Since before the first satellite launches within the Sol system, fiction writers and engineers alike assumed that long-duration space flights would require certain measures to keep the travelers happy and psychologically fit for continued duty. During the first Earth orbital and lunar landing missions, crew members listened to cassette tapes of their favorite music, and flight controllers periodically passed up capsule versions of the daily newspapers of the day. Documentation and video recordings were routinely transmitted to orbital stations and planetary outposts into the early part of the twenty-first century.

The desire to experience images, sounds, and tactile stimuli not normally encountered on a space vessel has followed explorers across the galaxy for the last four hundred years. Computer-driven projection imagery has filled starship crews' needs for provocative spaces and, with the addition of certain sport and recreational gear, provided an enjoyable model of reality. Various holographic optical and acoustic techniques were applied through the years, finally giving way to a series of breakthroughs in small forcefield and imaging devices that not only did not seriously impact starship mass and volume constraints, but actually nurtured hyperrealistic, flight-critical simulations. In the last thirty years, the starship Holodeck has come into its own.


Matter conversion subsystem creates physical props using replicators. Replicated props are generally created when an object is likely to be touched by the participant. Some props are animated under computer control by precision-guided tractor beams.

Holographic imagery subsystem creates three-dimensional images of simulated environments. Shaped forcebeams give physical substance to foreground objects so they have the illusion of being solid.

Substrate forcefield creates a "treadmill" effect, permitting participant to remain stationary while the simulated environment "scrolls" by, within the limits of the simulation program.


The Holodeck utilizes two main subsystems, the holographic imagery subsystem and the matter conversion subsystem. The holographic imagery subsection creates the realistic background environments. The matter conversion subsystem creates physical "props" from the starship's central raw matter supplies. Under normal conditions, a participant in a Holodeck simulation should not be able to detect differences between a real object and a simulated one.

The Holodeck also generates remarkably lifelike recreations of humanoids or other lifeforms. Such animated characters are composed of solid matter arranged by transporter-based replicators and manipulated by highly articulated computer-driven tractor beams. The results are exceptionally realistic “puppets,” which exhibit behaviors almost exactly like those of living beings, depending on software limits. Transporter-based matter replication is, of course, incapable of duplicating an actual living being.

Objects created on the Holodeck that are pure holographic images cannot be removed from the Holodeck, even if they appear to possess physical reality because of the focused forcebeam imagery. Objects created by replicator matter conversion do have physical reality and can indeed be removed from the Holodeck, even though they will no longer be under computer control.

The basic mechanism behind the Holodeck is the omnidirectional holo diode (OHD). The OHD comprises two types of microminiature device that projects a variety of special forcefields. The density of OHDs is 400 per cm, only slightly less than the active visual matrix of a multilayer display panel, and powered by standard medium-duty electro plasma taps. Entire walls are covered with OHDs, manufactured in an inexpensive wide-roll circuit printing process. A typical Holodeck surface comprises twelve subprocessing layers totaling 3.5 mm, diffusion bonded to a lightweight structural cooling tile averaging 3.04 cm thick. The primary subprocessor/emitter materials include keiyurium, silicon animide, and superconducting DiBe<2>Cu 732. Each single OHD measures 0.01 mm. The optical data network mechanism by which OHDs are sent impulses is similar to that for smaller display screens, though complete walls are broken down into manageable high-speed segments, each 0.61 mģ. Dedicated high-speed subsections of the starship main computers drive these room-sized displays.

In addition to their ability to project full-color stereoscopic images, OHDs manipulate forcefields in three dimensions to allow Holodeck visitors to "feel" objects that aren't really there. This tactile stimulation provides the proper feedback one might expect from a rock on the ground or a tree growing in a forest. The only limiting factors to the numbers and kinds of objects described by the computers are memory and time to record or calculate from scratch the originals of the desired objects, whether real or imagined, such as a Klein bottle.

Other stimuli, such as sound, smell, and taste, are either simulated by more traditional methods, such as speakers or atomizers, or built into the created objects using replicator techniques.

The optic version of an OHD emits a complete image of an overall environment based on its location in the installed surface panel. The visitor, however, sees only a tiny portion of any one OHD, in much the same manner as a fly's eye operating in reverse. As one moves about, the visible portions of the OHDs change, altering the view. The actual energy emissions are unlike direct visible EM projections, but rather polarized interference patterns. The image is reconstructed where the patterns intersect at the lens of the eye or other visual receptor.

The forcefield version creates a tiny steerable forcefield. Its larger cousins are the more familiar tractor beams and navigational deflector. Under computer control, over a vast number of OHDs, the cumulative field effect is substantial. If the Holodeck is recreating, for example, a large mass of rock, the computer would first create the three-dimensional surface of the rock. This is accomplished by commanding certain OHDs to intersect their fields at the required polygon coordinates. If the field strength is tuned to provide the proper mineral hardnesses, the mass will feel like rock. A vast library of recorded real substances is available, and custom settings may be commanded for experimental purposes.

The shaped forcefields and background imagery allow the visitor to experience volumes and distances apparently larger than the Holodeck room could physically accommodate. The environment can be scrolled to continue if desired, or set for bounding limits indicated by soft wall contacts and audible reminders of wall proximity.

In a working environment like a Federation starship, safety is of prime importance and is engineered into every system. Because the starship living environment is so highly controlled, the emotional release associated with encounters with limited real physical hazards has been shown to be of significant value in maintaining the psychological well-being of many crew members.

Simulated high velocities and forces are normally created by sensory illusions. While safeguards against critical bodily harm are programmed into the computers, certain scenarios can result in unavoidable sprains and bruises, even for experienced users. Hazards posed by "dangerous" lifeforms can seem exceedingly real and will fulfill most requirements.