JP7406791B2 - Artificial satellite - Google Patents

Description

The present invention relates to an artificial satellite.

An artificial satellite is equipped with an antenna for transmitting and receiving data to and from a ground station. Patent Documents 1 to 4 disclose antennas mounted on artificial satellites. For example, the antenna of Patent Document 1 has a configuration that can be suitably mounted on a small artificial satellite.

Patent No. 5991578 Japanese Patent Application Publication No. 10-270923 Japanese Patent Application Publication No. 11-186825 Japanese Patent Application Publication No. 11-186840

Small satellites equipped with the antenna of Patent Document 1 are being actively studied at research institutions such as universities. For example, a CubeSat, which is an example of a small satellite, has a cubic shape with a side of about 10 cm. Since the volume of the casing of such a satellite is limited, it is difficult to mount an attitude control device on board. An artificial satellite without an attitude control device will constantly change its attitude. As the satellite's attitude changes, the orientation of the antenna onboard the satellite also changes. Therefore, depending on the orientation of the antenna, it may not be possible to maintain good communication conditions with the ground station.

Therefore, an object of the present invention is to provide an artificial satellite that can maintain good communication conditions.

An artificial satellite that is an embodiment of the present invention includes a satellite main body and an antenna disposed on at least one main surface of the satellite main body, and the antenna is a loop antenna formed in an arc shape and rising from the main surface. be.

This satellite is equipped with a loop antenna. In the loop antenna, the directivity of the antenna can be set in a desired manner depending on the length of the arc-shaped portion. In other words, it is possible to widen the radiation angle. In this way, even if the direction of the antenna is not constant, it is possible to maintain a good communication state with the ground station.

In the above artificial satellite, the antenna can be elastically deformed, and the antenna may be switched from a first form along the main surface to a second form standing up from the main surface by the restoring force of the antenna. According to this configuration, the external dimensions of the artificial satellite can be reduced by using the first form. Moreover, by adopting the second form, a good communication state can be ensured.

The above artificial satellite may further include an antenna holding section that maintains the first form. According to this configuration, the state in which the external dimensions are reduced can be suitably maintained. Therefore, when mounted on a rocket or the like, the external dimensions of the artificial satellite can be kept within desired dimensions.

In the above artificial satellite, the antenna includes an antenna element that performs an antenna function, and the length of the antenna element may be shorter than the wavelength of the radio waves to be transmitted and/or received. According to this configuration, the radiation angle of the antenna can be widened.

In the above artificial satellite, the antenna may further include an antenna input/output section that transfers power to and from the antenna element, and a matching section connected between the antenna element and the antenna input/output section. According to this configuration, it becomes possible to adjust the matching between the antenna and the device connected to the antenna. Therefore, even better communication conditions can be maintained with the ground station.

In the above artificial satellite, the length of the antenna element may be greater than 0.6λ and smaller than 0.8λ with respect to the wavelength (λ) of the radio wave. According to this configuration, it is possible to set a good balance between the radiation angle and the radiation intensity of the antenna.

In the above artificial satellite, the length of the antenna element may be 0.7λ with respect to the wavelength (λ) of the radio wave. According to this configuration, it is possible to set a better balance between the radiation angle and the radiation intensity of the antenna.

According to the present invention, an artificial satellite capable of maintaining good communication conditions is provided.

FIG. 1 is a perspective view of an artificial satellite according to an embodiment in an expanded configuration. FIG. 2 is a plan view of the artificial satellite according to the embodiment in an expanded configuration. FIG. 3 is an enlarged side view of a cross section of the artificial satellite according to the embodiment when it is in a deployed configuration. FIG. 4 is a perspective view of the artificial satellite according to the embodiment in a non-deployed state. Parts (a) to (d) of FIG. 5 are diagrams showing the results of analyzing the directivity of the antenna of the comparative example. Parts (a) to (d) of FIG. 6 are diagrams showing the results of analyzing the directivity of the antenna of the embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an artificial satellite according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description will be omitted. Furthermore, each drawing is created for the purpose of explanation, and is drawn so as to particularly emphasize the target portion of the explanation. Therefore, the dimensional ratio of each member in the drawings does not necessarily match the actual one.

