The acceleration and the deceleration of the tumbling period of Rocket Intercosmos 11 during the first two years after launch

We have analysed the development of the tumbling period of Rocket Intercosmos 11 (1974-34-B) during the first 2 years after launch. We interpret the period increase, observed from August 1974 to June 1976, as being caused by torque moments due to eddy currents induced in the hollow cylinder by the magnetic field of the Earth. The spin-decay time of 1974-34-B was 1.13 yr. This compares well to results derived by Williams and Meadows in 1978 for other Soviet rocket bodies.The tumbling acceleration of 1974-34-B, observed in June 1974, is interpeted as outgassing effect of rest propellant which remained inside the rocket after burn-off. A model of the outgassing acceleration is developed and compared to the period measurements of 1974-34-B. A reasonable good agreement between observed and predicted periods can be derived by using a nonlinear regression fit. An initial mass ratio of the rest propellant and the empty rocket cylinder is estimated.