GB2062960A

GB2062960A - Telescopic boom

Info

Publication number: GB2062960A
Application number: GB8031264A
Authority: GB
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1979-09-28
Filing date: 1980-09-26
Publication date: 1981-05-28
Also published as: DE3035998A1; FR2466652B3; GB2062960B; NL8005367A; FR2466652A1

Abstract

A telescopic boom, particularly for use on a spacecraft to deploy equipment such as a solar array (2), comprises a plurality of tubular sections (9) able to move one from within another by the application of gas or hydraulic pressure within the sections and further comprises, to regulate and smooth the boom extension, a cable or the like extending from the boom tip along inside the boom to a store such as a reeling drum (30), from which the feed-out rate of the cable is governed by a device generating a speed dependent resistance to such feed-out. By way of example, this device may comprise a damper or an escapement mechanism coupled to the aforementioned reeling drum or an electric dynamo connected to a suitable electric load. A proposal for retracting the boom by hauling in the cable is made. <IMAGE>

Description

SPECIFICATION Telescopic booms This invention relates to telescopic booms particularly, but not exclusively, a telescopic boom of the kind used to deploy a structure such as a solar array on a spacecraft.

It is known to deploy a concertina-folded solar array on a spacecraft by means of a telescopic boom made up of a plurality of tubular sections initially nested one within another. To deploy the array, compressed gas is admitted to within the boom so that the sections which are sealed one to another are pushed out from their positions. It will be appreciated that a spacecraft has to be as light as possible.

Correspondingly, a telescopic boom and the equipment deployed thereby have to be designed to be as light as possible which means that they may be comparatively fragile. If the boom is extended in an uncontrolled manner, the sections will tend to move jerkily, they may bend, particularly in relation to each other, and become jammed and may suffer shock loading as each reaches the limits of its movement with respect to the one within which it was nested.

Apart from damage to the boom itself, the above effects may cause damage to the apparatus deployed.

According to the invention, there is provided a telescopic boom comprising a plurality of hollow tubular sections able to move one from within anotherto extend the boom and means for controlling the movement to the extended position, the movement control means comprising: an elongate flexible member extending within the boom and having an end attached to the boom at a position which is at least near the outer end of the boom when extended, spacer means mounted inside the boom for guiding the elongate flexible member spaced from the inner walls of the boom, and an operable combination of store means and feed-rate regulating means mounted at least near the inner end of the boom, the store means being operable for initially storing said elongate flexible member and for feeding-outthat member to allow the boom to extend and the feed-rate regulating means being operable for regulating the rate at which the elongate member is fed-out from the store means.

said spacer means may comprise a plurality of spacing collars respectively mounted at the inner ends of the tubular sections.

Advantageously the store means comprises a reel or drum upon which the flexible elongate member is wound and which is rotatable to allow the elongate member two be fed from the reel. Meanwhile, the feed rate regulating means may comprise a device such as an escapement mechanism coupled to the reel and operable to resist rotation thereof by applying a speed dependent retarding force. Instead of an escapement mechanism, the regulating means may comprise an alternative speed dependent force applying means, for example a rotary viscous fluid damper, a rotary friction damper, an electric dynamo our a rotary or reciprocating gas or liquid pump.

Advantageously, means are provided for hauling in the elongate flexible member to retract the boom from its extended position. For example, where the storage means comprises the aforementioned reel, there could be provided a motor for rotating the reel in the direction which winds in the elongate flexible member. Where the regulating means comprises an electric dynamo or a gas or liquid pump, functions of regulating the feed-out rate of the elongate member and of winding it in could be performed by the same element, i.e. there could be provided a suitable source of power which is feedable to a suitably constructed dynamo or pump to cause the dynamo or pump to run as a motor.

For a better undestanding of the invention and to show how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which, Figure 1 is a plan view of part of a spacecraft having a solar array extended therefrom by means of a telescopic boom, Figure 2 is a perspective view, partly sectioned, of the telescopic boom of Figure 1, Figure 3 is a sectioned scrap-view of part of a spacing web used in the telescopic boom, Figures 4 and 5 are two perspective views of respective alternative shapes of a spacing web usable in the telescopic boom, Figure 6 is a sectioned plan view of a cable reel and an escapement mechanism, Figure 7 is a section on the line IV IV in Figure 3, and Figure 8 is a diagrammatic view of part of another telescopic boom and means for regulating its rate of extension.

