The Portals

The Portals are giant space stations with a length of about 80km, which connect the different galaxies with wormholes, so that travel without timeloss is possible over the vast distances of billions of lightyears between the galaxies. They function in a way, that one station is placed in one galaxy and another station of the same design is placed in the other galaxy. Bouth stations are required to keep the wormhole open and stable. The portal that needs to be placed in the target galaxy, is first build in the starter galaxy and, when finished, shot by the catapult into the target galaxy. First the portal connection to the target galaxy is only open for use by the Praethorian military, but once the target galaxy is successfully integrated into the Empire, the connection is also opened for civilian use.
The first plans for this technology were formulated just a few months before the Praethorians anounced their plans to conquer another galaxy in the year 1514 BFOE.
Following this anouncement the government of the Old Empire allocated huge amounts of funds and resources towards the hundreds of researchers, who worked on the portals. After about two years of hard work the researchers had devoloped a plan, they were sure would function. It just had one problem: they still couldn't find a energy source, that could enable the portals to stabalize the wormholes, so they wouldn't immidiatly close again.
Just some weeks later the researchers realized, that the new Element of Thydorium, which was just discovered a few months prior, could be used in a new type of reactor to generate huge amounts of energy, which would be enough to keep the wormholes open and stable. This new Thydorium reactor would then also be used in the catapult. The researchers would then spend about a year to develope the reactor and complete the design of the portals and the catapult.