Geometrical instruments – Straight-line light ray type – Celestial
Patent
1986-09-15
1987-10-27
Martin, Jr., William D.
Geometrical instruments
Straight-line light ray type
Celestial
364455, G01C 108, G02B 2312
Patent
active
047020113
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
THIS INVENTION relates to improvements to navigation systems and in particular to improvements to celestial navigation systems.
BACKGROUND ART
Commonly, celestial navigation is carried out by employing a sextant which is used to measure at any one time the angle of a heavenly body such as the sun to the horizon. This can be either achieved by the use of marine type sextant which is used to measure the angle relative to the true horizon or a bubble-type sextant which measures the angle relative to an artificially-created horizon. In order to plot a position having measured the angle as above, it is necessary to accurately record and/or calculate the Greenwhich Mean Time at which the sight was taken after which it is necessary to resort to a Nautical Almanac which lists the position or each heavenly body in the sky for each second of each minute of each day of the year and tables such as Sight Reduction Tables to calculate the true position of the vessel or aircraft.
The above common method, whilst in general if accurately carried out enables the position of a craft such as a marine craft or aircraft to be accurately determined, suffers from a number of disadvantages. Firstly, there is the obvious disadvantage that the sextant must be used correctly so as to accurately measure the angle of the heavenly body to the horizon. Secondly, it is necessary to employ an accurate chronometer or other timing means which indicates the exact time at which the sight is taken. Furthermore, there must be a direct and accurate correlation between the time at which the sight is taken and the time noted on the chronometer to ensure an accurate fix. This often requires the use of two persons one who uses the sextant to measure the angle of the heavenly body and the other of whom reads the correct time on being given a signal by the person using the sextant. Having obtained the time and angle readings it is then necessary to resort to the requisite tables and Nautical Almanac to plot the required position. This can be a time consuming process and a process which can be prone to errors.
DISCLOSURE OF INVENTION
The present invention aims to overcome or alleviate at least some of the above disadvantages by providing an improved means of celestial navigation which is based on the use of a sextant type instrument but which eliminates the need for separate persons to measure the angle of the heavenly body and the time of the fix and which also eliminates the calculations associated with plotting the true position of the craft. The system of the present invention also enables the geographical position of a craft ,to be obtained accurates and rapidly. The present invention also provide sextant for use in such a system.
With the above and other objects in view, this invention resides broadly in a navigation system including a sextant of the type having an eye piece, a fixed horizon mirror aligned with said eye piece and a movable index mirror arranged to have its position varied to permit determination of the altitude angle of a heavenly body being observed, drive means associates with said index mirror and arranged to vary the position of said mirror, means for generating signals for actuating said drive means, said signal generating means providing signals proportional to the angle of movement of said index mirror and thereby signals proportional to the altitude angle of said heavenly body being observed, and calculating means operable to calculate from said signals, the reading of chronometer means at the time and date said body is observed, and stored data relating to the position of said body, said geographical position.
Suitably the drive means comprises a stepping motor which converts digital information into proportional mechanical movement and the signal generating means comprises a source of control pulses, the nubmer of pulses applied to the stepping motor being indicative of the extent of rotation of the stepping motor spindle and thus the angle through which the index mirror is moved. Preferably the st
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patent: 3571567 (1971-03-01), Eckermann
patent: 3854037 (1974-12-01), Feldman et al.
patent: 3968570 (1976-07-01), Leuchter
patent: 4104722 (1978-08-01), Evans
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