Satellite propulsion system

Abstract

The present invention relates to a propulsion system adapted for the transfer of an elliptic or circular transfer orbit to a GEO, MEO and / or HEO of a rideshare telecommunication satellite (1), the system comprising: at least two orbit raising thrusters (20), preferentially at least three 5 orbit raising thrusters, accommodated in a central portion (11) of a zenith face (10) of the satellite (1) opposed to the Earth when the satellite operates in transmission, at least three station keeping thrusters (30), preferentially at least four station keeping thrusters, each station keeping thruster being accommodated in a corner portion (12) of the zenith face (10).

Description

Satellite propulsion systemTechnical domain

[0001] The present invention concerns a propulsion system for rideshare satellites.Related art

[0002] Rideshare satellites, also known as secondary payload satellites, are small-sized satellites transported to orbit on a launch spacecraft which carries a primary payload. As a secondary payload, the rideshare satellite has to comply with the constraints imposed by the primary payload, in particular with the constraints of available space in the spacecraft, of launching schedule and of trajectory and orbit is typically determined by the entity launching the primary payload.

[0003] Therefore the entity launching the rideshare satellite needs to tailor the satellite and launch to those constraints which usually means specifically dimensioning the satellite and operating adaptation manoeuvres for the satellite to reach its orbit of operation.

[0004] Rideshare satellites are typically disposed around a central ring disposed around the longitudinal axis of the launch vehicle (i.e. spacecraft) which allows multiple secondary payloads to be secured radially around that axis. An industry standard is the family of EELV Secondary Payload Adapters (shortened as ESPA) consisting in a ring designed to support a primary payload on its top together with six secondary payloads laterally secured to the central ring through fixation ports.

[0005] This family of adapters allows securing secondary payloads weighting up to 700kg to fixation ports of a maximal diameter of 24STO12-156-PCTinches. Heavier payloads usually need to be secured to the spacecraft using the top port so as to be aligned with the axis of the spacecraft.

[0006] Hence, the available space for rideshare satellite corresponds to an annular region determined on the inside by the diameter of the central ring and on the outside by the inner diameter of the spacecraft. In order to maximize the efficiency of secondary payload satellites, manufacturers have to develop compact satellite configurations to match the geometry of available space and including a maximal number of features while complying with the weight requirements.

[0007] However, new classes of telecommunication satellites that are far smaller and cheaper than traditional telecom satellites are arising. It is desirable for such satellites to beneficiate of the ridesharing cost efficiency, however they usually exceed the maximal weight authorized by existing secondary payload adapters.

[0008] The new classes of satellites mentioned above are typically configured to operate in Geostationary orbit (GEO), Medium Earth orbit (MEO) and / or High Earth orbit (HEO).

[0009] Hence, an important feature of those satellites is a thruster architecture allowing them to be sent as rideshare satellite that is allowing them to switch from an elliptical or circular transfer orbit to which it is sent by the spacecraft to their orbit of operation. Additionally the thruster architecture also need to include station keeping thrusters allowing the satellites to maintain their orbit and orientation.

[0010] This architecture is taken into account in the seek for optimization of both the available space in the spacecraft and the weight efficiency. Indeed, powerful propulsion systems, such as those needed to switch from orbits, often require fuel tanks that are both bulky and heavy.STO12-156-PCT

[0011] In the state of the art, satellite's belonging to these new classes are attached to the launching spacecraft in a longitudinal orientation, i.e. the zenith / nadir direction of the satellite is aligned with the longitudinal axis of the spacecraft. Indeed, the existing separation rings and / or mass and / or mass distribution of the satellites prevent cantilevered orientation within the spacecraft. This prevents such satellites from being sent as secondary payloads, as there is only one such available spot in the spacecraft, which increases the mission's costs.

[0012] For telecommunication satellites, another important feature is the reflector system that allows signals to be transmitted from a satellite's antenna toward the Earth and vice-versa. Since the available space is limited, the size (and even the curvature) of the reflector(s) of rideshare satellites is limited as well. As a consequence, the distance between the emitting / receiving source and the corresponding reflector needs to be increased to achieve sufficient transmission quality. There is therefore a need for ways of increasing this distance while complying with the compactness, available space and weight requirements.Short disclosure of the invention

[0013] An aim of the present invention is to overcome limitations of the state of the art.

[0014] Another aim of the present invention is to provide a propulsion system that is adapted for rideshare satellites, in particular that is compact and efficient.

