Aeroballistic diagnostic system

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties therefor.

BACKGROUND OF THE INVENTION

Accurate measurement of the aeroballistic flight characteristics of spinning bodies, with on-board sensors, significantly contributes to the research and development of experimental projectiles, and to the diagnosis of existing munitions systems.

Various systems exist for obtaining projectile data while the projectile is still traveling within the bore of a gun barrel. The in-bore techniques have not been able to provide good quality measurements for many reasons. These in-bore techniques have included: 1) Hardwiring of sensors on-board the projectile directly to recording equipment located outside of the gun tube. This technique suffered from wire breakage and loss of data. 2) Radio frequency transmission of the in-bore data out of the gun. This technique has loss of data due to the ionized gasses obscuring the RF signal. 3) Laser beam transmission of the in-bore data out of the gun tube. The major difficulty with this technique was the critical alignment requirements of the transmitter and its receiving station. In addition, blow-by gasses leaking around the projectile as it traveled up the gun tube usually obscured and attenuated the laser light beam and resulted in further loss of data. 4) On-board recorders that store the in-bore measurements. Recovery of the projectile is extremely difficult. Many artillery projectiles are fired in excess of 20 km and penetrate deep into the earth. Many proving grounds fire into areas off limits or into water making recovery impossible. 5) An on-board telemetry system that stores the in-bore measurement data and then transmits it after a delay. This type of system has only measured the in-bore data and the volume taken up by the system has required major modification to the projectile.

For a complete analysis, data during the projectile's flight outside the gun barrel is also required. Ground-based instrumentation systems can provide some of these measurements, but are generally used for only limited portions of a projectile flight for reasons of both expense and practicability in application. In another system, such as shown in U.S. Pat. No. 5,909,275, light sensors positioned around a fuze-like body of a projectile, to sense the sun, are used to provide parameters pertaining to the solar attitude and solar roll angle.

There is a need, however, for a system which is capable of obtaining aeroballistic data, starting from a projectile's initial in-bore launch and throughout its entire flight with no loss of data.

SUMMARY OF THE INVENTION

The diagnostic system of the present invention meets the objective of obtaining aeroballistic data starting from a projectile's initial in-bore launch from a gun and throughout its entire flight, with no loss of data.

The diagnostic system includes a container which can attach to the projectile, and has a fuze shaped body. The interior holds a plurality of sensor arrays, one of which obtains projectile data during in-bore travel of the projectile. Other ones of the sensor arrays obtain projectile data during in-flight travel of the projectile. Also positioned within the container is a recording means which, when activated, stores the in-bore data, at a first rate, and reads the data out, at a slower rate, while the projectile is in-flight. The in-bore data and the in-flight data are encoded and provided to a utilization means, such as a transmitter and associated antenna, also within the container, for transmission of both in-bore and in-flight data to a ground station, for processing of the data. In another embodiment the utilization means is comprised of a microprocessor and guidance control unit for governing flight direction of the projectile.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood, and further objects, features and advantages thereof will become more apparent from the following description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which:

FIG. 1

is a side view, partially in section, of a projectile within a gun barrel.

FIG. 2

is a side view, partially in section, of the diagnostic system of the present invention.

FIG. 3

is an exploded view of the diagnostic system.

FIG. 4

is a block diagram of the diagnostic system of the present invention in a data transmission configuration.

FIG. 5

is a block diagram of the diagnostic system of the present invention in a control configuration.

FIG. 6

is a view, as in

FIG. 2

, showing an additional function of the apparatus.

FIG. 7

is a block diagram illustrating the microprocessor of FIG.

5

and two of its outputs.

FIGS. 8

to

14

are plots of actual data acquired during a test of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals.

FIG. 1

illustrates a projectile, an artillery shell

10

, traveling within the bore

12

of a projectile launcher, such as an artillery gun

14

. The artillery shell

10

is comprised of a case body

16

, filled with, for example, an explosive bursting charge, and includes a fuze

18

threaded into the front end of the case body for causing detonation of the charge as a result of impact with, or proximity to, a target.

In an embodiment of the present invention the conventional fuze

18

is replaced with a complete diagnostic system for obtaining not only information relative to the projectile's travel inside the bore

12

, but in-flight data as well. Although an artillery shell

10

is illustrated, the invention is also applicable to other projectiles such as tank rounds, munitions, rockets, missiles, sub-munitions bullets and other weapon systems.

FIG. 2

is a side view of a diagnostic system

20

, partially in section, in accordance with an embodiment of the present invention, and

FIG. 3

displays an exploded assembly schematic of the major components of the system used on gun tube launched artillery and other vehicles.

