Patent Description:
Orbital debris is defined as any human-made space object orbiting Earth that no longer serves any useful purpose. Orbital debris poses a risk to space missions. With an average low Earth orbit (LEO) impact velocity of <NUM>,<NUM> MPH, even the smallest of debris can cause significant damage. This is demonstrated by pits in Space Shuttle windows produced by paint chips impacting the windows.

Currently, there are over <NUM> million objects greater than <NUM> orbiting the Earth. However, less than <NUM> percent of debris that can cause mission-ending damage are currently tracked. Due to the dynamic nature of the near-Earth space environment, predicting the trajectory of the debris is extremely difficult, necessitating persistent monitoring.

While debris larger than <NUM> can be detected and tracked, smaller debris cannot be tracked using current capabilities. Debris that is too small to track is often termed lethal non-trackable debris (LNT), and can create significant damage to spacecraft and jeopardize space missions. The detection, tracking, and characterization of non-trackable space debris would support the safe operation of valuable space assets worldwide.

The number of estimated space debris objects greater than <NUM> as a function of time is provided by graph <NUM> in <FIG>. Line <NUM> corresponds to the number of rocket bodies, line <NUM> corresponds to the number of mission related debris, line <NUM> corresponds to the number of spacecraft, and line <NUM> corresponds to the number of fragmentation debris. The annotated increases in line <NUM> take into account <NUM>) the Chinese ASAT test conducted in <NUM>, <NUM>) the accidental collision between Iridium <NUM> and Cosmos <NUM> in <NUM>, and <NUM>) the Russian ASAT test conducted in November <NUM>. Line <NUM> corresponds to all of the number of objects in lines <NUM>-<NUM> added together.

Ground based sensors continue to improve their detection capabilities, but ground sensor detection sensitivity rapidly decreases with increasing altitude and is limited to observing high latitudes. The ground sensors in the U. Space Surveillance Network (SSN) can detect <NUM> objects at <NUM>,<NUM> altitude in low Earth orbit (LEO), and <NUM> objects at <NUM>,<NUM> altitude in geosynchronous equatorial orbit (GEO).

Unfortunately, ground-based sensors are not able to track small objects due to the debris' relatively high angular velocity and must remain in staring mode to count the number of objects passing through their small fields of view. The largest source of uncertainty exists in the ability to interpret the signal strength to determine the size or mass of the object passing through the field of view.

Current estimates for small debris are largely based on collisional detections during U. space shuttle missions, which have now been retired. These collisional detections were restricted to measuring debris strikes at altitudes below <NUM>, the upper limit of space shuttle operations, and were then used to estimate the small debris population at a range of altitudes. Indirect space-based techniques that do not rely on collisions, such as detecting plasma waves emitted from small debris particles, currently are range limited based on the size of debris particle, varying from <NUM> to <NUM>.

Prior art is found in <NPL>, and in <NPL>, showing that debris may be illuminated from Earth by the HAARP High Power HF Transmitter for excitation of Plasma waves, wherein a satellite can detect the debris.

An outer space-based debris detection system comprises first and second satellites. The first satellite is configured to propagate a first series of solitary plasma waves through an outer space detection area having a debris body therein. The debris body propagates second plasma waves therefrom. The second satellite is configured to be associated with the detection area and is configured to receive the first series of solitary plasma waves from the first satellite after interaction with the second plasma waves from the debris body to thereby detect the debris body.

The first satellite may comprise a voltage generator and a plasma perturbation tip coupled thereto. The first satellite may comprise a plasma perturbation tip.

The second plasma waves may comprise a series of solitary plasma waves. The second satellite may be configured to detect the debris body based on determining a phase shift in the first series of solitary plasma waves after interaction with the second series of solitary plasma waves.

The second plasma waves may comprise plasma perturbations. The second satellite may be configured to detect the debris body based on determining an amplitude change in the first series of solitary plasma waves after interaction with the second plasma perturbations.

