Patent Description:
Some aircraft have a gimbaled optical sensor system. The optical sensor system may be used to detect target objects that are located great distances from the aircraft. For example, the optical sensor systems detect target objects that are below the aircraft while the aircraft is in flight.

The optical sensor systems often include an optical sensor and a telescope optical assembly to magnify the light received by the optical sensor to allow the optical sensor to capture images of the target object at great distances. However, during flight of the aircraft the telescope optical assembly and the optical sensor are subjected to random vibration causing optical elements to move relative to one another, resulting in image jitter, which can reduce image quality of full motion video or still images.

Typically, very stiff materials (such as beryllium or silicon carbide) are utilized to build the telescope optical assemblies to increase image quality by limiting optics and telescope deformation which assists in mitigating the jitter. These materials tend to be expensive, which adds to the overall cost of the optical sensor system. Additionally under large enough vibration input levels material stiffness alone will not provide the required optical system stability and image quality will be impacted regardless of cost and complexity in telescope design.

<CIT> discloses a system for stabilizing an optical line of sight. An optical system including primary optics and relay optics includes a jitter rejection mirror located within the path of the relay optics. An auto alignment system is provided for maintaining alignment of the jitter rejection mirror in response to a control signal. An auto alignment sensor detects jitter in a reference beam passing through the jitter rejection mirror, and the generated control signal is used to reduce the jitter. The reference beam is supplied by a stabilized source of laser signals which are received by the primary optics, and relayed to the jitter rejection mirror.

<CIT> discloses a method and apparatus for stabilizing a line of sight of a radiant energy system. The line of sight of a main beam is positioned using a first reflector and a second reflector based on a reference beam that is inertially stabilized in a selected direction. The line of sight of the main beam is stabilized using the reference beam to counteract a number of disturbances created within an optical path of the main beam.

<CIT> discloses a line-of-sight corrector using piezo-electric crystals as actuators for the inertial platform stabilized tracking telescope of an astro navigational system. The tracking telescope includes a folded-type optical system, and the corrector is used to impart movement to the secondary mirror in the folded optical system to compensate for residual angular movements of the telescope which would otherwise perturb the image focused on the vidicon or solid state sensor in the telescope.

The present invention provides a light sensor system including a collimated reference light source that moves in unison with a primary mirror and/or an inertial measurement device, and/or the reference light source is directed toward an obscured region of the light sensor system. The reference light source may allow for improved jitter compensation based on feedback of the reference light. The feedback may be representative of the elastic deformation of the optics and telescope optical axis. The improved jitter compensation may allow for the light sensor system (e.g., the housing and/or mirrors) to be built with less stiff materials, which can reduce the cost of manufacturing the present light sensor system compared to previously known optical sensor systems. In cases of high vibration levels which would otherwise degrade the resulting image quality after material stiffness property selections have been exhausted, the light sensor system may provide jitter compensation to improve video or still image quality.

Directing the reference light source toward the obscured region allows the light sensor system to avoid or reduce any negative impact the reference light source or its associated components may have on the quality of the primary light detected. For example, the reference light source and/or a retroreflector may be arranged in the obscured region so that a minimal additional portion of the primary light, if any, is blocked from reaching the primary light sensor, compared to previously known optical sensor systems.

The light sensor system may include a primary mirror that directs the reference light from the primary mirror along a path of the primary light through the light sensor system to the reference light sensor. The reference light sensor may be able to detect structural movement of the primary mirror and/or other light reflectors that reflect the primary light and the reference light. At least part of the light sensor system may be adjusted based on the reference light directed to the reference light sensor. The adjustment allows correction of components of the light sensor system to compensate for jitter and increase the quality of the primary light received by the primary light sensor.

The adjustable light component (e.g., an adjustable light reflector, such as a fast steering mirror, or an adjustable light refractor, such as a Risley prism assembly) that receives the primary light may be adjusted based on the feedback of the reference light. For example, the adjustable light reflector may be adjusted based on the position and/or movement of the reference light to account for jitter in the light system.

The inertial sensor and the reference light source may be fixed relative to one another to accurately determine the non-inertial motion of the reference light source caused by relative deflections between optical components and the primary mirror. For example, the inertial sensor and/or the reference light source may be fixed in the obscured region to the same inertial sensor mount.

The term "light" is used herein to refer to visible light and invisible light. For example, the term light may be used herein to refer to radio waves, infrared waves, ultraviolet waves, electromagnetic waves having wavelengths anywhere from <NUM> nanometers (nm) to <NUM>, and/or X-rays.

The term "jitter" is used herein to refer to undesirable motion of the optical axis of the imaging system that occurs during a single frame integration time, which results in blurring the image.

