Deep-space relays stop forwarding in queue order: Moon and Mars share one buffer, and bundles are picked by freshness
Relay-side scheduling and dropping in deep-space DTNs are driven by destination-side information freshness, and in DTNSim simulations with a shared Moon–Mars relay buffer, masked Lagrangian PPO reaches the lowest mean aggregate excess AoI while meeting drop, expiry and inter-source fairness budgets.