The first satellite may comprise an array of plasma perturbation tips. The array of plasma perturbation tips may have different sizes. The second satellite may comprise a Langmuir probe array.

The debris body may comprise one of a pinned soliton debris body, a precursor soliton debris body, and a plasma perturbation debris body.

The first and second satellites may each comprise a communications system configured to use a timing reference to synchronize timing therebetween.

The second satellite may comprise a communications system configured to communicate data on the detected debris body.

Yet another aspect is directed to a method for detecting debris in outer space using the outer space-based debris detection system as described above.

The present description is made with reference to the accompanying drawings, in which exemplary embodiments are shown. However, many different embodiments may be used, and thus the description should not be construed as limited to the particular embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Referring initially to <FIG>, a space-based debris detection system <NUM> includes a network of LEO satellites <NUM>-<NUM> in communications with a central command <NUM>. The satellites <NUM>-<NUM> are configured to use plasma wave detection, called PLADAR (plasma detection and ranging) to detect the presence of space debris.

Debris orbiting the Earth within the ionosphere propagates plasma waves based on interaction of the debris with the ionospheric plasma. For example, debris <NUM>, <NUM> propagate plasma density solitary waves, or solitons. A soliton is a self-reinforcing wave packet that maintains its shape while it propagates at a constant velocity. Solitons will propagate without damping in a uniform environment.

The respective solitons generated by debris <NUM>, <NUM> may be referred to as pinned solitons <NUM> and precursor solitons <NUM>. Debris <NUM> propagates pinned solitons <NUM>, which travel with the debris at the same speed. Debris <NUM> propagates precursor solitons <NUM>, which advance upstream of the debris. Pinned solitons <NUM> are created when the debris velocity is greater than the ion acoustic velocity in a plasma. Precursor solitons <NUM> are created when the debris velocity is comparable to the ion acoustic velocity.

Not all debris within the ionosphere will propagate solitons, such as debris <NUM>. This may be due to the debris being at a higher altitude and/or being larger in size. Instead, debris <NUM> propagates plasma perturbations <NUM>, which does not maintain its shape. Instead, the plasma perturbations <NUM> are attenuating or damping in a uniform environment as the plasma wave travels.

As will be explained in detail below, debris detection is performed without requiring collision with the debris. A first satellite within the debris detection system <NUM> includes a plasma perturbation tip to propagate solitons through a detection area, which are received by a second satellite. The solitons may be actively generated or passively generated by the first satellite. The second satellite includes a plasma receiver, such as a Langmuir probe, to receive the solitons.

As the solitons from the first satellite travel through the detection area, they interact or collide with the plasma waves generated by the debris. This interaction or collision is determined by the second satellite, which indicates detection of debris within the detection area.

If the debris is generating solitons, then the detection is based on determining a phase shift in the solitons from the first satellite after interaction with the solitons from the debris. The magnitude of the phase shift may be further used to determine a size of the debris. If the debris is generating plasma perturbations, then the detection is based on determining a change in amplitude in the solitons from the first satellite after interaction with the plasma perturbations from the debris.

As an example, satellite <NUM> has a plasma perturbation tip to propagate a first series of solitons <NUM>. The first series of solitons <NUM> are received by satellites <NUM> and <NUM>. The solitons <NUM> are evenly spaced due to the periodicity of the solitons. The solitons <NUM> may be referred to as a train of solitons that propagate through space at regular intervals and amplitudes. The solitons <NUM> are evenly spaced due to the periodicity of the solitons. In addition, a timing reference <NUM> may be provided by satellite <NUM> to satellites <NUM> and <NUM>. The timing reference <NUM> establishes and synchronizes timing between satellite <NUM> and satellites <NUM>, <NUM>.