The spacecraft 1 in Figure 1 comprises a solar array 2 illustrated in its deployed position. The solar array comprises a rigid panel 3 constructed as a hollow housing of relatively small depth. The panel 3 is pivotably mounted to the spacecraft 1 by way of a yoke 4. The yoke is connected to the spacecraft 1 by a hinge having pivot axis 5 and to one end of the panel 3 by hinges having pivot axes 6. Before deployment, the panel 3 lies against the wall of the spacecraft 1 and later moves to the deployed position shown by the yoke 4 being pivoted about axis 5 in one direction and the panel 3 pivoting with respect to the yoke about axes 6 in the opposite direction. Within the panel 3 is mounted the fixed root tube 7 of a telescopic boom 8 which comprises a plurality of further tubular sections 9.Before deployment, the tubular sections 9 are nested one within another and within the root tube 7. They are pushed out one from anotherto deploy the array by admitting compressed gas from gas bottles 10 mounted at the yoke end of panel 3 via a control valve 11 and conduit 12 to the interior of the boom.

At intervals, the boom 8 carries cross-beams 13 lying in the plane of the panel 3 and, between the panel 3 and the first cross-beam and between each pair of cross-beams, are strung pairs of solar cell blankets 14. Before deployment, these blankets are concertina-folded along fold lines 15 so that they are all folded close against the outer end of panel 3. The blankets carry sets of solar cells 16 and further such cells are also mounted on the panel 3 as shown.

Referring now to Figure 2 also, each of the tubular sections 7 and 9 of the telescopic boom comprises a light thin-walled tube, made of light metal or composite material such as carbon fibre and resin, at the outer end of which is a flange 17. The flanges 17 may contain means (not shown) for sequencing the boom deployment, i.e so that when the gas pressure is applied, the tubular sections move one at a time ratherthan randomly depending on where the frictional resistance happens to be least at any particular time. One suitable sequencing means forms the subject of our U.K. Patent Application No.

8006751. A description thereof will not be given here since the sequencing means is not an essential feature of the present invention, and nor is knowledge of it required to understand the present invention. Each tube is sealed to the next larger tube buy a sliding ring seal 18, for example an elastomeric O-ring overwrapped with P.T.F.E. tape.

Mounted just inside the inner end of each tubular section 9 is a spacer web 19. Each spacer web comprises a rounded cruciform member made of P.T.F.E. and having a central hole 20 therein. Near the end of each arm of the member, overlapping slits 21 are formed from opposite sides of the arm as shown in Figure 3. The lengths of the arms of each member are made slightly oversized in relation to the internal diameter of the relevant tubular section but, due to the slits 21, a spring effect is created which enables the members to be contracted to fit the tubular sections and to then remain in position while adhesive used to bond the members to the tube walls becomes set.The spacer webs could be modified for example as shown in Figure 4 where it takes the form of a disc 22, preferably with holes 23 therein for weight-saving, and with axially extending lugs 24 or as shown in Figure 5 where the web 25 is again cruciform but for weight-saving has arms of thinner cross-section. At the end of each arm, a shoe 26 is formed to provide sufficient contact area for adhesive bonding to the tubular sections.

The inner end of the root-tube 7 is closed by a plate 27 having a port 28 for receiving the gas supply conduit 12 and a small central hole 29 through which there enters the boom, from a reeling drum 30, a cable 31. The gap between the cable and the walls of the hole 29 are sealed by a gland 32 made of low-friction material such as P.T.F.E. The cable extends along inside the boom through the central holes in the spacer webs 19 to the outer end of that one of the tubular sections 9 which is outermost when the boom is extended and is there attached to this tubular section. The reeling drum 30 is rotatably mounted to the wall of the panel 3 so that, as the boom extends from its deployed position, the cable can unwind to allow such extension.However, the reeling drum incorporates an escapement mechanism which applies to rotation of the reeling drum a speed-dependent retarding force thereby regulating the rate at which the cable unwinds and hence also the rate at which the boom extends.

As shown in Figures 6 and 7, the reeling drum comprises a hollow bobbin shaped housing 33 having cut-aways 34 in its walls for weight-saving.

