Spacefold drive
Spacefold drives are the physical means of travel between star systems. It works by essentially folding space around an object rather than moving the object itself, forming a bubble around it and negating the effects of time dilation. Once the required calculations and energy requirements are met, the transportation process is instantaneous. While quantum entanglement is used to transfer information between two points in space, this cannot be done with physical matter, and as such, a different form of travel is required when transporting people, cargo and other objects. Both of these technologies are considered critical for the sustainment of an active interstellar society.
Spacefold drives require substantially more energy than quantum entanglement. As a matter of fact, while spacefold drivers were experimented on in the early days of humanity's time in space, they did not become practical until the rise of the Valerian Empire when more efficient energy usage methods were discovered. The primary source of power used in Spacefold drives is deuterium.
Spacefold drives also have the side effect of producing dark energy which are believed to accelerate the expansion of the universe. As it is considered a form of pollution, spacefold drives became highly regulated during the time of the Federation. They are almost exclusively a public transportation and only the social elite tend to have their own private interstellar spacecraft.
While a spacefold drive can technically go anywhere in the universe, the destination location needs to have proper coordinates and calculations set up in advance. As such, it is considered extremely dangerous to attempt to explore beyond Charted Space as there is a risk of making a jump but not being able to come back due to lack of resources. As such, it is considered standard procedure to map nearby star systems and planets as a potential jump point - taking into account gravity wells, radiation and potential resupply locations in the event of fuel running out. For this reason, star charts are critical to exploration with Valerian-era star charts being considered extremely valuable.
After making a jump to a location, it is considered more energy efficient to do precise exploration with sublight spacecrafts and probes. Because of all the inherent risks associated with exploration, most space travel only tends to occur within the Milky Way Galaxy. The furthest known jump point is in the Large Magellanic Cloud.
Knowledge on how to create Spacefold drives was lost during the Blackout. It took almost one thousand years for the technology to be rediscovered, in part due to reverse engineering remnants of Valerian spacecraft.