ADCS, attitude determination and control system; how a spacecraft knows and changes where it is pointing. COTS, commercial off-the-shelf; ordinary terrestrial hardware flown without space-specific redesign. Dawn, dusk SSO, a sun-synchronous orbit riding the day/night terminator, giving near-continuous sunlight. GCR, galactic cosmic rays; high-energy particles from outside the solar system, effectively unshieldable. HBM, high-bandwidth memory; the memory stacks beside an AI accelerator, and its most radiation-sensitive part. ISL, inter-satellite link; a connection between spacecraft, now usually optical. ISAM, in-space assembly and manufacturing (and servicing). Kessler syndrome, self-sustaining collisional cascade of orbital debris. Latch-up, a destructive parasitic conduction path triggered by a single particle strike. PMAD, power management and distribution. PUE, power usage effectiveness; total facility power divided by IT power. SAA, South Atlantic Anomaly; where the inner radiation belt dips closest to Earth. SEU / SEE, single-event upset / effect; instantaneous fault caused by one particle. Specific power, watts generated per kilogram of hardware. TID, total ionising dose; cumulative radiation damage, measured in rad(Si). Two-phase loop, a cooling loop in which the coolant boils, carrying far more heat per unit of flow.