- Why does the satellite slow down if angular momentum is conserved? Doesn't that mean energy is lost?
- The satellite slows down precisely because angular momentum is conserved. As the yo-yo masses move outward, the total moment of inertia of the system increases. Since angular momentum (Iω) is constant, ω must decrease. Rotational kinetic energy (½Iω²) is not conserved in this process; it decreases. The 'lost' energy is converted into other forms, such as the kinetic energy of the outward-moving masses and ultimately heat when the tethers are severed or damped.
- Is this method used on real satellites?
- Yes, the yo-yo despin mechanism is a common, reliable technique used for decades to de-spin spacecraft and rocket stages after separation. It is favored for its simplicity, passivity (requiring no active control), and high reliability. Notable examples include the Mars Exploration Rovers and many communication satellites.
- What happens to the yo-yo masses after they are released?
- In the real maneuver, once the tethers are fully extended, they are typically severed or released at their attachment points. The masses, now moving with a tangential velocity nearly matching the satellite's original spin speed, fly away into space. The satellite is left spinning at the desired, much lower rate. The simulator models the system up to the point of full tether extension.
- Does the simulator show that the masses also have angular momentum?
- Absolutely. The key to understanding the formula is recognizing that the total angular momentum is the sum of the satellite's and the masses' contributions. Initially, the masses spin with the satellite at radius r_i. In the final state, they spin at the same new angular velocity ω_f but at the much larger radius L. The conservation equation accounts for the changing moment of inertia of both the satellite body and the two masses.