According to one aspect, the present disclosure provides a light sensor system including a housing; a primary mirror with a reflective side facing in a first direction to receive a primary light along a central axis of the primary mirror from a target object, wherein the primary mirror is disposed within the housing; a plurality of light reflectors, at least one of the plurality of light reflectors arranged to receive the primary light directly from the primary mirror, wherein each of the plurality of light reflectors is arranged in a path of the primary light such that each of the plurality of light reflectors receives and reflects the primary light, an inertial sensor mount that is fixed to the primary mirror, a reference light source having an output directed along the first direction, the reference light source attached to the inertial sensor mount, whereby the reference light source moves due to vibration of the primary mirror, and movable with the inertial sensor mount such that, when the inertial sensor mount moves, the output of the reference light source moves with the inertial sensor mount, and, when the primary mirror moves, the output of the reference light source moves with the primary mirror.

The features of the different aspects may be independently combined with one another or utilized separately. Thus, a light sensor system according to the present invention may include all of, any one of, or any combination of the reference light source that moves with the primary mirror, and the output of the reference light source that is directed toward the portion of the obscured region.

The foregoing and other features of the invention are hereinafter described in greater detail with reference to the accompanying drawings.

The principles of this present application have particular application to reducing the effects of jitter for aircraft light sensor systems, for example electro-optical/infrared turret systems that have a Three Mirror Anastigmat (TMA) form telescope to magnify the image of a target object, and thus will be described below chiefly in this context. It will be appreciated that principles of this invention may be applicable to other light sensor systems where it is desirable to reduce the effects of jitter, such as other telescope forms.

Referring now to the drawings and initially to <FIG>, an exemplary aircraft is designated generally by reference numeral <NUM>. The aircraft <NUM> can be provided with an exemplary light sensor system <NUM>. The light sensor system <NUM> may capture images of primary light received from a target object, such as an infrared heat signature of a vehicle thousands of feet below the aircraft <NUM>. In an embodiment, the aircraft is another type of vehicle, such as a ground operated vehicle.

The light sensor system <NUM> may include any or all of the components of the sensor system disclosed in <CIT>.

<FIG> illustrates a front view of the light sensor system <NUM> that may include a housing (e.g., a coarse pointing structure <NUM>), a primary mirror <NUM> (e.g., a parabolic primary mirror of a TMA telescope) disposed within the coarse pointing structure <NUM>, multiple light obstructions, and a reference light reflector (e.g., retroreflectors <NUM>-<NUM> that are shown in dashed lines hidden beyond the light obstructions). Referring briefly to <FIG>, an optical bench <NUM> (shown schematically) may fixedly attach the primary mirror <NUM> and the light obstructions to an inner gimbal assembly <NUM> (shown schematically) that movably attaches the optical bench <NUM> to the coarse pointing structure <NUM>.

Referring again to <FIG>, the light obstructions may form an obscured region <NUM> of the light sensor system <NUM> between the primary mirror <NUM> and the target object where the primary light from the target object is not able to pass through to reach a reflective side <NUM> of the primary mirror <NUM>. The light obstructions may be formed by a secondary mirror <NUM> (e.g., a hyperbolic secondary mirror of a TMA telescope) and/or multiple support arms <NUM> that extend radially outwardly from the secondary mirror <NUM> to attach the secondary mirror <NUM> to the inner gimbal assembly <NUM> (shown schematically in <FIG>) through the optical bench <NUM>. For example, the secondary mirror <NUM> may form a centrally-obscured region <NUM> of the obscured region <NUM> and/or the support arms <NUM> may form an obscured-spider-support region <NUM> of the obscured region <NUM>. A portion of the retroreflectors <NUM>-<NUM> may be in the obscured-spider-support region <NUM> (shown best in <FIG>).

The optical bench <NUM>, the inner gimbal assembly <NUM>, the coarse pointing structure <NUM>, and/or the support arms <NUM> may be made of a material with a stiffness of <NUM>,<NUM>,<NUM> pounds per square inch (psi), such as aluminum. Aluminum and other materials with a similar stiffness may be easier and less expensive to machine compared to high stiffness materials often utilized in previously known optical sensor systems. In an embodiment, the optical bench, the inner gimbal assembly, the coarse pointing structure, and/or the support arms may be made of a material with a stiffness of <NUM>,<NUM>,<NUM> psi or less. In another embodiment, the optical bench, the inner gimbal assembly, the coarse pointing structure, and/or the support arms may be made of a material with a stiffness of <NUM>,<NUM>,<NUM> psi or greater.

