A STUDY OF THE EFFECT OF ERRORS IN MEASUREMENT OF VELOCITY AND FLIGHT-PATH ANGLE ON THE GUIDANCE OF A SPACE VEHICLE APPROACHING THE EARTH

摘要

An analysis was made of the guidance of a space vehicle approaching the earth at supercircular velocity through an entrance corridor con¬taining a desired perigee altitude. Random errors were assumed in the measurement of velocity and flight-path angle and in obtaining the desired thrust impulse. The method described in NASA Technical Note D-191 of scheduling corrections at different values of the angle between perigee and the vehicle's position vector and a slight modification of this method were investigated as a means of correcting perigee altitude when the vehicle's predicted position was at programmed correction points not within a specified deadband about the desired perigee altitude. The study showed that modifying the angular method of NASA Technical Note D-191 by adding another correction near the initial point did not improve the effi¬ciency and accuracy of the angular method.nIt was found that in some cases the use of a correction procedure which included a deadband could be more costly in total corrective veloc¬ity than a procedure which neglected the deadband. This was especially true if a large degree of confidence was required in the total correc¬tive velocity. It was apparent from the results that a correction with a deadband limit in the guidance scheme was more sensitive to the ini¬tial conditions, the corrective procedure, the deadband, and the degree of confidence required than a correction without a deadband limit.