The diagnostic system

20

includes a battery cup

22

, power supply

24

, stem

26

, having threads

27

, sensor bus board

28

, accelerometer bracket

30

, optical sensors

32

, which fit into respective windows

33

in faring

34

, high-g accelerometers

36

, low-g accelerometer

38

with its associated board

39

, magnetometers

40

, signal conditioning and power regulation circuit

42

, data encoding in-bore delay recorder

44

, transmitter

46

, antenna

48

, windshield

50

, ceramic nose-tip

52

, PCM (pulse code modulation) encoder

54

, battery connector

56

and g-switch

58

.

More particularly, the diagnostic system

20

includes a container

60

, having an interior

62

, into which the various components are packaged. The container

60

is a conventional fuze body, which may be threaded into a standard artillery shell, such as used by NATO forces, thus requiring no modification to the artillery projectile body itself.

High-g accelerometers

36

, such as Model 7270, manufactured by Endevco, San Juan Capistrano, Calif., are rigidly mounted with accelerometer bracket

30

in the fuze body

60

to sense and measure the axial and radial acceleration environment that the projectile to which it is attached is subjected to, during launch. The low-g accelerometer

38

, such as Model ADXL78, manufactured by Analog Devices, Norwood, Mass., senses and measures the axial acceleration. The magnetometers

40

, such as Model HMC1002 manufactured by Honeywell, Plymouth, Minn., sense and measure the magnetic field. Optical sensors

32

, such as described in the referenced U.S. Pat. No. 5,909,275, sense the solar light. A 5V power supply

24

, such as the LiMnO

2

primary battery manufactured by Ultralife Battery, powers the system through the battery connector

56

. Power regulation is provided and all channels are conditioned, if required, by the signal conditioning and power regulation circuit

42

prior to being recorded and transmitted.

The in-bore delay recorder

44

design is intended to capture the high-g accelerometer portion of aeroballistic data while the projectile is in the bore of the gun. Specifications for this design include a 150 kHz digitizing rate at 12-bit resolution for 20 ms and 15 kHz playback rate with an effective data bandwidth of 60 kHz. This duration can be increased to 40 ms at the cost of reducing the data bandwidth in half. The circuit accomplishes this task by digitally recording the data from high-g accelerometers

36

in memory when triggered by the g-switch

58

, such as Model 8463-2 manufactured by Aerodyne Controls, Ronkonkoma, N.Y.

Once the data is stored, the memory is read and converted back to an analog signal for the purposes of working with any transmitter system. To accommodate the limited bandwidth of the transmitter

46

, the data from high-g accelerometers is read at one tenth the rate at which it was stored. This data is then played back, during in-flight travel of the projectile, by the in-bore delay recorder

44

in a continuous “loop” to enhance the probability that the data will not be lost due to a possible interruption of the telemetry link.

The diagnostic system

20

is designed to endure the high acceleration environment experienced during the gun launch of a ballistic flight vehicle and is designed to be compact and lightweight. The diagnostic system

20

must be able to withstand the linear accelerations of gun launching. Maximum acceleration levels are 30,000 times the earth's gravity, with 150,000 rad/sec

2

of angular acceleration for artillery cannon launching. The system must also withstand the spin-rate of 300 Hz or higher associated with high-speed artillery projectile flight. Surviving these accelerations and forces depends on the choice of materials of which the diagnostic system

20

is composed, and its packaging. For instance, the system uses chip-level and surface-mounted electronic components that are encapsulated in a potting material

64

(

FIG. 2

) such as STYCAST 1090. The small size of the electronic components and the rigidity of the potting material

64

increase the survivability of the entire diagnostic system

20

, during launch as well as in flight. In addition to surviving the high accelerations encountered, the system is also capable of surviving other stresses resulting from high rates of speed.

The diagnostic system

20

is intended to survive cannon launches with velocities in excess of Mach 3. Therefore, the windshield

50

is designed to withstand the extreme heat due to the aerodynamics, while maintaining the ability to appear transparent to radio-frequency transmission. The windshield

50

is made of a non-metallic material such as Nylon 6/6, and the nose-tip

52

is made of machineable ceramic. Nylon has high strength and tolerance to heat. The ceramic nose-tip

52

has extreme tolerance to heat, therefore, it is used on the very front of the fuze body

60

where the stagnation temperatures are extreme. The stem

26

and battery cup

22

are fabricated from aluminum, type 7075-T651, for optimal strength to weight ratio.

The invention is designed such that in can be assembled to any NATO compatible, or other artillery projectile. This requires that the stem

26

use specific threads

27

to interface to the projectiles, and to have a specific intrusion depth. The intrusion depth is the length of the fuze body

60

that can fit inside of an artillery projectile, and still maintain functionality.

A block diagram of the electronics portion of the diagnostic system

20

is illustrated in FIG.

