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    • 专利摘要:
    ABSTRACT Den föreliggande uppfinningen hänför sig till ett arrangemang för styrning av attityd ochbana för en geostationär rymdfarkost. Den geostationära rymdfarkosten har ettmasscentrum, och ett rymdfarkostorienterat koordinatsystem med en tangentriktning i hastighetsriktningen hos den geostationära rymdfarkosten, en ortogonalriktning ortogonal mot ett banplan och en radialriktning riktad motjordens centrum, innefattande: en uppsättning av åtminstone fem framdrivningsenheter, vari var och en avframdrivningsenheterna i uppsättningen är verksam att utöva en kraft pä rymdfarkostenvid aktivering, vilken kraft kan delas upp i tre kraftvektorkomponenteri nämndarymdfarkostorienterade koordinatsystem, vari en ortogonalkraftvektorkomponent harsamma tecken som de andra framdrivningsenheterna i uppsättningen, eller är noll, enradialkraftvektorkomponent som är noll för var och en av framdrivningsenheterna iuppsättningen, och en tangentkraftvektorkomponent, vari uppsättningen av åtminstonefem framdrivningsenheter är konfigurerade och anordnade att utöva linjärt oberoendekombinationer av krafter och vridmoment på den geostationära rymdfarkosten,varigenom den geostationära rymdfarkosten blir oberoende styrd i två translatoriskafrihetsgrader och tre rotationsfrihetsgrader. [Pub fig. s]
    公开号:SE1450027A1
    申请号:SE1450027
    申请日:2014-01-14
    公开日:2015-07-15
    发明作者:Sytze Veldman；Emil Vinterhav
    申请人:Ohb Sweden Ab；
    IPC主号:
    专利说明:

    AN ARRANGEMENT AND A SYSTEM FOR CONTROL OF ATTITUDE AND ORBITOF A GEOSTATIONARY SPACECRAFT TECHNICAL FIELD The present invention relates to an arrangement for control ofattitude and orbit of a spacecraft. More specifically thepresent invention relates to an arrangement for control of attitude and orbit of a geostationary spacecraft.
    BACKGROUND With reference made to figure 1 a conventional geostationary spacecraft (SC) generally designated 101 will be described.The SC 101 is inserted in a geostationary orbit 102 around earth 103. The geostationary orbit 102 plane is inclined an angle d relative the equatorial plane 104.
    The SC 101 needs precise control of both the position and theattitude. The position of the geostationary SC is limited to asmall region commonly denoted slot. The geostationary orbit isdivided into several of these slots; each slot is allocated todifferent operators that occupy each slot with at least one SC101. These slots are in the order of kilometers and it isgenerally not allowed to exceed the boundaries thereof withthe geostationary SC. By utilizing the concept of slots collisions between SC becomes very rare.
    Due to the limited number of available slots there is a needto occupy a slot with more than one SC. This co-location ofsatellites within the same slot requires much more precise control of attitude and orbit compared to what is necessary if only one SC is located within the slot. 1 Now with reference made to figure 2 a conventional SC 201 willbe discussed. Moreover, a spacecraft oriented coordinatesystem fixed to the SC 201 is introduced; this coordinatesystem is commonly designated 202 and is a right handcoordinate system. A first axis 203 of said spacecraftoriented coordinate system 202 is oriented in the velocitydirection of the SC 201 and is called the tangential axis. Asecond axis 204 of said spacecraft oriented coordinate system202 is pointing towards the center of the earth 103 and iscalled the radial axis. A third and last axis 208 of saidspacecraft oriented coordinate system 202 is normal to theorbital plane 102 and is called the orthogonal axis. Thespacecraft oriented coordinate system preferably originates ina point 206 corresponding to or being close to the position of the center of mass of the spacecraft 201.
    The SC 201 comprises several smaller propulsion units 207 thatare arranged to provide thrust force as well as torque on theSC 201. The SC 201 further comprises two large propulsionunits 208 arranged with thrust forces parallel and anti-parallel with the orthogonal axis of said spacecraft orientedcoordinate system 202. These two large propulsion units areused for control of the orbital plane by means of a norththrust and a south thrust, respectively. Typically, the largepropulsion units provide large amounts of thrust force during a relatively short activation time.
