The DS-1 Orbital Battle Station was originally designed by the Geonosians before the Galactic Republic and later the Galactic Empire took over the project. However, the plans for the battle station were stolen by the Rebel Alliance from Scarif, leading to its destruction at the Battle of Yavin, but not before it unleashed its planet-destroying cannon on Alderaan and Jedha City.
If the 1st Death Star had not been destroyed by Luke Skywalker and the Rebel alliance at the battle of Yavin, Palpatine had plans to destroy the planets of Mon Cala and Chandrilla, to continue striking fear into the galaxy. These planets were chosen because they were hotspots of rebel activity as well as having many high ranking Rebel leaders hailing from there, including Admiral Ackbar and Raddus from Mon Cala, and Mon Mothma from Chandrilla.