Turning to <FIG>, the light sensor system <NUM> may include a gimbal system <NUM> and may include a plurality of light reflectors that receive the primary light (e.g., the secondary mirror <NUM> and/or primary light reflectors <NUM>-<NUM>), a reference light source <NUM>, an inertial sensor <NUM> (e.g., a pair of fiber optic gyroscopes) attached to the primary mirror <NUM>, a reference light sensor <NUM> (e.g., a duo lateral photodiode or quad detector), and a primary light sensor <NUM> that receives the primary light.

The reflective side <NUM> of the primary mirror <NUM> faces in a first direction D<NUM> to receive the primary light along a central axis A of the primary mirror <NUM> from the target object. The reference light source <NUM> may be axially offset from the reflective side <NUM> along the central axis A in a second direction D<NUM> that is opposite the first direction D<NUM>. For example, the reference light source <NUM> may have an output <NUM> that is directed toward the retroreflector <NUM>, and that is offset from the reflective side <NUM> in the second direction D<NUM>. Offsetting the reference light source <NUM> behind the primary mirror <NUM> may minimize if not eliminate any reduction of primary light that is received by the reflective side <NUM>, compared to another embodiment where reference light source <NUM> is arranged between the reflective side <NUM> and the target object.

The output <NUM> may be arranged in the obscured-spider-support region <NUM>. Arranging the output <NUM> in the obscured-spider-support region <NUM> allows the retroreflector <NUM> to be arranged entirely in the obscured-spider-support region <NUM>, as shown in <FIG>. In an embodiment, the retroreflector is arranged at least partially in the obscured-spider-support region.

The retroreflector <NUM> may face in the second direction D<NUM> toward the reflective side <NUM> of the primary mirror <NUM>. The retroreflector <NUM> may include a reflective portion <NUM>, which may be arranged in the obscured-spider-support region <NUM> and oriented to receive the reference light from the output <NUM> of the reference light source <NUM>. The reflective portion <NUM> may be oriented to output the reference light toward the reflective side <NUM> of the primary mirror <NUM> prior to the reference light reaching any of the secondary mirror <NUM> and the primary light reflectors <NUM>-<NUM>. The reflective portion <NUM> may be configured to output the reference light parallel and laterally offset to the path of the input of the reference light. In an embodiment, the entire reflective portion is in the obscured region. In another embodiment, only a portion of the reflective portion is in the obscured region.

Arranging the reflective portion <NUM> in the obscured region <NUM> allows the retroreflector <NUM> to minimize if not eliminate the amount of primary light blocked by the retroreflector <NUM> compared to another embodiment where the reflective portion <NUM> is arranged partially or entirely outside of the obscured region <NUM>. For example, most of the retroreflector <NUM> is in the obscured region <NUM> (shown best in <FIG>) so that at most only part of the retroreflector <NUM> blocks primary light from reaching the reflective side <NUM>. In an embodiment, the retroreflector is entirely within the obscured region. In another embodiment, the retroreflector is mostly if not entirely outside of the obscured region.

Still referring to <FIG>, the light reflectors <NUM>-<NUM> that receive the primary light may be each arranged in a path of the primary light such that each of the light reflectors <NUM>-<NUM> receives and reflects the primary light. Each of the light reflectors <NUM>-<NUM> may be at least partially attached to the optical bench <NUM> so that each light reflector <NUM>-<NUM> at least partially moves with the optical bench <NUM>.

The secondary mirror <NUM> may be arranged to receive the primary light directly from the primary mirror <NUM>. For example, the primary light reflected by the reflective side <NUM> of the primary mirror <NUM> does not need to reflect off of another reflector before reaching the secondary mirror <NUM>.

The support arms <NUM> hold the secondary mirror <NUM> offset from the primary mirror <NUM> along the central axis A. For example, the support arms <NUM> are able to hold the secondary mirror <NUM> coaxially with the central axis A.

The primary light sensor <NUM> may be arranged to receive the primary light from the light reflectors <NUM>-<NUM>. The plurality of light reflectors <NUM>-<NUM> and the primary mirror <NUM> may be oriented such that the primary light is directed from the primary mirror <NUM> to the plurality of light reflectors <NUM>-<NUM>, and from the plurality of light reflectors <NUM>-<NUM> to the primary light sensor <NUM>. For example, a light control system <NUM> may receive the primary light and adjust the primary light to compensate for jitter before outputting the primary light to the primary light sensor <NUM>.