    The SC 201 further comprises a momentum wheel arrangement 209,usually in pyramidal configuration. The momentum wheelarrangement 209 comprises four rotating masses arranged in apyramidal configuration. The momentum wheel arrangement 209provides means for storing angular momentum in all directionswith some redundancy. Angular momentum of the SC 301 originates from thrust forces not directly passing through the center of mass. The angular momentum must be under strictcontrol otherwise the SC 201 starts to tumble and rotate in anuncontrolled manner. The control of rotation and direction ofthe spacecraft oriented coordinate system is within the art called attitude control.
    After the geostationary spacecraft is placed in its slotwithin the orbit, small forces and torques are needed tomaintain the position within the slot. Due to theperturbations of the position caused by the solar wind, thesolar light, the gravitational attraction from the moon and the non-spherical homogeneity of the Earth gravitational fieldand other sources. Even these small forces and torques cause abuildup of angular momentum for the spacecraft. This angularmomentum must be controlled or the spacecraft will start totumble and lose attitude control. The control of attitude isof great importance for a spacecraft due to the directions of solar panels and antennas for example.
    This control of the angular momentum buildup is conventionallyhandled by said momentum wheel arrangement 209. Basically, amomentum wheel is a rotating mass operatively connected tosome kind of mechanical drive. The angular momentum of the rotating mass is controlled by adjusting the rotational speedof the rotating mass. However, the rotating mass within themomentum wheel has a saturation speed that is the maximumrotational speed of the mass. When a momentum wheel isapproaching its maximum speed, the momentum wheel is withinthe art said to be saturated. In order to de-saturate themomentum wheel an external torque acting on the spacecraft isnecessary. This external torque is in the art often produced by activation of a propulsion unit. lO The use of momentum wheels for attitude control is connected with a number of problems.
    The first problem is associated with the mechanical aspects ofthe momentum wheel. The momentum wheel is by its nature heavyand bulky. Moreover, the momentum wheel is also an expensivepiece of machinery. The size and mass of the momentum wheel isa serious problem associated with the extreme cost of placinga spacecraft into a geostationary orbit. This mass of themomentum wheel can be traded for increased payload mass and hence capacity.
    The second problem is that the rotation of the momentum wheel causes small vibrations (micro-vibrations) on board the spacecraft, which can deteriorate the performance of sensitive optical instruments.
    Another problem is associated with the limited lifetime of moving mechanical parts, especially at high rotational speed.
    SUMARY An object of the invention is therefore to address theproblems and disadvantages outlined above, and to provide an improved arrangement for attitude and orbital control.
    This object and others are achieved by the arrangementaccording to the independent claim and by the embodiments according to the dependent claims.
    In accordance with one embodiment of the invention, anarrangement for attitude and orbital control of a SC isprovided. The SC has a center of mass and a spacecraftoriented coordinate system with a tangential direction in the velocity direction of the geostationary spacecraft, an 4 lO orthogonal direction orthogonal to an orbital plane and aradial direction directed towards the center of the earth,comprising: a set of at least five propulsion units, whereineach propulsion unit in the set is operable to exert a forceon the spacecraft, upon activation, which force can be dividedin three force vector components in said spacecraft orientedcoordinate system, wherein an orthogonal force vectorcomponent having the same sign as the other propulsion unitsa radial force vector component in the set, or being zero, being zero for each propulsion unit in the set, and atangential force vector component, wherein the set of at leastfive propulsion units being configured and arranged to exert linearly independent combinations of forces and torques on thegeostationary spacecraft, thereby the geostationary spacecraftbecomes controlled in two translational degrees of freedom and three rotational degrees of freedom independently.
    An advantage of particular embodiments is that an improved arrangement for attitude and orbital control is provided.
    BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic drawing of a conventional geostationary spacecraft in orbit around earth; Figure 2 is a schematic perspective cut-open drawing of a conventional spacecraft; Figure 3 is a schematic drawing of an embodiment of aspacecraft with the inventive arrangement for orbital and attitude control; lO Figure 4 is a flow chart illustrating the inventive method forarranging propulsion units on a spacecraft; andFigure 5 is a schematic perspective drawing of an embodiment of the inventive arrangement for orbital and attitude control.
    DETAILED DESCRIPTION In the following, different aspects will be described in moredetail with references to certain embodiments and toaccompanying drawings. For purposes of explanation and not limitation, specific details are set forth, such as particular scenarios and techniques, in order to provide a thorough understanding of the different embodiments. However, otherembodiments that depart from these specific details may also exist.
