GB2218189A - Impact detection - Google Patents

Abstract

A method of an apparatus for detecting impacts are disclosed and can be used in or as a missile fuse for detonating its explosive charge in response to impact of the missile with its target. A radiation detector 5 detects electromagnetic radiation produced (e.g. by oxidation of pulverised material) by the impact of the missile with the target. A rate of rise gate 6 transmits the resultant electrical signal to a threshold gate 8 only if its rate of rise exceeds a predetermined minimum. If the magnitude of the transmitted electrical signal exceeds the threshold set by threshold gate 8, the signal on line 10 detonates the missile's explosive charge. The impacting part of the missile may be coated with a fluorine containing material that reacts with the material of the target to enhance the radiation produced. <IMAGE>

Description

METHODS OF AND APPARATUS FOR IMPACT DETECTION The invention relates to the detection of impacts. More specifically, the invention relates to the detection of impacts of explosive projectiles for the purposes of fusing the explosive in response to the impact.

According to the invention, there is provided a method of impact detection, including the step of responding to electromagnetic radiation produced by the impact.

According to the invention, there is further provided apparatus for impact detection, comprising radiation detection means for responding to electromagnetic radiation produced by the said impact.

A missile fusing arrangement and a method of fusing a missile, both in accordance with the invention, will now be described, by way of example only, with reference to the accompanying diagrammatic drawing in which: Figure 1 is a block circuit diagram of one form of the arrangement; and Figure 2 is a block circuit diagram of another form of the arrangement.

The arrangements to be described are for the purposes of fusing missiles upon impact, that is, for detonating the explosive charge carried by the missile immediately following the impact of the missile with its target.

In accordance with a feature of the invention, the fusing arrangements to be described operate by detecting the radiation emitted as a result of the heating and chemical reactions which take place at the instant of the impact. These reactions will normally be or include an oxidation process, that is, oxidation by air of the material of the missile, and of the target, heated and disrupted or pulverised as a result of the impact.

Referring to Figure 1, the fusing arrangement illustrated is in the form of a radiation detector 5 carried by the missile and sited so as to be capable of viewing the impact. The radiation detector 5 is designed to respond to radiation within the wavelength band at which it will be emitted by the impact. If the impacting part of the missile or the impacted armour is made of titanium, for example, the colour temperature of the radiation generated at the impact will be such as to correspond to a peak radiation intensity at a wavelength of about 1 micrometre. A suitable form of detector for detecting radiation at this wavelength is a silicon photocell. Clearly, the selected photocell must be suitably fast in operation and silicon photocells can fulfill this criterion also.

A radiation detector operating at about 1 micrometre is advantageous because water has absorption bands at around 1 micrometre (for example, at 0.95 and 1.1 micrometres). Atmospheric moisture will therefore tend to absorb solar background radiation at these wavelengths, and thus in the region of the detecting wavelength of the detector 5, and thereby reduce possible interference of solar radiation.

Instead of arranging for the detector 5 to operate at about 1 micrometer, an alternative would be to arrange for it to detect radiation at the wavelength of a specific emission line or band of the chemical species present; in the case of oxidation of titanium, for example, this could be the emission band at about 0.4 micrometres.

The electrical output produced by the detector is fed to a rate of rise gate 6. The gate 6 will only allow the signal received to pass through if its rate of rise exceeds a predetermined rate of rise threshold.

Assuming that this threshold is exceeded, the detector signal is passed to a threshold detector 8. If, and when, the magnitude of the signal exceeds the threshold established by the threshold gate 8, a signal is produced on a line 10 and operates a suitable detonator 12 to fire the explosive charge of the missile either immediately or after a short delay calculated so as to allow the missile to penetrate to an optimum depth within the target before detonation.

The gates 6 and 8 have their thresholds selected so as to reduce the possibility of the fusing arrangement being incorrectly set off by extraneous sources of radiation.

Figure 2 shows an alternative circuit arrangement.

Here, the electrical output corresponding to the radiation detected by the detector 5 is fed to a low threshold gate 14 and also to a high threshold gate 16.

Gate 14 has two output lines, 17 and 18. When the (relatively low) threshold established by gate 14 is exceeded, an output is produced on line 17 and initiates a monostable 19. No output is produced on line 18.

Monostable 19 produces an output on a line 20 which persists for a predetermined relatively short period.