The light control system <NUM> may include an adjustable light component (e.g., the adjustable light reflector <NUM>), a beam splitter <NUM>, the reference light sensor <NUM>, a reference light filter <NUM> (e.g., a lens with a <NUM> or <NUM> nanometer (nm) notch filter) and control circuitry <NUM> (e.g., a processor and/or memory with programmed instructions). The beam splitter <NUM>, the reference light sensor <NUM>, and the reference light filter <NUM> may be fixedly attached to the optical bench <NUM>. In an embodiment, the adjustable light component is an adjustable light refractor, such as a Risley prism assembly.

Still referring to <FIG>, the control circuitry <NUM> is connected via information lines (e.g., electrical communication lines, shown as dashed lines) to the primary light reflector <NUM>, the adjustable light reflector <NUM>, the inertial sensor <NUM>, and to the reference light sensor <NUM>. The adjustable light reflector <NUM> is able to compensate for jitter based on gimbal compensation, acceleration and/or movement detected by the inertial sensor <NUM>, and/or detection of the reference light by the reference light sensor <NUM> (as shown best in the control system diagram of <FIG>).

For example, the control circuity <NUM> may instruct the adjustable light reflector <NUM> to compensate for jitter based on the detection of the reference light by the reference light sensor <NUM>. The reference light sensor <NUM> may output a digital signal based on the position or positions of the sensed reference lights, as explained further below with reference to <FIG>. In an embodiment, the reference light sensor outputs an analog voltage based on the position or positions of the sensed reference lights.

The control circuitry <NUM> may adjust the optical power of the reference light emitted by the reference light source <NUM> based on the optical power of the reference light sensed by the reference light sensor <NUM>. Adjusting the optical power allows the control circuity <NUM> to maintain a constant optical power of the reference light reaching the reference light sensor <NUM>. Maintaining constant optical power allows consistent noise performance. In an embodiment, the control circuitry adjusts the optical power of each reference light together or individually.

The beam splitter <NUM> may be arranged after the light reflector <NUM> to separate the reference light and the primary light. The beam splitter may have a relatively high reflective property for the reference light frequency to reflect the reference light toward the reference light sensor <NUM>. The beam splitter <NUM> may have a relatively low reflective property for the primary light frequency to allow the primary light to pass through to reach the primary light sensor <NUM>. For example, the beam splitter <NUM> may reflect light in the ultraviolet range and allow light in the visible range to pass through.

The light sensor system <NUM> may further include focus lenses <NUM> (e.g., electro-optical focus lenses), a primary light reflector <NUM>, and/or a primary light reflector <NUM>. The light control system <NUM> may direct the primary light to the primary light sensor <NUM> via the focus lenses <NUM>, the primary light reflector <NUM>, and/or the primary light reflector <NUM>.

The primary light sensor <NUM> may be any one of or multiple of a short wavelength infrared sensor, a jitter camera, a color digital television sensor, a wave front error sensor, and/or a monochrome low noise visible to near infrared sensor. In an embodiment, the light sensor system includes a light switch to select between the primary light sensor and another light sensor. For example, the light switch may be the five-position switch disclosed in <CIT>.

The gimbal system <NUM> may allow movement in multiple directions while allowing primary light in through a window <NUM> that blocks light with a wavelength that is detectable by the reference light sensor <NUM> (e.g., solar radiation), and allows the primary light to pass through. For example, the reference light sensor <NUM> may detect wavelengths anywhere from <NUM> to <NUM> and the window <NUM> may have a coating that blocks <NUM>% of <NUM> or shorter wavelengths.

The gimbal system <NUM> may include an azimuth base <NUM> attached to a housing of the vehicle <NUM> (shown in <FIG>), an azimuth yoke <NUM>, a coarse elevation gimbal <NUM>, and the inner gimbal assembly <NUM> (e.g., a fine elevation gimbal <NUM> and a cross elevation gimbal <NUM>), each of which are configured to coordinate pointing of the primary mirror <NUM> at the target object to be imaged.

Referring now to <FIG>, the reference light source <NUM> may be attached to the primary mirror <NUM> such that, when the primary mirror <NUM> moves, the output <NUM> moves with the primary mirror <NUM>. For example, the reference light source <NUM> may be attached to an inertial sensor mount <NUM> that is fixed to the primary mirror <NUM>. The reference light source <NUM> may be movable with the inertial sensor mount <NUM> such that, when the inertial sensor mount <NUM> moves, the output <NUM> of the reference light source <NUM> moves with the inertial sensor mount <NUM>.

Attaching the output <NUM> to move with the primary mirror <NUM> allows the reference light to move when the primary mirror <NUM> and/or the inertial sensor <NUM> moves.

