摘要:

AbstractOn May 16th of This Year the Secretary of the Department of Transportation authorized the announcement of the selection of Loran‐C as the radio navigation system to serve the coastal confluence region. He also instructed that the national plan for navigation be amended to reflect this decision, thereby ending a long period of uncertainty in U. S. policy relating to radio navigational aids. The decision will permit firm plans to be made by both users and manufacturers to derive the best cost benefits from the various radio navigation systems now sponsored by the federal government. This paper explores the impact of the decisions to provide for the co‐existence of Loran‐C and Omega hyperbolic systems with an orderly phase‐out of the Loran‐A network. The paper also discusses the current VORTAC and VLF/LF beacon systems in relation to the availability of hyperbolic systems having extensive coverage. A comparison of costs and accuracy of the various systems is provided. A bibliography of reference material is

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1975.tb01239.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Abstractdeep space navigation is an evolving technology which must constantly meet new challenges. During the 1960's, Mark‐I navigation, involving ground‐based radio tracking and flight path control, was adequate to meet the needs of various lunar, Venus, and Mars missions. During the 1970's, Mark‐II navigation, involving a combination of ground‐based radio and onboard optical measurements, but still utilizing ground‐based control, will be adequate for such missions as Viking 1975, Mariner Jupiter Saturn 1977, Pioneer Venus 1978, Mariner Jupiter Uranus 1979, and even a “standoff” asteroid or cometary‐nucleus flyby. In the 1980's and beyond, however, reaction time becomes more important for many of the advanced missions under consideration by NASA. Examples include precision asteroid/comet flybys and rendezvous, probe delivery, outer planet satellite tours, landers, rovers, sample returners, and other mission options. It is thus necessary to develop Mark‐Ill navigation, which can use onboard computation and control to avoid both round‐trip‐light‐time and certain earth‐based delays in data processing and decision making during time‐critical mission phases.In order to prepare for the era of autonomous navigation, this paper first examines existing techniques for spacecraft navigation by describing the basic elements of the Mark‐I and II navigation technologies. The remainder of the paper deals with identification of criteria which necessitate onboard navigation, and with promising solutions now under consideration. An attractive solution possibility is proposed which utilizes narrow‐angle optics, a charge‐coupled device area‐array image sensor, a small advanced onboard flight computer, and a simplified set of software algorithms. Onboard commands would be derived and sent to the appropriate spacecraft attitude control, propulsion, and science platform pointing subsystems. The proposed autonomous navigation system does not address all mission options, but focuses primarily on precision approach trajectory control and adaptive science instrument pointing for asteroid, cometary, and outer planet satellite missions. Excluded mission options include landing, surface rovi

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1975.tb01240.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1975.tb01241.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1975.tb01242.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Abstractthe requirement for a sensitive failure detection and isolation (FDI) capability for the space shuttle orbiter IMU system has been an important aspect of the development of the IMU for some time. In an earlier ION paper, a method for performing these functions for soft instrument failures in a 2‐IMU environment was presented1, along with preliminary results. Additional studies of the performance capabilities of the technique for realistic shuttle trajectories followed and were published.2The current paper addresses two areas which these earlier efforts showed to be potentially fruitful in improving the performance of the 2‐IMU soft FDI approach. It is shown that improvement of the sensitivity of the skewed IMU FDI mechanization can be accomplished by (1) more accurate knowledge of cluster to cluster attitude and (2) appropriate selection of isolation geometry. Reduction of relative azimuth uncertainty due to gyro‐compassing is shown to be possible by the use of the high accuracy gimbal angle readout devices to be used on the Space Shuttle IMU. Accelerometer FDI is shown in this paper to be significantly improved by the reduction of this error source. Additional improvement of the FDI capability is shown to be possible by careful selection of isolation geometry. It is shown that testing of the error vector against geometric spaces of various shapes changes the isolation probability, and that a very simply mechanized space has the attendant advantage of providing very high true isolation probabilities. Finally, data collected from Monte Carlo simulations of the FDI mechanization, applied to a Space Shuttle boost trajectory, are presented to demonstrate typical improvements which can be obtained through the application of these techn

