Whatever else may be said about man's first landing on the Moon, it was surely the most spectacular navigational achievement of all time.

In the following paper Dr. Mayer, Chief of the Mission Planning and Analysis Division at the Manned Space Flight Center, Houston, and Mr Osburn give a general outline of the operational use of the space navigation systems which contributed to the success of the first manned lunar exploration mission. The ground and onboard navigation systems, their interfaces with the Apollo guidance system, and their uses in various phases of lunar landing are reviewed. The navigation procedures are then discussed, with particular emphasis on the Apollo 11 mission, the first manned Moon landing. Post-flight analyses and actual mission results from Apollo 11 are examined to give an accurate assessment of the overall performance of the navigation system.

The paper was presented by Dr. Mayer at a joint meeting of the Institute and the Royal Astronomical Society held in London at the Royal Geographical Society on 1 October 1969 with Professor Sir Bernard Lovell, F.R.S., in the Chair.

A list of the terms and abbreviations used in the paper is given on page 148.

The Apollo navigation problem may be divided into two general areas. The position and velocity of the vehicle must be determined at some specified time, present or immediate past. (This will be referred to as orbit determination.) This information must then be utilized to determine the future course of the spacecraft. (This is referred to as trajectory prediction.) Ground orbit determination may be performed in either a low-speed or a high-speed mode. Low-speed computations require 5 to 10 minutes for processing, while high-speed solutions are available virtually instantaneously. The ground system utilizes both types of processors. Low-speed solutions are used for trajectory prediction and, in a few cases, for processing astronaut observations. The high-speed processor is used to monitor manœuvres such as the descent to the lunar surface and for special situations where near real-time orbit solutions are necessary. The spacecraft system uses only a high-speed processor, modified slightly to facilitate manual use by the astronaut in some cases.

Although it has been technologically possible for some years to give warning of ground collision hazards, the specialized radars for this purpose have been limited to military aircraft. Because of complex cost and installation problems, radar of this type have not been installed in civil aircraft.

This paper discusses possible developments in civil weather radar to enable it to give a warning of ground collision hazards. The paper was presented at an Ordinary Meeting of the Institute held in London on 19 November 1969 with the President in the Chair.

For the purpose of this paper, ground collision is defined as an error of navigation or height management, which results in a zero ground clearance. The error can, of course, be human or instrumental but the assumption is made that the aircraft was basically capable of avoiding the hazard. There has been a tendency to associate ground collisions, particularly hill and mountain collisions, with the older piston-engined aircraft. Its importance in terms of airlines operating modern jet aircraft is not always well appreciated. It is true that the normal operating altitude of jet aircraft almost eliminates ground collision hazards in the cruise phase, but in general they suffer from a longer response time and a higher approach speed, which makes them more vulnerable in the let-down and approach phase. Since in any event the let-down and approach phase accounted for about two-thirds of the accidents with piston-engined aircraft, ground collision hazards remain a serious problem with pure jet aircraft.

S.S.T. flight operations are likely to commence early in 1970 and meteorological briefing for all flight levels must therefore be established, especially for temperature, wind and clear-air turbulence. This paper, which was presented to the S.S.T. Working Group, outlines the accuracy of temperature prediction over 24-hour periods and suggests forecast rules. Finally the resultant requirements are stated.

Several conceptions of possible and desirable temperature forecasting accuracy have been expressed in relation to S.S.T. performance by different panels. For example, the Fausst WP 529 (Franco-Anglo-U.S.-S.S.T. Working Paper 529), revised 3 March 1967, recommends a maximum standard error of 3°C for temperature forecasts at the S.S.T. level, which means the accuracy of temperature forecasting must be within a range of ± 3°C in 68 per cent of all cases. After other recommendations, such as the I.C.A.O. S.S.T. panel, July/August 1968, the subsonic requirements may be adopted for the S.S.T. too; these recommendations allow a standard error of 1°·8C, i.e. the accuracy of temperature forecasts must be within a range of 1°·8C in 68 per cent, or 3°C in 90 per cent, of all cases.

For the integration of different navigational aids of an aircraft by a general purpose computer the following way is proposed: The basic navigational system is a doppler or inertial dead reckoning system (D.R.S.). The other navigational aids serve for control measurements, with the help of which the error of the D.R.-position and the most important systematic error sources of the D.R.S. are determined by least square adjustment during flight. These error quantities are then used for a corresponding correction of the D.R.S. The supplementary navigational aids are consequently used both for the correction of the D.R. position and for the calibration of the D.R.S. The method is described for the example of the integration of a doppler D.R.S. with Tacan.