Line 20 is connected to enable an AND gate 22 during the period of the monostable.

If and when the increasing output of the detector 5 exceeds the relatively high threshold of gate 16, an electrical output is produced on a line 23 and operates a trigger circuit 24 (which does not yet produce any output). Assuming that the radiation to which the detector 5 is responding is an impact flash, the radiation level will thereafter rapidly fall. As soon as the radiation level falls below the threshold of gate 16, the output of gate 16 will change state and the trigger circuit 24 will switch back. In switching back, it produces and thereafter maintains an output on a line 26 which is fed to a second input of the AND gate 22.

The output from detector 5 will continue to fall and will eventually fall below the threshold established by gate 14. The result will be an output produced on a line 18 which is fed to the third input of the AND gate 22. Assuming that the gate 22 is still enabled at this time (by its other two inputs), the gate will produce an output on a line 28 to operate the detonator 12 either immediately or after a suitable short delay.

Therefore, the detonator 12 will only be operated if the radiation from the detector 5 has risen to at least a relatively high threshold (corresponding to that established by gate 16) and then fallen below a relatively lower threshold (corresponding to that established by gate 14), all within a fixed predetermined period of time corresponding to that established by monostable 19. The circuit of Figure 2 thus provides improved protection against a false alarm caused by extraneous flashes of radiation.

As stated, the chemical reaction producing the flash of radiation would normally primarily be oxidation.

However, it may be advantageous under certain circumstances to coat the tip of the missile so as to produce an additional chemical reaction for enhancing the radiation intensity. For example, a coating comprising a high proportion of a fluorine-containing material could be applied to the missile tip. This coating, which could be an inorganic fluoride or a partially fluorinated polymeric substance, will undergo thermal pyrolysis on impact, and the gaseous fluorine atoms and molecules so produced are much more powerful oxidising agents than air. The amount of titanium consumed during the reaction, and/or the rate at which it is consumed, is thus enhanced, and therefore this process will produce a greater intensity of radiation that its oxidation.

Claims (17)

1. A method of impact detection, including the step of responding to electromagnetic radiation produced by the impact.

2. A method according to claim 1, including the step of monitoring the rate of rise of radiation and responding only to radiation whose rate of rise exceeds a predetermined minimum.

3. A method according to claim 1 or 2, including the step of responding only to radiation which within a predetermined length of time starting when the radiation first exceeds a relatively low threshold exceeds a relatively high threshold and then falls back by a predetermined amount.

4. A method of detonating an explosive charge within a missile in response to detection of the impact of the missile with its target, in which the said impact is detected by a method according to any preceding claim.

5. Apparatus for impact detection, comprising radiation detection means for responding to electromagnetic radiation produced by the said impact.

6. Apparatus according to claim 5, including inhibiting means for preventing the response unless the intensity of the radiation is increasing at at least a predetermined rate.

7. Apparatus according to claim 5 or 6, including inhibiting means for inhibiting the response unless, within a predetermined period of time starting when the intensity of the radiation first exceeds a relatively low threshold, the radiation intensity then exceeds a relatively higher threshold and falls back by a predetermined amount.

8. Apparatus according to any one of claims 5 to 7, in which the radiation detection means is arranged to detect electromagnetic radiation in a narrow waveband at about one micrometre.

9. Apparatus according to claim 8, in which the radiation detection means is a silicon photo diode.

10. A missile, including fusing means for detonating an explosive charge carried by the missile in response to the impact of the missile with its target, the fusing means comprising apparatus according to any one of claims 5 to 9.

11. A missile according to claim 10, in which the fusing means includes delay means for delaying the detonation of the explosive charge for a predetermined time after the detection means has responded to the said impact.

12. A missile according to claim 10 or 11, in which the impacting part of the missile externally carries a coating of material whereby the radiation produced in response to the impact is enhanced.

13. A missile according to claim 12, in which the coating material is fluorine-containing and the radiation enhancement arises from a reaction with fluorine.

14. A method of impact detection, substantially as described with reference to Figure 1 of the accompanying drawings.

15. A method of impact detection, substantially as described with reference to Figure 2 of the accompanying drawings.

16. Apparatus for impact detection, substantially as described with reference to Figure 1 of the accompanying drawings.

17. Apparatus for impact detection, substantially as described with reference to Figure 2 of the accompanying drawings.