GB2103011A

GB2103011A - Deployable sheet assemblies

Info

Publication number: GB2103011A
Application number: GB08218281A
Authority: GB
Inventors: Peter Truss
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1981-06-27
Filing date: 1982-06-24
Publication date: 1983-02-09
Also published as: GB2103011B; DE3223839A1; FR2508413B3; NL8202592A; FR2508413A1

Abstract

A deployable sheet assembly comprises a pair of concertina- foldable sheet portions 14, each movable from a furled compact condition to an extended generally planar condition. Prior to deployment, the furled sheet portions 14 lie in a generally side-by-side position adjacent a side wall 11 of a spacecraft so as not to protrude beyond the periphery thereof. On deployment the sheet portions 14 are unfolded to an outspread position, and also unfurled so as to define a deployed sheet assembly which extends substantially beyond the periphery of the side wall 11. This assembly allows the compact stowage of a solar array which in its deployed state has a relatively low aspect ratio for a given surface area. <IMAGE>

Description

SPECIFICATION Deployable sheet assemblies This invention relates to sheet assemblies deployable from a stowed, compact condition to an extended generally planar condition. In particular, but not exclusively, this invention is concerned with deployable sheet assemblies for spacecraft, for example deployable solar arrays.

In many of the known configurations of deployable sheet assemblies currently used for spacecraft, the maximum width of the sheet assembly is limited to the maximum dimension of the sidewall of the spacecraft to which the deployable assembly is to be attached. This is to prevent the stowed sheet assembly from protruding beyond the periphery of the sidewall and thus to allow the spacecraft to be relatively compact for launching.

However, particularly where the sheet assembly is a solar array for the spacecraft, the surface area of the sheet exposed to solar radiation must be relatively large to enable sufficient power to be generated for the operation of the spacecraft. Hence, in most current assemblies, the extended length of the array is much greater than the width of the sheet assembly, i.e. the aspect ratio of the sheet assembly is relatively high. This is a problem since, for a given surface area of sheet assembly, the higher the aspect ratio the higher the rotational inertia of the spacecraft, and the lower the natural frequency of the extended sheet assembly. These changes in the dynamic characteristics of the spacecraft may be incompatible with the control systems of the spacecraft.Moreover, the further the assembly has to be extended from the spacecraft, so the complexity of the deployment device and the bracing necessary increases together with the subsequent likelihood of failure.

According to one aspect of this invention, there is provided a deployable sheet assembly which includes two sheet portions which when in a compact furled condition lie in a generally sideby-side position, unfurling means for extending each from a compact furled condition to an unfurled generally planar condition and unfolding means for effecting relative hinging movement of the portions from a side-by-side position to an outspread position.

The sheet portions are conveniently of concertina foldable form. The assembly is preferably adapted so that said unfolding movement is effected prior to the unfurling of each sheet portion.

Advantageously, each sheet portion includes inner and outer beam means and the inner and outer beam means of one sheet portion are hingedly attached to respective inner and outer beam means of the other sheet portion, there being biass means adapted to urge the portions to their outspread position, releasable tie means to maintain the portions in their side-by-side position, and locking means to lock them in the outspread position on release of the tie means.

Preferably the unfurling means includes a pair of boom members pivotted together, one end of said pair being coupled to the inner beam means, the other end being coupled to the outer beam means, there being biass means to urge the boom members to an outspread position, tie means to maintain each sheet portion in a furled configuration, and locking means to lock said pair of boom members in the outspread position on release of said tie means.

Conveniently said sheet portion lie generally parallel prior to unfolding movement thereof.

In another aspect of this invention, there is provided a space craft including a deployable sheet assembly associated with a face thereof, said sheet assembly including two sheet portions mounted for relative hinging movement from a side-by-side position to an outspread position, the sheet portions being configured so that in their side-by-side position they lie generally within the periphery of said face but in their outspread position they extend beyond the periphery of said surface.

By way of example only one specific embodiment of deployable sheet assembly will now be described, reference being made to the accompanying drawings, in which: Figure 1 shows the sheet arrangement deployed on a space craft, and Figures 2 to 5 show sequential stages in the deployment of a sheet assembly on a space craft.

Referring to Figure 1, there is shown a spacecraft 10 which includes on each of its two opposed faces 11 a deployable sheet assembly in the form of a flexible solar array wing 12. Each solar array wing 12 comprises a pair of flexible solar cell blankets 13 arranged side-by-side, each suspended between inner and outer lightweight beams 14, 14' respectively. Each solar cell blanket 13, together with its associated inner and outer beams 14, 14', includes an array of solar cells on the surfaces thereof adapted in use to face the sun when the sheet assembly has been deployed. Each solar cell blanket 13 is foldable upon itself concertina-fashion to a stowed condition.

