Satellite identification system and method

Abstract

A self-contained identification tag arranged to be attachable to a resident space object (RSO), comprising: a processor, an antenna, an energy collector arranged to collect energy from the environment, and an energy store arranged to receive and store energy from the energy collector, wherein the processor is arranged to transmit a radio frequency (RF) identification signal via the antenna using the energy stored in the energy store.A system for identifying resident space objects, comprising: a radar arranged to determine an orbital path of the resident space object (RSO), and a receiver arranged to receive an identification signal from an identification tag attached to the RSO and determine a tag identity, wherein the system is arranged to determine the identity of the RSO using the determined orbital path and the determined tag identity.

Description

[Background technology]

[0001] This application relates to systems and methods for satellite identification.

[0002] When operating a satellite, it is important to know the satellite's location and orbital parameters. However, although radar and other tracking technologies can be used to track resident space objects, identifying a tracked resident space object can be difficult. That is, even after a satellite's location and orbital parameters have been determined, it may be difficult or impossible to determine the satellite's identity.

[0003] Current approaches to identifying satellites typically rely on the spacecraft operator to determine which satellites belong to them, which can be challenging if the operator is uncooperative or if the satellite is down upon arrival and has been out of communication since launch. This can also pose challenges for the satellite operator, who may not know which satellite belongs to them and must search all of the satellites to find it. When deploying a constellation of many satellites, identifying satellites can be time-consuming during initial operations. This can be particularly problematic when many small satellites, such as cubesats, are deployed together, as these satellites may be deployed close to each other in space, time, and orbit, and in some cases, the deployment order of different satellites may not be predetermined.

[0004] Additionally, it is desirable to be able to determine the identity of a satellite while it continues to be tracked. Knowing the identity of a satellite with certainty is crucial for regulatory compliance and accountability purposes. However, in practice, satellites may move close to each other or toward non-functioning objects, making it difficult to know with certainty which satellite or other object is which and to avoid "cross-tagging" of different objects.

[0005] Various approaches have been proposed for satellite identification, including the installation of radio frequency or optical beacons on satellites. However, these approaches have issues such as size and weight, the need to integrate the beacon power source with the satellite electronics, and limited beacon lifespan. Another proposed approach is to install radar or optical reflectors on satellites. However, the problem with this approach is that only limited identifying information can be provided using reflectors. Furthermore, all of these approaches have security issues, as the satellite's identity is exposed to all parties involved.

[0006] Therefore, it is desirable to provide an improved system and method for satellite identification.

[0007] The embodiments described below are not limited to implementations that address some or all of the drawbacks of the known approaches described above. Summary of the Invention

[0008] This summary is provided to introduce some concepts in a simplified form that are more fully described in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0009] In a first aspect, the present disclosure provides a self-contained identification tag attachably arranged to a resident space object (RSO), the tag including a processor, an antenna, an energy harvester arranged to harvest energy from the environment, and an energy store arranged to receive and store energy from the energy harvester, the processor arranged to transmit a radio frequency (RF) identification signal via the antenna using the energy stored in the energy store.

[0010] In a second aspect, the present disclosure provides a system for identifying a resident space object, the system comprising: a radar arranged to determine an orbital path of a resident space object (RSO); and a receiver arranged to receive an identification signal from an identification tag attached to the RSO and determine the identity of the tag, the system arranged to determine the identity of the RSO using the determined orbital path and the determined tag identity.

[0011] In a third aspect, the present disclosure provides a method for identifying a resident space object, the method comprising: attaching a self-contained identification tag to a resident space object (RSO), the tag including a processor, an antenna, an energy collection device, and an energy store; and further comprising: collecting energy from an environment using the energy collection device; storing the energy from the energy collection device in the energy store; and transmitting a radio frequency (RF) identification signal via the antenna using the energy stored in the energy store.

[0012] In a fourth aspect, the present disclosure provides a method for identifying a resident space object, the method including the steps of determining an orbital path of a resident space object (RSO) using a radar, receiving an identification signal from an identification tag attached to the RSO using a receiver, determining the identity of the tag, and determining the identity of the RSO from the determined orbital path and the determined identification of the tag.

