GB2279444A - Missile guidance system - Google Patents

Abstract

A missile guidance system for guiding a defence missile 2 to a ballistic target 1 includes means for tracking the target and continuously predicting its ballistic trajectory B and tangents thereto, means for continuously determining the relative position, velocity and acceleration of the missile and target and computing there from an interception time t, and guidance means for guiding the missile onto and along a tangent T to the predicted ballistic trajectory, ahead of the target, corresponding to the interception time, t. <IMAGE>

Description

MISSILE GUIDANCE SYSTEM The present invention relates to missile guidance systems, and in particular relates to a system for guiding a defence missile to a terminal ballistic missile (TBM). A TBM is a ballistic missile in the terminal phase of its flight.

A known missile guidance system uses proportional navigation techniques wherein ground based radars track both an incoming missile and a defence missile launched to destroy the incoming missile. The system continuously computes intercept points and transmits corresponding homing data signals to the control system of the defence missile. When the defence missile is within a predetermined range of the incoming issile, the defence missile's homing system is used to guide the missile to intercept the incoming missile.

Unfortunately in practice such systems often drive the defence missile along a curved track where the missile experiences unacceptably high 'g' forces. Any inability to follow manoeuvre demand, due to lags in the missile response, leads to a large miss distance.

The present invention provides a missile guidance system which drives a defence missile along a straight track as it approaches a ballistic target and does not impose unacceptably high 'g' demands on the missile.

According to the present invention a missile guidance system for guiding a defence missile to a ballistic target includes means for tracking the target and continuously predicting its ballistic trajectory and tangents thereto, means for continuously determining the relative position, velocity and acceleration of the missile and target and computing therefrom an interception time t, and guidance means for guiding the missile onto and along a tangent to the predicted ballistic trajectory, ahead of the target, corresponding to the interception time, t.

The flight of the missile along a final part of the tangent to the weapon trajectory may be controlled by a homing head and control system in the missile.

The means for continuously determining the relative position, velocity and acceleration of the missile may include an inertial reference system employing accelerometers and rate gyros in the defence missile.

An embodiment of the invention will now be described by way of example only with reference to drawings of which: Figure 1 is a diagram of a defence missile and tangent flight paths in accordance with the invention.

Figure 2 is a schematic circuit diagram of a missile guidance system for guiding a defence missile along a flight path such as that shown in Figure 1.

Referring to Figure 1, the approach of a TBM 1 on trajectory B is detected at a remote radar site (not shown).

Measurements of the TBM range and angular bearing are made and estimates of the current vector state of the TBM, ie: the TBM's postion, velocity and acceleration, at time t are made 0 by the system shown in Figure 2. An estimate of the time-to go, t togo, to interception of the TBM 1 eg an ATBM 2 launched from a site L depends on the relative state between the ATBM and the TBM, the future TBM dynamics, and the ATBM trajectory.

The latter will not be known until the interception point is calculated, and as this depends on the time-to-go value, an interactive calculation is used. The future dynamics of the TBM is predicted using the current TB state estimate and a mathematical model of TBM atmospheric drag and gravity. An estimate of the current state of the ATBM is obtained from data from an inertial reference unit carried in the ATBM and which forms part of the system of Figure 2.

The ATBM is guided along a path A onto a tangent approach line T which is a tangent to the TBM's flight path calculated from the TBM's predicted state at a time t = t + 0 t (shown at X in Figure 1). There will be some fluctuation go of the tangent direction during flight due to fluctuating errors in the state estimate of the TBM and refining of the predicted intercept point as the interception proceeds.

Eventually the missiles will close sufficiently to allow a homing seeker on the ATBM to acquire the TBM; thereafter the ATBM is controlled by outputs from its homing seeker. Point P in Figure 1 indicates the ATBM position when its homing seeker first locks onto the TBM when at position S.

Figure 2 shows a defence missile guidance system 1 which is fed with data from a ground station 2 via a secure data line. In the ground station 2, a state estimator 12 receives information relating to the flight of the TBM from missile surveillance and tracking radars (not shown). The state estimator 12 which is of conventional design and employs Kalman filtering techniques, continuously produces output signals indicative of the target missiles current position, velocity and acceleration [xTBM(t)|. A transmitter 13 transmits the signals in a secure manner to a receiver 11 carried in the ATBM.

In the defence missile guidance system 1, an inertial reference unit 9, which includes a set of accelerometers and rate gyros, derives in known manner the flight vectors of the ATBM [xATBM(t)]. Outputs from the inertial reference unit 9 and the receiver 11 are mixed in a mixer 10 and the relative position, velocity and acceleration, [xREL(t)l between the TBM and ATBM are derived.

A computer 14 computes from i EL(t) signals from the mixer 10 the time-to-go (go) to interception of the TBM by the ATBM, and computes predicted flight vectors (xTBM(t + t )) of the TBM from ;TBM(t) signals from the receiver for current values of t . Finally the computer 14 calculates an approach go line which is a tangent to the predicted trajectory of the TBM. A signal indicative of the tangent approach line from the computer 14 is intput to an injection phase controller 8 together with an input of xATBM(t) from the inerial reference unit 9 and the controller produces a control signal which is required to drive the ATBM onto the tangent approach line.

An autopilot 7 controls the flight of the ATBM in response to inputs from the controller 8 and the intertial reference unit 9 until a homing seeker 4 locks onto the TBM.

The seeker is a known strapdown system which measures range and look angles ie: the angles between the ATBM body axis and the ATBM to TBM sightline. An estimator circuit 5 for sightline spin includes a dynamic model of the motion of the ATBM and is driven by look angle signals from the seeker 4 and receives signals xATBM(t) from the inertial reference unit 9.

When the seeker locks onto the TBM the ATBM autopilot 7 response to homing phase controller signals which then supersede the injection phase signals. Homing phase control employs augmented proportional nagivation which requires target acceleration components in sightline axes and the estimator 5 estimates these components. A seeker which measures range and range rate, for example, an active radar seeker could be used rather than using a passive seeker and estimating range and range rate.

Claims (4)

1. A missile guidance system for guiding a defence missile to a ballistic target including means for tracking the target and continuously predicting its ballistic trajectory and tangents thereto, means for continuously determining the relative position, velocity and acceleration of the missile and target and computing therefrom an interception time t, and guidance means for guiding the missile onto and along a tangent to the predicted ballistic trajectory, ahead of the target, corresponding to the interception time, t.

2. A missile guidance system according to claim 1 further including a homing head and control system for controlling the flight of the missile along a final part of the tangent to the target trajectory.

3. A missile guidance system according to claim 1 or claim 2 wherein the means for continuously determining the relative position, velocity and acceleration of the missile may include an inertial reference system employing accelerometers and rate gyros in the defence missile.

4. A missile guidance system substantially as claimed herein with reference to the drawings.

4. A missile guidance system substantially as claimed herein with reference to the drawings.

Amendments to the claims have been filed as follows 1. A missile guidance system for guiding a defence missile to a ballistic target including means for tracking the target and continuously predicting its ballistic trajectory and tangents thereto, means for continuously determining the relative position, velocity and acceleration of the missile and target and computing therefrom an interception time t, and guidance means for guiding the missile onto and along a tangent to the predicted ballistic trajectory, ahead of the target, corresponding to the interception time, t.

2. A missile guidance system according to claim 1 further including a homing head and control system for controlling the flight of the missile along a final part of the tangent to the target trajectory.

3. A missile guidance system according to claim a or claim 2 wherein the means for continuously determining the relative position, velocity and acceleration of the missile includes an inertial reference system employing accelerometers and rate gyros in the defence missile.