The housing is rotatably mounted by means of bearings 35 on a shaft 36, one end 37 of which is extended to enable the shaft to be affixed to the wall of the panel 3 via fixing collar 38. A fixed gear wheel 39 is secured to shaft 36 within housing 33 and this gearwheel engages a smaller gear pinion 40 affixed to a shaft 41 which is rotatably mounted by bearings 42 in the side walls of housing 33 at a position off-set from the axis of rotation of the housing. Shaft 41 also carries a relatively large gearwheel 43 which engages a small pinion 44 affixed to a shaft 45. Shaft 45 is, like shaft 39, rotatably mounted by bearings 46 in the opposite walls of housing 33. Shaft 45 also carries a relatively large gearwheel 47. This gear engages an escapement member 48 mounted for oscillating movement on shaft 49 which is supported by bearings 50.The member 48 has the shape of a diametrical segment of a disc with a rectangular cut-out 51 at one edge to leave defined two spaced gear engaging teeth 52. The shape and position of member 48 and the tooth shape of gear wheel 47 are such that, as gear wheel 47 rotates, it contacts first one and then the other of the teeth 52 in out-of phase fashion and, in making such contact with one tooth 52, moves the member 48 so that the other tooth 52 comes to a position where it will be engaged. Thus, during rotation of gear 47, member 48 is caused to oscillate by its engagement with gear 47 and, at the same time, by oscillating, allows the gear 47 to rotate. Rotation of gear 47 about its own axis is transmitted back via the gears 39 and 43 and the small pinions 40 and 44, to appear as reduced speed rotation of the entire reeling drum about shaft 36.

The overall operation is such that, in order for drum 30 to rotate, escapement member 48 has to oscillate at a comparatively higher speed and so, due to the inertia of member 48, a strongly speed dependent retarding force is applied to the drum rotation. Thus, this force maintains reasonably smooth and constantthe unwinding speed of cable 31.

Instead of an escapment mechanism as shown, another kind of mechanism for applying a speed dependent retarding force could be coupled to or combined with the drum 30. For example, the drum could be coupled to an electric dynamo (not shown) connected to a suitable electrical load so that, as the drum rotates, the energy dissipated in the load would appear as a retarding force on the drum. As other alternatives (not shown), there could be used a rotary viscous fluid or friction damper or a rotary or reciprocating gas or fluid pump.

At least at present, the ability to retract a solar array from its deployed position on a spacecraft is not usually necessary. However, for other applications of the telescopic boom and sometimes for spacecraft, particularly future envisaged spacecraft, such a retraction capability may be desirable. This can be provided in the illustrated embodiment of the invention by coupling the reeling drum 30 to a suitable motor, for example an electric motor, so that when the array is to be retracted, the entire drum 30 along with its escapement mechanism is reversed-rotated to wind in the cable 31. The gas pressure within the boom and applied to extend the boom will probably have reduced due to leakage by the time the array is to be retracted.However, to be sure of the point, the pressure could be exhausted for example as soon as the array is fully deployed by way of exhaust ports formed in the boom and arranged so as to become open when the boom reaches full extension. If, as may be the case, the boom comprises latches which lock it into its extended position, suitable disengagement means are provided for unlocking it, for example electrical solenoids arranged to release the latches when required.

Where the means for applying a regulating force on the drum rotation comprises the aforementioned electric dynamo or pump, the means for retracting the boom can take the form of a source of power operable to drive the dynamo or pump as a motor.

For example, as shown in Figure 8, the reeling drum 30 could be formed as the rotor of an electrodynamic machine 53 which is suitable for operation either as a dynamo or as a motor and which is coupled by cable 54 to a changeover switch 55 within the spacecraft housing. Under the control of signals from the telecommand system (not shown) of the spacecraft, machine 53 can be coupled to a load 56 so that it operates as a dynamo or to an electrical power source 57 so that it operates as a motor.

By way of example, the spacecraft solar cell array in Figure 1 might be around twenty-five metres long when extended as shown and the telescopic boom might comprise say eighteen tubular sections each about one and a half metres long.

Instead of the cable 31, an alternative form of flexible elongate member may be used, for example a tape our a length of chain.

Instead of being arranged outside the inner end of the root tube 7, the cable reel and escapement mechanism could be made to suitable dimensions and housed inside the boom, thus making unnecessark the hole 29 and gland 32.