[0015] According to the invention, these aims are attained by the object of the appended claims.STO12-156-PCTBrief description of the figures

[0016] Examples of embodiments of the present invention are disclosed in the description illustrated by the appended figures, wherein:• Figure 1 illustrates a view from the bottom of a rideshare satellite showing a thruster architecture according to the invention.• Figure 2 illustrates a perspective view of a the rideshare satellite of Figure 1.• Figure 3 illustrates a perspective view of a rideshare satellite in deployed operating conditions with a thruster architecture according to the invention.• Figure 4 illustrates a perspective view of a rideshare satellite in compact stowed configuration with a thruster architecture according to the invention.• Figure 5 illustrates a perspective view of a rideshare satellite with thrusters mounted on gimbal mechanisms.Examples of embodiments of the present invention

[0017] Throughout the present text, the expression "zenith" and "nadir" are used to designate opposite directions respectively to the satellite when it is in operation mode, i.e. when the satellite is in its final transmission mode. The "zenith" designates the direction opposed to the Earth while the "nadir" designates the direction of Earth. Derivated expressions such as "zenith face" or "nadir face" are therefore to be understood as "face facing the zenith direction", i.e. "face opposed to the Earth" and "face facing the nadir direction", i.e. "face directed toward the Earth.STO12-156-PCT

[0018] Fig. 1 illustrates a bottom view of a propulsion system according to the present invention mounted on a rideshare satellite 1. The propulsion system comprises at least two orbit raising thrusters 20, for example two, three or four orbit raising thrusters 20. The propulsion system also comprises at least three station keeping thrusters 30.

[0019] Orbit-raising thrusters are thrusters configured to cause the satellite to move from the initial orbit, i.e. the orbit at which the spacecraft launches the satellite, e.g. an elliptical or circular orbit, to the operation orbit, i.e. the orbit at which the satellite is intended to operate in transmission, e.g. GEO, MEO and / or HEO. Any kind of chemical or electric / electromagnetic orbit thrusters can be used, e.g. cold gas, halleffect, ion thrusters. However, electric thrusters are preferential as they allow to decrease the need of on-board fuel / propellant.

[0020] Station keeping thrusters are thrusters configured to cause the satellite to operate change of direction in order maintain its orbit. They are usually used sequentially in successive orbital maneuvers. Again, any kind of chemical or electric / electromagnetic station keeping thrusters can be used, e.g. cold gas, hall-effect, ion thrusters. However, electric thrusters are preferential as they allow to decrease the need of on-board fuel / propellant.

[0021] According to one aspect of the invention, the station keeping thrusters 30 can be used in conjunction with orbit-raising thrusters to adjust trajectory during an orbit transfer. Hence, it removes the need of orientation mechanisms such as hinged arms for the orbit-raising thruster, increasing the compactness and decreasing the weight of the satellite. In one embodiment, the orbit-raising and / or station keeping thrusters are static, meaning that they cannot be oriented during maneuvers.

[0022] The orbit-raising thrusters are accommodated in a central portion of the zenith face 10, while the station keeping thrusters are accommodated in corner portions of the zenith face 10.STO12-156-PCT

[0023] In one embodiment illustrated in Fig. 1, the zenith face is rectangular. The at least three, for example four, station keeping thrusters are therefore accommodated in at least three corners of the rectangular face 10.

[0024] In one embodiment, the propulsion system is adapted for a satellite whose body, i.e. the portion formed by the outer faces of the satellite, is in the shape of a parallelepiped or, as illustrated in Fig. 2 in the shape of a trapezoidal prism. The zenith face 10 can form the small base of the trapezoidal prism.

[0025] In a non-illustrated embodiment, the propulsion system comprises eight station keeping thruster. Those eight thrusters are arranged as four pairs of station keeping thruster, each pair comprising a redundant station keeping thruster that can be configured to operate if the other thruster of the pair encounters a critical malfunction. Each redundant station keeping thruster is typically adjacent to its corresponding thruster.

[0026] According to an embodiment, the orbit raising thrusters 20 are oriented so that a thrust vector of each orbit raising thruster 20 points towards a mean centre of gravity when the satellite 1 is in an orbit raising configuration. Orbit raising configuration typically means that the reflector(s) of the satellite are stowed while the solar panel arrays are deployed. The particular mean centre of gravity depends in particular on the internal disposition of the satellite's payload and may vary depending on the mission of the satellite. Throughout the orbit transfer, the weight and weight distribution of the satellite can significantly vary as propellant / power is used. The mean centre of gravity can therefore computed by averaging the centre of gravity throughout the whole orbit transfer to limit the need for trajectory adjustments.

[0027] According to an embodiment, the station keeping thrusters 30 are oriented so that a thrust vector of each station keeping thruster 30STO12-156-PCTpoints towards a mean centre of gravity when the satellite 1 is in an orbit keeping configuration. Orbit keeping configuration typically means that the reflector(s) and the solar panel arrays of the satellite 1 are deployed, as illustrated in Fig. 3. While orbiting, the weight and weight distribution of the satellite can also significantly vary as propellant / power is used. The mean centre of gravity can therefore computed by averaging the centre of gravity throughout the whole intended orbit cycles to limit the need for trajectory adjustments.