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1975.tb01243.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Abstractthe problem of defining the relative and geographic coordinates of an acoustic sea‐floor transponder array is examined. Effects of refraction to slant ranges of 10 km are shown to be compensated for by the use of a harmonic mean sound speed. Ranges measured with an acoustic transponder are compared to those measured by a tellurometer. Methods of Cloverleaf measurement of acoustic transponder depth, Baseline Crossing measurement of transponder spacings, and an iterative technique for determination of array coordinates are described. All three methods are used to determine the configuration of a transponder triad in deep water near Antigua. The most efficient method of establishing relative and geographic coordinates of an array of sea‐floor acoustic markers is identified and discus

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1975.tb01244.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1975.tb01245.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractOmega is rapidly becoming an important member of the “family” of radio aids to navigation and will surely be accompanied by a form of differential Omega such as Micro‐Omega which can improve its accuracy by approximately 10:1 within a few hundred miles of any one of several differential Omega relay stations situated in the various critical areas such as the approaches to harbors.The optimum arrangement is shown to be one using a continuous transmission from an efficient HF antenna of relatively small size'. A differential Omega receiver, making use of a Micro‐Omega system, automatically receives and applies the necessary corrections directly and automatically to the standard Omega display.In this mode of operation, the advantage of continuous updating is achieved, which corrects for sudden ionospheric disturbances (SID errors) and removes the need of using correction tables. Micro‐Omega thus greatly reduces operator error and simplifies navigation.The Micro‐Omega system is directly compatible with existing Omega charts and existing Omega receivers can be updated to Micro‐Omega by simple low‐

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1975.tb01246.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractWith the closure of the Suez Canal the Cape Sea Route has become a major link in the flow of oil from the Middle East to the Western world.This means that an ever growing number of large and mammoth tankers can be encountered off the sea board of the Republic of South Africa. The presence of these ships poses the continual threat of pollution by marine disaster or grounding.A number of near disasters in the way of groundings has already taken place as well as a large collision and, as a result of this, South Africa scrapped her separation zones which had recently been introduced and introduced a 12 mile limit for tankers.This has brought other problems, such as load line difficulties, freak wave and weather damage, and navigational problems.Spin‐off problems encountered in the proliferation of these large ships are: difficulties in finding ports of refuge for deep drafted ships, docking and repair facilities and salvage equipment.South Africa is systematically overcoming these problems one‐by‐one and is introducing new tugs and antipollution measures together with extensive off‐shore servicing and a sympathetic understanding of the problems these big ships encounter off our

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1975.tb01247.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractSouth Africa has a well developed and thriving Merchant Navy backed up by an efficient and modern navy. In its early days all training for these two services was done overseas but in 1921 a training ship was donated to the country to enable young South Africans to train as naval cadets.This aim was later changed to training merchant navy cadets and a two year course was instituted leading to a school leaving certificate. During World War 2 the ship was returned to the British Navy and her cadets moved to a shore establishment which then became a nautical college. The aim of the course was changed once again when the SA Navy took over the college and both forces trained in the same establishment. A school leaving certificate became a necessary entrance qualification and the course was shortened to one year. In the interim a Naval Gymnasium was established for training Naval Cadets, a Military Academy for naval officers wishing to do a degree and a Nautical Academy for Merchant Navy officers studying for advancement.Rationalisation has led to the number of colleges being reduced to three by a process of mergers. Each of these colleges has a definite aim and is highly successful. The subjects taught are varied and interesting and the means employed to obtain most satisfactory results are of note. An intriguing sidelight is that although South Africa has never had any contact in this field with the USA, the syllabus envolved over the passage of time at one of her Academies is almost identical to that of Annapolis. The growing number of South African ships seen in US ports is mute testimony to the efficiency of her training methods.

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1975.tb01248.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY