Hera and its CubeSats connected by inter-satellite links

Once deployed, Hera's two CubeSats will remain connected to their Hera mothership through radio-based inter-satellite links. Their demonstration is a crucial mission objective. These inter-satellite links are the way that the Juventas and Milani missions will relay their findings back to Hera for transmission back to Earth.

These links will not only be used for communications but also to precisely assess the relative positioning and velocities of Hera and its two CubeSats. This will be done by measuring the slight degree of Doppler shift in their line-of-sight signals, revealing their corresponding rate of motion.

This tracking method will also be crucial in assessing the mass of the two asteroids. The ground-based tracking of this technique is well established for relatively massive objects, identifying slight tugs on a spacecraft from their gravitational pull, helping fix the gravitational field to an accuracy of a fraction of one percent.

While Hera employs X-band communications with the ground, its inter-satellite link system utilises S-band, with a maximum range of 60 km. Originally developed for terrestrial drones, the system comes from Portuguese company Tekever Space.