From the great number of different navigational aids, which are today available or in development, we can draw the conclusion that none of these navigational systems can satisfy all requirements. Therefore, for many years it has been the custom to combine several navigational aids, and thus the human navigator has the task of evaluating the different navigational information. This evaluation is, however, often disturbed by unfavourable conditions. In a high-speed aircraft for example the navigator is overburdened by a lack of time and space, errors in the navigational sensors, &c. This necessarily means that the evaluation of the data is reduced to a minimum, and that a great deal of the available information is lost.

The name log, to denote a device for measuring a ship's speed or the distance she has made through the water, appears to have come down to us from the Saxon log—‘a hewn trunk or branch of a tree’. Harboard amplifies this by remarking that the log is so named from the word ligen (Dutch liggen=to lie down) because it lies, as it were, immovable. It therefore seemed appropriate that the primitive contrivance for measuring a ship's speed—a wooden board attached to a line—should be called a log. The principle of this—the so-called common log to distinguish it from more sophisticated contrivances—is simple: a floating object cast from a ship tends to remain stationary after entering the sea. The line attached to the log-ship is allowed to render freely as the vessel sails away after the log is hove from the vessel's stern into the sea. A specified length of line which runs out in a measured interval of time or, what became more common practice, a measured length of line which runs out in a specified interval of time, is equivalent—at least approximately—to the distance travelled by the vessel in that interval.

This paper considers a practical solution to the stopping distance of ships, with particular reference to modern giant tankers. One solution to the problem has already been evolved by Captain H. Topley of the Honourable Company of Master Mariners. The present paper tackles the same subject from quite a different viewpoint.

The basic assumptions on which the mathematical treatment has been based is presented in Section 1, which also includes the calculation formulae of the speed and distance run at any time in a manœuvre, without proofs. Section 2 deals with clarifying the essential differences between Captain Topley's theory and the author's. The validity of the theories is examined in Section 3 by comparison with the results of actual ship tests. Section 4 presents calculation diagrams prepared by the author.

The only reliable data available by means of which captains can predict the stopping behaviour of their ships after ordering STOP ENGINES are the results of inertia tests conducted at the sea trials when the ships were built.

The inertia tests, however, are usually performed for only one case in which the approach speed is assigned to HALF AHEAD or the so-called manœuvring full ahead speed. Therefore most masters are glad of any knowledge of how to predict the movements of ships from any reduced speed.

Marketing a marine radar may not sound the most promising subject for a navigational paper. But in an age when almost anything is technically feasible, the direction of progress will be governed by many considerations which, if they are not themselves navigational, are nevertheless of great interest to those concerned with the subject. A new range of equipment for example must be related to the level of skill and training which actually prevails at sea; research and development costs must be seen in relation to the cost-effectiveness of the system; and finally purely operational factors such as traffic separation schemes may have to be taken into account. In this paper, originally presented in Paris to the French Institute of Navigation, some of these considerations are discussed in relation to the new Decca anti-collision radar.

Just over 25 years ago, in the summer of 1944, a United Kingdom conference on radio for marine transport concluded that radar would be of great value to merchant ships. They asked the Royal Navy to draw up a specification for the average ship. Discussion with various shipping interests confirmed that there was in fact a requirement for a radar set ‘for navigation and pilotage as distinct from a collision warning set, which would, of course, be a much simpler and cheaper device’. The later 1946 Ministry of Transport Specification referred to the requirement ‘to provide warning of the proximity of other surface craft and obstructions which will enable collision to be avoided’. Now of course, after 25 years of hard experience, we know that the matter of avoiding collision at sea is not apparently so simple.

In this paper the history and development of inertial systems for the merchant marine is traced from the gyro-compass, familiar at sea since the beginning of the century, to complete inertia systems and integrated systems such as doppler/inertia.

The paper was presented at the Marine Navigation Symposium held in Sandefjord, Norway, on 24–6 September 1969 and is reproduced with the permission of the organizers.

The gyro-compass was first fitted on board a ship as long ago as 1908. Its function has been as the main reference by which the ship is steered and to which navigation by dead reckoning and direction finding is referred. The compass has been developed continuously to provide a more reliable, more accurate, and smaller instrument costing typically £1000 to £2000.

Continued discussions on techniques of rhumb-line sailing might well be considered irrelevant in today's climate of navigational technology. However, there is apparently one group of navigators who have a need for rhumb-line sailing by computation as opposed to direct measurement from a chart: this group comprises the navigators of merchant ships.

It may well be argued that traditional methods are adequate and that, although imprecise, the resulting errors are swamped by the errors of the data used. This argument is satisfactory for established navigators but, with the great improvements that have taken place in nautical education, does not hold for the teaching of newcomers.

