A Cryo Tray, sometimes referred to as a Cryogenic Tray, is a long mechanical cargo container designed by the Kushan for the purpose of transporting large numbers of colonists aboard the Kushan Mothership for the eventual reclamation of their long lost homeworld, Hiigara. Each was designed with a capacity of up to 100,000 Cryo Pods, which carried living people frozen in sleep at extremely low temperatures using advanced cryogenic technology.
The best known cryo trays and the ones usually referred to in context were those used by the Mothership Fleet during the Exodus to Hiigara. Volunteering themselves to be frozen as early as twelve years prior to the expedition, these Kushan colonists are people who have bought, earned, or somehow else attained a ticket for the first journey to Hiigara. These people, who were thought to simply be extraordinarily rich or adventurous turned out ironically to be the only remnants of the Kushan people other than the actual Mothership Fleet's crew by the end of the Homeworld War.
Cryogenic technology was first developed by observing and testing with various animals on Kharak's surface that burrowed into the ground during the hot summers during hibernation. By analyzing certain patterns in the way that they slept and their metabolism changed during these hot summers it was easy enough for Kushan engineers, aided by technology provided from Khar-Toba, to eventually adapt the process for the purpose of freezing.
The cryo pods in question were first tested using small vessels with one-man crews, sent out to the edge of the Kharak System and then programmed by autopilot to turn around and head back while the pilot was in suspended animation. The tests proved effective, with surprising results suggesting that cryosleep was in many ways no more different than real sleep, the only difference being that it simply required less energy.
With the technology successfully tested, the first volunteers were frozen about twelve years before the launch of the Kushan Mothership. These adventurous, usually very young (although the process was restricted to only those legally of adult age and below the age of senior citizenship) pioneers in the field were then transported to underground facilities where they and additional volunteers overtime were stored until finally the Mothership was prepped for launch and the cryo pods were transferred to the orbital cryo trays.
Those fortunate enough to have attained a place aboard the cryo trays eventually proved to be the last and only survivors of the savage Taiidan attack on Kharak shortly after the Mothership's first hyperdrive test. Though the Taiidan fleet immediately scoured the surface of Kharak with their deadly Low Orbit Atmosphere Deprivation Weapons, the cryo trays were initially overlooked as they had only been broadcasting from a low-level maintenance frequency in Kharak orbit. Their fate was then left to a small handful of vessels which remained to finish the job, the Taiidan having figured that a few defenseless containers of frozen people wouldn't be much of an immediate threat.
Much to the surprise of those involved however, the Mothership Fleet arrived just in time to rescue the cryo trays and save their people from extinction. Once the Assault Frigates left to finish off the trays were captured or destroyed, the cryo trays themselves were salvaged and brought back to the Mothership for their intended storage. With this, the survival of approximately 600,000 Kushan colonists, the last remnants of their race, was ensured. Once the cyro trays were safely aboard, the Mothership left Kharak behind, forever.
Those who survived the attack on Kharak were known as Sleepers, based on the fact that they had been asleep when they were rescued. Many sleepers were awoken during the journey and given immediate emergency training to replenish the ranks of men killed by the Taiidan during the war. Those that awoke, and had not had time to come to terms with the fact that all their friends and family were dead, immediately became zealous patriots devoted only to one thing: to destroy those who had destroyed all they had known. Many others instead chose to commit suicide, unable to cope with the loss of their loved ones or of their home and culture. Though most in time came to terms with their mix of luck and misfortune, more than a few of these sleepers became bounty hunters, assassins, and pilot aces who spent their lives hunting down and killing Taiidan Imperials.
Two of the most famous examples of this are in Iifrit Tambuur, the lone survivor of his entire kiith and pilots of Somtaaw Mimics, both of whom came to place the individual deaths of Taiidan Imperialists over their own survival. In either case, though the cryo trays in the end were more than a luxury, the survival of their inhabitants continued to haunt history even after the war that had so nearly destroyed the Kushan people was over. For the sleepers, the cryo trays were a mixed blessing.