[0028] Advantageously, the orbit-raising and / or the station keeping thrusters are electric thrusters. In combination with small size and costefficient rideshare satellites, electric thrusters can significantly lower the costs of such missions with respect to cold gaz or combustion thrusters and are therefore particularly suitable. In a preferred embodiment, the orbit raising and station keeping thrusters are hall-effect thrusters.

[0029] In an embodiment illustrated in Fig. 5, one or more of the orbit raising 20 and station keeping thrusters are mounted on a thruster pointing mechanism 40. Such mechanisms allow change of orientation of the thrust vector of a thruster in order to change the direction of the satellite. In a preferred embodiment, the thruster pointing mechanism is a gimbal.

[0030] In an embodiment, all station keeping thrusters 30 are disposed on thruster pointing mechanisms 40. The orbit raising thrusters 20 may or may not be mounted on thruster pointing mechanisms.

[0031] The propulsion system of the present invention is particularly suited for satellites whose weight does not exceed 1800kg.

[0032] It is also suited for satellites whose external dimensions in stowed configuration as shown in Fig. 4 (reflectors and solar arrays stowed) does not exceed 4m in width, 2.5m in height and 3m in depth. The width typically corresponds to the dimension measured in the East-West direction,STO12-156-PCTthe height to the dimension measured in the zenith-nadir direction and the depth to the dimension measured in the North-South direction, when the satellite is in regular transmission configuration.

[0033] In an embodiment in which the satellite's body is in the shape of a trapezoidal prism, the width of the satellite in stowed configuration refers to the width of the large base of the trapezoid, possibly taking into account the arms of the reflectors that are stowed against the satellite's body. The height refers to the height of the trapezoid, possibly taking into account reflectors stowed against a base of the trapezoidal prism. The depth refers to the third dimension, possibly taking into account solar panel arrays stowed against the satellite's body.

[0034] In an embodiment, the propulsion system is configured for a satellite whose end-of-life electric power is inferior to 4kW.

[0035] In an embodiment, the orbit-raising thrusters 20 are accommodated within a separation (of fixation) ring disposed on the nadir face of the satellite's body. The separation ring is the satellite's attaching point to the spacecraft launching the satellite.

[0036] In the state of the art, satellite's with the above described requirements of weight and / or external dimensions are attached to the launching spacecraft in a longitudinal orientation, i.e. the zenith / nadir direction of the satellite is aligned with the longitudinal axis of the spacecraft. Indeed, the existing separation rings and / or mass distribution of the satellites prevent cantilevered orientation within the spacecraft. This prevents such satellites from being sent as secondary payloads, as there is only one such available spot in the spacecraft, which increases the mission's costs.

[0037] According to an aspect, the present invention surprisingly and advantageously allows such cantilevered orientations within the spacecraft. Indeed, the orbit-raising thrusters 20 can be accommodated within theSTO12-156-PCTseparation ring so as to project outside (at least partially) the zenith face 10 and the separation ring. This allows to shift the center of gravity of the satellite in the direction of the zenith face, which greatly reduces the physical constraints when the satellite is attached to the spacecraft. Indeed, the center of gravity is therefore closer to the longitudinal axis of the spacecraft.

[0038] In one embodiment, the fuel / propellant tank of the propulsion system can also be accommodated so as to protrude (at least partially) from the separation ring in order to further shift the center of gravity of the satellite toward the longitudinal axis of the spacecraft when attached to it.

[0039] According to another aspect, the present invention relates to A propulsion system adapted for the transfer of an elliptic or circular transfer orbit to a GEO, MEO and / or HEO of a rideshare satellite 1, the system comprising at least four station keeping thrusters 30, and at least four thruster pointing mechanism 40. Each station keeping thruster 30 being mounted on one of the thruster pointing mechanisms 40.

[0040] Thruster pointing mechanisms are mechanisms allowing to modify the thrust vector of a given thruster to modify the trajectory of the satellite.

[0041] In one embodiment, the at least four station keeping thrusters 30 are located in corner regions of the zenith face of the satellite. The thruster pointing mechanisms to greatly simplify the sequence of manoeuvres need to adapt / adjust the trajectory of the satellite. Indeed, instead of a complicated sequence of small adjustments with static station keeping thrusters, it is possible to change the continuously change the orientation of a thrust vector to modify the trajectory.

[0042] In one embodiment, the propulsion system only comprises station keeping thrusters mounted on thruster pointing mechanisms. Indeed, the possibility to orientate the station keeping thrusters using the thrusterSTO12-156-PCTpointing mechanism allows the station keeping thrusters to be used also for the orbit raising phase.

