Femto satellite positioning, wake-up, and direction estimation.

Abstract

Femto satellites are very small satellites that can be deployed in constellations from a larger mothership satellite for distributed measurements. They are too small to accommodate the GNSS receivers that many satellites use for navigation, but can be located with an electromagnetic beam from the mothership satellite. The mothership satellite scans this beam throughout the constellation of femto satellites. When a particular femto satellite is scanned by the beam, the femto satellite transmits an acknowledgment to the mothership satellite, for example, by retroreflecting the beam or via another radio link. The beam can be modulated with commands for the femto satellite, such as to make measurements or transmit previously acquired data, as well as commands to determine the position of the femto satellite, such as a timestamp or beam pointing information. The femto satellite can determine its position from the information modulated onto the beam or transmit a timestamp to the mothership satellite for location determination.

Description

Technical Field

[0001] <Cross-Reference to Related Applications> This application claims the benefit of priority under 35 U.S.C. § 119(e) of U.S. Patent Application No. 63 / 183,314 filed on May 3, 2021, which U.S. patent application is hereby incorporated by reference in its entirety into this specification for all purposes.

Background Art

[0002] Femtosatellites (spacecraft with a wet mass of less than 100 grams) are a focus of attention and a subject of growing interest within the new space industry. Due to the low mass and corresponding low cost per deployed free-flying spacecraft, femtosatellites are particularly promising as platforms for taking measurements that benefit from high spatial diversity. The small size of femtosatellites enables them to perform complex specific tasks, particularly localization. In this context, localization is the process by which the spatial position of a spacecraft can be determined, and other physical observable measurements can be related to known points in space. Larger spacecraft typically utilize Global Navigation Satellite Systems (GNSS), such as the United States' Global Positioning System (GPS) constellation, Russia's GLONASS constellation, Europe's Galileo constellation, or China's BeiDou constellation, to determine their position in space. This is difficult for femtosatellites, as most GNSS receivers are very large, very heavy (e.g., 30 grams or more), and consume a very large amount of power compared to the femtosatellite itself.

[0003] There are at least two approaches to locating a femtosphere satellite using radio signals from the satellite itself. The first approach relies on Doppler measurements performed by a mother spacecraft. Unfortunately, these Doppler measurements introduce significant errors in the estimated position and velocity (for example, a position error of about 5 km in a typical case of a perfectly circular orbit). Furthermore, Doppler measurements require continuous tracking over long periods to obtain positional information. This requires the femtosphere satellite to continuously transmit radio waves over long periods, which can be difficult for power reasons.

[0004] The second positioning approach is an inversion of the GPS constellation mechanism (GPS generates distance measurements between a receiver and several satellites whose positions are very well known, and then calculates the receiver's position based on its distance from at least four known points). This uses a large ground station network (many receivers on the ground in geographically diverse locations) and femto satellites with radios strong enough to be heard by a large number of receivers in that network. The femto satellites broadcast navigation beacons that are detected by at least four receivers at different known locations. This can be difficult due to the excessive power consumption of the femto satellites' radios and the potential need for a large number of receivers. Furthermore, positioning a large number of femto satellites using this approach can be difficult because femto satellites do not have a robust way to synchronize with each other, and they can transmit their navigation signals simultaneously, making it difficult for receivers to distinguish between different femto satellites. [Overview of the project]

[0005] In particular, for missions involving femto satellites with high spatial diversity, accurate localization is crucial to obtain high-value measurements, and therefore, an improved localization system compatible with the size, weight, and power (SWaP) limitations of femto satellites is desired. This localization can be achieved by scanning an electromagnetic beam over a portion of the external space containing the femto satellite using a spacecraft. For example, if the electromagnetic beam is a light beam, a solar cell may detect it and filter the output of the solar cell.

[0006] The spacecraft receives a radio frequency (RF) signal from the femtoplanet in response to the femtoplanet detecting an electromagnetic beam. This RF signal indicates when the femtoplanet detected the electromagnetic beam. The position of the femtoplanet relative to the spacecraft can then be estimated based on the beam's directional angle at the time the femtoplanet detected the beam. The distance from the spacecraft to the femtoplanet can then be estimated based on the time it took the electromagnetic beam to travel to the femtoplanet.

[0007] A femtosphere satellite can also detect an electromagnetic beam (e.g., a light beam, a terahertz wave beam, or an RF beam) scanned from a spacecraft across a portion of the external space including the femtosphere satellite. This electromagnetic beam may be modulated with information encoding the beam's angle of focus relative to the spacecraft. In this case, the femtosphere satellite can determine its position relative to the spacecraft based on the information encoding the beam's angle of focus relative to the spacecraft.