[0013] The preferred features may be combined as appropriate and in any aspect of the invention, as will be apparent to those skilled in the art. Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, in which: [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is an explanatory diagram of a satellite identification system according to a first embodiment. [Figure 2] FIG. 2 is an explanatory diagram of an identification tag according to the first embodiment. [Figure 3] FIG. 10 is an explanatory diagram of a satellite identification system according to a second embodiment. [Figure 4] 10A-10C are illustrations of an identification tag according to a third embodiment, and common reference numbers are used throughout the figures to denote similar features. DETAILED DESCRIPTION OF THE INVENTION

[0015] Embodiments of the present invention are described below by way of example only. These examples represent the best ways currently known to applicant for practicing the invention, but are not the only ways that they can be practiced. The description sets forth the functions of the examples and a sequence of steps for constructing and operating the examples, although the same or equivalent functions and sequences may be accomplished by different examples.

[0016] It is generally desirable to be able to reliably identify satellites in orbit. The present invention provides a radio frequency beacon onboard a satellite that emits a radio frequency (RF) signal that can be received by a ground station and used to identify the satellite. Desirable goals for such an RF beacon include: The beacon should be independent of the satellite power system. The beacon should not emit any RF signals except when over a receiving ground station. The beacon should operate in an open or already licensed frequency band. The beacon should be small and lightweight. The beacon should have an operational life of 10 years or more. The beacon should not use an active power source, such as a battery. As described in more detail below, the RF beacon of the present disclosure makes it possible to achieve all of these goals.

[0017] FIG. 1 is an explanatory diagram illustrating an example of a satellite identification system 1 according to a first embodiment. In the first embodiment of FIG. 1, a ground-based radar 2 is used to track satellites 10 and other resident space objects (RSOs) orbiting the Earth. In the illustrated embodiment, the radar is a large-aperture S-band pulse radar used to track satellites and other RSOs in Earth orbit. The radar 2 includes an antenna 3 that emits RF signals at a predetermined frequency or range of frequencies within a main beam 4 and receives reflected RF signals reflected back to the antenna 3 by objects within the beam 4. The radar 2 also includes a tracking system 5 that processes the reflected RF signals received by the antenna 3 to determine the positions of the satellites and other RSOs over time and their orbital tracks, for example, by calculating their respective ephemeris.

[0018] The tag receiver 6 and the radar 2 are co-located. The tag receiver 6 includes a receiving antenna 7 and a signal processing unit 8.

[0019] In summary, when a satellite 10 or other RSO equipped with an identification tag 9 passes through the radar 2's beam 4, the identification tag 9 responds to the radar 1's RF radar signal by transmitting an RF identification signal 11 containing an identification code. This RF identification signal is received by the tag receiver 6's receive antenna 7, and the tag receiver's signal processor 8 analyzes the received RF identification signal 11 to determine the identity of the satellite 10. The identity of the satellite 10 can be determined by comparing the identification code obtained from the received identification signal 11 with a stored database of identification codes for issued identification tags 9 and the respective identities of the satellites 10 to which the issued identification tags 9 are attached. The tag receiver 6 then passes the determined identity of the satellite 10 to the radar 2's tracking system 5, which can associate the satellite 10's identity with its determined orbital track or ephemeris. Typically, the RF identification signal 11 is transmitted at a frequency different from that of the radar beam 4 to reduce the possibility of interference between the radar 2 and the identification signal 11.

[0020] The satellite identification system 1 may compile a catalog of satellites 10 in which the identities of the satellites 10 are stored in association with the identification codes of the identification tags 9 on the satellites 10 and the orbital tracks or ephemeris of the satellites 10. This catalog may provide a robust means for identifying the satellites 10.

[0021] In one example, radar 2 may provide the determined orbital tracks or ephemerides of detected satellites and other RSOs, along with any associated satellite IDs, to a combined warning system. It will be appreciated that operation of the combined warning system and implementation of appropriate action for an identified combination will be more effective and efficient if the associated satellites 10 are clearly identified.

[0022] FIG. 2 shows a schematic diagram of an identification tag 20 according to the first embodiment.

[0023] The identification tag 20 is composed of a processor 21, an antenna 22, and a capacitor 23. The identification tag 20 is attached to the satellite 10.

