May I thank the Society for the immense compliment it has paid me tonight by the award of the Society's Gold Medal. Earlier this year I was prevailed upon by Council to prepare the Wright Brothers Lecture. This is an occupational hazard of the Director, RAE, and has led to a situation—unique in my experience—in which the Society has presented the Medal and then within a few minutes asked the recipient to stand up and earn it. I am not at all optimistic about the outcome—but will do my best.

During the first dozen years of space flight, from Sputnik to the initial Apollo lunar landing, the costs of space exploration and utilisation were not a major constraining factor. Indeed, the difficulty of initially penetrating beyond the earth's atmosphere and then the rapid extension of this capability to lunar distances (and beyond for unmanned spacecraft) dictated approaches that emphasised the highest performance, lightest weight, and the utmost in reliability that could be attained from the state-of-the-art available. As might be expected, conditions have changed. People are expecting a maturing relationship between the benefits achieved from space flights and the costs to attain them. Fortunately, approaches have been identified and the technology exists to greatly reduce the costs of space activities without degradation of safety or mission success. Of equal importance, we have identified many areas of actual or potential direct benefits from the ability to enter and operate in space which should be further developed. They include global communications, meteorology, earth surveys, materials processing, medicine, as well as the intellectual stimulation of scientific investigation and exploration, and others.

I shall discuss two examples of possible future deep space missions but first of all let me fill in a little of the scientific background in order to give you some idea of the kind of questions that we would aim to answer by undertaking these projects. It is now rather more than twelve years since the first spacecraft were placed in independent orbit round the sun. These were Lunik I and Pioneer IV which were the first satellites to make measurements in space outside the earth's gravitational field. In these twelve years as a result of the succession of space probes which has followed we have learned a great deal about the physics of interplanetary space where the situation is dominated by the solar wind and magnetic fields which it carries out from the lower corona. Let me remind you of the salient facts.

In 1957 the Air Registration Board initiated a series of Technical Notes to provide a permanent record of technical work, generally in the form of specific investigations or research, performed by members of ARB staff. Although used to convey the results of such work to persons and organisations outside ARB, as well as for dissemination of the information within ARB, the ARB Technical Note series has never been publicised, and circulation has consequently been small and only to selected persons and organisations.

For satellites that have part or all of their orbits extending into the earth's effective atmosphere, i.e. less than 500 miles, it is necessary to consider the contribution of the aerodynamic force in attitude dynamic studies. The importance of the aerodynamic torque is revealed by the fact that it is comparable to earth radiation at 500 miles, direct solar radiation at 400 miles, and depending on satellite geometry, can be as large as gravity gradient torque at 200-300 miles. Hence, in addition to solar and earth radiation torques, this paper includes the effect of the rarefied atmosphere on the response of gravity gradient satellites, thus covering the entire altitude range.

The technical note “Errors due to Pulsation in Orifice Meters” by J. Grimson and N. Hay in the April 1971 issue of the Aeronautical Journal adds some welcome data to a field in which there is insufficient experimental evidence from which an explanation of the characteristics of orifice meters operating under pulsating flow conditions might be obtained.

In reply to Dr. Jeffery's discussion, we would point out that we did not use a single property of a wave to describe the waveform and to be used as a measure of the intensity of pulsation. The parameter s was the actual cut-off ratio imposed at the source by the pulsator, whereas the ratio A/h was obtained from the differential pressure records at the meter.

In several recent reports reference is made to spanwise variations in the boundary layers growing in the working sections of various wind tunnels. Systematic investigations by Patel, Bradshaw and de Bray are in general agreement that these variations are caused by the screens which are fitted into the settling chambers of these tunnels to dampen out non-uniformities in the upstream flow. They conclude from their experiments that these variations will be much reduced if the downstream screen (or preferably the two downstream screens) has an open area ratio greater than about 0·57 and that these should be followed by a honeycomb to obtain the most steady and uniform flow, although a honeycomb in this position may increase the turbulence level in the working section.