Space Bridge

The Space Bridge is a form of interplanetary transport, allowing Transformers to move from one planet to another almost instantaneously without the need for a spacecraft, via a "short-cut" through the extra-dimensional realm of trans-warp space. Early models required machinery at both ends of the bridge to open a stable dimensional portal, but later iterations of the technology consisted only of a generator at the departure point, which could open bridges to the desired location without the need of a receiver at the other end.

History
Cybertronians first found of the existence of Space Bridge technology in Quintesson files revealing that they were stolen designs that were to be used to ship Cybertronians as slave across the galaxy. When the Quintessons were forced to flee, the Cybertronians inherited the Space Bridge design.

It was used to colonize/explore distant space. One ship, however encountered the fatal plague known as "Cosmic Rust". The plague spread through the Space Bridges forcing them to be shut down completely to prevent the plague from reaching Cybertron. The colonies were cut off from their original home and slowly adapted to individual ways of life while forgetting their origins.

During the Great Exodus, Shockwave stayed behind to reverse engineer the ancient space bridge technology and managed to build one underneath Kaon and Starscream intended to use it to launch an attack on the Autobots on Earth led by Optimus Prime. But it was sabotaged by Cliffjumper and Arcee, who used it to travel to Earth moments before it exploded.

A second Decepticon Space Bridge was built in Earth's orbit (how no-one noticed is amazing) for Starscream to use. It was used to bring Megatron back to Earth. An Autobot raid on the Nemesis damaged the controls needed for its operation forcing Soundwave to use an Earth satellite array to lock it onto Cybertron to summon a Terrorcon army. This bridge was destroyed when Arcee turned its own power onto itself causing a feedback loop and destroying it.

Starscream later ordered a third built, this time deep in an Energon mine. Megatron continued this after Starscream's exile. In excahnge for immedaite medical care, Starscream told the Autobots where to find the bridge so they could use it to get to Vector Sigma. Despite resistance from Megatron himself, they were successful. Megatron decided to move the bridge immediately.

It was moved to the dark side of the moon where neither human nor Autobot could find it. Megatron and Dreadwing used it to fly to Cybertron. Megatron used it to lead a Vehicon squad to Cybertron to find the Omega Lock. When the Lock was found Megatron used the Space Bridge to send its power to Earth creating a second Darkmount.

The bridge was later dismantled and incorporated into the Nemesis itself, granting Soundwave the ability to control at will. If Soundwave was absent the bridge could be worked from a standard control station.

Transformers: Robots in Disguise
In Pilot (Part 1), years after the restoration of Cybertron, Lieutenant Bumblebee was street patrol in Kaon with Cadet Strongarm when he received a vision from the deceased Optimus Prime to go to the Cybertron History Museum. Inside, Bumblebee found a disused space bridge with pre-set coordinates for Earth. Stepping through with Strongarm and the apprehended delinquent Autobot Sideswipe, they arrived on Earth to find the crash site of the prison ship Alchemor.

Trivia

 * The design of Space Bridges resembles Stargates from Stargate and Borg Transwarp conduits from Star Trek: Voyager.
 * Arcee holds the distinction of destroying two Space Bridges, simply by sabotaging the energon containment protocols.
 * Soundwave can open Space Bridges by himself, as shown in Thirst. Therefore, it is unknown why the Decepticons built their second one, because it was not required to be big and Soundwave could just open one himself.