ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1965.tb02145.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1965.tb02146.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Summarya comparison of self‐containedelectro‐optical, radio and inertial systems shows that the electro‐optical system is superior for several types of missions. Such missions are those having long term attitude control, navigation and guidance requirements. The electro‐optical system offers a passive method of orbit determination and yet, maintains the parameters relative to earth or lunar reference points. This system provides vehicle attitude, position and velocity by on‐board calculations using measurements taken by on‐board instrumentation. Such systems have no buildup of instrument error with time and do not depend on ground tracking support to maintain high accuracy knowledge and control of its own trajectory or orbital parameters.Computer simulation programs determine the magnitudes of the net errors obtained from a given navigation system. By the use of Kalman filtering techniques, the process is made iterativ

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1965.tb02147.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1965.tb02148.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstractthe feasibility of usinga hand‐held sextant for taking navigation measurements from on board a manned spacecraft is being studied at Ames Research Center. It would be advantageous to use a reliable, light‐weight, handheld instrument instead of a relatively complex, vehicle‐mounted, automatic or semiautomatic device for taking such measurements if it provided sufficiently accurate angular measurements. The primary objective of the Ames research program is to determine the operational feasibility, scope of application, and accuracy of the manual measurement technique. A flight simulation facility has been used for examining navigator performance and the operational problems of the sighting task with hand‐held sextants. Measurements of real star and lunar landmark angles are being obtained to evaluate the problems associated with absolute sighting accuracy. The accuracy typically considered necessary for space navigation is 10 arc seconds. A sighting experiment on board the Gemini spacecraft will be conducted to examine in a more realistic environment the feasibility and operational problems of using a hand‐held navigation sighting instrument and to validate the results of ground‐based investigations. The purpose of this paper is to describe some results of t

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1965.tb02149.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1965.tb02150.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1965.tb02151.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1965.tb02152.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1965.tb02153.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstractfor many of the poweredphases of a space mission, the trajectory conditions to be satisfied at cutoff can be specified by a “required velocity”, which is a function of position and time. Then, satisfaction of the trajectory conditions can be ensured by directing the vehicle's thrust vector parallel to the velocity difference vector (velocity‐to‐be‐gained vector). However, this simple steering law is, in general, nonoptimal. Therefore, it is of interest to seek approximately optimal steering laws for required‐velocity guidance. This has been done by analysis based on the calculus of variations and on certain approximations valid for “short” burns. The analysis shows that the optimal steering policy gives an approximately constant turning rate of the thrust direction with respect to inertial space, and can be realized by directing the thrust acceleration parallel to a modified velocity‐difference vector vd* which includes certain extra terms that ensure a nearly optimal turning rate of the thrust direction. The relation between steering laws, turning rates, and fuel‐optimality is discussed at some length. In a wide class of cases, the approximately optimal steering laws turn out to be essentially equivalent to the powered‐flight guidance law previously pro

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1965.tb02154.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY