Notes : The Dyson sphere was discovered by the USS Jenolen in 2294; whilst investigating the sphere, the Jenolen was damaged when it triggered an automated system and crashed on the surface. Captain Montgomery Scott was ultimately the only survivor of the accident, and was rescued by the Enterprise-D when it discovered the sphere in 2369.

The Dyson sphere is named for the 20th Century Earth scientist Freeman Dyson; Dyson suggested that civilizations could be classified by the amount of power which they could tap and control. He proposed that eventually a civilization would tap the entire energy output of a star; some suggested that this would best be achieved by orbiting huge numbers of solar collectors, but  this idea was quickly replaced by the idea of constructing a large solid sphere around it. This would not only allow all of the suns energy to be tapped if required, but would also potentially allow a colossal living area to be built.

Whilst exploring the sphere the enterprise was pulled inside by an automated system. It was found that the sun within the sphere had at some time in the past begun to emit periodic bursts of intense radiation, rendering the surface uninhabitable. The builders of the sphere were apparently unable to correct this situation, and had been forced to abandon the sphere in the distant past. The Enterprise, with the assistance of the USS Jenolen, was able to escape from the sphere - unfortunately the Jenolen was destroyed during the operation, although no casualties were incurred.

Starfleet subsequently despatched several science vessels to the sphere, and has been investigating it ever since. Certainly the greatest feat of engineering known to exist, physical data regarding the Dyson sphere tends to consist of extremes. It has a diameter of two hundred million kilometres - approximately two thirds the size of the Earths orbit around its sun. The total enclosed volume is  4.19 x 10²⁴ km³, while with an average thickness of 2,400 metres the total volume of the spheres structure itself is some 3.02 x 10¹⁷ km³.

The interior surface has an area of over 1.25 x 10¹⁷ km², which is equal to some 245 million average class M planets. Statistical studies indicate that there are some 20 million class M planets in our galaxy - making the sphere over twelve times greater in area than every inhabitable planet in the galaxy put together. Initial studies of the interior indicate that the surface was class M, consisting of about 40% land and 60% water. Studies of the size and density of population centres indicate an average population density on land of 15 people per km²; this approximately one quarter the current population density of the Earths land area. If this truly does represent the average population density of the whole land area of the sphere, then it would hold up to 3,000,000,000,000,000,000 people. The interior environment would be somewhat strange to a person used to living on a planet; there is no night-day cycle within the sphere, nor are there any seasons or other natural cycles.

So far comparatively little of the technology of the sphere builders has been discovered; they apparently removed most of it when they abandoned the sphere. So far studies of the technology have centred on the materials technology, the structural integrity system and  the artificial gravity network which lies beneath the spheres surface. Little progress has been made on the former front; the sphere is made of a variety of materials, many of them unknown; the basic structure is made of carbon-neutronium, a material which combines the density of the diamond form of carbon with the strength of neutronium. It has proven extremely difficult to subject this material to testing because of its virtual invulnerability to most testing methods, and so far nothing has been learned about its manufacture or practical methods of utilizing it. Research into the structural integrity technology has yielded better results; the SIF systems used on the Dyson sphere are not all that dissimilar to those in use in the Federation, although they are on a vastly larger scale both in terms of the power of individual systems and the number of those systems. Some interesting systems have been uncovered, and this technology is currently at the Alien Technology Evaluation Centre of this institute to determine if it can be applied to Federation vessels and structures.

The gravity field generators are also yielding some interesting results; the system not only provides for a 0.895 gravity environment on the interior surface, but it is also apparently the main method of radiating energy into space. Under normal circumstances a Dyson sphere would act much like a massive greenhouse, containing the entire energy output of the star within it until the surface temperature reached a point at which conduction and radiation processes through and away from the surface could send the heat into space. The sphere builders have apparently overcome this process by using the waste heat produced to power the gravity generator network; this energy is then radiated harmlessly into space. While this rather neatly solves the thermal problem, it does ensure that the sphere is an source of intense gravimetric interference which can make it difficult to operate warp drives and sensors in the area around it.

Investigations into the Dyson sphere are continuing, but given the colossal scale of this structure it is unlikely that the task of exploring it will be completed for many centuries, perhaps even millennia.