[0008] Such femtosphere satellites may include a solar cell array, filters, and circuitry. During operation, the solar cell array converts the incident solar radiation into a direct current (DC) component and the electromagnetic beam from the spacecraft into an alternating current (AC) component. Filters operably connected to each solar cell in the solar cell array separate the DC component from the AC component, and circuitry operably connected to the filters detects the AC component. The circuitry also activates at least one electronic component of the femtosphere satellite in response to the solar cell array receiving the electromagnetic beam from the spacecraft. For example, the electronic component may be a radio that transmits an acknowledgment of the electromagnetic beam to the spacecraft or a sensor to perform measurements in response to the electromagnetic beam. The circuitry can estimate the direction from the femtosphere satellite to the spacecraft based on the AC component. The femtosphere satellite may also include a retroreflector to retroreflect at least a portion of the electromagnetic beam back to the spacecraft.

[0009] The operation method of a femtoplanet may include receiving an electromagnetic beam scanned by a spacecraft over a portion of the external space including the femtoplanet via a solar cell array on the femtoplanet. In response to the solar cell array receiving the electromagnetic beam, the femtoplanet may activate at least one electronic component. It may also transmit an acknowledgment of the electromagnetic beam to the spacecraft. Transmitting an acknowledgment may include retroreflecting at least a portion of the electromagnetic beam to the spacecraft and / or transmitting a high-frequency signal, a terahertz signal, or an optical signal from the femtoplanet to the spacecraft. Furthermore, the femtoplanet may activate sensors in response to the solar cell array receiving the electromagnetic beam.

[0010] The direction from a femtometer satellite to a spacecraft can be estimated based on the alternating current (AC) component of the output of the solar cells in the solar cell array. Estimating the direction may involve determining the amplitude of each AC component, comparing the amplitudes of each AC component, and estimating the direction based on the amplitudes of each AC component. It may also involve determining the in-phase and quadrature (IQ) components of each AC component, calculating the difference between each IQ component, and estimating the direction based on the difference between each IQ component.

[0011] Another spacecraft can locate a femto satellite by scanning an electromagnetic beam across a portion of the external space containing the femto satellite. In response to detecting the electromagnetic beam, the spacecraft receives an acknowledgment from the femto satellite. This acknowledgment may indicate or include a timestamp associated with the electromagnetic beam. The spacecraft determines the beam's angle of view associated with the timestamp and estimates the femto satellite's position relative to the spacecraft based on the beam's angle of view.

[0012] The spacecraft may receive an acknowledgment by detecting a portion of the electromagnetic beam retroreflected from the femtosphere satellite, in which case the spacecraft can estimate the distance from the spacecraft to the femtosphere satellite based on the round-trip flight time of the electromagnetic beam between the spacecraft and the femtosphere satellite. The spacecraft may also receive an acknowledgment by detecting a radio frequency (RF) signal from the femtosphere satellite in response to the detection of the electromagnetic beam.

[0013] In some cases, a spacecraft can modulate an electromagnetic beam with commands for a femto satellite. The spacecraft can also modulate the electromagnetic beam with a series of timestamps while scanning it. In this case, the acknowledgment includes timestamps received by the femto satellite, and estimating the femto satellite's position relative to the spacecraft involves aligning the beam's direction to the timestamps. The spacecraft can estimate the distance from the spacecraft to the femto satellite based at least partially on the time the electromagnetic beam travels to the femto satellite.

[0014] The electromagnetic beam may also be a light beam, in which case the solar cells on the femtoplanet can detect the light beam. The output of the solar cells can be filtered into DC and AC components; the DC component powers the electronic components of the femtoplanet, and the AC component, encoded with commands, activates the sensors of the femtoplanet.

[0015] All combinations of the aforementioned concepts and any additional concepts discussed in more detail below (on the premise that such concepts are not contradictory) constitute part of the subject matter of the invention disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure constitute part of the subject matter of the invention disclosed herein. Terms used herein, which may also appear in any disclosure incorporated by reference, should be given meanings that most coincide with the specific concepts disclosed herein.

[0016] Those skilled in the art will understand that the drawings are presented primarily for illustrative purposes and are not intended to limit the scope of the subject matter of the invention as described herein. The drawings are not necessarily to a fixed proportion, and in some examples, different aspects of the subject matter of the invention disclosed herein may be shown in exaggerated or enlarged in the drawings to facilitate the understanding of different features. In the drawings, similar reference letters generally refer to similar features (e.g., functionally and / or structurally similar elements). [Brief explanation of the drawing]

