The Transit navigational satellite system is expected to be in operational use during the second half of 1962, though not perhaps with its full quota of four satellites. The system, which will be of considerable significance to both air and surface navigation, is here described by its originators, Dr. Kershner and Dr. Newton, of Johns Hopkins University in the United States. Using a single of the two frequencies transmitted by the satellite, the mean navigation error will be about one mile, limited by refraction. Using both frequencies the mean error will be about ½ mile, limited by the accuracy of the satellite coordinates that will be transmitted. With elaborate equipment, it will be possible to navigate to about 0·1 mile, although the satellite coordinates that will be available to the ordinary user will not reflect this full accuracy. When all four satellites are in orbit, a fix will be available every 110 minutes, on the average, with occasional intervals of 220 minutes between fixes.

The Transit system of navigation is based upon the observation, by radio, of artificial satellites. The basis of the method is to determine the line-of-sight velocity of the satellite towards, or away from, the observer at various times as the satellite moves across the sky. With a knowledge of the corresponding orbital positions and velocities of the satellite, the observations can be used to determine, without ambiguity, the position of the observer.

Beside measuring changes of distance by means of the doppler effect on frequencies transmitted by a satellite, it is possible to observe altitudes and azimuths or the rates of change of these quantities. Advantages and disadvantages of such observations are compared with the Transit programme; the formulae for position lines determined by rates of change of altitude and azimuth are derived and discussed. Measurements of distance, at present feasible only by radar, may be possible in future by comparison of atomic clocks; the evaluation is simpler than for all other observations of satellites.

It has already been explained that one has to correct for the effect of the ionosphere upon the doppler shift in order to track the Transit satellites with sufficient accuracy. At the Radio Research Station, Slough, the converse problem is being investigated; we are looking at the effect of the ionosphere upon the Transit satellite signals in order to find out about the ionosphere itself. In fact the doppler correction term is directly related to one of the quantities of major interest, the electron content of the ionosphere. This is the number of electrons in a unit column up to the satellite height. We are interested in the daily, seasonal and solar variation of this quantity.

This paper, a shortened version of one presented at the joint meeting of the British, French and German Institutes of Navigation held in Dusseldorf last May, reports work undertaken in Germany on the automatic detection and solution of air collision situations. The work is being carried out jointly at the Berlin Technical University and the Telefunken Company at Constanz, in close consultation with the German air traffic control authorities.

Captain Lumsden's paper was written for the convention held in Düsseldorf on 16, 17 and 18 May 1961 (Journal, 14, 480). It describes the siting of harbour radar equipment from the point of view of giving warning of approaching ships to the shore authorities, giving navigational assistance to shipping, and port surveillance. In most cases the choice of site for the aerials and displays will have to be a compromise with these three uses of shore radar in mind.

The three main elements of a harbour radar are the scanner, which must be sited to survey the area of interest, with the transceiver close by to avoid waveguide losses, and the displays which may be required in a room close to the scanner or in a room distant from it.

A system is proposed which would be capable of adding information concerning the true motion of objects, to the normal relative display. The method requires the use of two Tenicon storage tubes (ME 1260).

The use of marine radar has not eliminated collisions at sea. The reasons for this failure are generally associated with limitations in interpreting the available information, rather than in the equipment itself. One particular problem is the assessment of the time, course and speed of a ship from the information presented on a radar display, which is relative to the observer. It is possible to calculate this information, but the direct presentation of a true course on the display would be advantageous. A solution is to modify the final PPI display so that the centre of the scan, normally fixed at the centre of the cathoderay tube, is displaced continuously at a velocity corresponding to the observer. The true speed and course of a ship can therefore be assessed from the track built up from echoes received during successive scans.

This paper, which was presented at an Ordinary Meeting of the Institute held in London on 17 November 1961, discusses aspects of high-speed, high-altitude navigation which will have a bearing on the selection of a navigation system and control philosophy for supersonic transports. The effects of certain separation criteria on systems accuracy are described, as are meteorological factors bearing on operation of the aircraft. Estimated performance capabilities which relate to traffic control and navigation are described. An analysis is offered of the effects of particular system accuracies on the selection of components of a navigation system and, finally, an integrated system is described, with arguments presented for certain levels of redundancy, reliability and automation.

A doppler navigation system measures velocity relative to the surface of the Earth. If the surface is moving, as for example when flying over an ocean, the doppler will indicate a false ground-speed and/or drift, according to the direction of surface movement.

Trials carried out by the Experimental Navigation Division of the Aeroplane and Armament Experimental Establishment at Boscombe Down show that there is a positive correlation between doppler system error and the surface wind direction when flying over the sea in an aircraft which has an accurate heading reference system. The analysis of all data is by no means complete, but as the spread of errors is so small it is thought that users of doppler navigation systems may wish to see the trend of results and to accept a few simple rules to compensate for the surface movement.

The value of the surface movement for a doppler equipment having a 1 percent correction for spectrum distortion is about 3 kt. for a surface wind velocity of 10 kt., 4 kt. for a wind velocity of 18 kt., 5 kt. for a wind velocity of 30 kt. and 6 kt. for a wind velocity of 50 kt. or more. The cardinal rule is that the doppler navigation system will indicate a position upwind of the correct position.

Clearly there is little point in applying an across-track correction of say 6 kt.

The following notes, from one of the contestants in the single-handed transatlantic race 1960, will be of great interest to a number of people concerned with wind and weather observations and the performance of small boats in heavy weather. Dr. Lewis's track in 1960 was by the great circle from Plymouth to New York, from New York up to St. John's, Newfoundland, and then back across the Atlantic to Lerwick in the Shetlands.