Wavefront correction for aerodynamic and atmospheric effects on optical sensors on high-speed vehicles.

Abstract

A system and method for measuring and compensating for aero-optical and aero-thermal effects on a window / dome (102) of an EO / IR sensor on a supersonic vehicle. Range gating of the laser pulse measures and separates aerodynamic and atmospheric effects. Separate control algorithms and control loops with different update rates simplify the control algorithm and improve overall performance. Using a MEMS MMA (124) with tip / tilt / piston capabilities as a deformable mirror to provide wavefront correction improves overall performance. The compensated laser pulse can also be used to actively illuminate a target to provide both active and passive detection.

Description

[Technical Field]

[0001] (Reference to Related Application) This application claims the benefit of priority to U.S. Provisional Application No. 63 / 248,623, filed September 27, 2021, which claims the benefit of priority to U.S. Patent Application No. 17 / 725,872, filed April 21, 2022, the entire contents of each of which are incorporated by reference.

[0002] (Technical field) The present invention relates to an optical sensing system onboard a supersonic vehicle with a high-resolution electro-optical infrared (EO / IR) sensor, and more particularly to a system and method for sensing and correcting aerodynamic effects (optical and thermal) on or immediately in front of a vehicle window. The system can also be configured to measure and compensate for atmospheric effects such as turbulence between the vehicle and a target. [Background technology]

[0003] Air vehicles such as missiles, rockets, guided projectiles, drones, and manned aircraft use EO / IR sensors to detect, track, classify, and select aim points on targets. It is important that the target's actual location within the sensor's field of view (FOV) be very close to the target's location as detected by the EO / IR sensor. Certain in-flight conditions, such as aerodynamic effects on or immediately in front of the sensor's optically transparent window / dome, or atmospheric effects (e.g., turbulence) between the sensor and the target, can introduce errors in the target's location that affect system performance.

[0004] Aerodynamic effects include aero-optical and aero-thermal effects. Aero-optical effects are caused by variations in the refractive index due to differences in the temperature and pressure of the air surrounding the vehicle. This can be caused by air compression, turbulence from a thick boundary layer, physical distortion of the dome, shock waves, plasma, or atmospheric turbulence. These refractive index changes affect light passing through this air by creating phase differences across the wavefront, known as wavefront distortion, which broadens and distorts the light focused at the image plane. Wavefront distortion can also change the apparent angle of arrival of light entering the EO / IR sensor. Aero-thermal effects are caused by heating of the window / dome and optical system due to air compression caused by a vehicle operating at high speeds. When the window heats up, the refractive index changes and the window's shape becomes distorted. This affects light passing through the window and optical system by creating phase differences across the wavefront, broadening and distorting the light focused at the image plane. Wavefront distortion and shape distortion caused by window heating can also change the apparent angle of arrival of light entering the EO / IR sensor.

[0005] Most existing air vehicles do not fly fast enough (e.g., supersonic) or do not have EO / IR imaging systems with sufficient resolution that aerodynamic or atmospheric effects are not significant enough to require correction or to justify the cost, volume, and weight in the overall system design. Some high-speed systems use a look-up table (LUT) that is a function of vehicle speed to look up target data derived from captured images and apply corrections in software. The optical system is modeled to estimate aero-optical and aero-thermal effects as a function of speed. Software solutions do not significantly increase weight, volume, or cost. However, the actual conditions and flight path of the air vehicle may be more complex than can be represented by the model. This can degrade the quality of estimates of target state information, such as target position and target velocity. Ultimately, the LUT is a "model," not a measurement. The effects of optical wavefront distortion, which reduces sensor resolution, are typically not addressed when mounted on high-speed air vehicles and must be accommodated within the error budget of system performance. Summary of the Invention

[0006] The following is a summary of the invention to provide a basic understanding of some aspects of the invention. This summary is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description and claim definitions that are presented later.

[0007] The present invention provides a system and method for measuring and correcting aero-optical and aero-thermal effects on the windows / domes of EO / IR sensors on supersonic vehicles.

