Rocket accuracy improvement device

DEDICATORY CLAUSE

The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to us of any royalties thereon.

BACKGROUND OF THE INVENTION

Currently a typical free flight rocket, comprised of a warhead and a motor, spins the entire rocket assembly in the same direction and has a relatively high moment of inertia. At motor burn-out, the rocket undergoes an abrupt reversal of spin direction. This reversal, caused by an aerodynamic torque from the fins, creates a perturbation in the rocket trajectory, making the trajectory erratic. A more predictable trajectory and thus greater accuracy in the rocket aim would be achieved if the spin of the warhead could be separated from the spin of the motor at the time of motor burn-out. Such separation would reduce the effective roll inertia of the rocket and enable the warhead, and thus the entire rocket, to maintain the original trajectory.

SUMMARY OF THE INVENTION

Rocket Accuracy Improvement Device

102

, when coupled between warhead

103

and motor

101

of a typical free flight rocket

100

, isolates the warhead from the rocket motor in the roll axis using a plurality of ball bearings and thereby enables the warhead to spin independently of the motor. This reduces the effective roll inertia of the rocket at the time of spin reversal at motor burn-out. Further, the separation of the warhead from the motor allows the efficient rapid initial spin-up of just the motor during motor boost. This rapid initial spin-up reduces the effects of thrust misalignment and rocket imbalance that are largely responsible for rocket dispersion, thus setting the rocket on a more accurate trajectory at the start.

During the powered stage of the rocket flight, a portion of the motor spin is transferred to the warhead due to the bearing drag torque, with the warhead reaching its maximum spin rate at the time the motor burns out. Therefore, even when the motor reverses its spin, the angular momentum of the warhead tends to act gyroscopically to maintain the trajectory of the rocket, thus achieving a much more predictable flight path for the rocket.

DESCRIPTION OF THE DRAWING

FIG. 1

depicts the position of the Rocket Accuracy Improvement Device in a typical free flight rocket comprising a warhead and a motor.

FIG. 2

is a cross-sectional diagram of a preferred embodiment of the Rocket Accuracy Improvement Device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawing wherein like numbers represent like parts in each of the figures,

FIG. 1

shows where in a typical free flight rocket

100

, such as HYDRA

70

, the Rocket Accuracy Improvement Device (hereinafter referred to as the “Device”) should be placed while

FIG. 2

shows the structural details of a preferred embodiment of the Device.

As shown in

FIG. 1

, the Device is coupled between motor

101

and warhead

103

by screwing motor adapter

201

into the forward section of the motor so that the motor adapter spins with the motor and by screwing warhead adapter

204

into the warhead. The motor adapter has threaded portion

210

and the forward section of the motor has a corresponding threaded segment (not shown). The warhead adapter may be a simple hollow aluminum shell that has internal screw thread

212

matching that on the rear portion of the warhead.

The warhead adapter is adjacent and connected to housing

202

via radial screws

203

. The housing, which spins with the warhead, is the outer shell that contains therein ball bearings

205

which fit between the housing and spindle

214

and are mounted to ride on the spindle. The spindle is a feature that extends from motor adapter

201

and, as illustrated in

FIG. 2

, extends even farther forward past the ball bearings with short threaded end

216

which mates with spacer

207

and locknut

208

. The spacer and locknut are used to pre-load ball bearings

205

. The pre-loading is accomplished by tightening the locknut against the threaded end of the spindle on which the ball bearings ride to a pre-determined torque value to ensure both the smooth operation of the Device and to tune the spin rate of the warhead during flight. The pre-loaded ball bearings, such as Miniature Precision Bearing S3342MCHH5-LO2 and Torrington B545DD, allow the warhead and the motor of a rocket to spin independently of each other and isolate the warhead from the erratic spin profile of the rocket motor at motor burn-out.

With the warhead and the motor thusly de-coupled, the rocket accelerates in the spin axis much more rapidly when the rocket motor is ignited and the exhaust gases cause the rocket both to accelerate out of the launch tube and to spin. The increased spin rate, in turn, causes any off-axis thrust present in the rocket to integrate towards zero much more quickly and result in a straighter initial flight path for the rocket. This tendency to stabilize the rocket occurs during a critical period in the rocket flight when aerodynamic forces are at a minimum. During the powered stage of the flight, a portion of the motor spin is transferred onto the warhead due to the bearing drag torque, the spin of the warhead reaching its maximum rate at the time of the motor burn-out. The warhead thus imparts its maximum gyroscopic stabilizing effect and continues spinning in its initial direction when the motor has expended its fuel and reverses its spin direction. The reduction of the mass of the motor by the weight of the expended fuel at this point in the rocket flight means greater influence of the now-dominant gyroscopic forces imparted by the spinning warhead to decrease trajectory dispersion significantly.

Although a particular embodiment and form of this invention has been illustrated, it is apparent that various modifications and embodiments of the invention may be made by those skilled in the art without departing from the scope and spirit of the foregoing disclosure. An example is removable plugs

206

, along the exterior of housing

202

, that allow the insertion of assembly tools to secure the Device tightly onto the rocket during the production of the rocket. Accordingly, the scope of the invention should be limited only by the claims appended hereto.