[0024] The processor 21 includes a stored identification code. When the satellite 10 and its attached identification tag 20 pass through the beam 4 of the radar 2, the antenna 22 collects or absorbs electrical energy from the electromagnetic field of the received radar signal incident on the antenna 22 and stores this electrical energy in a capacitor 23. The electrical energy stored in the capacitor 23 is used to power the processor 21. The processor 21 measures the amount of electrical energy stored in the capacitor 23, for example, by comparing the voltage difference across the capacitor 23 with a predetermined threshold. When the processor 21 determines that sufficient electrical energy is stored in the capacitor 23, for example, when the voltage reaches the threshold, the processor 21 uses the electrical energy stored in the capacitor 23 to transmit the stored identification code via the antenna 22 as a coded waveform that forms the RF identification signal 11.

[0025] In the first embodiment, the identification tag 20 is arranged to transmit an RF identification signal 11 at a transmission frequency that is a fixed offset from the frequency of the radar 2 .

[0026] From the above discussion, it has been seen that identification tag 20 is a passive RFID type tag. Passive RFID tags are typically used at short distances of a few centimeters up to about 12 meters. It has never been suggested that passive RFID type tags could be used at distances of a few kilometers, let alone orbital distances of hundreds of kilometers or even over 1000 kilometers.

[0027] In the example where radar 2 is a high-power, large-aperture, S-band pulsed radar with a 50% duty cycle and a transmit pulse length of 12.5 ms, the power incident on identification tag 20 and the DC energy that identification tag 20 can collect and store in capacitor 23 from a single incident radar pulse are shown in Table 1 below for various orbital ranges between satellite 10 and antenna 3 of radar 2.

[0028] The values in Table 1 assume that the identification tag 20 is capable of collecting and storing 30% of the electromagnetic power incident on the antenna 22 of the identification tag 20 .

[0029] [Table 1]

[0030] The transmission power required for the identification tag 20 to transmit the RF identification signal 11 varies depending on the characteristics of the tag 20's transmission system and the tag receiver 6's receiving system, the ambient noise environment, the signal-to-noise ratio (SNR) required to reliably receive the RF identification signal 11, and the distance between the satellite 10 and the tag receiver 6's receiving antenna 7.

[0031] Examples of the required signal strength at the receiving antenna 7 (tag reader) and the corresponding required transmission power of the identification tag for different orbital ranges between the satellite 10 and the receiving antenna 7 of the tag receiver 6 are shown in Table 2 below.

[0032] The example in Table 2 shows a required SNR of 13 dB, with the other parameters showing the typical values specified above.

[0033] [Table 2]

[0034] The energy required by the identification tag 20 to transmit the RF identification signal 11 depends on the required number of bits that make up the stored identification code, the chip rate (bandwidth) of the identification tag 20, and the required transmission power according to Table 2 above. An example of the number of radar pulses (reader pulses) from the radar 2 is shown in Table 3 below, which the identification tag 20 must receive and collect as energy to provide the energy required for identification codes with different numbers of bits and ranges between the satellite 10 and the antenna 3 of the radar 2.

[0035] [Table 3]

[0036] As explained above, the duty cycle of the radar 2 in this example is 50% with a 12.5 ms transmit pulse. Therefore, the time required for the identification tag 20 to collect enough energy from the radar signal to transmit the identification signal 11 is 5 ms multiplied by the number of reader pulses shown in Table 3. It will be appreciated that the power required for operation of functions of the identification tag 20 other than transmitting the identification signal is small in comparison and need not be considered here.

[0037] In the example system shown in Table 3 using a 12-bit code and where the satellites are at a distance of 500 km, it takes four 1-millisecond radar pulses, which takes 20 milliseconds, to charge the identification tag 20 with enough energy to transmit the identification signal 11. Once the identification tag 20 is charged, it transmits the identification signal 11 containing the 12-bit code over a period of 4 milliseconds. In another example system shown in Table 3 using a 48-bit code at a range of 750 km, it takes 75 1-ms radar pulses, which takes 375 milliseconds. The identification tag 20 then transmits the identification signal 11 containing the 48-bit code over a period of 16 milliseconds.

[0038] In this example, the satellite 10 is typically in the beam 4 of the radar 2 for more than 1.0 second, and from the examples above and the figures in Table 3, it can be seen that this is generally sufficient for the identification tag 20 to collect enough energy to transmit the identification signal 11. Only in the most demanding use case shown in Table 3, i.e., when a 48-bit code is used with a satellite at a distance of 1000 km, does the time required to charge the identification tag 20 become so long, about 1.185 seconds, that problems may arise.

