Aeronautics and astronautics – Missile stabilization or trajectory control – Remote control
Reexamination Certificate
2000-11-17
2002-10-22
Gregory, Bernarr E. (Department: 3662)
Aeronautics and astronautics
Missile stabilization or trajectory control
Remote control
C244S003100, C244S003140, C244S003240, C342S357490, C701S213000
Reexamination Certificate
active
06467721
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the correction of the path of a trajectory, effected in accordance with an expected target offset, wherein the path of the trajectory is measured satellite-supportedly on board a ballistically or quasi-ballistically fired projectile by increasing its aerodynamic drag coefficient so as to cause it to turn from an initial trajectory path into a steeper transitional trajectory towards the target.
2. Discussion of the Prior Art
A process of that kind is known from WO 98/01719. It is based on a procedure of using a satellite navigational apparatus on board the projectile to determine the trajectory which is currently being followed, and, from a comparison with a target-optimised trajectory, when a point on the trajectory which is derived from the comparison is reached, releasing aerodynamic braking devices for correction with the greatest possible degree of target accuracy of the subsequent trajectory. Problems arise in terms of practical implementation however by virtue of the fact that the numerous external influencing factors acting on a trajectory path still act on the trajectory even after the braking means are released and therefore the corrected trajectory does not then result in the operative mechanism in the projectile being delivered accurately on the target.
It is known from EP 0 138 942 B1 to locate a target for example by means of radar from the cannon and to determine in the fire control computer elevation and charge for a ballistic trajectory path which extends somewhat beyond the target, then to measure the launch speed of the projectile from the barrel and shortly thereafter by means of radar to ascertain the instantaneous position of the projectile relative to the cannon. Comparison of that instantaneous position with the reference position, on the basis of the calculated ballistic trajectory path, is used to determine the target layoff which is actually to be expected, the final step being to derive therefrom when aerodynamic braking effects should be activated at the projectile such as extending braking flaps or blowing off an aerodynamic projectile tip in order to suitably reduce the remaining trajectory on the basis of the new aerodynamic conditions and thereby to reduce the layoff from the target. This procedure also again only involves comparing a real to a predetermined ideal trajectory path in order to determine the attainment of a braking time so that once again the initialisation time for the braking means is error-ridden in dependence on external influences and then the interference effects which thereafter still act on the modified trajectory necessarily result in an additional target layoff.
Such a correction measure in respect of the braked transition from an initial trajectory path into a trajectory which is optimised after the apogee thereof is all the same substantially less expensive than the installation of a target sensor, control system and regulating loop for automatic, target-seeking final approach flight of a projectile. On the other hand, in consideration of the projectile speed being high in particular in the initial phase, the procedure for determining the real trajectory path from the measurement of initial instantaneous points on the trajectory is highly imprecise. The trajectory path which is actually flown however should be known to a very high degree of accuracy in order to be able to provide for optimum timing, after the apogee, of the braking manoeuvre for reducing the trajectory for the purposes of achieving a lower degree of scatter in the target area. Another problem in regard to a ground-supported process is also the reliability of a communication link for transmitting the braking triggering time or directly the braking command from the firing control computer to the projectile as, in view of the high speed of the projectile, the projectile can fly at any event in some sections of its trajectory in an ionised atmospheric shell which adversely affects a radio communication.
SUMMARY OF THE INVENTION
In consideration of those factors, the object of the present invention is to develop the process of the general kind set forth, which in itself is promising but which is still too inaccurate for the aspects of a practical situation, in such a way that it is possible to achieve substantially more precise target acquisition by way of a reduction in trajectory, as a result of an increase in the aerodynamic braking moment.
Accordingly the procedure according to the invention is based on the notion, as is known per se as such, of reducing the longitudinal scatter, which is very much greater in comparison with transverse scatter, of a ballistically or quasi-ballistically delivered projectile, in that the holding point is firstly laid behind the measured target position and then that trajectory is shortened. However, that laying effect is now only effected to such an extent that the transitional trajectory guides the projectile precisely on to the target after braking of the projectile having regard to a current error budget, on the theoretically shortest trajectory, wherein in accordance with the invention that given error budget is determined for as long as possible along the trajectory path to the braking moment from a comparison with the trajectory path which is theoretically predicted for given error parameters.
The projectile may be for example a drive-less projectile or missile which is fired from a mortar or from a howitzer, but also for example an artillery rocket with its rocket motor which acts to increase the range initially along a quasi-ballistic trajectory. The real transitional trajectory into which the projectile is then moved from its initial trajectory path by means of the aerodynamic braking effect lies between the flattest or shortest (minimum) and the highest or longest (maximum) trajectory of the current scatter fan or range and in principle can be converted by the braking action into the shortest trajectory, that is to say the trajectory which leads directly to the target.
Determining the current trajectory path does not involve having recourse to the procedure for determining the trajectory from the cannon, which is inevitably really inaccurate and technically unreliable due to interference effects. On the contrary, as is known per se, the initialisation point for the braking manoeuvre is autonomously determined on board the projectile, without therefore also being reliant for that purpose on a data link to a ground station. For that purpose the projectile is again equipped with a satellite receiving device for determining the actual initial trajectory path. As a deviation from the state of the art of the general kind set forth, the braking manoeuvre however is now not already triggered when a predetermined point on the trajectory is reached, but in accordance with the invention the initial trajectory path is compared to the theoretical launch curve over a period of time which is as long as possible, for as many trajectory points as possible. The build-up of the trajectory deviations which are ascertained therefrom, system-governed determining factors and preferably additionally measurements by sensor means for example on board the projectile and/or from the ground, such as in particular in accordance with DE 41 20 367 A1, are used as the basis for parametric determination of the current interference influences. These are in particular wind directions and strengths at different heights but also for example the error budget of the launch device (known transverse and heightwise aiming inaccuracies of the cannon) and influences of the intensity of the launch or firing charge, which varies depending on environmental considerations. With such knowledge, it is then possible by means of the usual external-ballistics approaches to pre-calculate really accurate information about the interference effects which even after release of the braking means still continue to act on the transitional trajectory which the projectile the
Kautzsch Karl
Leininger Jurgen
Reindler Albrecht
Wittmann Jurgen
Diehl Munitionssysteme GmbH & Co. KG
Gregory Bernarr E.
Scully Scott Murphy & Presser
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