FIG. 1 is a perspective view of the artificial satellite 1. FIG. 1 shows a state in which an artificial satellite 1 placed into orbit is in operation. The artificial satellite 1 is an ultra-small artificial satellite called a CubeSat. The artificial satellite 1 is a so-called piggyback satellite, and is placed into orbit together with the main satellite by utilizing the extra launch capacity of a large rocket. Furthermore, the artificial satellite 1 may be sent as a payload to a space station in orbit, and ejected from the space station into orbit.

The artificial satellite 1 includes a satellite body 10 and an antenna 20.

The satellite main body 10 has functional units that realize a predetermined mission. Functional units include power supplies, communication devices, control devices, etc. Note that the control device is a device that controls the electrical operation of the artificial satellite 1. In other words, the artificial satellite 1 does not include a device or function for actively controlling the attitude of the satellite body 10 as an essential element. The artificial satellite 1 without an attitude control device maintains a state of motion with respect to an inertial frame according to the law of inertia. In other words, the attitude of the artificial satellite 1 can always change over time.

The satellite main body 10 has a substantially rectangular parallelepiped shape, and more specifically, it may have a substantially cubic shape. The size of the satellite body 10 is, for example, 10 cm x 10 cm x 10 cm, 10 cm x 10 cm x 20 cm, 10 cm x 10 cm x 30 cm, etc. The satellite main body 10 when it is cubic has six exposed walls 11A to 11F. A power generation panel 12 is provided on each of these exposed walls 11A to 11F. Note that the power generation panel 12 does not need to be provided on all exposed walls 11A to 11F, and may be provided on some exposed walls as necessary. An antenna 20 is provided on one of the exposed walls 11A to 11F.

The antenna 20 is a so-called loop antenna. The antenna 20 is designed to achieve a predetermined radiation angle and radiation intensity. Specifically, as described above, the attitude of the artificial satellite 1 can always change over time. In other words, the orientation of the antenna 20 with respect to the ground station also constantly changes over time. In such an operation, if the antenna 20 has strong directivity, a good communication state may be achieved depending on the orientation of the antenna 20 with respect to the ground station. On the other hand, depending on the orientation of the antenna 20 with respect to the ground station, good communication conditions may not be achieved. Therefore, in the artificial satellite 1, a good communication condition is continuously achieved by balancing the radiation angle and the radiation intensity. In other words, the antenna 20 is set at a radiation angle and radiation intensity that can maintain communication with the ground station no matter what the attitude of the artificial satellite 1 is.

As shown in FIGS. 2 and 3, the antenna 20 is composed of several components. Specifically, the antenna 20 includes an antenna element 21, a matching section 22, and an antenna input/output section 23.

The antenna element 21 is a part that functions as an antenna. The antenna element 21 is made of a wire rod having a multilayer structure, and the wire rod is formed in an arc shape to have a diameter determined by conditions described below.

The antenna element 21 has a main line portion 21m, a conductive coating portion 21n, and an insulating coating portion 21p. The main line portion 21m may be made of, for example, spring steel. The conductive coating portion 21n is, for example, a copper plating layer. The insulating coating portion 21p is made of a resin material having electrical insulation properties, and may be a tube made of Teflon (registered trademark), for example.

The main dimensions of the antenna element 21 are set based on the frequency (λ) of radio waves to be transmitted and received. For example, the frequency of radio waves is 437 MHz. In a typical loop antenna, the length of one circumference (circumferential length: L) of the antenna element 21 is set to 1λ for such a radio wave frequency (λ). For example, if the frequency is 437 MHz, the circumferential length (L) is approximately 68.6 cm. This state is a so-called resonance state. On the other hand, in the artificial satellite 1 of this embodiment, the circumferential length (L) of the antenna element 21 is set to be shorter than the wavelength of the radio wave. That is, the circumferential length (L) of the antenna element 21 is set to 0.6λ or more and 0.8λ or less. As an example, the circumferential length (L) of the antenna element 21 may be set to 0.7λ. In this state, the circumferential length (L) of the antenna element 21 is a non-resonant state, as opposed to a resonant state in which the circumferential length (L) is 1λ.