4

. The output signals from the various sensor arrays

32

,

36

,

38

and

40

are provided to the signal conditioning and power regulation circuit

42

where the signals are assigned appropriate voltage levels and otherwise modified for acceptance by subsequent circuitry.

When the normally open g-switch

58

is closed, upon the attainment of a certain acceleration level when the projectile is fired and in the gun bore, the in-bore data recorder

44

is caused to commence recording. Recording of in-bore data at a high speed first rate, for example 150 ksamples/sec, continues for a predetermined period of time (measured in milliseconds) . After the projectile

10

has cleared the gun bore

12

(

FIG. 1

) all of the stored data in recorder

44

is read out at a second rate, for example 15 ksamples/sec, which is less than the record rate. This allows the in-bore data to be encoded, along with the in-flight data in PCM encoder

54

, and be transmitted by transmitter

46

, which has a limited bandwidth.

The encoded and transmitted in-bore, as well as in-flight data, is received by a ground station

70

where the data may be recorded and subsequently analyzed by known software programs for perfecting projectile design. Alternatively, the data may be used to correct any gun parameters, such as azimuth and elevation angles, for a subsequent launch.

In addition to, or as an alternative, the diagnostic system of the present invention may be used such as illustrated in

FIG. 5

, which duplicates the elements of

FIG. 4

, except for the transmitter arrangement. More particularly, the arrangement of

FIG. 5

is utilized for real-time flight control of the projectile, which would have a plurality of controllable surfaces.

In the embodiment of

FIG. 5

, the encoded data is provided to an on-board microprocessor

74

which analyzes the data and provides control signals to the in-flight guidance control circuit

76

. The guidance control circuit

76

is coupled to a plurality of flight control surfaces, such as moveable fins

78

, to modify the trajectory of the projectile, if necessary. Although not illustrated in

FIG. 5

, the apparatus may also include a GPS receiver for inputting navigational information to the microprocessor

74

.

FIG. 6

essentially duplicates the cross-sectional view of

FIG. 2

, however, with a reduced size battery indicated by numeral

24

′, within the battery cup

22

. The remainder of the battery cup

22

is occupied by a detonator device

80

operable to set off the main charge of the projectile to which the fuze-like container

60

is attached, via aperture

82

in the end of battery case

22

.

The detonator device

80

may be activated by impact with a target. Alternatively, and as indicated in

FIG. 7

, activation of the detonator may be accomplished by the on board microprocessor

74

, if provided, as in the embodiment of FIG.

5

.

FIGS. 8

to

12

, by way of example, illustrate measured data that has been recorded and processed, as a function of time, from an actual flight test of a 120 mm M831 tank training projectile and

FIGS. 13 and 14

show optical sensor data from an actual flight test of a 155 mm artillery projectile.

In

FIG. 8

, illustrating measured in-bore axial acceleration, time 0.0 is represented when the g-switch

58

closes and the set-back acceleration reaches a maximum approximately 2 ms later and thereafter tapers off until about 7 ms when it exits the gun and experiences set-forward acceleration.

In

FIG. 9

, illustrating measured in-bore radial acceleration, time 0.0 is represented when the g-switch

58

closes and the projectile is balloting as it travels down the bore until it exits the gun at about 7 ms.

In

FIG. 10

, illustrating the measured in-flight axial acceleration, time 0.0 is represented from when the fire pulse to initiate the propelling charge was activated. The acceleration is negative because it is experiencing drag forces. Large vibrations from unsteady rolling behavior peaking at about 2 s and a Mach number transition at about 5 s can be observed in the frequency content of the data.

In

FIG. 11

, magnetometer sensor data has been reduced to obtain the projectile's pitch angle relative to the Earth's magnetic field, Sigma-M.

In

FIG. 12

, the magnetometer data has been reduced to obtain the projectile roll rate relative to the Earth's magnetic field.

In

FIG. 13

, the optical sensor data has been reduced to obtain the projectile's roll rate relative to the sun's solar vector.

In

FIG. 14

, the optical sensor data has been reduced to solar pitch rate as a function of solar yaw rate for the entire trajectory.

It will be readily seen by one of ordinary skill in the art that the present invention fulfills all of the objects set forth herein. After reading the foregoing specification, one of ordinary skill in the art will be able to effect various changes, substitutions of equivalents and various other aspects of the present invention as broadly disclosed herein. It is therefore intended that the protection granted hereon be limited only by the definition contained in the appended claims and equivalents. Having thus shown and described what is at present considered to be the preferred embodiment of the present invention, it should be noted that the same has been made by way of illustration and not limitation. Accordingly, all modifications, alterations and changes coming within the spirit and scope of the present invention are herein meant to be included.