The inertial sensor <NUM> may be fixed to the inertial sensor mount <NUM> such that, when the output <NUM> of the reference light source <NUM> moves, the inertial sensor <NUM> would be moved with the output <NUM>. For example, when the reference light source <NUM> moves due to vibration of the primary mirror <NUM> the inertial sensor <NUM> moves with the output <NUM>.

The light sensor system <NUM> may include at least a second reference light source <NUM> with a corresponding output <NUM>. For example, when the outputs <NUM> and <NUM> of the reference light sources <NUM> and <NUM> move the inertial sensor <NUM> would be moved with the outputs <NUM> and <NUM>.

The output <NUM> of the reference light source <NUM> may be arranged opposite the output <NUM> of the reference light source <NUM> relative to the central axis A. For example, the respective output <NUM> or <NUM> of the reference light source <NUM> and the reference light source <NUM> may be diametrically opposite one another relative to the central axis A (i.e., spaced circumferentially apart <NUM>° from one another relative to the central axis A).

The reference light sources <NUM> and <NUM> may be collimated light sources. The reference light sources <NUM> and <NUM> may include a collimator <NUM>, a prism assembly <NUM>, and a fold prism <NUM> that are mounted to the inertial sensor mount <NUM>. The collimator <NUM> may be attached to the inertial sensor mount <NUM> such that, when the primary mirror <NUM> moves, an output <NUM> of the collimator <NUM> moves with the primary mirror <NUM>.

Still referring to <FIG>, a reference light generator <NUM> (e.g., a light emitting diode (LED) such as a violet LED) may have an output that is optically connected to the corresponding collimator <NUM>. For example, a fiber optic cable directs light generated by one of the reference light generators <NUM> to the corresponding collimator <NUM>. The collimator <NUM> is able to collimate the light generated by the corresponding reference light generator <NUM> into parallel or substantially parallel rays to form the reference light that is output by the output of the fold prism <NUM>. For example, the output of the fold prism <NUM> may be aligned with a through hole <NUM> (shown best in <FIG>) formed in the inertial sensor mount <NUM>. The fold prism <NUM> may be aligned with the corresponding retroreflector <NUM> (shown best in <FIG>).

The prism assembly <NUM> may be attached to the inertial sensor mount <NUM> such that, when the primary mirror <NUM> moves, the prism assembly <NUM> moves with the primary mirror <NUM>. The prism assembly <NUM> may include a pair of Risley prism pairs <NUM> and spur gears <NUM> that are coupled to each prism of the Risley prism pairs <NUM> to adjust each prism <NUM>. The spur gears <NUM> may be configured to adjust the alignment of the prisms <NUM>.

In an embodiment, the two reference light sources include a single laser diode and a <NUM>:<NUM> fiber splitter. In another embodiment, more than two reference light sources are utilized. Each reference light source may be collimated. For example, each reference light source may be identical to one another. Each corresponding output may be equally spaced from the central axis and/or arranged equally spaced circumferentially apart from one another.

The inertial sensor mount <NUM> may be fixed to the primary mirror <NUM> such that the inertial sensor mount <NUM> moves with the primary mirror <NUM>. The inertial sensor mount <NUM> may be made of a material with a stiffness of <NUM>,<NUM>,<NUM> psi, such as aluminum, to keep the inertial sensor mount <NUM> fixed to the primary mirror <NUM>. In an embodiment, inertial sensor mount may be made of a material with a stiffness of <NUM>,<NUM>,<NUM> psi or less. In another embodiment, inertial sensor mount may be made of a material with a stiffness of <NUM>,<NUM>,<NUM> psi or greater.

<FIG> illustrates a cross-section of the light sensor system <NUM>. Each reference light source <NUM> and <NUM> may be arranged in the obscured region <NUM>. For example, the output <NUM> of the reference light source <NUM> may be directed toward a portion of the obscured region <NUM> such that, when the output <NUM> provides the reference light, the reference light would pass through the portion of the obscured region <NUM>. The output <NUM> and <NUM> of each reference light source <NUM> and <NUM> may be directed along the first direction D<NUM> toward the corresponding retroreflector <NUM> or <NUM>.

The output of the fold prism <NUM> may form the output <NUM> of the reference light source <NUM>. In an embodiment, the output of the reference light source may be formed by another component of the reference light source, such as a Risley prism or an output of the collimator. For example, at least one Risley prism pair may be attached to the inertial sensor mount and configured to form the output of the reference light source that outputs the reference light to the corresponding retroreflector. It should be appreciated that the output <NUM> of the reference light source <NUM> may be similarly formed.