[0039] Thus, it has been found that the identification tag 20 can collect enough energy to transmit an identification signal in most circumstances. However, it may be necessary to limit the length of the identification code used on identification tags 20 aboard satellites 10 sent into high orbits.

[0040] Because the identification tag 20 of the first embodiment transmits the identification signal 11 using power collected from the radar 2 signal, it is understood that the identification tag 20 does not emit the RF identification signal 11 only when it is over the radar 2, i.e., within the radar 2 beam. Therefore, the identification tag 20 achieves the objective of not emitting an RF signal except when it is over the tag receiver 6, which may be desirable to minimize the risk of interference with the operation of the satellite 10 and to reduce RF disturbances and noise that may affect the operation of other satellites. Furthermore, the identification tag 20 is self-contained and independent of any satellite power system, which may be desirable to ensure that the identification tag 20 does not interfere with the operation of the satellite 10 and to enable the identification tag 20 to continue operating even if the satellite 10 itself ceases to function due to a power failure or the like. Furthermore, there is no need to test and certify whether the identification tag 20 is compatible with the satellite 10 system. Furthermore, the identification tag 20 can operate in the same open or licensed frequency band as the radar 2, but at an offset frequency. This may avoid issues with the identification signal interfering with other users of the electromagnetic spectrum. Furthermore, the identification tag 20 does not include an active power source, such as a battery. Therefore, the risk of damage to the satellite 10 due to a failure of the active power source is avoided. Because the identification tag 20 uses power collected from the radar 2, the operational life of the identification tag 20 is limited only by the life of its electronic components, which can be easily adjusted to exceed 10 years in a space environment by selecting appropriate components. This offers the advantage of allowing continuous identification throughout the entire period the satellite 10 is in orbit, which may continue long after the satellite 10 system has ceased functioning. Because the identification tag 20 is small in size, typically a few centimeters and weighing less than 100 grams, one or more identification tags can be deployed on the satellite 10 without significantly affecting the satellite's operation or the launch weight of the satellite 10.

[0041] The identification tag 20 of the first embodiment has the advantage over passive reflectors, such as Van Atta arrays, of being able to freely select the form of the identification signal 11, such as an identification code. Passive reflectors generally rely on the shape of the illuminating radar signal and are generally limited to generating a reflected signal of a closely related shape. In particular, passive reflectors cannot transmit freely selectable codes when illuminated by a radar signal. The identification tag 20 of the first embodiment may offer the advantage of being smaller than passive reflectors, such as Van Atta arrays.

[0042] In some examples, it may be desirable for the identification signal 11 to include an encrypted identification code so that only authorized users of the system 1 can use the identification signal 11 to identify the satellite 10. Thus, the identification signal 11 may include an encrypted identification code. However, if the encrypted identification code is not changed, anyone receiving the identification signal 11 can easily use the identification signal to identify the satellite 10 on which the identification tag 20 is located as the same satellite 10. This is because, among other things, the identification tag 20 transmits the identification signal 11 when illuminated by any radar signal that has sufficient incident power and has approximately the same frequency as the radar 2.

[0043] Thus, the identification tag 20 may be configured to transmit an identification signal 11 that includes a different encrypted identification code each time it is transmitted. In one example, a predetermined, pseudo-random series of identification codes may be used, and the tracking system 5 may compare the received codes to a list indicating which codes are assigned to which satellites 10. In another example, the identification tag 20 may be configured to combine the satellite's 10 identification code with the time in a predetermined manner and encrypt the result before transmission, and the tracking system 5 may be configured to decode the received identification signal 11 to recover the satellite's 10 identification code. In another example, the identification tag 20 may be configured to combine the satellite's 10 identification code with a counter or random value in a predetermined manner and encrypt the result before transmission, and the tracking system 5 may be configured to decode the received identification signal 11 to recover the satellite's 10 identification code.

[0044] All of the above examples may be used to ensure that only authorized users of the system 1 can identify the satellite 10 using the received identification signal 11.

[0045] FIG. 3 shows a satellite identification system 30 according to the second embodiment.

[0046] As described above, in the satellite identification system 1 according to the first embodiment, the identification tag 20 transmits an identification signal 11 including an identification code in response to irradiation of the identification tag 20 by the radar 2. The satellite identification system 30 is similar to the satellite identification system 1 according to the first embodiment, but is modified so that an identification request signal is transmitted to the satellite identification system 30.