The antenna element 21 includes an element main body 21a and an element end 21b. The element main body 21a is a portion that stands up from the exposed wall 11A and has an arcuate shape. The element end portion 21b extends to the back surface 11A2 of the exposed wall 11A through a through hole in the exposed wall 11A. The element end portion 21b is fixed to the exposed wall 11A by being held between the bolt 41 and the exposed wall 11A. In other words, the element end portion 21b includes a first portion held between the bolt 41 and the exposed wall 11A, a second portion bent at approximately 90 degrees (approximately right angle) from the first portion, and a second portion that is bent from the first portion at approximately a right angle. A third portion extends in the thickness direction of the exposed wall 11A and continues to the element main body 21a through the through hole of the exposed wall 11A.

The matching unit 22 performs impedance matching between the antenna element 21 and an external device (for example, a communication control device). The matching part 22 includes a pair of conductor parts 22a extending along the exposed wall 11A, and a U-shaped connection part 22b that connects an end of one conductor part 22a to an end of the other conductor part 22a. . Matching between the antenna element 21 and external equipment is set according to the length of the conducting wire portion 22a. For example, the length of the matching section 22 may be set to be slightly shorter than 0.3λ, which is 1λ minus 0.7λ, the circumferential length of the antenna element 21. Further, the shortness of the length of the matching section 22 may be set in consideration of the influence of surrounding members such as a solar panel. The conducting wire portion 22a is arranged on the back side of the exposed wall 11A (that is, on the inside of the satellite main body 10). For example, like the antenna element 21, the conducting wire portion 22a may be made of a wire having a multilayer structure. The matching end portion 22t of the matching portion 22 is one end portion of the conducting wire portion 22a. The matching end portion 22t is arranged on the antenna element 21 side. The matching end portion 22t is drawn out from the back surface 11A2 of the exposed wall 11A to the front surface 11A1 (main surface) through the through hole of the exposed wall 11A. The matching end portion 22t is fixed to the surface 11A1 side of the exposed wall 11A by a nut 42. As described above, the nut 42 and bolt 41 fix the element end 21b on the back surface 11A2 side of the exposed wall 11A. Therefore, the matching end 22t is electrically connected to each of the element ends 21b via the bolt 41 and nut 42.

The other end of the matching section 22 is arranged on the opposite side to the position where the antenna element 21 is arranged. The other end of the matching section 22 is a connecting section 22b. Specifically, the connecting portion 22b is drawn out from the back surface 11A2 of the exposed wall 11A to the front surface 11A1 through a through hole in the exposed wall 11A. The pulled-out connecting portions 22b are electrically connected to each other by U-shaped connecting portions.

The antenna input/output section 23 is provided on the other end side of the matching section 22. That is, in this embodiment, the antenna input/output unit 23 is a part of the matching unit 22. The antenna input/output unit 23 provides a signal to the antenna element 21 connected via the matching unit 22 and receives a signal from the antenna element 21 . For example, a coaxial cable 43 is connected to the antenna input/output section 23. Therefore, signals are transmitted and received via the coaxial cable 43 to the communication device housed in the satellite body 10.

Antenna 20 can take two forms. Specifically, antenna 20 can take a non-deployed configuration and a deployed configuration. These two configurations are irreversibly switched from the non-deployed configuration to the deployed configuration.

<Non-deployed form (first form)>
FIG. 4 shows the artificial satellite 1 in a non-deployed configuration. The non-deployed form is, for example, a form that can be taken when the artificial satellite 1 is mounted on a rocket. The non-deployed form can also be said to be a form in which the antenna 20 is not deployed. Therefore, when the artificial satellite 1 is in the non-deployed state, the external dimensions of the artificial satellite 1 can be considered to be approximately the same as the external dimensions of the satellite main body 10.