[0017] [Figure 1A] Figure 1A shows a mother satellite illuminating a femto satellite (sprite) within a constellation (group of sprites) consisting of multiple femto satellites with a scanning electromagnetic beam (e.g., a terahertz beam), and a femto satellite sending a response to the mother satellite via an ultra-high frequency (UHF) radio link or other suitable communication channel. [Figure 1B] Figure 1B shows the scanning beam from the mother satellite sweeping across the entire femtosphere satellite. [Figure 1C] Figure 1C is a block diagram of the mother satellite shown in Figures 1A and 1B. [Figure 2A] Figure 2A is a block diagram of a femtoplanet that receives and responds to a scanning electromagnetic beam from a mother satellite or other spacecraft. [Figure 2B] Figure 2B shows an embodiment of a femto satellite architecture for receiving and responding to scanning electromagnetic beams from a mother satellite or other spacecraft. [Figure 3A] Figure 3A shows a side view of the solar cell and transparent grid in the femtoplanetary architecture configuration shown in Figure 2B. [Figure 3B] Figure 3B is a plan view of the arrangement of solar cells / grilles in the solar cell array shown in Figure 2B. [Figure 3C] Figure 3C is a perspective view of the alignment of solar cells / grilles in the solar cell array shown in Figure 2B. [Modes for carrying out the invention]

[0018] Figure 1A outlines a mechanism by which a mother satellite 100 or other spacecraft can locate a femto satellite 200 by scanning a beam 101 of pulsed or continuous electromagnetic radiation over a region of space containing the femto satellite 200. This localization technique is particularly useful for use in a distributed constellation of femto satellites. Precise localization of these femto satellites allows them to perform precisely localized measurements with high spatial diversity. These capabilities are potentially useful for investigating the Earth's magnetic field 11, natural or artificial radiation environments in space, or radio frequency (RF) environments. They may also find applications in localizing Internet of Things (IoT) devices, such as network-enabled appliances or domotics sensors within a Li-Fi network.

[0019] Before the positions of multiple femto satellites 200 are determined, the femto satellites are deployed as follows, starting with the launch of the mother satellite 100 into orbit. Once the mother satellite 100 is in orbit, it deploys one or more femto satellites 200 within a constellation or group 2000 in a desired orbit. This orbit may be the same as or different from the target orbit of the mother satellite 100 from which they were deployed, provided that appropriate orbital maneuvers can be achieved. One or more of the multiple femto satellites 200 may be deployed from a spacecraft other than the mother satellite 100.

[0020] Each femtosatellite 200 is small (e.g., with a wet mass of less than 100 grams) and may not include navigation components or subsystems. In particular, the femtosatellite 200 may not have a GNSS receiver, as GNSS receivers tend to be heavy (e.g., accounting for 30% or more of the femtosatellite's mass) and consume a relatively large amount of power. When the femtosatellites 200 are deployed, the mothership satellite 100 or another spacecraft scans or sweeps a narrow beam 101 of electromagnetic radiation across the entire femtosatellite constellation 2000. The mothership satellite 100 may scan this electromagnetic beam 101 at a predetermined speed in a predetermined pattern such as a raster scan pattern. The mothership satellite 100 can also step or direct the electromagnetic beam 101 at a series of discrete predetermined angles, or at each of a series of discrete positions.

[0021] The electromagnetic beam 101 may be a light beam generated by a laser and steered by a scanning mirror, an optical phased array, a tunable grating, or other beam steering element. It may be a terahertz (THz) beam generated by a terahertz wave source and steered by a terahertz wave beam steering element such as a THz phased array. Alternatively, it may be an RF (e.g., millimeter-wave or microwave) beam scanned by an RF phased array or a scanning antenna. The wavelength of the electromagnetic beam partially determines the achievable spatial resolution and / or angular resolution of the estimated positions of the femtosatellites, and shorter wavelengths generally provide finer spatial and angular resolution.

[0022] In any case, the modulator on the mothership satellite 100 can modulate the amplitude, frequency, and / or phase of the electromagnetic beam 101 with commands for the femto-satellite (e.g., a "wake-up" command, a query for information, etc.). The modulator can also modulate the electromagnetic beam 101 with information about simultaneous timestamps, as well as the absolute position of the mothership satellite, the position relative to another object (e.g., another spacecraft), the instantaneous pointing angle of the electromagnetic beam 101, the scanning speed, and / or the scanning pattern tracked by the electromagnetic beam 101. For example, the modulator 100 may modulate the electromagnetic beam 101 with information encoding a series of timestamps, and optionally the pointing angles at those timestamps. The mothership satellite 100 and / or the femto-satellite 200 can use this information to estimate the position of the femto-satellite relative to the absolute position of the mothership satellite 100 and / or the femto-satellite, as described below

