M.Sc Thesis

M.Sc StudentKurovsky Vladimir
SubjectFeasibility Study of the Guidance System of an
Exo-Atmospheric Interceptor
DepartmentDepartment of Aerospace Engineering
Supervisors PROF. Benveniste Natan
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


The research deals with the feasibility of a specific guidance system of an exo-atmospheric interceptor. Since the miss distance is determined only at the “last moment”, the present research suggests an interceptor controlled by a solid propellant reaction jet system. This operating system is applied during the last three seconds.

In order to save weight of the warhead, a kinetic interception (hit to kill) is preferable. As a result, the jet system configuration becomes critical. In general, the Thrust Vector Control (TVC) system suffers from a relatively large time constant and possesses an inverse response. Therefore, in the last three seconds before interception, it is best to maneuver using nose or a combination of nose and tail reaction jets.

In the present study, a ring shaped jet system with two concentric propellant layers and four nozzles for pitch and yaw control is proposed. The concentricity of the layers allows a constant burning area, which produces a constant hot gas mass flow rate. The propellant is a HTPB/AP type with a relatively low combustion temperature and the jets are controlled using a Pulse Width Modulation (PWM) method in order to maintain a constant chamber pressure.

In order to study the performance of the proposed jet system, a computer simulation was developed using two feedback loops. The inner loop consists of an autopilot and the outer loop consists of a guidance law, and the simulation includes a 2g step and a two consecutive opposite step target maneuvers.

Four jet configurations having rotation or translation (divert) modes were examined: (1) - locked TVC with nose jet control (rotation), (2) - nose-tail jet control (rotation), (3) - nose-tail jet control (translation), (4) - a combined TVC with center of mass jet system (translation).

The simulation results show that interceptors having jet system with non zero-thrust capability achieve smaller miss distance than interceptors having jet system with zero-thrust capability.

As expected, a translation (divert) system requires a larger jet thrust than a rotation system. However, the use of an advanced guidance law can significantly reduce (in some cases by half) the divert thrust requirement. Moreover, a divert configuration achieves close to zero miss distance, independent of the target maneuver initiation time or maneuver type, while maintaining the interceptor’s attitude aligned with the Line Of Sight (LOS) direction. On the other hand, rotation configuration cannot match the translation miss distance properties. The best miss distance performance is achieved using configuration (4) above.

It appears that the jet system operation causes acceleration oscillations, which can be harmful to the interceptor’s hardware.  However, it has been demonstrated that the jet system can be mounted to the fuselage using shock absorbing material.

In the frame of the experimental part of the research an experimental system has been designed and built in order to simulate the performance of a gas generator solid propellant based reaction jets system and measure the dynamic response to thrust direction changes.