[0008] In one embodiment, an optical sensor for a supersonic flight vehicle, where an optical window to the sensor is subject to aero-optical and aero-thermal effects during flight, includes a pulsed laser that emits laser pulses through the optical window using a clock-referenced timing code; a clock-referenced wavefront sensor that detects returning laser pulses within a short time delay window to measure aero-optical and aero-thermal effects on or just before the optical window; an optical detector; an optical path that couples light received through the optical window to the optical detector; and a deformable mirror positioned in the optical path that responds to command signals that perform a piston-like movement orthogonal to the plane of the mirror to correct the wavefront of the received light for the measured aero-optical and aero-thermal effects.

[0009] In a different embodiment, the wavefront sensor detects the returning laser pulses within a long time delay window to measure atmospheric effects beyond the optical window, and the pulses for the long time delay window can be lengthened to improve the SNR.

[0010] The returned laser pulse within a long time delay window can be corrected and sensed by an optical detector to identify the target's location ("active imaging"). A first control algorithm and control loop measures aero-optical and aero-thermal effects and updates the deformable mirror at a slow update rate, while a second control algorithm and control loop measures atmospheric effects and updates the deformable mirror at a fast update rate. Separating the control algorithms and loops simplifies the algorithm and improves performance.

[0011] In different embodiments, the deformable mirror is one of: (a) a single mirror with a piston actuator; (b) multiple segmented mirrors with respective piston actuators; or (c) multiple segmented mirrors with respective tip, tilt, and piston actuators. In one configuration, the deformable mirror comprises a microelectromechanical system (MEMS) micromirror array (MMA) including multiple mirrors that independently respond to command signals to tip and tilt about a first axis and a second axis, respectively, and translate along a third axis with three degrees of freedom (3DOF) to piston the wavefront for wavefront correction. This device allows a translation range along the piston third axis of more than one wavelength at the wavelength of the laser or the central wavelength of the received light. This device allows tip and tilt to control local tilt to reduce aberrations.

[0012] In various embodiments, the deformable mirror is positioned at or near (as far as implementation within the sensor allows) the optical conjugate of the optical window (the source of wavefront distortion). Multiple deformable mirrors can be positioned near different optical conjugates of different sources of wavefront distortion. A first deformable mirror can be positioned at the pupil conjugate in the optical path, and a second deformable mirror can be positioned at the intermediate image conjugate.

[0013] In one embodiment, an optical sensor for a supersonic vehicle, in which an optical window to the sensor is subject to aero-optical and aero-thermal effects during flight, includes one or more optical detectors and an optical path that couples light from a target returned through the optical window to the optical detector. A laser emits laser energy to a beam combiner in the optical path that couples the laser energy and propagates in the optical path through the optical window. A wavefront sensor in the optical path detects the returned laser energy (split by a beam splitter) to measure aero-optical and aero-thermal effects on or just before the optical window. A deformable mirror, located in the optical path upstream of the wavefront sensor and laser, pistons perpendicular to the plane of the mirror in response to command signals to correct the wavefront of the emitted laser energy and to correct the wavefronts of the returned laser energy and the received passive light for the measured aero-optical and aero-thermal effects. The one or more optical detectors are configured to sense both the wavefront-corrected returned laser energy and the wavefront-corrected received passive light to form active and passive images of the target. In one configuration, the laser emits laser pulses with a timing code referenced to a clock, and the wavefront sensor detects the returning laser pulses referenced to the clock within a short time delay window to measure aero-optical and aero-thermal effects at and near the vehicle window. The laser emits pulses with a long time delay window to also measure atmospheric effects from the optical path beyond the vehicle window. In one configuration, gimbals are used to point the laser and optical path.

[0014] In one embodiment, an optical sensor for a supersonic vehicle, in which an optical window to the sensor is subject to aero-optical and aero-thermal effects during flight, includes an optical detector, an optical path that couples light received through the optical window to the optical detector, and a MEMS MMA disposed in the optical path. The MMA comprises multiple mirrors that independently respond to command signals to tip and tilt about a first axis, tilt about a second axis, and translate along a third axis with three degrees of freedom (3DOF) to pistonically move to correct the wavefront of the received light for the measured aero-optical and aero-thermal effects. The MMA allows a translation range along the third axis of the piston that exceeds one wavelength at the center wavelength of the received light. The MMA allows tip and tilt to control local tilt to reduce aberrations. The command signal to the MEMS MMA is provided by a CW or pulsed laser with (a) a velocity-indexed LUT and (b) a wavefront sensor that may or may not be integrated into the optical path to the detector and may be on- or off-vehicle.

