Failure & Recovery — Solar Conjunction Scenario

The Conjunction Problem

Approximately every 26 months (the Earth-Mars synodic period), the two planets pass near solar conjunction — the Sun appears between Earth and Mars. The Sun's corona raises the noise floor until no reliable direct link exists. This is not a transient outage; it is a predictable, ~2-week period of zero direct-path availability.

Orbital Geometry

The conjunction exclusion is defined by a phase angle threshold: when the Sun-Earth-Mars angle drops below 10 degrees, the direct path is considered unusable. The predict_contact_windows() function in src/orbital/contact_windows.py implements this as a hard exclusion:

if phase_angle < 10 degrees: skip window

At this geometry, the solar corona causes: - Solar plasma scintillation — free electrons in the corona cause rapid phase and amplitude fluctuations on RF signals - Optical extinction — the Sun's intense brightness makes photon-counting detection impossible - Increased path loss — signals grazing the Sun's limb experience additional attenuation

The Fallback Chain

AETHERIX's failure handling is layered — each layer degrades gracefully to the next:

Tier 0 (Normal):  Optical 1550 nm, 50-200 Mbps
    ↓ (optical fails: clouds, pointing, conjunction)
Tier 1:            Ka-band RF, 2-10 Mbps (penetrates clouds)
    ↓ (Ka degraded: solar plasma scintillation during conjunction)
Tier 2:            X-band RF via Lagrange relays, lower rate
    ↓ (all direct paths blocked: conjunction blackout)
Tier 3:            Store-and-forward via ES-L4 / ES-L5 Lagrange relays

Why the Lagrange Relays Work

The Lagrange relays at ES-L4 and ES-L5 sit ~60 degrees ahead/behind Earth in its orbit around the Sun. This means they have line-of-sight to both Earth and Mars around the solar limb even during conjunction, when the direct Earth-Mars path is occulted. They provide 50–70% availability during conjunction — not 100%, because the geometry is marginal and the relay path is longer (higher path loss), but vastly better than the 0% of the direct path.

The Recovery Ramp

Links do not snap back to full rate once the angle passes 10 degrees — the corona is still hot. AETHERIX ramps capacity back gradually:

The drained backlog order is fixed by the QoS scheduler: EMERGENCY first, then MISSION_CRITICAL, HIGH_PRIORITY, BULK last. Buffer occupancy returns below 0.9% and congestion_control stands down.

Data Triage During Conjunction

During the ~2-week conjunction, the RL agent's priority-aware routing becomes critical: - P0 Emergency bundles routed immediately via Lagrange relay using LTP red segments with custody - P1 High Science queued behind P0 with same reliability guarantees - P2 Standard stored locally on Mars assets until direct links resume - P3/P4 deferred entirely

The 780-day synodic period means the conjunction is predictable — the agent learns to pre-position data before it starts. The total Mars surface buffer capacity (167 nodes × 64–256 GB each) can store the full conjunction backlog.

Availability Math

The combined optical + RF availability is computed as:

A_combined = 1 − (1 − A_optical)(1 − A_rf)
           = 1 − (1 − 0.957)(1 − 0.99)
           = 1 − 0.043 × 0.01
           = 0.9996  →  99.96%

The 99.96% combined figure exceeds the 99.9% target. During conjunction, however, both optical and Ka degrade, and availability drops to the Lagrange relay's 50–70%.