The invention described herein was made in the performance of official duties by an employee of the Department of the Navy and may be manufactured, used, licensed by or for the Government for any governmental purpose without payment of any royalties thereon.
The invention described herein relates to solid fuel rocket motors and in particular to rocket motors having desensitizing safety features.
According to Military Standard 2105B, HAZARD ASSESSMENT TESTS FOR NON-NUCLEAR MUNITIONS, no munition which is subjected to a slow heating, referred to in the standard as xe2x80x9cslow cook-offxe2x80x9d, may have a reaction greater than a Type V reaction. This reaction is described in the standard as follows: xe2x80x9cThe energetic material ignites and burns non-propulsively. The case may open, melt or weaken sufficiently to rupture nonviolently, allowing mild release of combustion gases. Debris stays mainly within the area of the fire. This debris is not expected to cause fatal wounds to personnel or be hazardous fragment beyond 15 m (49 ft).xe2x80x9d In the prior art, venting of various munitions has been accomplished by sealing the munition with a meltable material, such as nylon. Other mechanical venting methods are also known. For example, U.S. Pat. No. 5,035,181, Tacks et al describes a pop off for the fuze to lessen the cook-off hazard. Other types of munitions have used desensitizing fluids to inert a munition until a short time prior to arming. An example of such a munition is the small bagged packets of anti-personnel munitions which are carried in an aircraft canister filled with freon. Upon discharge from an aircraft, the small bags scatter around the target rapidly drying. Once dry, the munition is highly sensitive and will detonate upon any disturbance. Various venting, both mechanical and melting types have been applied to rocket motors. Likewise, various desensitizing means have been applied. However, no prior art method meets the Type V burning standard for slow cook-off of rocket motors. A need exists for a means of desensitizing a rocket motor fuel at the time of an inadvertent slow cook-off.
Accordingly, it is an object of the invention to provide a solid fuel rocket motor having non-energetic reaction characteristics when subjected to slow cook-off.
It is a further object of the invention to provide a solid fuel rocket motor that is ready to operate, but retains the insensitivity characteristics.
It is another object of the invention to provide a solid fuel rocket motor that is de-energized by a desensitizing fluid in the event of slow cook-off.
It is yet another object of the invention to provide a solid fuel rocket motor with a desensitizing unit which requires no external inputs (self-contained).
The invention is an enclosure that is connected via a tube to the interior of a solid fuel rocket motor. In one embodiment, a plug made from a material having a low melting point seals the connecting tube between the enclosure and the interior of the solid fuel rocket motor. The melting point of the plug material is chosen so that it is below the expected cook-off temperature of the particular rocket. The enclosure has a fill port that is sealed by a cap. The enclosure contains a fluid that will desensitize the solid rocket fuel when the two materials come into contact. In normal storage, or in ready deployment, the desensitizing fluid within the enclosure is separated from the propellant charge and has no effect on the rocket motor. If however, the rocket motor is subjected to slow cook-off, the meltable plug melts, turning into a liquid. The liquidized plug, along with the desensitizing fluid is now forced down the connecting tube and into the interior of the solid fuel rocket motor by pressure generated within the enclosure. The pressure, in one embodiment, in the enclosure is generated by compressed gas. In another embodiment, a spring driven piston pressurizes the desensitizing fluid. In operation, the desensitizing fluid contacts the solid rocket fuel, degrading its energetic qualities. When the cook-off temperature of the rocket is reached, the degraded propellant reacts much more slowly, meeting the Type V reaction requirement. During normal operation, that is, without any cook-off conditions being realized, of the rocket motor the desensitizing fluid will not come into contact with the solid fuel within the rocket motor. This is because during normal conditions, there will not be enough time for the plug to melt during the function time of the rocket, and also the pressure generated in the interior of the rocket motor will prevent any fluid flowing from the enclosure finding its way into the interior of the rocket motor.
In general, the desensitizer unit forms part of a rocket motor assembly and with the rocket motor thereof capable of experiencing a cook-off condition having a temperature within a first predetermined range. The rocket motor has a rocket case having a forward end, an exhaust end, and an interior in which a propellant charge capable of being desensitized is located. The desensitizer unit comprises:
(a) an enclosure having an exit port and a fill port;
(b) a cap which seals the fill port;
(c) a fluid located in the enclosure and comprised of a composition capable of desensitizing the propellant charge;
(d) a plug placed in the exit port of the enclosure and having a melting point at a second predetermined temperature range which is less than the first predetermined temperature range; and
(e) a tube connecting the exit port of the enclosure to the forward end of the rocket case.
In operation, when the rocket motor experiences the cook-off condition, the plug has already melted and opened the exit port to allow the desensitizing fluid to flow down the tube into the rocket case so that the propellant charge is desensitized.