Instead of compressed gas, the boom could be extended hydraulically. Also, between each two tubular sections of the boom, there could be provided suitable control ports for the gas or hydraulic fluid, for example to provide the aforementioned sequencing of the boom extension.

Particularly in a spacecraft, more than one telescopic boom may be provided. For example, more than one solar array such as that shown in Figure 1 may be used or there may be one or more arrays like that shown in Figure 1 except that, instead of the single boom and blanket arrangement extending from the outer end of panel 3 as shown, there could be two booms and correspondinglytwo blanket arrangements extending in the opposite directions A and B from the side edges of the panel. Particularly in this latter case, the deployment of the two booms may be synchronised by having the respective cables wound on respective portions of the same reeling drum. Where this is not convenient, the synchronism of deployment of two or more booms may still be accomplished by coupling the reeling drums mechanically or, particularly in the case where the speed regulating means comprises a dynamo, by way of a suitable electrical circuit.

Claims

1. Atelescopic boom comprising a plurality of hollow tubular sections able to move one from within another to extend the boom and movement control means for controlling the movement to the extended position, the movement control means comprising: an elongate flexible member extending within the boom and having an end attached to the boom, spacer means mounted inside the boom for guiding the elongate flexible member spaced from the walls of the boom, store means mounted for storing said elongate flexible member and for feeding out that member to allow the boom to extend, and feed-rate regulating means coupled to the flexible elongate member and operable for regulating the rate at which it is fed-out from the store means.

2. Atelescopic boom according to claim 1, wherein said spacer means comprises a plurality of spacing members mounted in respective ones of said tubular sections and having portions defining a hole in the member for guiding said flexible elongate member spaced from the walls of the tubular sections.

3. A telescopic boom according to claim 2, wherein each spacing member comprises a web member made of low-friction plastics material and having a central portion wherein there is said hole and arm portions which extend from said central portion towards the walls of the tubular section and are fixed thereto by adhesive.

4. Atelescopic boom according to claim 3, wherein said arm portions are resiliently deformable to reduce the lengths thereof.

5. A telescopic boom according to claim 1, wherein said store means comprises a rotatably mounted reeling drum for having the elongate flexible member wound thereon and said feed-rate regulating means is coupled to the reeling drum for applying a speed-dependent retarding force to its rotation.

6. A telecopic boom according to claim 5, wherein said feed-rate regulating means comprises an escapement mechanism which includes a rotationspeed increasing transmission system and an inertia-generating oscillatory member coupled to the transmission system for regulating, via the transmission system, the speed of rotation of said reeling drum.

7. Atelescopic boom according to claim 5, including drive means coupled to said reeling drum for rotating it to rewind said elongate flexible member and hence retract the boom from said extended position.

8. A telescopic boom according to claim 7, wherein said drive means comprises a power source coupled via control means to said feed-rate regulating means, and the feed-rate regulating means is operable either as a load for applying a speeddependent retarding force to rotation of the reeling drum or, when connected to said power source via said control means, as a motor for rotating the reeling drum to rewind the flexible elongate member.

9. A telescopic boom according to claim 8, wherein the feed-rate regulating means comprises an electro-dynamic machine operable as a dynamo or a motor and coupled via selector switch means to an electrical load and a source of electrical powder.

10. A spacecraft having a solar array which includes support means connected to the spacecraft and operable for supporting the solar array, at least one concertina-foldable sheet member connected at one end to the support means, and a telescopic boom connected between said support means and the opposite end of said at least one sheet member and operable for being extended to unfold the sheet member, the telescopic boom comprising;; a plurality of hollow tubular sections able to move one from within another to extend the boom, fluid pressure applying means connected to the boom for applying fluid pressure therein to move the tubular sections out from within one another as aforesaid, an elongate flexible member of which one end is connected to the tip of the boom and which extends back along the length of the boom, store means supported by said support means adjacent the inner end of said boom and operable for storing said elongate flexible member and for feeding out that member to allow the boom to extend, and, feed-rate regulating means coupled to said store means for applying a speed dependent resistance to the feeding-out of the elongate member and thereby to smoothly regulate the extension of the boom.

11. Atelescopic boom substantially as hereinbefore described with reference to the accompanying drawings.