[0015] These and other features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0016] [Figure 1] An optical sensor in which the transmitted beam is used as a source for wavefront measurement and correction, as well as for both active and passive detection. [Figure 2] FIG. 1 illustrates aerodynamic and atmospheric effects between a supersonic vehicle and a target. [Figure 3] FIG. 1 is a simplified optical schematic in which a laser beam is folded back into the optical path of a passive detector, the laser return is split to a wavefront sensor, and a deformable mirror is controlled to correct the wavefront of the active return or passive light for aerodynamic and atmospheric effects. [Figure 4]A pulsed laser is range-gated to separately measure the aerodynamic effects on or just before the window / dome and the atmospheric effects between the vehicle and the target. [Figure 5] In an embodiment, separate control algorithms and control loops are configured to update the deformable mirror corrections to account for slow aerodynamic effects and faster atmospheric effects, respectively. [Figure 6] FIG. 1A is a diagram of a known embodiment of a tip / tilt / piston (“TTP”) MEMS MMA; and FIG. 1B is a diagram of a known embodiment of a single mirror that operates to tip, tilt, and piston to scan and correct a laser beam. [Figure 7] FIG. 10 illustrates the use of a MEMS MMA piston to perform primary wavefront correction and tip / tilt to provide local tilt correction to reduce aberrations. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention provides a system and method for measuring and correcting aero-optical and aero-thermal effects on the window / dome of an EO / IR sensor on a supersonic vehicle. At flight speeds exceeding Mach 1 (supersonic speeds) and the high resolution of modern EO / IR sensors, the aerodynamic effects (aero-optical and aero-thermal effects) on the sensor window / dome become even more exacerbated and become more problematic for higher resolution sensors. Atmospheric effects beyond the window / dome to the target also have a significant impact on high resolution sensors.

[0018] 1 and 2, a supersonic vehicle 10, such as a missile, rocket, or projectile, is equipped with a gimbaled optical sensor 14. The gimbaled optical sensor shines a laser beam 16 toward a scene 18, which reflects the light to produce a laser return 20, which is collected by the sensor's telescope. Within the sensor's field of view (FOV) 22, passive radiation or visible reflection 24 is also collected by the sensor's telescope. The gimbal scans the laser beam 16 and sensor FOV 22 over a wider dynamic field of view 26 to detect targets 28. The laser beam, and therefore the return light, may be in the same band as the passive light or in a different band. For example, the passive light may span a portion of the near-infrared (NIR) band, while the laser beam occupies a very narrow band (a few nm) around a specific wavelength(s) in the NIR band. Alternatively, the passive light may span a portion of the NIR band, while the laser beam occupies a narrow band around a specific wavelength(s) in the visible band. Other combinations of in-band and out-of-band active and passive light also exist. The sensor may be configured to be insensitive to laser return.

[0019] The wavefront sensor detects the laser return 20 to measure aero-optical effects 30 and aero-thermal effects 32 on or just before the optical window / dome 34, and possibly atmospheric effects 36 (e.g., turbulence) beyond the window / dome to the target 28. A deformable mirror positioned in the optical path pistons perpendicular to the plane of the mirror in response to command signals to correct the wavefront of the received light for the measured aero-optical and aero-thermal effects, and possibly atmospheric effects.

[0020] In one configuration, a laser emits laser pulses with a timing code referenced to a clock, and a wavefront sensor detects returning laser pulses referenced to the clock within a short time delay window to measure aero-optical and aero-thermal effects, and within a long time delay window to measure atmospheric effects and form an active image. In one configuration, gimbals are used to point the laser and optical path.

[0021] In one configuration, the deformable mirror is a MEMS MMA that includes multiple mirrors that independently respond to command signals to tip and tilt about a first axis and a second axis, respectively, and to piston in translation along a third axis with three degrees of freedom (3DOF) to correct the wavefront of the received light for measured aero-optical and aero-thermal effects. The MMA allows for a translation range along the piston's third axis that exceeds one wavelength at the wavelength of the laser or the center wavelength of the received light. The MMA allows for tip and tilt control to reduce aberrations by controlling local tilt.