Debris <NUM> within a detection area propagates a second series of solitons <NUM>, i.e., pinned solitons. The second series of solitons <NUM> interact with the first series of solitons <NUM>. This interaction, when received by satellites <NUM> and <NUM>, causes a phase shift in the first series of solitons <NUM>. After this interaction, the first series of solitons <NUM> become unevenly spaced due to the phase shift, as indicated by references <NUM>(<NUM>) and <NUM>(<NUM>). This allows satellites <NUM> and <NUM> to detect the debris <NUM> based on the respective received phase shifts <NUM>(<NUM>) and <NUM>(<NUM>).

The central command <NUM> is in communications with satellite <NUM>, as indicated by dashed line <NUM>. Although not shown, the central command <NUM> is also in communications with satellites <NUM>-<NUM>. In the above example, satellites <NUM> and <NUM> provide debris detection data to the central command <NUM> when the debris <NUM> has been detected. The central command <NUM> is able to construct a debris field map based on the debris detection data. The central command <NUM> may use the debris detection data to catalog the debris <NUM>, as well as track a trajectory of the debris <NUM> since satellites <NUM> and <NUM> are providing respective debris detection data.

In response to the trajectory of the debris <NUM> potentially crossing paths with space assets <NUM> and <NUM>, the central command <NUM> may provide commands to the space assets <NUM> and <NUM> to optimize mission performance, as indicated by dashed lines <NUM>, <NUM>. Such commands may alter a path of the space assets <NUM> and <NUM> to avoid collision with the debris <NUM>.

As another example, satellite <NUM> has a plasma perturbation tip to propagate its own first series of solitons <NUM>, which are received by satellite <NUM>. In addition, a timing reference <NUM> may be provided by satellite <NUM> to satellite <NUM>. Debris <NUM> within a detection area propagates a second series of solitons <NUM>, i.e., precursor solitons. The second series of solitons <NUM> interact with the first series of solitons <NUM>. This interaction, when received by satellite <NUM>, causes a phase shift in the first series of solitons <NUM>. After this interaction, the first series of solitons <NUM> become unevenly spaced due to the phase shift, as indicated by reference <NUM>(<NUM>). This allows satellite <NUM> to detect the debris <NUM>. Satellite <NUM> provide debris detection data to the central command <NUM> when the debris <NUM> has been detected.

As yet another example, satellite <NUM> has a plasma perturbation tip to propagate its own first series of solitons <NUM>, which are received by satellite <NUM>. In addition, a timing reference <NUM> may be provided by satellite <NUM> to satellite <NUM>. Debris <NUM> within a detection area propagates second plasma waves <NUM>, i.e., plasma perturbations, which are not solitons. The second plasma perturbations <NUM> interact with the first series of solitons <NUM>. This interaction, when received by satellite <NUM>, causes a change in amplitude (i.e., attenuation or damping) of the first series of solitons <NUM>. After this interaction, the first series of solitons <NUM> may remain evenly spaced but have been attenuated, as indicated by reference <NUM>(<NUM>). This allows satellite <NUM> to detect the debris <NUM>. Satellite <NUM> likewise provides debris detection data to the central command <NUM> when the debris <NUM> has been detected.

Referring now to <FIG>, a pair of satellites <NUM>, <NUM> operating in the debris detection system <NUM> will be discussed. Satellites <NUM>, <NUM> may also be referred to as first and second satellites. In this case, the debris <NUM> to be detected within a detection area propagates a second series of solitons <NUM>, i.e., pinned solitons or precursor solitons.

The first and second satellites <NUM>, <NUM> are configured so that the trajectory of the detected debris <NUM> may be determined by multiple debris detection data collected by the second satellite <NUM>. This is in contrast to the above example, where the central command <NUM> collectively used both of the individual debris detection data provided by satellites <NUM> and <NUM> to track a trajectory of the debris <NUM>.