    Modern propulsion systems often comprise at least one electricpropulsion unit. In future spacecraft it is likely that themajority of the propulsion units used for attitude and orbitalcontrol will be of electric type. Such an electric propulsionunit exhibits different characteristics compared to a chemicalpropulsion unit. Among these differences, the most importantdifference maybe that an electrical propulsion unit providessmaller amounts of thrust but operates with longer activationtimes.
    Hence, almost continuous activation is likely to be a normal mode of operation in the future. With continuousoperation the possibility to control attitude and orbit of the SC using the propulsion units for that purpose is a reality.
    In order to control the attitude and the orbit of ageostationary SC two translational and three rotationaldegrees of freedom must be controlled. The two translationaldegrees of freedom are the tangential direction and the orthogonal direction. For a geostationary SC it is not 6 necessary to directly control the radial position of the SC bymeans of a propulsion unit having a radial force component.
    Instead, the radial position is controlled by means of thevelocity in the tangential direction due to its connectionwith the orbital velocity. Finally, the three rotational degrees of freedom are yaw, pitch and roll directions. Thus, five degrees of freedom must be controlled.
    In figure 3 is an embodiment of an arrangement for attitudeand orbit control according to the invention disclosed. Inthis embodiment attitude and orbit control are maintained by aset of at least five propulsion units 301-305. Each propulsionunit 301-305 in the set is operable to exert a correspondingforce on the spacecraft fwl-fwg, upon activation. The forcefrom each propulsion unit can be described using three forcevector components in said coordinate system fixed to thespacecraft. Said force consists of an orthogonal force vectorcomponent having the same sign as the other propulsion unitsin the set, or being zero. Said force further consists of aradial force vector component being zero for each propulsion unit in the set, and a tangential force vector component.
    Finally, the set of at least five propulsion units being configured and arranged to exert linearly independent forcesand torques on the geostationary spacecraft. All torques inthe following are calculated relative the center of mass ofthe spacecraft. The at least five propulsion units 301-305 are located at corresponding positions :gm-13%_ Thereby, thegeostationary spacecraft becomes controlled in twotranslational degrees of freedom and three rotational degrees of freedom during one orbital revolution.
    The torque from a propulsion unit relative center of mass is defined according to: lO r=rxf (l)where I is the torque,the force f. r is the vector from center of mass to The operator “x” is the vector cross product.The linear independency of the forces and torques can beverified using a matrix with each row corresponding to the force and torque from a corresponding propulsion unit.
    Such a matrix is given below for the embodiment disclosed in figure 3.fšo14: fÉo1¿1 fšorz T3o1a: T3o1¿» T3o1¿fšozaf fÉo2¿1 fšozß Tsozaf T3o2¿» T3o2¿M= f3o3,x f3o3,y f3o3,z T3o3,x T3o3,y T3o3,z (2)fÉo44: fÉo4¿1 fÉo4z T3o4a: T3o4¿» T3o4¿fšosa: fšosßf fšoaz Tsosa: T3o5¿/ Tsosß In this matrix x denotes the tangential component, y denotes the radial component and z denotes the orthogonal component.
    According to the invention the second column will be zero due to the fact that no radial force component exists from the propulsion units. Hence, matrix M can be reduced to:fšo14: fšo1z T3o1@: T3o1¿» T3o1¿fšozx fsozz Taozx Tsozy TäozzM' = f3o3,x f3o3,z T3o3,x T3o3,y T3o3,z (3)fÉo44: f§o4z T3o4@: T3o4¿» T3o4zfšosa: fšosz Tsosa: T3o5¿/ Tsosß If matrix M' in (3) can be reduced to the identity matrix thenthe force and the torque vectors are linearly independent.Thereby, the geostationary spacecraft becomes controlled intwo translational degrees of freedom and three rotational degrees of freedom independently.
    In figure 4 a method for positioning and adjusting thedirection of the propulsion units on a geostationary SC will be disclosed.
    The first step 401 comprises selecting at least two propulsionunits from the set of at least five propulsion units to form afirst group. Each propulsion unit in the first group haseither a common positive tangential force vector component ora common negative tangential force vector component for eachpropulsion unit in the first group. The at least twopropulsion units are arranged on separate sides of the center of mass of the spacecraft in the radial direction.
    The first group is configured to provide both positive andnegative components of torque parallel with the tangentialdirection and the orthogonal direction of the spacecraft.Furthermore, the first group is arranged to provide positiveand negative torque components parallel to the radialdirection on the spacecraft.