[0047] 3, like the first embodiment, a satellite identification system 30 according to the second embodiment includes a radar 2 and a tag receiver 6 arranged in the same position as the radar 2. The tag receiver 6 includes a receiving antenna 7 and a signal processing device 8, and further includes an interrogation signal transmitter 31.

[0048] In operation of the satellite identification system 30, the tag receiver 6 is arranged to transmit an interrogation signal 32 from the interrogation signal transmitter 31 via the antenna 7 when it is necessary to identify a satellite 10. In the satellite identification system 30, the identification tag 20 is arranged to transmit an identification signal 11 only in response to receiving the interrogation signal 32. It will be appreciated that the identification tag 20 must pass through the beam 4 of the radar 2 in order to have the power necessary to transmit the identification signal 11, but in the satellite identification system 30 of the second embodiment, the identification tag 20 does not automatically transmit the identification signal 11 even if there is sufficient energy to do so.

[0049] The satellite identification system 30 of the second embodiment can avoid the unintentional transmission of the identification signal 11 in response to an incoming radar signal and can more effectively avoid emitting RF signals except when located above the tag receiver 6.

[0050] In some examples, the satellite identification system 30 according to the second embodiment may employ encryption so that only authorized users of the system 1 can use the identification signal 11 to identify the satellite 10 .

[0051] In one example encryption configuration, the identification tag 20 may contain a tag-specific private key and a tag receiver public key, and the tag receiver 6 may contain the tag receiver private key and a list of tag-specific public keys for different identification tags 20. In operation, the tag receiver 6 may transmit an encrypted interrogation signal 32; for example, the interrogation signal 32 may include an encrypted combination of a time and a random challenge. The identification tag 20 decodes the interrogation signal 32 and, if it identifies the interrogation signal as authentic, responds by transmitting an identification signal 11 that includes an encrypted combination of an identification code, a time, and a random challenge. The tag receiver 6 decodes the received identification signal 11 to obtain the identification code of the identification tag 20.

[0052] In other examples, different encryption configurations may be used. In some examples, the interrogation signal 32 may include an encrypted combination of a time, a random challenge, and the identification code of the identification tag 20 from which the interrogation signal 32 is transmitted. In such examples, the identification tag 20 may be configured to respond only to interrogation signals 32 that include its identification code. In some examples, the identification tag 20 may be configured to rate-limit responses. In some examples, the identification tag 20 may further include a clock and be configured to ignore older interrogation signals 32 to prevent "replay" type attacks using recorded interrogation signals 32. In some examples, the interrogation signal 32 may include a counter, random value, or pseudorandom value instead of a time value to prevent "replay" type attacks.

[0053] In general, it is desirable for each identification tag 20 to be given a unique identification code so that the identification tag 20 and the satellite 10 to which it is attached can be unambiguously identified. This may be absolutely unique, with each identification code being used only by one identification tag 20, or an identification code may be reused only if the identification tag 20 using that code is confirmed to be unusable, for example, if the satellite 10 to which the identification tag 20 is attached deorbits. In other examples, the identification code may be virtually unique, and in situations where there is no possibility of confusion, the same identification code may be used for identification tags 20 attached to satellites 10 in sufficiently different orbits that they can be easily distinguished by a combination of information from radar 2 and tracking system 5.

[0054] In some use cases for the satellite identification systems according to the first and second embodiments, the identification tags 20 or 30 may be located on multiple different satellites 10 that are part of a single launch or constellation, or multiple identification tags 20 or 30 may be located on multiple portions of a single satellite 10. In such use cases, multiple different identification tags 20 or 30 may be simultaneously powered on by radar beam 4 or simultaneously queried by interrogation signal 32. In such cases, it may be desirable for the identification tags 20 or 30 to use orthogonal communication codes so that identification signals 11 from multiple identification tags 20 or 30 can be received and correctly decoded even when multiple identification tags 20 or 30 transmit simultaneously. The orthogonal communication codes may be implemented using something similar to CDMA or OFDM, with each identification tag 20 or 30 assigned a specific chip sequence or multiplexed transmission frequency.

[0055] In some examples, all identification tags associated with a single satellite, a single launch, or a single constellation of satellites may be coordinated to use orthogonal communication codes without aligning the communication codes used by all identification tags to be orthogonal.