Referring still to <FIG> and later to <FIG>, the reference light from each reference light source <NUM> and <NUM> may be directed to the light reflectors <NUM> and <NUM> along the path of the primary light (shown best in <FIG>). For example, each reference light travels through an opening <NUM> of the primary mirror <NUM> and the hole <NUM> prior to reaching the corresponding retroreflector <NUM> or <NUM>, or any of the primary light reflectors <NUM> or <NUM>-<NUM> (shown in <FIG>). The reference lights travel from the corresponding reference light source <NUM> or <NUM> through the obscured region <NUM> to the correspondence retroreflector <NUM> or <NUM>. Each retroreflector <NUM> or <NUM> redirects the corresponding reference light along the path of the primary light.

Referring now to <FIG>, for example, the retroreflector <NUM> redirects the corresponding reference light toward the primary mirror <NUM> parallel to the incoming primary light (e.g., parallel to the central axis A). The reference light may be laterally offset from the incoming primary light.

The reference light may impinge the primary mirror <NUM> and the primary mirror <NUM> may reflect the reference light toward the secondary mirror <NUM>. For example, the reference light impinges an obscured portion <NUM> (shown best in <FIG>) of the primary mirror <NUM> and is reflected to the secondary mirror <NUM>.

The reference light may continue to follow the path of the primary light. For example, the reference light may reflect off the secondary mirror <NUM> to the primary light reflector <NUM>, from the primary light reflector <NUM> to the primary light reflector <NUM>, from the primary light reflector <NUM> to the primary light reflector <NUM>, from the primary light reflector <NUM> to the primary light reflector <NUM>, and from the primary light reflector <NUM> and the remaining primary light reflectors <NUM> and <NUM> (shown in <FIG>) to the reference light sensor <NUM> of the light control system <NUM>.

Referring again to <FIG>, as discussed above, the reference light may be directed to from the light reflectors <NUM>-<NUM> to the reference light sensor <NUM>. The reference light may reflect off the primary light reflector <NUM> toward the primary light reflector <NUM>, from the primary light reflector <NUM> to the primary light reflector <NUM>, from the primary light reflector <NUM> to the beam splitter <NUM>, and from the beam splitter <NUM> to the reference light sensor <NUM> through the reference light filter <NUM>.

The reference light sensor <NUM> may detect the reference lights after the reference lights reflect off each light reflector <NUM>-<NUM>. The reference light sensor <NUM> may be able to detect displacement of the reference lights that is due to structural dynamics of the primary mirror <NUM> and any of the light reflectors <NUM> and/or <NUM>-<NUM>.

For example, the reference sensor <NUM> may detect the position, movement, and/or angle of the reference light (e.g., azimuth and elevation motion of the primary light sensor <NUM>). The position, movement, and/or angle of the reference light may be based the structural movement information of the primary mirror <NUM> and/or the light reflectors <NUM>-<NUM>. Accordingly, the primary light reflector <NUM> can compensate for jitter based on the detected reference light.

The adjustable light reflector <NUM> may be adjusted in accordance with the control system described below. For example, the adjustable light reflector <NUM> and/or another adjustable light reflector (e.g., primary light reflector <NUM>) are adjusted based on the reference light to compensate for jitter of the light sensor system <NUM>. The adjustable light reflector <NUM> may be adjustable based on the structural movement information of each reference light relative to the other. In an embodiment, one or more of the adjustable light reflectors is adjustable based on the structural movement information of a reference light independent of any other reference light.

The reference light source <NUM> may provide the reference light at a frequency that is offset from the electromagnetic frequency range of the corresponding primary light sensor <NUM>. For example, the primary light sensor <NUM> may be able to detect light within the infrared range and the reference light source <NUM> may provide the reference light within the ultraviolet light range such that the primary light sensor is unable to detect the reference light.

Referring now to <FIG> and <FIG>, the reference light filter <NUM> of the light sensor system <NUM> may include a light mask <NUM> before the reference light sensor <NUM> to any light that is not near the position of the reference light (e.g., to block solar radiation) from reaching the reference light sensor <NUM>. As shown in <FIG>, when there is no jitter, each reference light may be directed to the same position on the reference light sensor <NUM>. When jitter is present, both reference lights may both be directed to a second position on the reference light sensor <NUM>. If the primary mirror <NUM> (shown in <FIG>) is elastically deformed due to the jitter, the primary mirror <NUM> may cause the reference lights to be directed to different positions on the reference light sensor <NUM>.

In an embodiment, the position of each sensed reference light is output separately. The reference lights may be turned on and off in an alternating fashion (i.e., time modulated) so that the output digital signal is specific to the reference light that is on when the digital signal is output. Detecting the position of each reference light individually allows the reference light sensor to detect the elastic deformation of the primary mirror based on relative movement of each reference light output by the corresponding reference light source. For example, more than two reference lights may be time modulated so that only one reference light is on at any given time to allow the reference light sensor to detect the deformation of the primary mirror.

