Alcubierre Drive

“
Fun fact: Did you know that this ship can get to any position in the galaxy in mere seconds? This is due to the Alcubierre drive invented in the early 2030s. The drive works by creating a wave in the time-space to actually make time and, well, space flow around the ship!"
— Ship's C.O. in Helldivers 1.

The Alcubierre Drive is the means by which spacecraft designed by Super Earth, such as the Super Destroyer, are able to traverse the galaxy at faster than light speeds.

According to Helldivers 1, it was invented in the 2030s, indicating that Super Earth's expansion into other planets began around this time.

The Fuel

The Element-710 produced by the Terminids is noted to fuel the Alcubierre Drive in Helldivers 2. It should be noted that Super Earth only discovered the E-710 during/after the First Galactic War (Element-710 is not mentioned in Helldivers 1) the fuel used to leave the Sol System is unknown.