Parts I and II of this series of papers have dealt with the development of ion thrusters for use in an orbit transfer manoeuvre, and of various types of micro thruster for position and attitude control. The present paper deals with the actual satellite electric propulsion system and configuration needed for expansion manoeuvres. The control problems both during the expansion phase and subsequently in the required orbit are discussed. Short analyses for two specific cases (ELDO launcher and Black Arrow) are presented in which payloads and missions are defined.

Burt has shown that all the orbital elements of a spacecraft can be changed by means of a small continuous thrust. He gave particular attention to the problem of expanding from a low orbit to a synchronous one, and the change of orbit inclination and orbit eccentricity was also considered. Such a type of manoeuvre is eminently suitable to electric propulsion because the high exhaust velocities possible lead to a small propellant mass; this mass saving is achieved at the expense of the time taken for the manoeuvre.

In ref. (1) Pope presents a theoretical analysis of the buckling of rectangular plates tapered in thickness under uniform load in the direction of taper. An experimental investigation into the end load buckling problem for a plate having simply-supported edges with the sides prevented from moving normally in the plane of the plate is described in ref. (2). For these boundary conditions the theoretical solution is exact. However, the compatability equation is not satisfied exactly when the sides are free to move in the plane of the plate. This experimental investigation demonstrates that the buckling load is nevertheless adequately predicted by the analysis in these circumstances.

The Black Brant IV shown in Fig. 1, is a two-stage sounding rocket with a 15KS-25 000 booster motor stabilised with three fins and a 9KS-11 000 motor, a 5·3 fineness ratio conical noise and an 11·5° conical flare forming the second stage. Basically, the second stage is the single stage Black Brant III rocket, but uses a conical flare instead of three fins at the aft end for aerodynamic stability. This paper reviews the static stability of a Black Brant IV second stage with a flare and two fin-flare combinations.