    With reference now made to figure 3, the propulsion units 304 and 305 are selected to belong to said first group.
    The second step 402 involves selecting at least threepropulsion units from the set of at least five propulsion units to form a second group.
    The second group is configured to provide a tangential forcecomponent opposite said first groups tangential force component. At least two propulsion units in the second groupbeing arranged on separate sides of the center of mass of the spacecraft in the radial direction.
    In figure 3 the propulsion units 301 and 303 are arranged onseparate sides of the center of mass.301,302 and 303 form the second group.
    The propulsion units All at least three propulsion units in the second group beingarranged to exert both positive and negative torque componentsin the tangential direction and in the orthogonal direction on the spacecraft.
    The torque components in the radial direction from the secondgroup can counteract and balance the torque contribution in the radial direction from the first group.
    In figure 5 is an embodiment of an arrangement according tothe invention disclosed. A spacecraft generally designated 500is illustrated. The spacecraft has a spacecraft oriented coordinate system (SOCS) 508 with the origin at the center of mass 509 of the spacecraft 500. The tangential axis 510 is directed in the velocity direction of the spacecraft 500. Theorthogonal axis 512 is directed in the normal direction of theorbital plane and the radial axis 511 is directed towards the center of the earth.
    The spacecraft 500 comprises a rectangular first panel 506 with the normal thereof pointing in the (1,1,0) direction of the SOCS 508. The first panel is mounted on the outside of thespacecraft. The first panel 506 comprises a first electricpropulsion unit 501 arranged in a first corner of the firstpanel 506. A position vector rwl gives the position of thefirst electric propulsion unit 501, the first electricpropulsion unit 501 provides a thrust force fwl that isparallel with the normal of the first panel 506. In a secondcorner on the first panel 506 opposite to the first corner ofthe first panel 506 is a second electric propulsion unit 502arranged at a position given by a position vector rwg, and a thrust force fimgparallel with thrust force fwl.
    A second panel 507 is arranged on the outside of the spacecraft 500 with a normal pointing in the (-1,1,0) l0 direction of the SOCS 508. The second panel 507 comprises athird electric propulsion unit 503 with a position vector rwgand a thrust vector fwg being parallel with the normal of thesecond panel 507. The second panel 507 further comprises afourth electric propulsion unit 504 with position vector rw4and a thrust vector fw4 being parallel with thrust vector fwg.The fourth electric propulsion unit 504 is arranged in anopposite corner to the third electric propulsion unit 503 on the second panel 507.
    A fifth propulsion unit 505 is arranged in a free non-occupiedcorner of the second panel 507, the fifth propulsion unit 505has a position vector rw5 and a thrust vector fw5 being parallel with the other thrust vectors on the second panel 507.
    By calculating the corresponding matrix using equation (2) we obtain the following matrix: fšo1@: fšo1¿1 fšo1z T5o1a: T5o1¿/ T5o1¿fšoza: fšozßf fšozz Tsoza: Tsozßf Tsozß!45= fšosa: fšosßf fšosz Tsosa: Tsosßf Tsosßfšo4@: fšo4¿1 fšo4z T5o4@: T5o4¿/ T5o4zfšosa: fšosßf fšosz Tsosa: Tsosßf Tsosß Since the electric propulsion units has no force component inthe radial direction the corresponding column three in M5 willbe zero and can be deleted from the matrix M5. This results in a reduced matrix M6: fšo1@: fšo1¿» T5o1;: T5o1¿/ T5o1¿fšoza: fšo2¿» Tsoza: Tsozßf TsozßD46= fšosa: fšo3¿» Tsosa: T5o3¿/ Tsosßfšo4@: fšo4¿» T5o4;: T5o4¿/ T5o4zfšosa: fšo5¿» Tsosa: Tsosßf Tsosß ll This matrix M6 can be reduced to the identity matrix. Thus,indicating that the spacecraft becomes controlled in twotranslational degrees of freedom as well as in all rotationaldegrees of freedom.
    In order to further elucidate the invention a numericalexample in connection with figure 5 is given below.
    Three parameters a=0.625, b=0.375 and c=0.5 are used togenerate the positions of five propulsion units. force and corresponding In the table below are the position, torque given for each of the five propulsion units.
