What two critical factors severely constrain the direct communication link a rover uses via its High-Gain Antenna (HGA)?

Power and data rate

The direct link to Earth, facilitated by the directional High-Gain Antenna (HGA), is severely limited by inherent physical restrictions on the rover platform. First, the rover operates on finite power reserves, meaning it cannot sustain the high-power transmission necessary for a strong signal across interplanetary space continuously. Second, due to this limited power and the immense distance, even with a precisely aimed directional antenna, the resulting data rate achieved is relatively low compared to other methods. Consequently, this direct path is often reserved only for critical, low-volume communications like emergency checks or essential status reports when relay assets are unavailable.