The first satellite <NUM> includes an array of plasma perturbation tips <NUM>(<NUM>)-<NUM>(<NUM>), which may be generally referred to as plasma perturbation tips <NUM>. Each plasma perturbation tip <NUM> is configured to propagate a respective first series of solitons through the outer space detection area having the debris <NUM> therein. As advantage of the first satellite <NUM> propagating more than one first series of solitons is that the second satellite is able to provide multiple debris detection data based on the respective interactions of each of the first series of solitons with the second series of solitons <NUM> from the debris <NUM>. The multiple debris detection data is to be used to determine a trajectory of the debris <NUM>.

Plasma perturbation tip <NUM>(<NUM>) propagates a first series of solitons <NUM>(<NUM>), plasma perturbation tip <NUM>(<NUM>) propagates another first series of solitons <NUM>(<NUM>), and plasma perturbation tip <NUM>(<NUM>) propagates yet another first series of solitons <NUM>(<NUM>). The first series of solitons <NUM>(<NUM>)-<NUM>(<NUM>) may be generally referred to by reference number <NUM>. Even though three plasma perturbation tips <NUM>(<NUM>)-<NUM>(<NUM>) are shown, this is not to be limiting, as one or more plasma perturbation tips may be used.

The plasma perturbation tips <NUM> are metal and are embedded in an insulating material <NUM>. The size and shape of the plasma perturbation tips <NUM> may vary. The size of the plasma perturbation tip <NUM> sets a width of the first series of solitons <NUM> being propagated from that plasma perturbation tip <NUM>. The solitons may travel further when a smaller width soliton is used, which is an advantage for ranging.

The plasma perturbation tips <NUM> may be carried by the first satellite <NUM> using a rigid boom <NUM>. The rigid boom <NUM> extends away from the first satellite <NUM>, and may be configured out of a composite material that is insulated. As an alternative to the rigid boom <NUM>, the plasma perturbation tips <NUM> may be coupled to the first satellite <NUM> using carbon fiber tethers.

As noted above, the first series of solitons may be actively or passively generated. To actively generate the first series of solitons <NUM>, a voltage generator <NUM> provides an electrical signal to each of the metal plasma perturbation tips <NUM>. To passively generate the first series of solitons <NUM>, interaction of each metal plasma perturbation tip <NUM> with the ionospheric plasma inherently propagates the first series of solitons <NUM> without the need for the voltage generator <NUM>.

Even though there is periodicity in the first series of solitons <NUM> when passively generated, greater control of the solitons is provided when actively generated. When the first series of solitons <NUM> are actively generated, a forcing function is used. The level of voltage applied by the voltage generator <NUM> to each metal plasma perturbation tip <NUM> sets the amplitude of the respective forcing functions.

By varying the amplitude and/or the shape of the forcing function allows different types of solitons <NUM> to be generated. This allows the second satellite <NUM> to more accurately detect the debris <NUM>. In addition, the different types of solitons <NUM> may serve as fingerprints of the debris <NUM> allowing for differentiation of the interactions of the first series of solitons <NUM> with the second series of solitons <NUM> from the debris <NUM>.

The first satellite <NUM> includes a controller <NUM> coupled to the voltage generator <NUM> for control thereof. The controller <NUM> is also coupled to a communications system <NUM>. The communications system <NUM> allows for communications with the second satellite <NUM>, as well as with central command <NUM>. The communications may be based on radio frequency (RF) signals or optical signals. Also, the communications system <NUM> allows a timing resource to be provided to synchronize timing with the second satellite <NUM>.

The second satellite <NUM> includes a plasma receiver <NUM> configured to receive the respective first series of solitary plasma waves <NUM> from the first satellite <NUM> after interaction with the second series of solitons <NUM> from the debris <NUM>. The plasma receiver <NUM> may be a Langmuir probe array.

A Langmuir probe array <NUM> is a device used to determine the electron temperature, electron density, and electric potential of a plasma. The Langmuir probe array <NUM> has a plurality of electrodes <NUM> that are used to receive the respective first series of solitons <NUM> from the first satellite <NUM>, and after interactions of the respective first series of solitons <NUM> with the second series of solitons <NUM> from the debris <NUM>.

