Release of daughter missiles

Daughter missiles 11 are catapulted forward from a mother missile 10 when a rocket motor 12 of the mother no longer accelerates the missiles. A catapult force generated at a piston head 43 by the pressure of gas from the rocket motor on rearward facing surfaces 26 of the daughters is large enough to shear pins 34 holding the daughters to the mother, but only when the forces of reaction of the daughters 11 on the piston 43, due to acceleration, have fallen off. Preferably the daughters are thrown outwardly at release, most preferably by axial spinning of the structure of the mother to which they are mounted.

FIELD OF THE INVENTION 
This invention relates to a method of, and apparatus for, effecting the 
release of a plurality of daughter missiles from an elongate mother 
missile in flight of the mother missile, with substantially no loss of 
forward momentum of the daughter missiles. 
BACKGROUND OF THE INVENTION 
The present Applicants are currently seeking to provide a missile system in 
which aerial guided "daughter" missiles fly along a line of sight to a 
target and which are accelerated to flight speed by a rocket-propelled 
mother missile. The release of the daughter missiles from the mother 
missile is required to occur when the, or the final, rocket motor of the 
mother missile is all burnt. Any undue disturbance to the designed flight 
paths of the daughter missiles and loss of their forward momentum during 
their release is to be avoided. It is one object of the present invention 
to meet these requirements. 
SUMMARY OF THE INVENTION 
According to one aspect of the present invention there is provided a method 
of effecting the in-flight discharge of a daughter missile forwardly from 
a rocket-propelled mother missile after a period of acceleration of the 
daughter missile brought about by the burning of the rocket motor of the 
mother missile, characterised by the steps of i) establishing before the 
end of said period of acceleration a catapult force for accomplishing said 
forward discharge and ii) utilising the force of reaction to the 
acceleration of said daughter missile to oppose the catapult force, 
whereby the catapult force is insufficient to bring about the forward 
discharge during the said period of acceleration yet sufficient as soon as 
the period of acceleration ends. 
According to a second aspect of the present invention there is provided an 
aerial guided missile comprising a mother missile and at least one 
daughter missile carried on the mother missile, the mother missile having 
a rocket motor for accelerating the missile for a period along a flight 
path towards a target, and the daughter missile being mounted for 
in-flight forward discharge from the mother missile at the end of the 
period of acceleration, characterised by means to impose on the daughter 
missile during the period of acceleration a catapult force sufficient to 
accomplish said forward discharge in the absence of the acceleration to 
which the missile is subject during the said period of acceleration, yet 
which is insufficient while it is opposed by the force of reaction of the 
daughter missile on the mother missile, present during said period of 
acceleration. 
It is convenient to rely upon the pressure of the propellent gas of the 
rocket motor (normally a second stage motor) to provide the catapult 
force. This can be delivered to the or each daughter missile by a piston 
arranged to contact the daughters and to be urged forwardly by the gas 
pressure. If desired, a shear pin can be used to prevent premature forward 
movement of the piston. Premature forward discharge can be prevented by 
pinning the or each daughter missile to the mother missile with a 
fastener, the pinning force of which is arranged to be overcome by the 
catapult force at the moment of release of the or each daughter missile. 
One way of achieving the pinning is to use a shear pin which is broken at 
the moment of release. 
A number of daughter missiles can be mounted alongside each other on a 
sleeve (otherwise called a shoe) slidable on the axis of the mother 
missile, the daughter missiles being arranged evenly around the sleeve 
axis. The sleeve may be biased to a storage disposition at the rear of its 
range of movement. Such biasing is effective to absorb handling shocks 
prior to release of the daughter missiles. The fastener by which each 
daughter missile is fastened by a pinning force to the sleeve has a grip 
adapted to be broken by the shear forces imposed on it by the catapult 
force when the mother missile is no longer accelerating. Preferably, each 
fastener is a single shear pin level (along the length of the missile) 
with the centre of gravity of the daughter missile. 
Preferably, the daughter missiles have a radially outward acceleration at 
their moment of release. This can be given them by arranging for the 
daughter missile structure to be spinning at the moment of release and/or 
by accelerating the daughter missiles outwardly (as by ramps) in a forward 
movement on the mother missile from a flight disposition to a release 
disposition. 
For a better understanding of the present invention, and to show more 
clearly how the same may be carried into effect, reference will now be 
made to the accompanying drawings.