[0022] 3, 4, and 5, an embodiment of an optical sensor 100 for a supersonic vehicle, in which an optical window / dome 102 to the sensor is subject to aero-optical and aero-thermal effects during flight, includes one or more optical detectors 104 and an optical path 106 including multiple optical elements that couple light from a target returned through the optical window / dome 102 to the one or more optical detectors. The optical path is appropriately routed to point on a dynamic field of view (FOR) via a two-axis gimbal. Alternatively, pointing can be achieved by steering the vehicle. The optical path 106 includes a focusing element 103 located behind the optical window / dome 102, a field lens optical element 105, and optical elements 107 and 109 that relay the intermediate rear element 105 to the detector 104.

[0023] A pulsed laser 108 (UV, IR, visible) is coupled into the optical path via a beam combiner 112 and emits laser pulses 110 that are transmitted through an optical window / dome. The laser pulses contain a timing code referenced to a clock 114. A clock-referenced wavefront sensor 116 is positioned in the optical path relative to a beam splitter 118 to detect returning laser pulses within a short time delay window 120 to measure aero-optical and aero-thermal effects on or just before the optical window, and within a long time delay window 122 to measure atmospheric effects beyond the window / dome to the target. The short and long time delay windows correspond to shorter and longer round-trip times of the laser pulse 110, respectively, for range gating. A deformable mirror 124 is positioned in the optical path and pistons perpendicular to the plane of the mirror in response to command signals from a mirror controller 126 to correct the wavefront of the received light for the measured aero-optical and aero-thermal effects. For simplicity, the deformable mirror 124 is depicted in an unfolded optical layout. It functions as a folding mirror that can apply phase corrections to the wavefront by actively articulating the mirror or mirror elements. A processor 128 receives the wavefront measurements and calculates actuation command signals that are provided to the mirror controllers.

[0024] In various embodiments, the deformable mirror 124 is positioned at or near (as implementation within the sensor allows) the optical conjugate of the window (the source of wavefront distortion). Multiple deformable mirrors 124 can be positioned at or near different optical conjugates of different sources of wavefront distortion. A first deformable mirror can be positioned at the pupil conjugate in the optical path, and a second deformable mirror can be positioned at the intermediate image conjugate.

[0025] The returned laser pulses within a long time delay window can be corrected by a deformable mirror and sensed by an optical detector ("active imaging") to identify the target's location.

[0026] In one embodiment, a single-point measurement of the laser through the window / dome can be compared to a model based on the geometry, materials, temperature gradients, compression effects, etc. across the window / dome. For example, a model might describe linear heating of the window, with the area near the leading edge of the vehicle being hotter than the far edge. An analytical model can predict the heating of the window during high-speed flight given the angle of attack and atmospheric conditions. By directly measuring the wavefront through the window at a particular time, this can be compared to the model to determine what conditions create this wavefront (thermal fluctuations) through this portion of the window, and consequently predict the temperature and shape of the window elsewhere outside of the optical footprint on the window.

[0027] Referring now to FIG. 5 , a first control loop 140 receives short-time delay window measurements of aero-optical and aero-thermal effects (141), applies a control algorithm for aerodynamic effects at a slow update rate to calculate waveform conjugates (142), and updates command signals to actuate the deformable mirror at a slow update rate (143). A second control loop 145 receives long-time delay window measurements of atmospheric effects (146), applies a control algorithm for aerodynamic effects at a fast update rate to calculate waveform conjugates (147), and updates command signals to actuate the deformable mirror at a fast update rate (148). Separating the control algorithms and loops simplifies the algorithms and improves performance. One or both of the control algorithms may be, for example, a proportional-integral-derivative (PID) control loop algorithm.

[0028] The speed of the update rate refers to the relative change in wavefront distortion over time. When wavefront distortion affects the performance of an aircraft's EO / IR system, the changes occur over a variety of time scales. Aerodynamic heating of a window can occur over several seconds. Aerodynamic heating and deformation of the window surface results in a corresponding optical path difference that varies depending on the rate of heating and the rate of change of the sensor's field of view through the window. Other aberrations can change relatively quickly. Specifically, air in turbulent flows can have density and temperature fluctuations that change very rapidly depending on the flow velocity. It can be advantageous to have a relatively slow optical correction loop that responds to larger, slowly changing optical path distortions (e.g., aerodynamic effects) and a fast optical correction loop that responds to smaller, rapidly changing optical path distortions (e.g., atmospheric effects). This allows the time bandwidth and optical path difference dynamic range of correction components, such as deformable mirrors and MMAs, to be matched to the physical processes causing the optical distortions.