[0056] In the first and second embodiments described above, separate radar antennas 3 and receiving antennas 7 are used. In other examples, these antennas may be combined so that the radar antenna 3 is used for both transmitting and receiving radar signals and for receiving identification signals.

[0057] 4 shows a schematic diagram of an identification tag 40 according to the third embodiment. The identification tag 40 can be used in place of the identification tag 20 described in the first and second embodiments.

[0058] The identification tag 40 includes a processor 41, an antenna 42, a capacitor 43, and a solar cell 44. The identification tag 40 is attached to the satellite 10. The identification tag 40 of the third embodiment is similar to the identification tag 20 of the first and second embodiments, except that the identification tag 40 is an active tag having a power source other than radar.

[0059] In operation of the identification tag 40, when the satellite 10 and attached identification tag 40 are exposed to sunlight or other sufficiently strong light, the solar cell 44 generates electrical energy from the light incident on the solar cell 44 and stores this electrical energy in the capacitor 43. The electrical energy stored in the capacitor 43 is used to power the processor 41, which contains a stored identification code. When the satellite 10 passes through the beam 4 of the radar 2, a radar signal is received via the antenna 42. When the processor 41 determines that the received radar signal reaches a predetermined signal strength, it uses the electrical energy stored in the capacitor 43 to transmit the stored identification code via the antenna 42 as an encoded waveform that forms the identification signal 11. The solar cell 44 may include an area of photovoltaic (PV) material.

[0060] The transmit power required for the identification tag 40 depends on the characteristics of the transmitting and receiving systems, the noise environment, the required SNR, and the distance between the satellite 10 and the receiving antenna 7. The identification tag 40 is designed to operate at a 4 mm radiator with 20% efficiency, generating approximately 1 dBm of power in direct sunlight. 2 In the example where the tag receiver 6 includes a 0.5 meter dish antenna with a gain of 27 dBi, the required signal transmission strength at the identification tag 40 and the corresponding required transmission power at different orbital ranges between the satellite 10 and the tag receiver 6's receiving antenna 7 are shown in Table 4 below.

[0061] [Table 4]

[0062] The corresponding power required to transmit a single full-length sequence and the resulting duty cycle, taking into account the power available from the solar cell, is shown in Table 5 below.

[0063] From Table 5, 4 mm 2 It was found that a small solar cell could provide enough energy for power transmission from an identification tag 40 with a duty cycle of 58% and a range of up to 1000 km.

[0064] The identification tag 40 offers similar advantages to the identification tag 20 of the first and second embodiments. Additionally, the use of the higher frequency C-band allows for a smaller antenna than the lower frequency S-band antenna of the identification tag 20, thereby allowing the identification tag 40 to be smaller than the identification tag 20. In some applications, it may be desirable to use the ISM allocated C-band for the identification signal 11.

[0065] [Table 5]

[0066] The identification tag 40 receives the identification signal 11 using the receiving antenna 7, and in some examples may use the receiving antenna 7 to transmit an interrogation signal 32 to trigger transmission of the identification signal 11. The receiving antenna 7 may be smaller than the radar antenna 3, and in some examples, the receiving antenna 7 may be steerably positioned so that it can track the target satellite. This may allow the target satellite 10 to be observed for a longer period of time than the systems of the first and second embodiments, and may help to successfully receive the identification signal from the identification tag 40 on the satellite 10, because the satellite 10 must be within the beam 4 of the radar 2 to be powered.

[0067] In some examples, the encryption tag 40 may include a battery for storing energy instead of or in addition to a capacitor.

[0068] For the avoidance of doubt, the various encryption and signal orthogonality options described above may also be used with the encrypted tag 40 of the third embodiment.

[0069] In the third embodiment above, the encrypted tag 40 may be arranged to transmit an identification signal 11 at a predetermined time rather than responding to an interrogation signal 32 .

[0070] In the second and third embodiments above, the tag receiver 6 uses a single antenna 7 to transmit the interrogation signal 32 and receive the identification signal.

[0071] In other examples, transmission and reception may be separated and antennas used for these different functions.

[0072] In the third embodiment described above, the encryption tag 40 includes a solar cell that generates power to operate the encryption tag 40. In other examples, the encryption tag 40 may include additional or alternative configurations for collecting power from the environment, such as generating power from satellite vibrations.

