Slipspace field pod

Slipspace Field Pods are the Forerunner equivalent of the UNSC's cryotubes.

Instead of freezing a being in a stasis, they put the user into Slipspace, where time stops without motion. It is unknown whether these would work during Slipspace transit, because they freeze units by putting them in Slipspace itself. If they don't work in Slipspace transit, then it is apparent that they were used not like the cryo tubes, as a method to prevent aging during travel but as a mini fallout shelter to survive the Halo's detonation.

Forerunner Slipspace pods are somehow connected to slipspace and normal space, the actual bodies contained inside the pods are within slipspace, making them safe from nearly everything. (Nearly means that they might be able to get killed if they are engaged within Slipspace, otherwise, normal space cannot hurt the person inside.)

They are visible via an afterimage seen within the pod, essentially a snapshot of the moment they "left" time. Although not technically in our space, those stored "within" the pods may be transported by moving the pods themselves. This method works as the Slipspace generator is located on each pod. If a person comes too close to the pod they will develop nausea, and a feeling of light-headiness due to exposure of an unshielded Slipspace field.

Currently, the method of releasing one from these pods is unknown.

On the sides of the pods there are Forerunner icons which Dr. Catherine Halsey translated into "That which must be protected . . . behind the sharpened edge of the shield . . . beyond the reach of the swords. . . for the reclaimed".

Team Katana of SPARTAN-III Gamma Company are in Slipspace Field Pods and are with the other survivors of the Battle of Onyx in the Shield World.

Theory behind the Technology
Being in a Slipspace Field Pod, can be compared to getting sucked into a black hole, or what scientists think would happen if that were to occur. The gravity of the black hole distorts time the closer you get, at a certain point, stopping time for those affected (although a black hole singularity would probably kill a person), and if another person was watching, they would see you frozen in time. You are visibly there, but at the same time you are not, you are stuck in a vacuum of time, which might be what causes those afterimages, from the pods in Halo: Ghosts of Onyx.