[0023] The beam 101 of electromagnetic radiation can activate a specific femto-satellite 200 to perform measurements, transmit data, or both. When the beam 101 of electromagnetic radiation irradiates the femto-satellite 200, the femto-satellite 200 responds by returning an acknowledgment (acknowledgement response) to the mothership satellite 100. For example, the femto-satellite 200 can retroreflect a portion of the electromagnetic beam 101 back to the mothership satellite 100, in which case the mothership satellite 100 can determine the direction to the femto-satellite 200 from the pointing angle and timestamp modulated on the retroreflected electromagnetic beam 101. Alternatively or additionally, the femto-satellite 200 can detect and demodulate the electromagnetic beam 101, and acknowledge the electromagnetic beam 101 by transmitting an acknowledgment to the mothership satellite 100 via a separate communication channel, such as an ultra-high frequency (UHF) channel 223, as shown in FIG. 1A. This acknowledgment may include the timestamp and / or pointing angle modulated on the electromagnetic beam 101, and / or a timestamp indicating when the femto-satellite received the electromagnetic beam 101.

[0024] In either case, the mother satellite 100 receives an acknowledgment from the femto satellite and uses it to determine the direction, azimuth, or angle from the mother satellite 100 to the femto satellite 200. If the acknowledgment includes a modulated beam angle or other directional information on the electromagnetic beam 101 when it illuminated the femto satellite 200, the mother satellite 100 can use that information to estimate the direction or angle from the mother satellite 100 to the femto satellite 200. If the acknowledgment includes a timestamp indicating when the femto satellite 200 detected the electromagnetic beam 101, the mother satellite 100 can look up the corresponding beam angle of the electromagnetic beam 101 in its memory and use that beam angle to estimate the direction to the femto satellite 200.

[0025] In some cases, the femto satellite 200 can also estimate the direction or bearing to the mother satellite 100 from information modulated on the electromagnetic beam 101. For example, if the electromagnetic beam 101 is modulated at its directional angle, a processor on the femto satellite 200 can demodulate and use that information to estimate the direction to the mother satellite 100. The femto satellite 200 can transmit this estimation back to the mother satellite 100 or to another receiver in space or on the ground via a separate channel 223. It can also use this information to process data collected by onboard sensors.

[0026] The mother satellite 100 can also estimate the distance to the femto satellite 200 based on the round-trip flight time of the electromagnetic beam 101 to the femto satellite 200. To verify the mechanism, considering a pulsed electromagnetic beam 101, each pulse is modulated by a timestamp indicating when the mother satellite 100 transmitted that pulse, according to a clock on the mother satellite 100. If the femto satellite 200 retroreflects the pulse back to the mother satellite 100, the mother satellite 100 detects the retroreflected pulse, recovers the timestamp, and compares the timestamp to the current time on the clock. If the femto satellite 200 transmits an acknowledgment via a separate channel (e.g., UHF channel 223), the acknowledgment may include a timestamp, and in some cases, this involves measuring or estimating latency or additional delay associated with the detection and retransmission of the timestamp. The difference between the current time and the timestamp is the round-trip flight time between the mother satellite 100 and the femto satellite 200. The product of the round-trip flight time (after subtracting any non-propagating latency or delay) and the pulse propagation speed (speed of light) is the distance from the mother satellite 100 to the femto satellite 200.

[0027] The mother satellite 100 can determine the distance and direction to the femto satellite 200 from the same pulse or separate pulses. If the mother satellite 100 determines the direction or direction to the femto satellite 200 from the first (modulated) pulse, it can use a second (unmodulated) retroreflected pulse to determine the distance to the femto satellite 200 by measuring the time between transmitting the second pulse and receiving the retroreflection.

[0028] By measuring the direction and distance of the femtosecond satellite 200 relative to the mother satellite 100, it is possible to calculate the position of the femtosecond satellite relative to the mother satellite 100. Furthermore, if the absolute position of the mother satellite is known, it is possible to calculate the absolute position of the femtosecond satellite based on its position relative to the mother satellite 100 and the absolute position of the mother satellite.

[0029] Figure 1B shows the scanning beam 101 when sweeping across the entire femto satellite 200. Considering the distance from the mother satellite 100 to the femto satellite 200 and the size of the antenna or optics used to generate the scanning beam 101, the diameter of the scanning beam 101 is generally larger than the maximum lateral dimension of the femto satellite (and its solar cells). For more accurate angular measurements, the scanning beam 101 may also have a top-hat-like spatial amplitude profile with sharp leading and trailing edges. The leading and trailing edges can be detected on the femto satellite 200 to provide a better indication of when the illumination by the beam 101 began, how long the illumination lasted, and when the illumination ended. If the divergence angle and angular scanning velocity of the electromagnetic beam 101 are known or can be estimated or measured, these times can be used to estimate the diameter of the electromagnetic beam 101 and the distance from the mother satellite 100 to the femto satellite 200. Assuming that the femto satellite 200 is in the far field of view, the beam diameter is proportional to the distance and the generation of the divergence angle.