Each of the two pairs of adjacent beams 14, 14', are hinged together and include bias means to urge them to an opened, colinear configuration and also locking means to lock each pair in the opened configuration. A four part hinged boom comprising portions 15, 16, 17 and 18 extends between the outer beams 14' and the face 11 of the spacecraft to which the solar array wing 12 is attached. Referring to Figure 4, the outer end of boom portion 1 5 is hingedly attached to the outer pairs of beams 14', whilst the inner end of boom portion 1 6 is hingedly attached to the inner pair of beams 14. Spring actuation means are provided between each adjacent pair of boom portions, which actuation means include bias means to urge the pair into a straightened configuration and locking means to lock them in that configuration.

Similar means are provided between the inner end of boom portion 1 8 and surface 11 to urge boom portion 18 into a position perpendicular to the face 11 and to lock boom portion 1 8 in that configuration.

When the solar array wings 12 are in their stowed condition-e.g. when the spacecraft 10 is in a state ready for launching, each solar cell blanket 1 3 is stowed concertina-fashion on itself to be sandwiched between the inner and outer beams 14, 14' respectively and held in this condition by constraints 1 9 extending between the inner and outer beams.

In this condition, boom portions 1 5 and 1 6 are of necessity folded together to lie parallel. The stowed solar cell blankets 13, sandwiched between their respective inner and outer booms 14, 14' are also folded together to lie parallel to, and adjacent, folded boom portions 1 5 and 1 6.

Boom portion 18 is folded flat against the face 11 of the spacecraft and boom portion 17 folded parallel against boom portion 1 8. The stowed configuration is therefore as shown in Figure 2, the assembly held against the face 11 of the spacecraft 10 to prevent unfolding of the respective actuation means by means of hold downs 20.

When it is wished to depioy this assembly, the hold downs 20 are released. Boom portions 1 7 and 1 8 straighten and lock in direction perpendicular to face 11. Simultaneously packed blankets 13 and their associated inner and outer beams 14, 14' together unfold to be locked parallel to the face 11. Constraints 1 9 are then released, either actively or passively to allow each blanket 1 3 to move from its packed condition to an opened, generally planar condition, as shown in the Figure 5.

Typical dimensions of the deployed assembly shown in Figure 1 are as follows: Maximum side of face 11 3 metres Width of blanket 6 metres Length of blanket 6 metres Extended length of boom portions 17 and 18 4.5 metres The above described embodiment allows a relatively large width deployable assembly to be stowed on a spacecraft having a limited sidewall area and minimises deployed configuration constraints. The embodiment allows large fold widths giving greater choice in the selection of solar cells and in stringing arrangements. Inner and outer beams 14, 14' together with boom portions 1 6 to 18 require no further bracing to achieve high stiffness when deployed. The above embodiment provides a low aspect ratio solar array of relatively high efficiency, combined with low weight and complexity.

The biassing necessary for each of the spring actuation means may be found to be less than that required for a relatively high aspect ratio solar array, and therefore the lower stowage pressures enable the degree of vibration initiated during deployment to be reduced.

Whilst in the described embodiment the blankets 1 3 are concertina-foldable to a stowed condition, this invention may be incorporated in arrangements in which the blankets 13 are rolled into a stowed condition.

Claims

1. A deployable sheet assembly which includes two sheet portions which when in a compact furled condition lie in a generally side-by-side position, unfurling means for extending each from a compact furled condition to an unfurled generally planar condition and unfolding means for effecting relative hinging movement of the portions from a side-by-side position to an outspread position.

2. A deployable sheet assembly according to Claim 1, adapted so that said unfolding movement is effected prior to the unfurling of each sheet portion.

3. A deployable sheet assembly according to Claim 1 or Claim 2, wherein said sheet portion included inner and outer beam means and the inner and outer beam means of one sheet portion are hingedly attached to respective inner and outer beam means of the other sheet portion, there being biass means adapted to urge the portions to their outspread position, releasable tie means to maintain the portions in their side-byside position, and locking means to lock them in the outspead position on release of the tie means.

4. A deployable sheet assembly according to Claim 3, wherein the unfurling means includes a pair of boom members pivotted together, one end of said pair being coupled to the inner beam means, the other end being coupled to the outer beam means, there being biass means to urge the boom members to an outspread position, tie means to maintain each sheet portion in a furled configuration, and locking means to lock said pair of boom members in the outspread position on release of said tie means.

5. A deployable sheet assembly according to any of the preceding Claims, wherein each sheet portion is concertina-foldable between furled and unfurled conditions.

6. A deployable sheet assembly according to any of the preceding Claims, wherein said sheet portions lie generally parallel prior to unfolding movement thereof.

7. A space craft including a deployable sheet assembly associated with a face thereof, said sheet assembly including two sheet portions mounted for relative hinging movement from a side-by-side position to an outspread position, the sheet portions being configured so that in their side-by-side position they lie generally within the periphery of said face but in their outspread position they extend beyond the periphery of said surface.

8. A space craft according to Claim 7, wherein each of said sheet portions is extendable from a furled condition to an extended, generally planar condition.

9. A deployable sheet assembly, substantially as hereinbefore described with reference to and as illustrated in, any of the accompanying drawings.

10. A space craft substantially as hereinbefore described with reference to and as illustrated in, any of the accompanying drawings.