The use of an Inductive Wireless Power and Data transfer system as sounding rocket umbilical

Abstract

The objective of this thesis is defining the feasibility of using an Inductive Wireless Power and Data transfer system (IWPD) as sounding rocket umbilical. An Umbilical is used to supply power and communicate with the rocket in the last moments before launch. The power is used to keep the batteries fully charged and the communication is used for arming and disarming procedures. An IWPD system uses magnetically coupled coils, or inductors, to transfer power and data. This principle is used in transformers where a magnetic core creates a high coupling. In the umbilical the coils cannot be placed around a single core. This comes from the fact that one coil is outside the rocket and one coil is inside the rocket. Coupling of two coils separated by air is obtained by the magnetic field they produce. The coupling is defined as the magnetic field shared by the two coils in reference to the field that only passes one of the coils. To determine the coupling a simplified model was made which allowed the coupling to be plotted to the distance between the coils. The power transfer between a pair of coupled coils is dependent on the coupling between the coils. The magnetic field will not dissipate energy unless it goes through conductive materials. This means that magnetic energy is stored in the field and can be reclaimed. Making the inductors resonate with the addition of capacitors keeps the energy in the circuit. This resonance makes the power transfer non linear to the coupling of the coils. Circuit calculations are presented to determine the transfer of the IWPD in respect to frequency, supply and load conditions. The transfer is then used to determine the best setup to be used for an IWPD umbilical. The resonance of the system is used as frequency response of an oscillator. This oscillator is used to overcome the frequency shift of the system. The proposed system is compared with a more conventional umbilical. This comparison is made in three fields. Performance, Interference and Safety. In Performance an IWPD is as suited for the task as conventional system. Both will be able of supplying sufficient power and date. In Interference the IWPD is much better. It separates the umbilical from the skin and structure of the rocket. For Safety the results are balanced. The conventional systems perform better on electromagnetic interference (EMI). While the IWPD performs better on Electrostatic discharge (ESD). The IWPD might perform less on EMI this however does not have to be a problem. Increasing the electromagnetic compatibility (EMC) of the electronics and the distance to dangerous materials in the rocket will create a safe working situation.