In a book entitled The Black Tide, Richard Petrow presents a panoramic view of the events concerning the loss of the Torrey Canyon on the Seven Stones on 18 March 1967. The massive spillage of oil made it into a world disaster which called for a complete revision of many of the principles on which maritime transport is based. For seamen, however, the really important part comes before the spillage, when the ship stranded in apparently ideal navigational conditions. The Liberian Commission of Inquiry threw little light on the subject and criticism of the master does little to satisfy those with a professional knowledge of the sea. Here Commandant Oudet, relying heavily on the facts disclosed in Petrow's book, examines the circumstances of the disaster and comes out with strong criticisms of the Commission of Inquiry. If the subject is not exclusively navigational, it must be of great concern to all navigators.

Mr. Petrow's book contains what professionals need, even though the author recognizes that many questions must still remain unanswered. He has had access to the record of the Commission's investigations, but not to the report of the observer whose presence at the inquiry was secured by the British Government in spite of the owners' protests. While Mr. Petrow was able to spend four days interviewing Captain Rugiati, six months after the accident, he was unable to pursue his investigation by speaking with eye-witnesses, either those whose evidence was received by the Commission or those whom they failed to question.

Captain W. Burger and Captain A. G. Corbet in their general comment on the meeting of the Technical Committee in London, 16 April 1969, gave a curious and instructive hypothetical example of end-on encounter, a problem in navigation which they and others have found by experiments to have importance and practical difficulties. Their example is set in surface navigation at sea, and especially when using radar in fog. Two ships close with each other (in their example head-on and green-to-green), the two tracks being straight and parallel, and separated (in their example by half a mile). Should both ships stand on? My answer is affirmative, my argument difficult.

If one makes the fruitful assumption that neither ship in this example alters course or speed, and then tries to plot The Edge [ of regression of The (mutual) Line (of bearing)], he discovers that the result is not a non-singular parabola, but rather simply a fixed finite point, i.e. at best a degenerate parabola—yet clearly there can be no finite collision, and collision at infinity is an empty threat. What do plotters of The Edge make of this paradox? Here handbook summaries will not do.

Distance off by measuring the elevation of a mountain top above the horizon has been a popular means of finding position at sea ever since Captain Lecky published his famous tables. This popularity persists into the radar age because distance off can often be found from a vertical sextant angle long before a ship is within effective radar range of the coast. In view of this it is surprising that the standard textbooks on navigation give scant attention to this method and any seaman finding himself without Lecky's tables would find little guidance elsewhere.

Wing Commander E. W. Anderson in The Principles of Navigation indicates that the whole angle subtended by a mountain at a ship can be found by adding half the estimated distance off in miles to the visible angle in minutes, having first corrected this angle for dip and refraction. This can be proved by simple geometry by showing that the angle subtended by the part of a mountain hidden to an observer at sea-level is equal to half the distance off.

In a very interesting paper which appeared recently the author, Capitão Mário Gama of the Portuguese Merchant Navy, describes a direct method for computing position lines from star (or planet) observations.

The principal feature of Captain Gama's method is the systematic manner in which he arrives at an intercept to the extent, not only of saving time in sight reduction, but also in reducing the possibility of blundering.

The method employs the Computed Tables of Altitude and Azimuth (HD 486) and involves timing a series of star-sights, the ship making headway meanwhile, by means of a stop watch which is set at zero at a noted chronometer time shortly before the observations commence. The following example, given in the original paper, in reducing sights of Vega and Denebola observed during morning twilight of 25 Feb. 1959, in D.R. position Lat. 10°10′ S., Long. 73°48′ E., will serve to illustrate the method.

A Great deal has already been written about possible amendments to the Collision Regulations, but as there may be an international conference on the subject in 1972 the various schemes should be discussed as much as possible so that their advantages and disadvantages will be fully appreciated.

Criticism of the present Steering and Sailing Rules is mainly concerned with Rule 21. Disadvantages of this rule include the following:

(1) If a giving-way vessel on a crossing course takes no action the privileged vessel must not act until collision cannot be avoided by the giving-way vessel alone. By such time collision is likely to be inevitable.

(2) Small sailing vessels which may not easily be seen, especially at night, are required to maintain course and speed for large power-driven vessels.

(3) High-speed vessels such as hovercraft are required to maintain course and speed for low powered ships crossing from the port side.

(4) No provision is made for different types of hampered vessel approaching one another so as to involve risk of collision. If deep-draught vessels in certain areas are to be included in this category in the future the question of priorities may have to be considered.