The second satellite <NUM> includes a controller <NUM> coupled to the plasma receiver <NUM>. The controller <NUM> includes a processor to analyze interactions of the first series of solitons <NUM> with the second series of solitons <NUM> from the debris <NUM>. Detection of the debris <NUM> is based on determining respective phase shifts in the first series of solitons <NUM> from the first satellite <NUM> after interaction with the second series of solitons <NUM> from the debris <NUM>.

The overall arrival time of each first series of solitons <NUM> after interaction with the second series of solitons <NUM> from the debris <NUM> can be used to determine the location of the debris <NUM> between the first and second satellites <NUM>, <NUM>. Multiple measurements of the debris <NUM> with the Langmuir probe array <NUM> can be used to determine the orbital trajectory of the debris <NUM>.

For example, interactions of the first series of solitons <NUM>(<NUM>) with the second series of solitons <NUM> from the debris <NUM> causes a phase shift (i.e., a time delay) as indicated by reference <NUM>(<NUM>). Instead of the solitons <NUM>(<NUM>) being evenly spaced, there is a time delay such that the solitons <NUM>(<NUM>) become unevenly spaced. Interactions of the first series of solitons <NUM>(<NUM>) with the second series of solitons <NUM> from the debris <NUM> causes a phase shift as indicated by reference <NUM>(<NUM>). Interactions of the first series of solitons <NUM>(<NUM>) with the second series of solitons <NUM> from the debris <NUM> causes a phase shift as indicated by reference <NUM>(<NUM>).

The controller <NUM> may provide the multiple debris detection data to the communications system <NUM> for transmission to the central command <NUM>. The multiple debris detection data is used to advantageously determine the orbital trajectory of the debris <NUM>. The communications system <NUM> also allows for communications with the first satellite <NUM>. The communications may be based on radio frequency (RF) signals or optical signals. The communications system <NUM> allows a timing resource to be received to synchronize timing with the first satellite <NUM>.

The first satellite <NUM> is configured to provide a transmit function, wherein the first series of solitary plasma waves <NUM> are propagated by the plasma perturbation tips <NUM>. The second satellite <NUM> is configured to provide a receive function, wherein the plasma receiver <NUM> receives the respective first series of solitary plasma waves <NUM> from the first satellite <NUM> after interaction with the second series of solitons <NUM> from the debris <NUM>. Although the transmit and receive functions are in separate satellites, transmit and receive functions may be combined into a single satellite. For example, one side of the satellite may provide the transmit function whereas an opposite side of the satellite may provide the receive function. A network of dual function satellites may be used to detect space debris as described above.

Referring now to <FIG>, images of distinct soliton plasma waves before and after collision will be discussed. Image <NUM> is of soliton A plasma waves <NUM> advancing in space as time elapses before collision. Soliton A plasma waves <NUM> are labeled Atf. Soliton A plasma waves <NUM> may be propagated by a satellite. Image <NUM> is of soliton B plasma waves <NUM> advancing in space as time elapses before collision. Soliton B plasma waves <NUM> are labeled Btf. Soliton B plasma waves <NUM> may be propagated by debris.

Image <NUM> is of soliton A plasma waves <NUM> after collision with soliton B plasma waves <NUM>. After collision, soliton A plasma waves <NUM> are labeled A'tf and soliton B plasma waves <NUM> are labeled B'tf. The collision can result in a scattering effect, similar to a cue ball hitting a pool ball.

A plot <NUM> showing the scattering effect of soliton A plasma waves <NUM> with soliton B plasma waves <NUM> at a particular instant in time (i.e., t=<NUM>) will be discussed in reference to <FIG>. The collision produces measurable displacements in time and spaces, which can be correlated with the presence of a specific debris body.

Line <NUM> corresponds to soliton Atf as a function of wave amplitude versus an arbitrary space unit (AU) before collision. Line <NUM> corresponds to soliton Btf as a function of wave amplitude versus an arbitrary space unit (AU) before collision.