[0029] In different embodiments, the deformable mirror is one of: (a) a single mirror with a piston actuator; (b) multiple segmented mirrors with respective piston actuators; or (c) multiple segmented mirrors with respective tip, tilt, and piston actuators. In one configuration, the deformable mirror comprises a MEMS MMA including multiple mirrors that independently respond to command signals to tip and tilt about a first axis and a second axis, respectively, and piston along a third axis in three degrees of freedom (3DOF) to correct the wavefront of the received light for measured aero-optical and aero-thermal effects. This device allows a translation range along the piston third axis of more than one wavelength at the wavelength of the laser or the central wavelength of the received light. This device allows tip and tilt to control local tilt to reduce aberrations.

[0030] 6A-6B, an exemplary MEMS MMA 150 comprises multiple independently and continuously controllable mirrors 152 for redirecting light with 3 DOF. Each mirror is capable of at least "tip" (rotation about the X axis), "tilt" (rotation about the Y axis), and "piston" (translation along the Z axis perpendicular to the XY plane), where X, Y, and Z are orthogonal axes in three-dimensional space.

[0031] The MEMS MMA preferably has a tip and tilt range of at least -15° x +15°, a steering range of + / -30° x 30°, and a piston (translation) motion of at least + / -15 microns (at least 1 / 2 wavelength in either direction) at a rate of at least 1 KHz (<1 ms). Additionally, the MEMS MMA must have a sufficient number of mirrors, mirror size / resolution, fill factor, motion range, response time, response accuracy, and uniformity across the array.

[0032] One such MEMS MMA is described in U.S. Pat. No. 10,444,492, entitled "Flexure-Based, Tip-Tilt-Piston Actuation Micro-Array," which is incorporated herein by reference. As shown in FIGS. 1-3 of the '492 patent, this MEMS MMA uses flexures 154 to support each mirror 152 at three fulcrums (or vertices) of an equilateral triangle. The three different fulcrum pairs define three axes at 60 degrees to each other in the XY plane. Each mirror pivots about each axis to tip, tilt, and piston in XYZ space in response to actuators 156. This MEMS MMA is currently being commercialized by Bright Silicon Technology for "digitally controlling light."

[0033] 7, the mirrors 152 translate 158 perpendicular to the plane of the array to correct the wavefront 160 of the light (laser pulses or passively received light). The mirrors can also tip / tilt to provide local tilt to reduce aberrations resulting from discontinuities between adjacent mirrors.

[0034] While several illustrative embodiments of the present invention have been shown and described, numerous variations and alternative embodiments will occur to those skilled in the art. Such variations and alternative embodiments are contemplated and can be made without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. 1. An optical sensor for a supersonic flight vehicle, wherein an optical window to the optical sensor is subjected to aero-optical and aero-thermal influences during flight, the optical sensor comprising: The clock and a pulsed laser that emits laser pulses through the optical window using a timing code based on the clock; a wavefront sensor referenced to the clock that detects a returning laser pulse within a first time delay window set to a length suitable for measuring the aero-optical and aero-thermal effects on or immediately before the optical window; an optical detector; an optical path that couples light received through the optical window to the optical detector; a deformable mirror disposed in the optical path, the deformable mirror performing a pistonic movement orthogonal to the plane of the deformable mirror in response to a command signal to correct the wavefront of the received light for the measured aero-optical and aero-thermal effects. Optical sensor.

2. The optical sensor of claim 1 , wherein the wavefront sensor detects a returning laser pulse within a second time delay window set to a length suitable for measuring atmospheric effects beyond the optical window.

3. The optical sensor of claim 2 , wherein the pulsed laser is controlled to lengthen the laser pulse relative to the second time delay window.

4. The optical sensor of claim 2 , wherein the returned laser pulses within the second time delay window are corrected and sensed by the optical detector to identify the location of a target.

