Every mass bolted onto the truss is tracked individually with its own position relative to the station's core. Each frame the scene recomputes the true center of mass and moment of inertia about it:
x_com = Σ(m_i·x_i) / Σm_i
I = Σ m_i·[(x_i − x_com)² + y_i²]
ω = L / I
When a segment or panel finishes bolting on slightly off-axis, it imparts a small torque impulse — angular momentum L jumps by an amount set by the misalignment slider. With RCS off, L is then conserved exactly: as I grows while the truss extends, ω = L / I falls, the same way a figure skater's spin slows when they extend their arms — and rises again if the structure were to fold inward. With RCS on, small thrusters apply a damping torque proportional to −ω (a simple reaction-control law), bleeding L back toward zero and firing visibly harder the faster the station is spinning.
- Assembly progress — bolts truss segments (0–60%) then unfurls solar arrays (55–100%), exactly as the 3D version.
- Bolt-on misalignment — how much angular momentum each completed segment/panel injects; 0% builds a perfectly balanced station that never tumbles.
- Arm reach — poses the two-joint manipulator toward the current build edge.