The collision between soliton Atf and soliton Btf is indicated by line <NUM>. As a result of the collision, soliton A'tf is delayed in space as indicated by arrow <NUM> and soliton B'tf is advanced in space as indicated by arrow <NUM>. Soliton A'tf is slowed down and soliton B'tf is sped up.

Referring now to <FIG>, a plot <NUM> correlating phase shift to a radius of the detected debris will be discussed. In addition to the phase shift being used to detect a debris body, the phase shift may be further used to estimate a size of the debris body.

In this case study, solitons A were purposefully generated with a forcing function of <NUM>. The forcing function corresponds a plasma perturbation tip having a size of <NUM> to propagate solitons A.

Solitons A propagated by the <NUM> plasma perturbation tip were collided with plasma waves (i.e., solitons B) produced by debris bodies of varying size. The temporal difference between the arrival time of soliton A at a plasma receiver without a collision, and the measured arrival time when a collision took place with soliton B, were tabulated as a function of the debris radius.

The nearly vertical line <NUM> between upper diamond <NUM> and lower diamond <NUM> is considered the crossover point when soliton A and soliton B collide. The crossover point is aligned with a debris radius of <NUM>. Solitons A and B are considered to have the same properties at the time of collision. If a size of the plasma perturbation tip was changed to <NUM>, then the crossover point would be shifted to <NUM>.

The phase shift may be negative <NUM> or positive <NUM>. A negative phase shift <NUM> starts with lower diamond <NUM> and angles to the left side of the plot, and a positive phase shift <NUM> starts with upper diamond <NUM> and angles to the right side of the plot. The phase shift <NUM> is negative when the debris radius is less than <NUM>, and is positive <NUM> when the debris radius is greater than <NUM>.

The difference in the time of arrival of the solitary wave changes as a function of the debris radius, meaning that not only can collisions with debris be indirectly detected with this method, but that debris sizes can also be categorized!.

Referring now to <FIG>, a flowchart <NUM> illustrating a method for operating the debris detection system <NUM> as described above will be discussed. From the start (Block <NUM>), the method includes operating a first satellite <NUM> at Block <NUM>. The first satellite <NUM> is operated to propagate a first series of solitary plasma waves <NUM> through an outer space detection area having a debris body <NUM> therein. The debris body <NUM> propagates a second plasma waves <NUM> therefrom. A second satellite <NUM> is operated at Block <NUM>. The second satellite <NUM> is associated with the detection area and is configured to receive the first series of solitary plasma waves <NUM>(<NUM>) from the first satellite <NUM> after interaction with the second plasma waves <NUM> from the debris body <NUM> to thereby detect the debris body <NUM>. The method ends at Block <NUM>.

As described above, the debris detection system <NUM> may be used to assemble debris maps. Another use case of the satellites in the debris detection system <NUM> is that at least two of the satellites may be configured as low cost satellites used to protect a high value asset, such as a larger more expensive satellite. The low cost satellites travel ahead of the high value asset, and provide actionable intelligence about mission ending or compromising debris threats. In addition to the low cost satellites detecting debris ahead of the high value asset, another use case is for the low cost satellites to detect the presence of hostile satellites or other space objects ahead of the high value asset. Detection of the hostile satellites and other space objects is similar to detecting debris since the hostile satellites and the other space objects propagate plasma waves.

Claim 1:
An outer space-based debris detection system (<NUM>) comprising:
a first satellite (<NUM>) configured to propagate first solitary plasma waves (<NUM>) through an outer space detection area having a debris body (<NUM>) therein, the debris body (<NUM>) propagating second plasma waves (<NUM>) therefrom; and
a second satellite (<NUM>) configured to be associated with the outer space detection area and configured to receive the first solitary plasma waves (<NUM>) from the first satellite (<NUM>) after interaction with the second plasma waves (<NUM>) from the debris body (<NUM>) to thereby detect the debris body (<NUM>).