This is an idea for either a plot or simple underlying discovery for a campaign.
The Apollo group of asteroids are a group of near-Earth asteroids, the first asteroid of this group which was discovered by German astronomer Karl Reinmuth in the 1930s. They are Erde crossing asteroids – meaning they cross Erde’s orbit. The Apollo asteroid group includes a total of 6,923 known asteroids. More than a thousand Apollo asteroids are large enough and may get close enough to Earth to be known as potentially hazardous asteroids.
The construction of the Home Fortress along the Amor group was less in a reaction to potential resistance threats and more in reaction to an escalation between the two major powers and a new weapon of mass destruction. This weapon, first developed by the Empire and later the Reich, involved massive contra-grav engines installed on Apollo group asteroids. These engines were large enough to shift the orbit of the asteroid and direct it to any target on Erde with precision.
The Empire secretly began a project, called Fire Sky, in an effort to shift the balance of power in the system, but it did not take long for Reich intelligence to learn of it. This lead to a massive escalation of Near Erde Asteroid Redirection Systems (NEARS). In reaction to this escalation, the Reich also began construction of Home Fortress and the Empire followed close behind with their version. Eros became the center of military activity for several years.
Various technologies were developed to not only direct the asteroid but also protect it on re-entry to maximize effectiveness. Directed Field manipulation systems made possible by advancements in contra-grav systems, micro-manipulation of gravity fields, as well as advanced automated targeting allow these asteroids to be directed fairly easy as any target the controlled power wishes.
The weaponization of these near-Erde asteroids is not all known among normal citizens of the solar system. Only top intelligence leaders of both sides know about it as well as the few personnel involved in the operation of the systems. Resistance groups have learned of bits and pieces a military operation that goes beyond the cover story of Home Fortress but the exact nature is vague.