[0030] If necessary, the scanning beam 101 can be pulsed, modulated, or both to activate the femto satellite 200 and / or to assist in estimating the distance and direction from the mother satellite 100 to the femto satellite 200. In Figure 1B, the scanning beam 101 is shown including three pulses 1-3, each radiated at a different time. Each pulse may be modulated with a timestamp indicating when it was transmitted by the mother satellite 100 (e.g., 00:01, 00:02, and 00:003). If the mother satellite 100 maintains a record of the beaming angle of the electromagnetic beam 101 at each timestamp, the timestamp detected by the femto satellite 200 can be used to determine the beaming angle from the mother satellite 100 to the femto satellite 200.

[0031] The pulses can also be used to estimate the distance from the mother satellite 100 to the femto satellite 200. For example, if the interval between pulses is longer than the time it takes for a pulse to propagate from the mother satellite 100 to the femto satellite 200 and back, the mother satellite 100 can measure the distance to the femto satellite 200 by timing the round-trip propagation time of the pulse and multiplying that propagation time by the pulse velocity.

[0032] <Mothership Architecture> Figure 1C is a block diagram showing some elements of the mother satellite 100. The mother satellite 100 includes either a modulating laser or other light source 112 for "waking up" the femto satellite 200, or a pulsed laser or other pulsed light source 114 for ranging, or both. The pulsed light source 114 has a high duty cycle and can emit ranging signals. Data can be encoded in the ranging signal by the presence or absence of pulses, or the time between pulses. The query light source 112 is modulated with a signal whose narrow bandwidth matches the bandwidth of the amplifier on the femto satellite 200. Data can be encoded in the phase of the modulated signal. A transmitting optical system 110 (a lens for focusing and / or collimating the beam), a MEMS mirror for beam direction manipulation, a beam splitter for combining or splitting the beam, and / or other optical components scan the light from the modulating light source 112 and / or pulsed light source 114 as a scanning beam across the entire region of space including the femto satellite 200.

[0033] The mother satellite 100 may also include a receiving optics system 120 (e.g., lenses, mirrors, beam splitters, and / or other components) for collecting light 203 reflected or transmitted to the mother satellite 100 by the femto satellite 200. The transmitting optics system 110 and the receiving optics system 120 may be combined into a single optics system and may share an aperture on the mother satellite 100. The receiving optics system 120 couples the received light 203 to a directional camera 122 capable of estimating the angular position of the femto satellite 200 relative to the mother satellite 100, and / or to a ranging detector 124 that times the arrival of (retro)reflected pulses. The transmitting optics system 110 and the receiving optics system 120 may be directed at the entire body of the mother satellite 100, or, in combination with a gimbal for the optics, or directional mirrors within the transmitting optics system 110 and the receiving optics system 120, they may be directed at the femto satellite 200, or scanned over the entire femto satellite 200.

[0034] The attitude determination and control system 130 determines and controls the orientation of the mother satellite 100. This is controlled by a processor or controller 140 (e.g., MCU) which monitors or sets the position and orientation of the mother satellite, controls the light sources 112 and 114, and determines the distance and (relative and / or absolute) orientation of the femto satellite 200 based on signals from the direction camera 122 and rangefinder 124.

[0035] <Femto satellite architecture> Figures 2A and 2B show several embodiments and implementations of the femtoplanet 200 shown in Figure 1A. Figure 2A is a block diagram of the femtoplanet 200, which comprises a solar cell 202, (multiple) filters 204 as needed, a microcontroller unit (MCU) 210 or other processor or controller, a radio unit 220 and an antenna 222, a sensor payload 230, and a retroreflector 206 as needed. The solar cell 202 is connected to the MCU 210, the radio unit 220, the sensor payload 230, and other electronic equipment, and supplies them with power by converting incident sunlight and other optical radiation into electricity. The solar cell 202 can also detect the scanning beam 101 from the mother satellite 100 when the scanning beam 101 is an optical scanning beam (Figure 1A). When the optical scanning beam is modulated, the solar cell 202 generates an output that includes both a low-frequency, or direct current (DC) component, for powering electronic devices, and a higher-frequency, or alternating current (AC) component, which is modulated. A filter 204, which may be implemented as a bias tee, separates the AC and DC components, directing the DC component to a power regulating circuit for powering electronic devices. The filter 204 also directs the AC component to an MCU 210 for processing.

[0036] The MCU 210 receives and responds to signals modulated on the scanning beam. These signals may include commands to the femto satellite 200, including commands to perform measurements with sensors in the sensor payload 230, commands to transmit data acquired by sensors in the sensor payload 230 and stored in memory on the femto satellite, or commands to transmit other information, including health, safety, and / or other status information. The MCU 210 responds to these commands by triggering the appropriate sensors or radio 220.

