Reaction Wheel ADCS Simulator

Target attitude

Roll (X) 0°

Pitch (Y) 0°

Yaw (Z) 0°

Reaction wheels

X wheel0 RPM

Y wheel0 RPM

Z wheel0 RPM

⚠ Wheel saturation — this axis has run out of torque authority. Trigger a momentum dump to recover control.

Attitude error

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Body rate

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How it works

Each of the three reaction wheels spins about one body axis. Total angular momentum of the wheel+satellite system is conserved: when the control law commands a wheel motor to speed up, the wheel gains angular momentum in one direction and the satellite body reacts by rotating the opposite way — no propellant needed.

I_body·dω_body/dt = −τ
I_wheel·dω_wheel/dt = +τ
τ = Kp·(θ_target − θ_body) − Kd·ω_body

Saturation — a wheel can only spin so fast. Once it hits its speed limit it can no longer absorb more momentum, so it stops producing useful reaction torque on that axis.
Momentum dump — magnetorquer coils push against Earth's magnetic field to apply an external torque that bleeds the wheel back down toward zero speed, restoring headroom, without touching the propellant tanks.

MAGNETORQUER DESATURATING

Satellite body Reaction wheel Magnetic field line

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