of disaster became less common after about 800 pd, when the original, crude hyperships made it possible to conduct extensive surveys of potential colony sites before the slower colony ships departed, but by that time the generation ships were a thing of the past, anyway.

In 305 pd, cryogenic hibernation finally became practical. It had long been possible to cryogenically preserve limbs and organs, though even the best anti-crystallization procedures then available were unable to prevent some damage to the preserved tissues. But where minor damage to an arm or a liver was acceptable, damage to a brain was not, and the early cryogenic pioneers' enthusiastic predictions about indefinite suspension of the life processes had proven chimerical.

It was Doctor Cadwaller Pineau of Tulane University who, in 305, finally cut the Gordian knot of cryogenic hibernation by going around the crystallization problem. He found that by lowering the hibernator's temperature to just barely above the freezing point he could maintain the physiological processes indefinitely at about a 1:100 time ratio. In other words, a hibernating human would age approximately one year for every century of hibernation, and his nutritional and oxygen requirements were reduced proportionately. Over the next several decades, Pineau and his associates further refined his process, working to overcome the problem of muscular atrophy and other physiological difficulties associated with long comatose periods, and eventually determined that optimum results required a hibernating individual to rouse and exercise for approximately one month in every sixty years (ie., after six physiological months), which remained a fixed requirement throughout the cryogenic colonization era.

What this meant was that the life support capabilities of a cryo ship could be vastly reduced in comparison to those of a generation ship. Moving at .8 c, the colonists experienced a 60% time dilation effect; in other words, each sixty-year period of hibernation used up one century of voyage time by the standards of the remainder of the universe. Thus an entire one-century voyage could be made without a single "active" period and would consume only 7.2 apparent months of the traveler's life span. Longer voyages would require periodic awakenings, but they could be staggered, permitting the currently roused crew to use only a fraction of the life support the entire crew would require. The result was to permit far larger numbers of colonists to travel on a given sized ship with a far lower subjective time passage.

A further boost to colonization came about in 725 pd with the advent of the first hyper drive. The casualty rates among early hyperships were so severe that it took a rather daredevil mentality to go aboard one, and colonists weren't normally noted for that sort of personality. To claim a new home world they would take risks, yes, but not risks they could avoid.

But what the hyperships provided was a survey vehicle which could travel more than sixty times as fast as a sublight ship, and the people who went in for discovering and exploring (as opposed to settling) new worlds had just the sorts of mentalities to risk hyper travel. A situation thus arose in which survey ships, generally operated by private corporations, undertook the high-risk job of locating potential colony sites which were then auctioned to prospective colony expeditions. Even with the hyper drive, this required that everyone involved take a very long view of things, but humanity adjusted to that just as it had once adjusted to the novelty of instant communication to any point on a single planet.

It is believed that the first Warshawski Sail colony ship was the Icarus, which departed Old Earth on September 9, 1284 pd, under the command of Captain Melissa Andropov (and, despite its name, provided over two centuries of dependable, reliable service before it was finally scrapped in 1491 pd), but for well over five hundred years, the dichotomy of FTL hypership survey expeditions and sublight hibernation colony transports remained the standard.

When the transition finally occurred, there were several very unfortunate instances in which unscrupulous operators used the new hyper sail technology to pass hibernation ships en route to their new homes. When the original colonists arrived, it was only to find well-established (and armed) claim-jumpers already squatting on their planned home worlds. If there was an already established colony in the vicinity, it might take a hand to assist the original colonists, even to the extent of lending military aid to eject the claim-jumpers, in order to discourage such unsavory elements from ruining the neighborhood. If there was no such well-inclined planet in the vicinity, the original colonists were out of luck, particularly since their technology might be several centuries less advanced than that of the thieves they confronted. In some cases, this created a domino effect. Expeditions which found themselves dispossessed of their colony sites often lacked the resources to return whence they had come (even if they had the inclination) and many opted to risk settling an unsurveyed world if there were stars with habitable planets (or which were likely to have such planets) in the vicinity. Many of them came to grief as the old generation ship colonies had in attempting to settle worlds other than the ones they had planned their original expedition's equipment list to meet, and those which did not often wound up displacing yet another group of legitimate colonists. Other such instances ended far more happily, with the second group of settlers discovering a world which was already partly settled and a group of "squatters" who paid their own way with the improvements they had already made and were integrated peaceably into the ranks of the "legitimate" colonists.

With the advent of Icarus and her later sisters, however, the entire pattern of colonization shifted. It was now possible to make a 500 light-year voyage in barely two-and-a-half years, an interval which dropped steadily as improvements in Warshawski technology became available. Hibernation was still used on most colony ships, but now it was simply to cram in the largest possible number of passengers, not a necessity. Indeed, as higher and higher speeds became possible, the hibernation features began to fall by the wayside.