    X rx fx TX 1 [-a,b,c] [-1,1,0] [-0.5,-0.5,-0.25]2 [-b,a,-c] [-1,1,0] [0.5,0.5,0.25] 3 [-b,a,c] [-l,l,O] [-0.5,-O.5,0.25]4 [b,a,c] [1,1,0] [-0.5,0.5,-0.25]5 [a,b,-c] [l,l,O] [O.5,-O.5,0.25] This data in the table gives a corresponding matrix M using (2) and the above given values for a,b and c: -1 1 0 -05 -05 -025-1 1. 0 05 05 025M=-1 1 () -05 -05 0251 1 0 -05 05 -0251 1 0 05 -05 025 This matrix can be reduced to the identity matrix I: I-l |OOOOPJOOOP-*OOOP-*OOOb-*OOOPJOOOO 12 lO This reduction to the identity matrix proves that the thrusterconfiguration in this example causes control of twotranslational degrees of freedom as well as three rotationaldegrees of freedom independently.
    Thus, the spacecraft is fully controlled.
    The above mentioned and described embodiments are only givenas examples and should not be limiting to the present invention. l3
    权利要求:
    Claims (4)
    [1] 1. l. An attitude and orbital control arrangement for ageostationary spacecraft, having a center of mass and aspacecraft oriented coordinate system with a tangentialdirection in the velocity direction of the geostationaryspacecraft, an orthogonal direction orthogonal to an orbitalplane and a radial direction directed towards the center ofthe earth, comprising:a set of at least five propulsion units, wherein eachpropulsion unit in the set is operable to exert a force on thespacecraft, upon activation, which force can be divided inthree force vector components in said spacecraft orientedcoordinate system, wherein an orthogonal force vector component having the samesign as the other propulsion units in the set, or being zero,a radial force vector component being zero for eachpropulsion unit in the set, and a tangential force vector component, wherein the set of at least five propulsion unitsbeing configured and arranged to exert linearly independentcombinations of forces and torques on the geostationaryspacecraft, thereby the geostationary spacecraft becomescontrolled in two translational degrees of freedom and three rotational degrees of freedom independently.
    [2] 2. An attitude and orbital control arrangement for ageostationary spacecraft according to claim l, wherein the setof at least five propulsion units being arranged in a first group and a second group of propulsion units having an orthogonal force vector component with the same sign, whereinthe first group comprises at least two propulsionunits, and the first group has a positive tangential force l4 lO vector component, and at least two propulsion units beingarranged on separate sides of the center of mass of thespacecraft in the radial direction, the first group beingarranged to provide both positive and negative torquecomponents parallel with the tangential direction and theorthogonal direction on the spacecraft relative the center ofmass of the spacecraft, as well as torque components parallelto the radial direction on the spacecraft relative the centerof mass of the spacecraft, the second group comprises at least three propulsionunits, wherein the second group has a tangential forcecomponent opposite said first groups tangential forcecomponent, wherein at least two propulsion units in the secondgroup being arranged on separate sides of the center of massof the spacecraft in the radial direction, and all threepropulsion units being arranged to exert both positive andnegative torque components in the tangential direction and inthe orthogonal direction on the spacecraft relative the centerof mass of the spacecraft, and torque components in the radialdirection on the spacecraft relative the center of mass of thespacecraft that can counteract and balance the torque contribution in the radial direction from the first group.
    [3] 3. An attitude and orbital control arrangement for ageostationary spacecraft according to claim 2, whereinthe first group of propulsion units is arranged on afirst panel having a normal with a positive tangentialcomponent and a positive orthogonal component, and each ofsaid propulsion units in the first group is arranged on saidfirst panel with the propulsion force direction parallel tosaid normal of the first panel, wherein the first groupcomprises two propulsion units arranged on opposite corners of the first panel, lO the second group of propulsion units is arranged on asecond panel having a normal with a negative tangentialcomponent and a positive orthogonal component, and each ofsaid propulsion units in the second group is arranged on saidsecond panel with the propulsion force direction parallel tosaid normal of the second panel, wherein the second groupcomprises three propulsion units arranged at three corners of the second panel.
    [4] 4. An attitude and orbital control arrangement for ageostationary spacecraft according to claim l or 2, wherein said propulsion units being electrical propulsion units. l6
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    同族专利:
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    SE539330C2|2017-07-04|
    引用文献:
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    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    SE1450027A|SE539330C2|2014-01-14|2014-01-14|Arrangements for controlling attitude and trajectory of a geostationary spacecraft|SE1450027A| SE539330C2|2014-01-14|2014-01-14|Arrangements for controlling attitude and trajectory of a geostationary spacecraft|
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