[0043] In another embodiment, the propulsion system also comprises at least two orbit raising thrusters 20 mounted on the at least one thruster pointing mechanism. Each station keeping and orbit raising thruster can have its own thruster pointing mechanism or several thrusters can be mounted a same thruster pointing mechanism.

[0044] According to another aspect, the present invention relates to a propulsion system for the transfer of an elliptic or circular transfer orbit to a GEO, MEO and / or HEO of a rideshare satellite 1, the system comprising at least two orbit raising thrusters 20, and at least one thruster pointing mechanism. The at least two orbit raising thrusters 20 are mounted on the thruster pointing mechanism.

[0045] This thruster pointing mechanism is typically located as before within a separation ring on a zenith face of the satellite so as to face the spacecraft when attached to it.STO12-156-PCT

Claims

Claims1. A propulsion system adapted for the transfer of an elliptic or circular transfer orbit to a GEO, MEO and / or HEO of a rideshare telecommunication satellite (1), the system comprising: at least two orbit raising thrusters (20), preferentially at least three orbit raising thrusters, accommodated in a central portion (11) of a zenith face (10) of the satellite (1) opposed to the Earth when the satellite operates in transmission, at least three station keeping thrusters (30), preferentially at least four station keeping thrusters, each station keeping thruster being accommodated in a corner portion (12) of the zenith face (10).

2. Propulsion system according to the preceding claim, wherein the zenith face is rectangular.

3. Propulsion system according to any of the preceding claims, wherein a satellite's body formed by outer faces is in the shape of a parallelepiped or a trapezoidal prism wherein the zenith face forms a small base of the trapezoidal face.

4. Propulsion system according to any of the preceding claims, the at least three station keeping thrusters (30) comprising four main station keeping thrusters (31) and four redundant station keeping thrusters (32).

5. Propulsion system according to any of the preceding claims, wherein the at least two orbit raising thrusters (20) are oriented so that a thrust vector of each orbit raising thruster (20) points towards a mean centre of gravity when the satellite (1) is in an orbit raising configuration, (stowed reflectors, deployed solar arrays)6. Propulsion system according to any of the preceding claims, wherein the at least three station keeping thrusters (30) are oriented so that aSTO12-156-PCTthrust vector of each station keeping thruster (30) points towards a mean centre of gravity when the satellite (1) is in an orbit keeping configuration.

7. Propulsion system according to any of the preceding claims, wherein the at least two orbit raising thrusters (20) and the at least three station keeping are electric thrusters8. Propulsion system according to the preceding claims, wherein the at least two orbit raising thrusters (20) and the at least three station keeping are Hall-effect thrusters.

9. Propulsion system according to any of the preceding claims, comprising at least one thruster pointing mechanism, at least one orbit raising thruster (20) and / or station keeping thruster (30) being mounted on the at least one thruster pointing mechanism.

10. Propulsion system according to the preceding claim, wherein the at least one thruster pointing mechanism is a gimbal.

11. Propulsion system according to any of the claims 9 to 10, comprising four station keeping thrusters and four thruster pointing mechanisms, each station keeping thruster being mounted on one of the thruster pointing mechanisms.

12. Propulsion system according to any of the preceding claims, wherein a maximal weight of the satellite is less than 1800kg.

13. Propulsion system according to any of the preceding claims, wherein maximal dimensions of the satellite in stowed configuration are less than 4m in width, 2.5m in height and 3m in depth.

14. Propulsion system according to any of the preceding claims, wherein an end of life payload power of the satellite is less than 4kW.STO12-156-PCT15. Propulsion system according to any of the preceding claims, wherein the at least two orbit raising thrusters (20) are accommodated within a separation ring disposed in the central portion of the zenith face (10).

16. A propulsion system adapted for the transfer of an elliptic or circular transfer orbit to a GEO, MEO and / or HEO of a rideshare satellite (1), the system comprising: at least four station keeping thrusters (30), at least four thruster pointing mechanism, each station keeping thruster (30) being mounted on one of the thruster pointing mechanisms.

17. Propulsion system according to the preceding claim, further comprising at least two orbit raising thrusters (20) mounted on the at least one thruster pointing mechanism.

18. A propulsion system adapted for the transfer of an elliptic or circular transfer orbit to a GEO, MEO and / or HEO of a rideshare satellite (1), the system comprising: at least two orbit raising thrusters (20), at least one thruster pointing mechanism, the at least two orbit raising thrusters (20) being mounted on the thruster pointing mechanism.

19. Rideshare satellite comprising a propulsion system according to any of the preceding claims.STO12-156-PCT

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