[0037] The signal modulated on the optical scanning beam may also include a timestamp and / or directional information, as described above. The MCU 210 can use this information to determine or estimate the absolute or relative position of the femto satellite. It can also transmit back the timestamp and / or directional information, the estimated position, or both, via radio 220 and antenna 222 to the mother satellite 100 and / or one or more other receivers. If antenna 222 is a phase array, the transmission direction can be manipulated to point in the opposite direction to the direction the scanning beam from the mother satellite is pointing.

[0038] The femto satellite 200 may also include a corner cube retroreflector or cat's eye retroreflector 206 oriented in the same direction as the solar cell 202. The retroreflector 206 reflects incident radiation back to its source with little to no scattering. If the incident radiation is a modulated optical scanning beam from a mother satellite or other spacecraft, the retroreflector 206 reflects the modulated optical scanning beam back to the mother satellite or other spacecraft. This simplifies the positioning process as seen from the femto satellite, as the scanning beam does not need to be detected or used to trigger radio transmission. It also eliminates any latency associated with the detection and processing of optical scanning beams on the femto satellite, potentially improving the accuracy of distance measurements in time of flight. In fact, with a retroreflector 206 reflecting a modulated optical scanning beam, the femto satellite can be positioned even when off (unpowered).

[0039] Figure 2B shows a more detailed diagram of the solar cell 202 and associated circuitry within the femto satellite 200. The solar cell 202 and associated circuitry can receive an optical scanning beam from the mother satellite and determine the vector from the mother satellite, which is the source of the light beam, to the femto satellite. Figure 2B also shows a system in which the light beam triggers the femto satellite to wake up (become active), and a terahertz wave phase array or laser diode (LD) and micro-electromechanical system (MEMS) mirror 320 can transmit a return signal along the incident vector to the mother satellite. Using the solar cell 202 of the femto satellite as a sensor to activate the femto satellite 200 offers significant size or performance advantages. A separate detector with similar performance would occupy a similar area in size to the solar cell 202.

[0040] In this example, there are four solar cells 202 in the solar cell array. Solar cells 202 receive both DC, or low-frequency, power components from the sun and higher-frequency AC components from the mother satellite's orbital signal. For example, the orbital signal can use submodulation, which can filter or separate the orbital signal from sunlight and the Earth's background light.

[0041] Each solar cell 202 is connected to a separate filter 204. In Figure 2A, these filters 204 are implemented as transimpedance amplifiers (TIAs) 302, each combined with a bandpass filter 304. The signals from each filter 204 pass through a receiving circuit using frequency filtering, and the amplitude is extracted by another circuit 306 using either in-phase and quadrature (IQ) demodulation, peak detection, or root mean square (RMS) detection. A summing node 308 sums the RMS amplitudes of the filtered and amplified solar cell outputs. The summed output is processed by a wake-up controller 310 or another processor. If necessary, the circuit receiving signals on the femto satellite 200 can be tuned to be sensitive to a specific submodulation frequency range in order to selectively wake up that femto satellite 200.

[0042] IQ demodulation, at the expense of increased complexity, utilizes a submodulation stage to provide the advantages of a slow data link from the carrier to the femto satellite 200. Circuits 312 and 314 use the difference between the IQ components to determine the orientation angle of the solar cell 202 relative to the mother satellite. In other words, the power received by the solar cell 202 depends on the angle of incidence of the incident light. This is also true for the signal output that the solar cell 202 receives from the mother ship. Three or more cells can be used to determine the orientation of the mother satellite from the femto satellite 200. The direction in which the solar cell 202 receives the maximum output may be distorted to make the orientation observable. This can be achieved by oriented the solar cells 202 themselves in different directions, by using an optical grating on the surface of each solar cell 202, or by adapting cell surface texture processing.

[0043] <Solar cells and grids for femtoplanets> Figures 3A-3C illustrate in more detail one implementation of the femtoplanet's solar cell array 202 and grating. Figure 3A shows one solar cell 402 and one grating 404 in profile. Grating 404 is a blazed grating and has a diffraction efficiency that varies with the angle of incidence. In the configuration shown in Figure 3A, the diffraction efficiency of the grating is higher off-axis than perpendicular incidence, and the coupling efficiency of the in-axis beam is lower than that of the off-axis beam. Grating 404 changes the coupling efficiency of solar cell 402, with the highest coupling efficiency being achieved here at a distorted angle (not perpendicular incidence). This change in coupling efficiency with respect to the angle of incidence can be used to determine the angle of incidence of the scanning beam 101, as described below.