When in the non-deployed configuration, the antenna element 21 is bent along the exposed wall 11A. More specifically, the antenna element 21 is double-wound or triple-wound, and has a diameter (D1) smaller than the diameter (D) when unfolded. Further, the antenna element 21 is bent at a substantially right angle at the third portion protruding from the through hole toward the surface 11A1. In other words, the antenna element 21 undergoes bending deformation in the extending direction and torsional deformation centered on the extending direction. These bending deformations and torsional deformations are in a range smaller than the stress and strain indicating the yield point of the spring steel forming the main line portion 21m. By keeping the bending deformation and torsional deformation within such ranges, the bending deformation and torsional deformation remain in the so-called elastic region. As a result, upon releasing the force maintaining the deformation, the antenna element 21 can return to its original shape. Therefore, as the material for the main line portion 21m of the antenna element 21, it is preferable to select a material with a wide elastic range.

The antenna element 21 in the non-deployed state undergoes bending and twisting deformations as elastic deformations. Therefore, in order to maintain this deformed state, it is necessary to apply a force that counters the restoring force caused by bending and torsional deformation. Therefore, the artificial satellite 1 has an antenna holding section 30 for maintaining the deformed state. The antenna holding portion 30 resists restoring force caused by bending deformation. This restoring force can be said to be along the surface 11A1 of the exposed wall 11A, for example. Furthermore, the antenna holding portion 30 resists restoring force caused by torsional deformation. This restoring force can be said to be along the normal direction of the surface 11A1 of the exposed wall 11A, for example.

For example, the antenna holding section 30 includes three pins 31A, 31B, and 31C, two holding threads 32A and 32B, and a thread cutting section 33. Pins 31A, 31B, and 31C stand up from surface 11A1 of exposed wall 11A. The pins 31A, 31B, and 31C are arranged at the vertices of an equilateral triangle or an isosceles triangle when viewed from above. For example, pin 31C is arranged between element ends 21b. The pins 31A and 31B are spaced apart from each other between the power generation panels 12. The holding thread 32A is stretched between the pins 31A and 31C. The holding thread 32B is stretched between the pins 31B and 31C. The holding threads 32A, 32B generate forces that counteract the two restoring forces mentioned above. Note that the bent antenna element 21 may be in contact with the pins 31A and 31B. In this case, the pins 31A and 31B can also be treated as generating a force that opposes the restoring force along the surface 11A1 of the exposed wall 11A.

Then, the thread cutting section 33 cuts the holding threads 32A and 32B, respectively. The timing at which the thread cutting section 33 cuts the holding threads 32A and 32B may be determined according to a desired definition. For example, the time elapsed after the control device mounted on the satellite main body 10 started operating may be counted, and the cutting operation may be performed after a predetermined period of time has elapsed. This predetermined time may be the time from when power is turned on to the artificial satellite 1 mounted on a rocket until it is launched into orbit from the rocket. Furthermore, as another example, the disconnection operation may be performed based on changes that occur when the artificial satellite 1 is separated from the rocket (for example, impact, ON/OFF of a mechanical switch), etc. As a result of the cutting action, the force opposing the restoring force is released, so that the restoring force causes the antenna element 21 to transition into the deployed configuration.

Note that the above configuration is an example of the antenna holding section 30. The antenna holding section 30 is not limited to the above example as long as it is a mechanism that can generate these resistance forces and release the resistance forces at a predetermined timing. For example, various configurations may be adopted for cutting the holding threads 32A and 32B. For example, the structure for cutting the holding threads 32A and 32B may be a structure in which the holding threads 32A and 32B are cut mechanically with a cutter or the like, or a structure in which the holding threads 32A and 32B are cut by heating the nichrome wire under timer control. good.

Furthermore, in the antenna holding section, a configuration may be adopted in which the antenna element 21 in the non-deployed state is held by an elastic member such as a clip instead of the pins 31A and 31B. Specifically, an elastic member such as a clip is elastically deformed by a load directed toward the satellite main body 10 side. This deformation is maintained by the holding threads 32A, 32B. Then, when the holding threads 32A and 32B are cut, the deformation of the elastic member such as the clip is released. The holding threads 32A and 32B may be cut by using a timer to count the passage of the scheduled time when they reach the orbit, and when the scheduled time is reached. The cutting may be performed using heating of a nichrome wire. As a result, the deformed state of the antenna element 21 is also released.

