Aeronautics and astronautics – Missile stabilization or trajectory control – Stabilized by rotation
Reexamination Certificate
2001-06-12
2003-02-18
Gregory, Bernarr E. (Department: 3662)
Aeronautics and astronautics
Missile stabilization or trajectory control
Stabilized by rotation
C244S003100, C244S003150, C244S003190, C244S003240, C701S207000, C701S213000, C342S357490, C342S357490, C342S450000, C342S451000
Reexamination Certificate
active
06520448
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention pertains to the field of navigation and guidance of spinning vehicles and/or projectiles.
2. Description of the Prior Art
In many applications, such as artillery shell or missile guidance, the vehicle to be guided is spinning rapidly. Guidance systems integral to such spinning vehicles require significant real-time processing capacity. This is because all of the sensor inputs and guidance actuator controls must be corrected to account for the effects of the spinning body. Neutralizing these unwanted rotational artifacts can only be accomplished if the orientation of the spinning body can also be determined in real-time. Practically speaking, it is difficult to determine the rotational orientation of a spinning body. Gyros have traditionally been used to sense orientation. Use of gyros in these kinds of applications is problematic because the scale-factor errors exhibited by spin-axis gyroscopes result in significant cumulative attitude estimate error.
Other means for determining the attitude of a spinning vehicle have included the use of spinning accelerometers or strain sensors mounted on a spinning wheel. These prior art apparatus provide for the measurement of the vehicle's rotation-rate. Measurements utilizing spinning accelerometers are referred to as Coriolis rate measurements because of sinusoidal Coriolis acceleration artifacts they include. To remove these artifacts, the sensor signals must be demodulated. This normally involves a secondary sensor that indicates the rotational position of the spinning wheel relative to the body of the spinning vehicle. Such secondary rotational orientation sensors might include sun trackers or magnetic field sensors. These types of sensors may not be appropriate for every environment and they may not work well in certain geographic regions when the vehicle is aligned with the earth's magnetic field.
These obstacles have caused known guided-projectile technology to use mechanical de-spinning systems in order to isolate the guidance system from the spinning projectile. These mechanically de-spun projectiles are excessively expensive and notoriously unreliable. The de-spinning mechanism adds unwanted cost, size, and complexity. A cost-effective technique for determining a spinning vehicle's attitude in real time is desirable. Once this type of real-time attitude determination becomes available, it becomes possible to remove rotation artifacts from the guidance system.
SUMMARY OF THE INVENTION
As a vehicle spins during flight, any antenna mounted on the circumference will view signal sources with an apparent modulation of amplitude and phase. This phenomenon can be exploited to determine the attitude of a spinning vehicle relative to navigation source it uses for guidance. Once the attitude can be determined, then guidance control and any secondary sensors can be demodulated to remove rotational artifacts.
In the present invention, a method for determining the trajectory and the attitude of a spinning vehicle is specified. This method comprises the use of an antenna mounted on a spinning vehicle in a manner that enables the antenna to receives a navigation signal from a navigation source. The navigation source can comprise a NAVSTAR Global Positioning System (GPS) satellite, a satellite from a similar satellite navigation system (generically referred to as Global Navigation Satellite System GNSS) such as a Global'naya Navigatsionnaya Sputnikovaya Sistema (GLONASS) satellite, or it may be terrestrially deployed.
The method goes on to comprise a step for tracking the apparent modulation of the navigation signal. Either the amplitude of the signal, the phase of the signal or both the amplitude and phase of the navigation signal are tracked. The navigational signal is decoded in order to extract the position of the vehicle relative to the navigation source. The rotational position relative to the navigation source is then calculated from vectors that define the direction from the spinning vehicle to the navigation source.
The position information extracted from the navigation source is used to establish a trajectory for the spinning vehicle. Additionally, inertial sensors are used to anticipate high-speed maneuvers that could not ordinarily be tracked using the navigation sources alone. The trajectory is conformed to such anticipated variance from the navigational solution. Because the inertial sensors are spinning collectively with the vehicle, they must be demodulated to remove rotational artifacts to that Coriolis and lateral acceleration components can be utilized in the trajectory solution.
Receiving the radio signal comprises the steps of converting the radio frequency to a lower intermediate frequency. The intermediate frequency is digitized so that is can be processed digitally. During signal processing, rotational artifacts are removed from the signal using estimates of rotation rate and attitude. In one variant of the present invention, the rotational artifact is removed by amplifying the signal when the navigation source is in the field of view of the antenna and attenuating the signal when the navigation source is not plainly visible. In one alternative, the signal is tracked using three channels, one for a centered estimate of the roll angle, one for a retarded estimate of the roll angle and one channel for an advanced estimate of the roll angle.
Embodied in an apparatus, the present invention comprises an antenna that receives radio signals and a receiver that accepts the radio signals from the antenna. In operation, the antenna is mounted on a spinning vehicle so that a navigation signal can be received from a navigation source. The receiver selects the navigation signal from amongst all of the signals received by the antenna. The navigational signal can be generated by a GPS satellite, another GNSS satellite or a terrestrial source.
A tracking unit comprises a capability to track amplitude modulation, phase modulation or amplitude and phase modulation that is imparted onto the navigation signal as a result of the rotation of the spinning vehicle. This imparted modulation has also been previously referred to as apparent modulation. The present invention further comprises a decoding unit that extracts position information from the navigation signal and creates successive samples of the vehicles position.
A modulation geometry processor accepts the successive samples of vehicle position from the decoding unit and generates source vectors that define the direction from the spinning vehicle to the navigation source. The present invention further comprises an attitude estimator that calculates the rotational position of the vehicle relative to the navigation source based on the source vectors. The attitude estimator bases the calculated estimate on the amplitude modulation, the phase modulation or the amplitude and the phase modulation imparted onto the navigation signal, i.e. the apparent modulation. The actual position of the vehicle is maintained by a position estimator and is based on position information extracted from the navigation signal by the decoding unit and the source vectors calculated by the modulation geometry processor.
The present invention further comprises a guidance processor that maintains a trajectory for the spinning vehicle that is based on the position information extracted from the navigation signal. The position unit uses inertial sensor inputs to anticipate high-velocity maneuvers thereby conforming the navigation-source based trajectory to the vehicle's actual flight. The sensor inputs are demodulated by an inertial sensor demodulator that removes rotation artifacts by applying the estimated rotation position relative to the navigation source.
The receiver of the present invention comprises a radio frequency (RF) section that converts RF signals into an intermediate frequency (IF). The IF signal is then digitized by a digitizer and routed to a signal processor. The signal processor accepts the digital stream and remo
Doty James H.
McGraw Gary A.
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