5. 10. The optical sensor of claim 1, wherein the deformable mirror is one of: (a) a single mirror with a piston actuator; (b) multiple segmented mirrors with respective piston actuators; or (c) multiple segmented mirrors with respective tip, tilt, and piston actuators.

6. the deformable mirror comprises a micro-electro-mechanical system (MEMS) micro-mirror array (MMA); the MMA comprises a plurality of mirrors that tip and tilt about a first axis and a second axis, respectively, and pistonically move in translation along a third axis in three degrees of freedom (3 DOF) in response to command signals to correct the wavefront; The optical sensor of claim 1 .

7. The optical sensor of claim 6 , wherein the range of translation of the piston along the third axis exceeds one wavelength of the pulsed laser or a central wavelength of the received light.

8. The optical sensor of claim 6 , wherein the mirror is tip and tilt to control local tilt and reduce aberrations.

9. The optical sensor of claim 1 , wherein the deformable mirror is positioned at or near an optical conjugate of the optical window.

10. The optical sensor of claim 1 , wherein the plurality of deformable mirrors are positioned at or near different optical conjugates of different sources of wavefront distortion.

11. The optical sensor of claim 1 , wherein a first deformable mirror is positioned at a pupil conjugate position and a second deformable mirror is positioned at an intermediate image conjugate position in the optical path.

12. a first control algorithm and control loop for measuring the aero-optical and aero-thermal effects and updating the deformable mirror at a slow update rate; a second control algorithm and control loop for measuring the atmospheric effects and updating the deformable mirror at a fast update rate; The optical sensor of claim 2 .

13. 1. An optical sensor for a supersonic flight vehicle, wherein an optical window to the optical sensor is subjected to aero-optical and aero-thermal influences during flight, the optical sensor comprising: one or more optical detectors; an optical path that couples light from the target returned through the optical window to the optical detector; a laser that emits laser energy; a beam combiner in the optical path that combines the laser energy to propagate in the optical path through the optical window; a beam splitter for splitting off a portion of the returning laser energy; a wavefront sensor configured to detect the portion of the returned laser energy to measure the aero-optical and aero-thermal effects on or immediately before the optical window; and a deformable mirror disposed in the optical path upstream of the wavefront sensor and the laser, the deformable mirror pistoning perpendicular to the plane of the deformable mirror in response to command signals to correct the wavefront of the emitted laser energy and to correct the wavefronts of the returned laser energy and received passive light for the measured aero-optical and aero-thermal effects; the one or more optical detectors are configured to sense both the wavefront corrected returned laser energy and the wavefront corrected received passive light to form active and passive images of the target. Optical sensor.

14. the laser emits laser pulses using a timing code based on a clock; the wavefront sensor detects return laser pulses referenced to the clock within a first time delay window set to a length suitable for measuring aero-optical and aero-thermal effects and within a second time delay window set to a length suitable for measuring atmospheric effects to form the active image; The optical sensor of claim 13.

15. 1. An optical sensor for a supersonic flight vehicle, wherein an optical window to the optical sensor is subjected to aero-optical and aero-thermal influences during flight, the optical sensor comprising: an optical detector; an optical path that couples light received through the optical window to the optical detector; a microelectromechanical system (MEMS) micromirror array (MMA) disposed in the optical path, the MMA comprising a plurality of mirrors that tip and tilt about a first axis and a second axis, respectively, and piston-likely translate along a third axis in three degrees of freedom (3 DOF) in response to command signals independently to correct the wavefront of the received light for aero-optical and aero-thermal effects measured by the optical detector; Optical sensor.

16. 16. The optical sensor of claim 15, wherein the range of translation of the piston along the third axis exceeds one wavelength at the center wavelength of the received light.

17. 16. The optical sensor of claim 15, wherein the mirror tip and tilt to control local tilt and reduce aberrations.

18. 16. The optical sensor of claim 15, wherein command signals to the MEMS MMA can be provided by (a) a look-up table (LUT) indexed by the speed of the hypersonic vehicle, or (b) a continuous wave (CW) or pulsed laser with a wavefront sensor either integrated in the optical path to the optical detector or not integrated in the optical path to the optical detector, the wavefront sensor being on the hypersonic vehicle or off the hypersonic vehicle.

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