Note that even in this non-deployed state, the antenna element 21 can function as an antenna. In this case, the performance as an antenna can be maintained, although the performance is lower than that when the antenna element 21 is in an expanded state. As a result, even if deployment of the antenna element 21 fails for some reason, the antenna element 21 will not lose its function as an antenna. Therefore, regardless of whether the antenna element 21 is deployed successfully or not, it can function as an antenna. As a result, even if deployment of the antenna element 21 fails, the communication function is not lost and operation can be continued within a limited range.

<Development form (second form)>
FIG. 1 shows an artificial satellite 1 in a deployed configuration. The restoring force of the antenna element 21 causes the antenna element 21 to change from the non-deployed state to the deployed state. In other words, the antenna element 21 itself has a function of restoring the shape of the unfolded form. Specifically, the main line portion 21m that constitutes the antenna element 21 exhibits restoring force. Antenna 20 does not require additional actuators to deploy antenna element 21. By simplifying the mechanism for deploying the antenna element 21 in this way, specifically by reducing the number of component parts of the antenna 20, the success rate when deploying the antenna element 21 can be increased.

<Effect>
The artificial satellite 1 includes a satellite body 10 and an antenna 20 disposed on an exposed wall 11A of the satellite body 10. The antenna 20 is a loop antenna that is formed in an arc shape and stands up from the surface 11A1 of the exposed wall 11A.

This artificial satellite 1 is equipped with a loop antenna. In the loop antenna, the directivity of the antenna 20 can be set in a desired manner depending on the length of the arc-shaped portion. In other words, it is possible to widen the radiation angle. Then, even if the direction of the antenna 20 is not constant, it is possible to maintain a good communication state with the ground station.

The antenna 20 can be elastically deformed. The antenna 20 is switched from a non-deployed configuration along the exposed wall 11A to an expanded configuration in which it stands up from the exposed wall 11A by the restoring force of the antenna 20. According to this configuration, the external dimensions of the artificial satellite 1 can be reduced by setting it in a non-deployed form. Further, by using the expanded configuration, a good communication state can be ensured.

The artificial satellite 1 further includes an antenna holding section 30 that maintains the non-deployed state. According to this configuration, the state in which the external dimensions are reduced can be suitably maintained. Therefore, when mounted on a rocket or the like, the external dimensions of the artificial satellite 1 can be kept within desired dimensions.

Antenna 20 includes an antenna element 21 that performs an antenna function. The length of the antenna element 21 is shorter than the wavelength of the radio waves to be transmitted and/or received. According to this configuration, the radiation angle of the antenna 20 can be widened.

The antenna 20 further includes an antenna input/output section 23 that transfers power to and from the antenna element 21, and a matching section 22 connected between the antenna element 21 and the antenna input/output section 23. According to this configuration, it becomes possible to adjust the matching between the antenna 20 and the device connected to the antenna. Therefore, even better communication conditions can be maintained with the ground station.

In the above artificial satellite, the length (L) of the antenna element 21 is greater than 0.6λ and smaller than 0.8λ with respect to the wavelength (λ) of the radio wave. Furthermore, as an example, the length (L) of the antenna element is 0.7λ with respect to the wavelength (λ) of the radio wave. According to this configuration, it is possible to set a better balance between the radiation angle and the radiation intensity of the antenna.

For example, parts (a) to (d) of FIG. 5 are examples of analysis results showing the directivity of the antenna 120 when the antenna element is 1λ. Part (a) of FIG. 5 is a diagram of the artificial satellite 100 and the radiation intensity S100 viewed from an oblique direction. Part (b) of FIG. 5 is a plan view of the artificial satellite 100 and the radiation intensity S100. Part (c) of FIG. 5 is a front view of the artificial satellite 100 and the radiation intensity S100. Part (d) of FIG. 5 is a side view of the artificial satellite 100 and the radiation intensity S100. As shown in parts (a) to (d) of FIG. 5, it can be seen that when the antenna element is set to 1λ, the distribution of the radiation intensity S100 is biased (see symbol SP). In other words, when the antenna element is set to 1λ, the directivity becomes donut-shaped, and there is a direction in which no gain is produced.

