Communications: directive radio wave systems and devices (e.g. – Return signal controls external device – Missile or spacecraft guidance
Reexamination Certificate
1998-08-14
2001-03-20
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls external device
Missile or spacecraft guidance
C342S084000, C342S085000, C342S097000, C342S114000, C342S119000
Reexamination Certificate
active
06204801
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to missile guidance systems. Specifically, the present invention relates systems for determining missile closing rate and relative range with respect to a target.
2. Description of the Related Art
Missiles are used in a variety of demanding applications ranging from explosives delivery to satellite launching applications. Such applications often require accurate target closing rate and closing distance information to make in-flight steering and arming adjustments.
Missile guidance algorithms depend on accurate closing distance, i.e., range, and closing rate information to accurately time the activation of missile arming procedures and to successfully direct a missile to its target. Poor or corrupted missile closing rate and/or range information may cause premature missile detonation or missile targeting error.
In active missile systems, a transmitter onboard the missile facilitates ranging, i.e., a determination of the distance between the missile and the target. By measuring the round trip signal travel time for a signal transmitted via the transmitter and reflected back from the target, a range estimate is obtained.
Semi-active systems utilize a stationary or semi-stationary transmitter or illumination source. Semi-active missile systems often rely on an initial estimate of the target position and in-flight kinematic measurements provided by an onboard missile accelerometer such as an inertial reference unit (IRU) to estimate range. These systems typically lack the ability to accurately determine range when a target is in motion. Range estimated in this way is often grossly inaccurate and can result in inefficient missile guidance, increased fuel consumption and miss-timed missile detonation. All of these characteristics tend to reduce missile effectiveness.
To facilitate the determination of missile position, missiles used in military applications often include an IRU for taking missile kinematic measurements. The IRU has a sensor that detects changes in missile inertia. The changes in inertia are then used to compute missile acceleration, velocity, and position. The current missile position and velocity are calculated with reference to an initial position and velocity, respectively. However, initialization error and IRU measurement error accumulate over the flight of a missile, severely degrading missile position and target closing rate estimates.
In semi-active missile systems that rely on IRU measurements, an initial range measurement is stored in an onboard missile guidance computer. Activation of arming procedures is determined via the initial range measurement. However, if a maneuvering target accelerates or decelerates after missile launch, error in the range information grows in direct proportion to the deceleration or acceleration. Error in the range information may result in premature missile detonation or targeting errors.
Hence, a need exists in the art for a system for facilitating accurate determination of missile range, that is immune to IRU initialization error, and that is applicable to semi-active missile systems. There is a further need for a system for facilitating accurate determination of range to a rapidly maneuvering or accelerating target.
SUMMARY OF THE INVENTION
The need in the art is addressed by the system for determining the range between a missile and a target of the present invention. In the illustrative embodiment, the inventive system is adapted for use with a semi-active missile system and includes a first circuit for generating a periodic signal that is periodically frequency modulated. A second circuit determines a closing rate at which the missile is approaching the target via the periodic signal. A third circuit determines a value containing information corresponding to the range and the closing rate via the periodic signal. A fourth circuit determines the range from the closing rate and the value.
In a specific embodiment, the first circuit includes an illumination system. The illumination system includes a periodically modulated carrier signal generator that generates the periodic signal. The periodically modulated carrier signal generator includes a frequency source, a frequency modulator, and an illumination system computer. The illumination system computer runs software for adjusting the modulation parameters of the frequency modulator.
The second, third, and fourth circuits are included in a receiver system onboard the missile. The receiver system includes a front receiver located near the front of the missile and a rear receiver located near the rear of the missile. The missile system further includes receiver system computer that runs software that implements the fourth circuit. The receiver system includes a local oscillator that provides a reference frequency to the receiver system. The local oscillator derives the reference frequency from the periodic signal provided by the first circuit. In illustrative embodiment, the fourth circuit runs computer software that subtracts the closing rate from the combination of closing rate and range and provides the range in response thereto.
The receiver system computer is connected to the rear receiver and the rear local oscillator. The rear receiver and the rear local oscillator are connected to a downconverter in the receiver system. A front receiver and the rear receiver provide input to the downconverter. The rear local oscillator provides a reference frequency to the downconverter and the downconverter outputs a downconverted signal in response thereto. A Fast Fourier Transform circuit receives the downconverted signal and outputs a processed signal in response thereto to the receiver system computer.
The illumination system has an illumination system computer connected to a frequency source and a frequency modulator. Outputs of the frequency source and the frequency modulator are input to a combiner, the output of which is connected to a transmitter. The illumination system computer runs software for controlling the frequency of the frequency source, and modulation parameters of the frequency modulator.
The novel design of the present invention is facilitated by the periodically modulated carrier signal provided by the periodically modulated carrier signal generator. The periodically modulated carrier signal allows software running on the receiver system computer to extract range information from a combination of range information and closing rate information. The receiver system computer extracts range information via the periodically modulated carrier signal during periods of no modulation of the periodically modulated carrier signal. Similarly, the receiver system computer extracts the combination of range and closing rate information during periods of modulation of the periodically modulated carrier signal. Software running on the receiver system computer can then easily extract range information from the combination of range and closing rate information by subtracting off closing rate.
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Meltzer Harvey J.
Sharka David
Collins David W.
Lenzen, Jr. Glenn H.
Raytheon Company
Sotomayor John B.
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