[0073] In the above embodiments, antenna 7 is used to receive identification signal 11 and, in some examples, also to transmit interrogation signal 32. In some examples, antenna 7 may be omitted and antenna 3 of radar 2 may be used as a common antenna to perform these receiving and transmitting tasks in addition to transmitting and receiving radar signals.

[0074] In the above embodiment, a high power, large aperture S-band pulsed radar is used. In other examples, alternative types of radar may be used.

[0075] The above embodiments include ground-based radar. In other examples, radars located in different locations may be used. In some examples, the radar may be located on a spacecraft or satellite.

[0076] In the illustrated embodiment, the radar 2 and receiver 6 are shown co-located at one location. In other examples, the radar 2 and receiver 6 may be located at separate locations. Additionally, in some examples, the antennas of the radar 2 and / or receiver 6 may be located separate from other portions of the radar 2 and / or receiver 6 and connected by suitable communication means.

[0077] In the above embodiments, an identification signal is employed that includes an identification code. In other examples, the identification signal may not include a code but may allow identification based on other characteristics of the identification signal.

[0078] The above embodiments describe identification tags placed on satellites. Typically, the identification tags are attached to the satellites before launch. However, in some examples, identification tags may be placed on satellites or other orbital objects in space. This may be done, for example, by dedicated satellites to improve identification and tracking of satellites or other orbital objects already in orbit.

[0079] In the above embodiments, some functionality may be provided by software. In other examples, the functionality may be provided in whole or in part in hardware, such as by dedicated electronic circuitry.

[0080] In the above embodiments, portions of the system may be implemented as any form of computing and / or electronic device. Such devices may include one or more processors that are microprocessors, controllers, or other suitable types of processors that process computer-executable instructions to control the operation of the device to collect and record routing information. In some examples, such as when a system-on-chip architecture is used, the processor may include one or more fixed function blocks (also called accelerators) that implement portions of the method in hardware (rather than software or firmware). Platform software, including an operating system or other suitable platform software, may be provided with computing-based devices to enable application software to run on the devices.

[0081] Computer programs and computer-executable instructions may be provided using any computer-readable media accessible by a computing-based device. Computer-readable media include, for example, computer storage media such as memory and communication media. Computer storage media, such as memory, include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer-readable instructions, data structures, program modules, or other data. Computer storage media includes, but is not limited to, RAM, ROM, EPROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVDs) or other optical storage devices, magnetic cassettes, magnetic tape, magnetic disk storage devices or other magnetic storage devices, or other non-transmission media that can be used to store information for access by a computing device. In contrast, communication media may embodi computer-readable instructions, data structures, program modules, or other data in a modulated data signal, such as a carrier wave or other transport mechanism. As defined herein, computer storage media does not include communication media.

[0082] As used herein, the terms "processor" and "computer" refer to any device with processing capability that is capable of executing instructions.

[0083] It is understood that the benefits and advantages described above may pertain to one embodiment or to multiple embodiments, and embodiments are not limited to those that solve any or all of the stated problems or have any or all of the stated benefits and advantages.

[0084] A reference to "an" item refers to one or more of those items. As used herein, the term "comprising" means including the specified method steps or elements, but such steps or elements do not constitute an exclusive list and the method or apparatus may include additional steps or elements.

[0085] The above description of preferred embodiments is given by way of example only, and it will be understood that various modifications may be made by those skilled in the art. While various embodiments have been described above with a certain degree of particularity or with reference to one or more individual embodiments, those skilled in the art could make many modifications to the disclosed embodiments without departing from the spirit or scope of the invention.

Claims

1. 1. A self-contained identification tag attachably disposed on a resident space object (RSO), said tag comprising: a processor; The antenna and an energy harvester arranged to harvest energy from the environment; and an energy store arranged to receive and store energy from the energy harvester; The processor is arranged to transmit a radio frequency (RF) identification signal via the antenna using energy stored in the energy store.

2. The tag of claim 1 , wherein the tag is not connected to any power source or power distribution system of the RSO.

3. 3. A tag according to claim 1 or claim 2, wherein the antenna is an energy harvester and is arranged to harvest energy from radar signals incident on the tag.

4. 4. The tag of claim 3, wherein the processor is arranged to transmit the RF identification signal when sufficient energy is stored in the energy store.