The light mask <NUM> may include a fused silica lens. The light mask <NUM> is able to reduce solar radiation before the reference light reaches the reference light sensor <NUM>.

Referring now to <FIG>, the light mask <NUM> may include a masking portion <NUM> that blocks solar radiation and a reference light through path <NUM> that allows the reference lights to pass through to reach the reference light sensor <NUM> (shown in <FIG>). The reference light through path <NUM> may be aligned with the reference lights to allow the reference lights to pass through the light mask <NUM> to the reference light sensor <NUM> (shown in <FIG>). For example, the nominal position of each reference light is illustrated as a corresponding circle within the reference light through path <NUM>.

<FIG> illustrates a control system diagram of the light sensor system <NUM> (shown in <FIG>). The control circuitry <NUM> (shown in <FIG>) and/or other circuitry (e.g., a processor and/or memory with programmed instructions) may be configured to perform any portion of or all of the summation, subtraction, or integration functions of the control system diagram. For example, the control circuitry <NUM> may receive sensor data from each sensor described above and perform the summation, subtraction, and integration functions of the control system diagram.

As illustrated in <FIG>, a subtractor <NUM> may receive a reference light sensor command (Reference Sensorcmd) (e.g., integrated rate error motion) and a reference light sensor feedback (Reference Sensorfb) that is based on the position detected by the reference light sensor <NUM> (e.g., based on a motion of the reference light). The subtractor <NUM> may subtract the reference light sensor feedback from the reference light sensor command and the result may be input into a reference light sensor compensator <NUM> to account for jitter detected by the reference light sensor <NUM>.

A subtractor <NUM> may receive an image motion compensator angle command (e.g., an Adjustable Reflector Anglecmd) that is output from the reference light sensor compensator <NUM>, and may receive an angle feedback of the adjustable reflector <NUM> (e.g., an Adjustable Reflectorfb) based on an amount of motion of the adjustable light reflector <NUM> (shown in <FIG>). The subtractor <NUM> may subtract the Adjustable Reflectorfb from the Adjustable Reflector Anglecmd. The result may be input into an image motion compensator (e.g., an adjustable reflector compensator <NUM>), the output of which may be provided to the adjustable light reflector <NUM>.

The adjustable light reflector <NUM> may cause an image motion compensator output motion (e.g., an angle change of the reference light caused by the adjustable reflector θAR). The angle change of the reference light caused by the adjustable reflector θAR may be summed by an adder <NUM> with a jitter motion θJITTER that is based on disturbance introduced to the light sensor system <NUM> (shown in <FIG>) (e.g., disturbance based on the structural dynamics of the light sensor system <NUM> and vibration of the aircraft <NUM> (shown in <FIG>)). The resulting output is the motion of the reference light (e.g., an angle of the reference light θRL relative to the position of the inner gimbal assembly <NUM> (shown in <FIG>)).

The angle of the reference light θRL may be summed by an adder <NUM> with an optical bench motion (e.g., a position θIG of the inner gimbal assembly <NUM> with respect to a forward direction of the aircraft <NUM>). A system operator may adjust the position θIG of the inner gimbal assembly <NUM> to adjust the orientation of the optical bench <NUM> so that primary mirror <NUM> (shown in <FIG>) is directed at the target object. The resulting output may be a line of sight motion θLOS (e.g., residual error remaining after corrections have been made based on the Reference Sensorfb and a rate feedback (Ratefb)).

The control system may further include a subtractor <NUM> that subtracts the Ratefb that is based on the output of the inertial sensor <NUM> from a rate command (Ratecmd) that is based on a target position of the line of sight (e.g., the target object) of the light sensor system <NUM>. The resulting output may be integrated by an integrator <NUM> and the resulting integration may be the Reference Sensorcmd that may be input into an inner gimbal compensator <NUM>. The output of the inner gimbal compensator <NUM> may be summed by an adder <NUM> with a disturbance torque TDist. The disturbance torque TDist may be the resulting total force or torque exerted on the imaging components of the light sensor system <NUM> (shown in <FIG>), including the total external forces acting on the imaging components through the inner gimbal assembly <NUM> (shown in <FIG>). For example, forces mainly due to vibration of the aircraft <NUM> (shown in <FIG>).

The disturbance torque Toist may present errors in the position θIG of the inner gimbal assembly <NUM> that direct the optical bench <NUM> away from the target object. These position errors may be fed forward in the Reference Sensorcmd so that the adjustable reflector <NUM> adjusts to compensate for the position errors and jitter, as discussed above.