DETAILED DESCRIPTION 
The missile comprises a mother missile 10 and three daughter missiles 11 
carried by it. The mother missile 10 has a first rocket motor R1 and a 
second motor R2 which fire in sequence, and flight control surfaces 17, 
which are also adapted to impart a spin to the mother missile during its 
flight. At the front of the propellent material 12 of the second stage 
motor R2 is a light alloy motor head piece 13 held to the casing 22 of the 
motor R2 by a threaded collar 23. 
The head piece carries a hollow, daughter missile abutment and fairing 
structure 24 which,has three forward-facing abutment pads 25 which abut 
the rear faces 26 of the daughter missiles 11. 
An axial spigot part 14 on the head piece 13 carries a support cylinder 15 
which extends as far as a pointed nose 16. The spigot 14 bounds a pressure 
reservoir chamber A, closed by the cylinder 15 and nose 16. (In an 
alternative embodiment, the reservoir is closed not by the nose 16, but by 
a bulkhead across the hollow cylinder 15. This allows telemetry equipment 
to be installed in the cylinder, between the bulkhead and the nose.) When 
the second stage motor R2 is ignited, the chamber A becomes filled with 
compressed gases from the propellent material 12 by passage of these gases 
through a non-return valve 18 in the head piece 13. The structure of the 
valve 18 is not shown, but it is of the "pastille" type. 
The cylinder 15 has on its cylindrical surface an annular recess 20, on 
which is slidable axially, but not rotatably, a sleeve 21. Three daughter 
missiles 11 are carried on the sleeve 21, each being secured to it by a 
shear pin fastener 34. The missiles 11 are disposed at angles of 
120.degree. to each other around the circumference of the sleeve 21, as 
shown in FIG. 2. A helical spring biasing means 31 is housed in the space 
between the cylinder 15 and the sleeve 21 between the end surface 23 of 
the recess 20 and a forward facing abutment surface 32 of the sleeve 21. 
FIG. 2 shows a protective outer skin 50 and restraining blocks 51 and 52 of 
expanded polystyrene or other extremely lightweight material, which skin 
and blocks are caused to fall away from the daughter missiles 11 at some 
point before the second motor stage R2 becomes all-burnt but which, up to 
that point in the flight of the missile, serve to protect the daughter 
missiles from accidental damage and, during the early part of the flight 
of the missile, afford aerodynamic streamlining of the missile as a whole. 
Present indications are that such streamlining is not essential, so the 
skin and blocks could be dispensed with. 
Referring now to FIG. 3, a plurality of apertures 19 through the support 
cylinder 15 and the spigot 14 permit passage of the propellent gases to a 
gas pressure chamber 39 bounded by a working annulus 40 of a piston 41 and 
the cylinder 15. A first O-ring 42 on the head end 43 of the piston and a 
second O-ring 44 on the external surface 47 of the cylinder 15 maintain 
the working space 39 gas-tight. The head end 43 of the piston is in 
contact with the rearward-facing surface 26 of the daughter missile 11 and 
a shear pin restraining means 46 resists relative movement of the piston 
on the annular external surface 47. Latest indications are that this shear 
pin 46 in unnecessary. 
After launch of the mother missile, compressed propellent gases enter the 
working space 39 to generate a catapult force F on the piston 41, but the 
combination of inter alia i) the shear resistance of the shear pin 46, ii) 
the reaction R of the three daughter missiles, the sleeve and the piston 
41, to the thrust of the rocket motor 12 on the head end 43 of the piston 
41 and iii) the biasing force B of the spring 31, is effective to prevent 
the gas pressure from driving the daughter missiles forwardly relative to 
the support cylinder 15, but only for as long as the rocket motor 12 is 
delivering full thrust, i.e. generating acceleration of the daughter 
missile structure of daughter missiles 11, sleeve 21 and piston 41, and 
the reaction force R. 
Release of the daughter missiles is required at the time of maximum 
velocity of the mother missile, at the moment when the second (and last) 
stage of the motor is all-burnt. When the thrust from the motor R2 falls 
off, there is a consequent decline in the force of reaction R on the head 
end 43 of the piston 41 (although drag forces on the daughter missiles 
will provide some residual pressure on the piston). The catapult force F 
on the piston, arising from the accumulated pressure of gas in the working 
space 39, is now high enough for the piston to shear the shear pin 46 and 
drive the piston forward, in turn driving forward the assembly of the 
sleeve 21 and three daughter missiles 11. This forward movement compresses 
the helical spring 31 up to the point when the turns of the spring abut 
each other, no substantial further compression occurs and there is rapid 
deceleration of the sleeve 21 on the cylinder 15. 
This rapid deceleration of the sleeve 21, and continuing pressure of the 
head 43 of the piston on the daughter missiles 11, brings about shearing 
of the shear pins 34, thereby severing the connection between the daughter 
missiles and the sleeve 21. The forward movement of the daughter missiles 
which takes place between shearing of the pin 46 and the pins 34 can 
therefore be seen as a forward movement from a flight disposition to a 
launch disposition. 
In embodiments which do not include a shear pin 46, the catapult force F is 
resisted by the pinning force P, up to the breaking stress of the shear 
pin 34, the reaction R of the three daughter missiles to acceleration of 
the mother missile, and any drag forces acting on the daughter missiles. 
The mass of the daughters is large relative to that of the sleeve 21. 
In such embodiments, the forward movement to the launch disposition, and 
compression of the spring 31, is considered to occur during the phase of 
acceleration of the mother missile. At the end of the period of 
acceleration there is no further forward movement of the sleeve 21, but 
the decline in the reaction force R results in shearing of the pins 34 and 
forward discharge of the daughters 11. 
The mother missile spins during burning of the motor 12, and the spinning 
motion endows the daughter missiles with a tendency to accelerate 
outwardly away from the longitudinal axis of the mother missile at the 
moment of fracture of the shear pins 34. Optimum release is achieved when 
the shear pins 34 are located level with the centre of gravity of the 
daughter missiles along their length. 
The sleeve 21 can be replaced by a set of three cradles, one for each 
daughter missile, and arranged around the support cylinder 11. The cradles 
can be supported in a way which allows limited radially outward 
acceleration, e.g. up ramps, during the forward movement to the launch 
disposition, for endowing the daughter missiles with an acceleration 
radially outwardly which supplements the acceleration due to spinning or 
provides acceleration in a case where the mother missile is not spinning. 
If desired, the sleeve 21 and shear pins 34 could be avoided by providing 
each of the daughters with, for example, a front pin and a rear pin which 
slide in a respective slot in the support cylinder 15, each slot being 
open at a forward end thereof to allow the pins to move radially outwardly 
when the daughter reaches the launch disposition.