[0044] Figures 3B and 3C show a 4x4 square array 202 of solar cells 402 and grids 404. Each solar cell 402 has its own grid 404. The solar cells 402 are arranged within the array 202 on the surface of the femto satellite 200, and the grids point in different directions. In this example, the grid vector of each grid (direction perpendicular to the grid lines of that grid) points to the corresponding corner of the square array 202. The grids 404 modulate the coupling efficiency, and therefore the received light output, as a function of the incident angle. When the scanning beam 101 is aligned with a particular grid vector, the corresponding solar cell 402 produces the highest output (strongest signal), even if all of the solar cells 402 are uniformly illuminated. Conversely, solar cells 402 whose grid vectors are not aligned with the scanning beam 101 produce weaker signals, for example, as in Figure 3C, where the lower right and upper left solar cells produce the strongest and weakest signals, respectively. The femto satellite 200 and / or the mother satellite 100 can estimate the instantaneous direction of the scanning beam 101 using the amplitude difference between the solar cell outputs. If the incident light has a non-uniform spatial amplitude profile, the solar cell surface can be further subdivided, and several exposed sections (sections without a grid) can be used to estimate the light intensity distribution.

[0045] <Conclusion> While various embodiments relating to the invention have been described and illustrated herein, those skilled in the art will readily conceive of various other means and / or structures for carrying out the functions described herein and / or obtaining one or more of the results and / or advantages, and each of such variations and / or modifications will be considered to be within the scope of the embodiments relating to the invention described herein. More generally, those skilled in the art will readily understand that all parameters, dimensions, materials and configurations described herein are illustrative, and that the actual parameters, dimensions, materials and / or configurations will depend on the specific application in which the teachings of the invention are used. Those skilled in the art will be able to recognize or confirm many equivalents of the particular embodiments relating to the invention described herein simply by ordinary experimentation. Thus, it will be understood that the embodiments described herein are presented only as examples, and that embodiments relating to the invention may be practiced in ways other than those specifically described and claimed, within the scope of the appended claims and their equivalents. Embodiments relating to the invention of this disclosure cover each individual feature, system, article, material, kit and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and / or methods is included within the scope of the inventions of this disclosure, provided that such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent.

[0046] Furthermore, various inventive concepts may be embodied in one or more methods, and examples of such methods have been provided. The actions performed as part of the method may be ordered in any preferred manner. As a result, embodiments may be constructed in which the actions are performed in a different order than those exemplified, and this may include performing some of the actions simultaneously, even if they are shown as consecutive actions in the exemplary embodiments.

[0047] All definitions defined and used herein should be understood to govern dictionary definitions, definitions incorporated by reference in documents, and / or the common meanings of the defined terms.

[0048] As used herein and in the claims, the indefinite articles "a" and "an" should be understood to mean "at least one" unless explicitly stated otherwise.

[0049] As used herein and in the claims, the phrase “and / or” should be understood to mean “either or both” of the connected elements, that is, elements that are connected in some cases and disjunctive in others. Multiple elements listed with “and / or” should be interpreted as “one or more” of the same type, i.e., coordinating connected elements. Other elements may be present, at will, in addition to those specifically identified by the “and / or” clause, whether related or not to the specifically identified elements. Therefore, as a non-restrictive example, a reference to “A and / or B” when used with unrestrictive language such as “including” may refer to A only in one embodiment (optionally including elements other than B), B only in another embodiment (optionally including elements other than A), and both A and B in yet another embodiment (optionally including other elements), and so on.

[0050] As used herein and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as inclusive, that is, including at least one of a number of elements or a list of elements, and optionally, two or more additional items not listed. Only terms that are explicitly indicated to be the opposite, such as “only one of” or “exactly one of” or, as used in the claims, “consisting of,” refer to including exactly one of a number of or listed elements. In general, as used herein, the term “or” shall be interpreted only when preceded by an exclusive term such as “either,” “one of,” “only one of,” or “exactly one of” to indicate an exclusive choice (i.e., “one or the other, but not both”). “Consisting of” shall, as used in the claims, have the usual meaning as used in the field of patent law.

[0051] As used herein and in the claims, the phrase “at least one” in relation to a list of elements should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of all the elements specifically listed in the list of elements, nor excluding any combination of the elements in the list of elements. This definition also allows for the possibility that elements other than those specifically identified in the list of elements may exist, whether related to or unrelated to the specifically identified elements, to which the phrase “at least one” refers. Therefore, as a non-restrictive example, "at least one of A and B" (or equivalently "at least one of A or B," or equivalently "at least one of A and / or B") may refer to, in one embodiment, no B and optionally two or more A's, with at least one A (optionally including elements other than B); in another embodiment, no A and optionally two or more B's, with at least one B (optionally including elements other than A); and in yet another embodiment, optionally two or more A's, with at least one A and optionally two or more B's, with at least one B (optionally including other elements), and so on.