The output of the adder <NUM> may be provided to an inertial load integrator <NUM>. The output of the inertial load integrator <NUM> may be an optical bench rate of motion (e.g., an inner gimbal rate of motion θ̇IG), which may be integrated by an integrator <NUM> to provide the position of the inner gimbal assembly θIG that is added to the position of the reference light θRL.

Turning now to <FIG>, an exemplary embodiment of the light sensor system is shown at <NUM>. The light sensor system <NUM> is substantially the same as the above-referenced light sensor system <NUM>, and consequently the same reference numerals are used to denote structures corresponding to similar structures in the light sensor systems. In addition, the foregoing descriptions of the light sensor system <NUM> is equally applicable to the light sensor system <NUM> except as noted below. Moreover, it will be appreciated upon reading and understanding the specification that aspects of the light sensor systems may be substituted for one another or used in conjunction with one another where applicable.

The light sensor system <NUM> allows the reference light to move with the primary light past the primary light reflectors <NUM> and <NUM>. In this embodiment, the beam splitter <NUM> does not reflect the reference light before the reference light reaches the primary light reflector <NUM>. The beam splitter <NUM> may be positioned to receive the primary light and the reference light from the primary light reflector <NUM> so that the beam splitter <NUM> may split the reference light and the primary light. For example, beam splitter <NUM> reflects the reference light to the reference light sensor <NUM>, and the primary light passes through the beam splitter <NUM> to reach the primary light sensor <NUM>.

The reference light sensor <NUM> may detect the structural dynamics of a focus lens <NUM> and the primary light reflectors <NUM> and <NUM> in addition to the structural dynamics of preceding optical components, as discussed above with reference to <FIG>. For example, the reference light filter <NUM> and the reference light sensor <NUM> may be positioned to receive the reference light after the reference light moves past the primary light reflectors <NUM> and <NUM>.

Turning now to <FIG>, an exemplary embodiment of the light sensor system is shown at <NUM>. The light sensor system <NUM> is substantially the same as the above-referenced light sensor systems <NUM> and <NUM>, and consequently the same reference numerals are used to denote structures corresponding to similar structures in the light sensor systems. In addition, the foregoing descriptions of the light sensor systems <NUM> and <NUM> are equally applicable to the light sensor system <NUM> except as noted below. Moreover, it will be appreciated upon reading and understanding the specification that aspects of the light sensor systems may be substituted for one another or used in conjunction with one another where applicable.

The light sensor system <NUM> allows the reference light to move with the primary light past the first focus lens <NUM>. The light sensor system <NUM> includes a beam splitter <NUM> before the primary light reflector <NUM>.

In this embodiment, the beam splitter <NUM> does not reflect the reference light before the first focus lens <NUM> after the reference light is reflected by the primary light reflector <NUM>. The beam splitter <NUM> may be positioned to receive the primary light and the reference light from the primary light reflector <NUM> so that the beam splitter <NUM> may split the reference light and the primary light. For example, the reference light passes through the beam splitter <NUM> to reach the reference light sensor <NUM>, and the beam splitter <NUM> reflects the primary light to the primary light sensor <NUM> via the primary light reflector <NUM>.

The reference light sensor <NUM> may detect the structural dynamics of the first focus lens <NUM>. For example, the reference light filter <NUM> and the reference light sensor <NUM> may be positioned to receive the reference light after the reference light moves past the first focus lens <NUM> and the beam splitter <NUM>.

Claim 1:
A light sensor system (<NUM>) including:
a housing (<NUM>);
a primary mirror (<NUM>) with a reflective side (<NUM>) facing in a first direction (D<NUM>) to receive a primary light along a central axis (A) of the primary mirror from a target object, wherein the primary mirror is disposed within the housing;
a plurality of light reflectors (<NUM>, <NUM>-<NUM>), at least one of the plurality of light reflectors arranged to receive the primary light directly from the primary mirror, wherein each of the plurality of light reflectors is arranged in a path of the primary light such that each of the plurality of light reflectors receives and reflects the primary light;
an inertial sensor mount (<NUM>) that is fixed to the primary mirror; and
a collimated reference light source (<NUM>) having an output (<NUM>) directed along the first direction, the reference light source attached to the inertial sensor mount, whereby the reference light source moves due to vibration of the primary mirror, and movable with the inertial sensor mount such that, when the inertial sensor mount moves, the output of the reference light source moves with the inertial sensor mount, and, when the primary mirror moves, the output of the reference light source moves with the primary mirror.