As mentioned above, an artificial satellite without an actuator for attitude control constantly rotates. Therefore, for communication with the ground, it is important that there is no directivity in all directions that would result in valleys where radio waves cannot be received.

On the other hand, parts (a) to (d) of FIG. 6 are examples of analysis results showing the directivity when the antenna element 21 is set to 0.7λ. As shown in parts (a) to (d) of FIG. 6, there are no directions in which the radiation intensity S is particularly strong or in which it is particularly weak. It was found that the radiation intensity S was generally uniform in any direction. In other words, it was found that the antenna 20 of the artificial satellite 1 of this embodiment can obtain an all-sky all-round gain. In other words, the artificial satellite 1 of this embodiment is able to secure directivity characteristics in which the gain in all directions (all-sky gain) does not decrease in three dimensions, which is necessary for a small satellite whose attitude cannot be controlled. I understand. The all-sky all-round gain shown in FIG. 6 is due to the adoption of a non-resonant antenna as a characteristic of the antenna 20.

Furthermore, the artificial satellite 1 has the following additional effects.

The antenna 20 of the artificial satellite 1 is a loop antenna. Therefore, when a component (for example, a tether) extends from the artificial satellite 1 in addition to the antenna 20, the component is unlikely to be caught because the antenna 20 is arc-shaped. Therefore, the success rate of the mission of the artificial satellite 1 can be increased.

The antenna 20, which is a loop antenna, is advantageous in that the balance between the radiation angle and the radiation intensity can be adjusted. When it is highly necessary to continuously maintain a communicable state, the radiation angle can be set to have priority over the radiation intensity, as described above. On the other hand, if there is little need to continuously maintain a communicable state, the radiation intensity can be set to have priority over the radiation angle. Additionally, if the satellite is equipped with an attitude control device such as a thruster or reaction wheel, it can actively control its attitude. In other words, it is possible to set the antenna 20 in a desired direction with respect to the ground station. Even in such a case, settings can be made to give priority to the radiation intensity over the radiation angle.

1...Artificial satellite, 11A to 11F...Exposed wall, 11A1...Front surface, 11A2...Back surface, 12...Power generation panel, 20...Antenna, 21...Antenna element, 21b...Element end, 21m...Main line part, 21n...Conductive coating part , 21p...Insulation coating part, 22...Matching part, 22a...Conductor part, 22b...Connection part, 22t...Matching end part, 23...Antenna input/output part, 30...Antenna holding part, 31A, 31B, 31C...Pin, 32A , 32B... Holding thread, 33... Thread cutting section, 41... Bolt, 42... Nut, 43... Coaxial cable.

Claims (5)

The satellite body,
A loop antenna disposed on at least one main surface of the satellite main body, formed in an arc shape and standing up from the main surface, capable of elastic deformation, and capable of changing from a first shape along the main surface to a first shape along the main surface. An antenna that switches to a second form that stands up from a surface by restoring force ;
an antenna holding part that maintains the first form of the antenna,
The antenna includes an element end fixed to an exposed wall forming the main surface of the satellite main body,
The antenna holding part is
a first pin disposed near the end of the element and protruding from the main surface;
a second pin and a third pin that are arranged at the apexes of a triangle together with the first pin when the main surface of the satellite main body is viewed in plan, and protrude from the main surface;
a first holding thread stretched between the first pin and the second pin;
a second holding thread stretched between the first pin and the third pin,
In the artificial satellite, the antenna in the first form is disposed between the first holding string, the second holding string, and the main surface of the satellite main body. The antenna includes an antenna element that performs an antenna function,
The artificial satellite according to claim 1 , wherein the length of the antenna element is shorter than the wavelength of radio waves to be transmitted and/or received. The antenna is
an antenna input/output unit that transfers power to and from the antenna element;
The artificial satellite according to claim 2 , further comprising a matching section connected between the antenna element and the antenna input/output section. The artificial satellite according to claim 2 or 3 , wherein the length of the antenna element is greater than 0.6λ and smaller than 0.8λ with respect to the wavelength (λ) of the radio wave. The artificial satellite according to claim 2 or 3 , wherein the length of the antenna element is 0.7λ with respect to the wavelength (λ) of the radio wave.

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