[0052] In the claims and the above specification, all transitional phrases, such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and similar phrases, are understood to be unrestrictive, meaning they include but are not limited to them. Only the transitional phrases “consisting of” and “consisting essentially of” are considered closed or semi-closed transitional phrases, respectively, as described in Section 2111.03 of the U.S. Patent Examination Procedure Manual.

Claims

1. It is a femto satellite, A solar cell array that converts incident solar radiation into a direct current (DC) component and an electromagnetic beam from a spacecraft into an alternating current (AC) component, Multiple filters are operably connected to each solar cell in the solar cell array and separate the DC component from the AC component, A circuit operably connected to the plurality of filters, which detects the AC component when the solar cell array receives the electromagnetic beam from the spacecraft and activates at least one electronic component of the femto satellite. Equipped with, The circuit estimates the direction from the femto satellite to the spacecraft based on the AC component. Femto satellite.

2. The femto satellite according to claim 1, wherein the at least one electronic component includes a radio unit for transmitting an acknowledgment of the electromagnetic beam to the spacecraft.

3. The femtosphere satellite according to claim 1, wherein at least one electronic component includes a sensor that receives the electromagnetic beam and performs measurements.

4. The femto satellite according to claim 1, further comprising a retroreflector that retroreflects at least a portion of the electromagnetic beam and returns it to the spacecraft.

5. The steps include: the solar cell array of a femto satellite receives an electromagnetic beam scanned by a spacecraft over a portion of the external space including the femto satellite; When the solar cell array receives the electromagnetic beam, the step of activating at least one electronic component of the femto satellite, The femto satellite sends an acknowledgment of the electromagnetic beam to the spacecraft. The steps include: estimating the direction from the femto satellite to the spacecraft based on the alternating current (AC) component output from the solar cells in the solar cell array; Methods for operating femto satellites, including those mentioned above.

6. The method according to claim 5, wherein the transmission of the acknowledgment includes retroreflecting at least a portion of the electromagnetic beam to the spacecraft.

7. The method according to claim 5, wherein the transmission of the acknowledgment includes the step of transmitting at least one of a high-frequency signal, a terahertz signal, and an optical signal from the femto satellite to the spacecraft.

8. The estimation of the aforementioned direction The steps include determining the amplitude of each of the aforementioned AC components, The steps include comparing the amplitudes of each of the aforementioned AC components, A step of estimating the direction based on the amplitude of each of the AC components. The method according to claim 5, including the method described in claim 5.

9. The estimation of the aforementioned direction The steps include determining the in-phase and orthogonal (IQ) components of each of the aforementioned AC components, The step of calculating the difference between each of the aforementioned IQ components, A step of estimating the direction based on the difference between each of the aforementioned IQ components. The method according to claim 5, including the method described in claim 5.

10. The method according to claim 5, further comprising the step of activating the sensors of the femto satellite when the solar cell array receives the electromagnetic beam.

11. The method according to claim 5, wherein the step of receiving the electromagnetic beam includes the step of coupling the electromagnetic beam with a plurality of grids, each grid in the plurality of grids is located on separate solar cells in the solar cell array and has grid vectors pointing in different directions.

12. The femto satellite comprises the steps of decoding a timestamp encoded in the electromagnetic beam and information relating to the directional angle of the electromagnetic beam, The femto satellite determines its position relative to the spacecraft based on the timestamp and information regarding the direction of the electromagnetic beam. The method according to claim 5, further comprising:

13. The method according to claim 5, further comprising the step of decoding a wake-up command encoded in the electromagnetic beam in the femto satellite.

14. The method according to claim 5, further comprising the step of estimating the direction of the electromagnetic beam based on the difference in the output amplitudes of a plurality of solar cells in the solar cell array.

15. The steps of filtering the output of the solar cell array into a direct current (DC) component and an alternating current (AC) component, The steps include sending the DC component to a power adjustment circuit for supplying power to the electronic equipment of the femto satellite, The steps include sending the aforementioned AC component to a microcontroller unit for processing, and The method according to claim 5, further comprising:

16. The femtoplanet according to claim 1, wherein the plurality of filters include one filter provided for each solar cell of the solar cell array.

17. The femto satellite according to claim 1, wherein the plurality of filters send the DC component to a power adjustment circuit for supplying power to the electronic equipment of the femto satellite and the AC component to a microcontroller unit for processing.

18. The femto satellite according to claim 1, further comprising a plurality of grids, each grid in the plurality of grids being arranged in separate solar cells of the solar cell array and having grid vectors pointing in different directions.

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