5. The tag of claim 1 or claim 2, wherein the energy harvester includes a solar cell.

6. A tag according to any one of the preceding claims, wherein the energy store is a capacitor.

7. A tag according to any one of the preceding claims, wherein the processor is arranged to transmit the RF identification signal at predetermined times.

8. A tag according to any one of the preceding claims, wherein the processor is arranged to transmit the RF identification signal in response to receiving an interrogation signal.

9. The tag of claim 8 , wherein the tag is positioned to receive the interrogation signal via the antenna.

10. 10. A tag according to claim 8 or claim 9, wherein the interrogation signal is encrypted.

11. A tag according to any one of the preceding claims, wherein the identification signal is encrypted.

12. 1. A system for identifying resident space objects, said system comprising: a radar positioned to determine the orbital path of a Resident Space Object (RSO); a receiver arranged to receive an identification signal from an identification tag attached to the RSO and determine the tag identity; The system is configured to determine an identity of an RSO using the determined orbital path and the determined tag identity.

13. 13. The system of claim 12, wherein the system is configured to store the determined orbital paths of the plurality of RSOs in combination with the determined tag identifiers for each to form an RSO identification catalog.

14. 14. The system of claim 12 or claim 13, wherein the system further comprises a transmitter arranged to transmit an interrogation signal to prompt an identification tag attached to the RSO to transmit an identification signal.

15. A system according to any one of claims 12 to 14, wherein the identification signal is encrypted.

16. 16. The system of claim 15, wherein the interrogation signal is encrypted.

17. A system according to any one of claims 12 to 16, wherein the radar and the receiver are co-located.

18. A system according to any one of claims 12 to 17, wherein the radar and the receiver use a common antenna.

19. The system of claim 14 , wherein the radar, the receiver, and the transmitter all use a common antenna.

20. A system according to any one of claims 12 to 16, wherein the radar and the receiver are at separate locations.

21. The system according to any one of claims 12 to 20, wherein the radar is an S-band pulsed radar.

22. A system according to any one of claims 12 to 21, wherein the radar is ground-based or located on a spacecraft or satellite.

23. A system according to any one of claims 12 to 22, further comprising at least one identification tag according to any one of claims 1 to 11.

24. 1. A method for identifying a resident space object, comprising: Attaching a self-contained identification tag to a resident space object (RSO), said tag comprising: a processor; The antenna and an energy harvesting device; an energy store; The method further comprises: Harvesting energy from the environment using an energy harvester, storing the energy from the energy harvester in an energy store, and using the energy stored in the energy store The method further includes transmitting a radio frequency (RF) identification signal via the antenna.

25. 25. The method of claim 24, wherein the tag is not connected to any power source or power distribution system of the RSO.

26. 26. A method according to claim 24 or claim 25, wherein the antenna is an energy harvester and is arranged to collect energy from radar signals incident on the tag.

27. 27. The method of claim 26, wherein the processor is arranged to transmit an RF identification signal if the energy store contains sufficient stored energy.

28. A tag according to any one of claims 24 to 27, wherein the energy store is a capacitor.

29. A method according to any one of claims 24 to 28, wherein the processor transmits the RF identification signal at a predetermined time.

30. A method according to any one of claims 24 to 29, wherein the processor transmits the RF identification signal in response to receiving an interrogation signal.

31. 31. The method of claim 30, wherein the tag receives the interrogation signal via an antenna.

32. 32. A method according to claim 30 or claim 31, wherein the interrogation signal is encrypted.

33. A method according to any one of claims 24 to 32, wherein the identification signal is encrypted.

34. 1. A method for identifying a resident space object, comprising: determining an orbital path of the Resident Space Object (RSO) using a radar; and receiving an identification signal from an identification tag attached to the RSO using a receiver; determining a tag identity; determining an identity of the RSO from the determined orbital path and the determined tag identity.

35. 35. The method of claim 34, further comprising storing the determined orbital paths of the plurality of RSOs in combination with their respective determined tag identifiers to form an RSO identification catalog.

36. 36. The method of claim 34 or claim 35, further comprising transmitting an interrogation signal to an identification tag attached to the RSO to prompt the identification tag to transmit an identification signal.

37. The method of any one of claims 34 to 36, further comprising the step of encrypting the identification signal.

38. 37. The method of claim 36, including the step of encrypting the interrogation signal.

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