Patent Description:
The volumetric capacity of the launch vehicle is a major constraint on the design of a spacecraft, and consequentially every system onboard the launch vehicle needs to be as space efficient as possible. This includes solar arrays and antennas as shown in <FIG>, which are typically packaged with a deployment structure to stow in a compact package but also reliably deploy to a great length. The weight of the launch vehicle is another critical design parameter because of the thrust power needed during launch. NASA estimates that it currently costs approximately <NUM>,<NUM> dollars to launch a mass of one Imperial pound (<NUM> grams) into low earth orbit.

Thus, when considering the design of deployable structures for space, as well as structural stiffness the packaging ratio and mass are important. The packaging ratio determines the relative length change of the structure, from the stowed to the deployed configuration. The mass of the structure is important due to high launch costs, and sufficient stiffness is required to resist load on the structure from an AOCS (attitude & orbit control system) of the associated orbiter. In addition, deployment of the structure must be reliable and controlled, to prevent damage to attached components.

Deployable space structures generally use Collapsible Tube Masts (CTM) and the Storable Tubular Extendable Members (STEM). These are tube structures that can be flattened and rolled for storage and can also deploy to great lengths. However, CTM and STEM usually require relatively large mechanisms to control the speed and direction of deployment. Scaling-up known deployable space structures and achieving suitable geometry in the deployed configuration also present engineering challenges.

Example embodiments consistent with this disclosure provide deployable structures which perform well in some or all of the above-mentioned design aspects, and address the above-mentioned or related shortcomings and other problems in this field.

<CIT> discloses a sparse-isogrid columnar lattice structure including rigid ring frames connected by a mirrored symmetric double helix pattern. <CIT> discloses a deployable truss formed from a plurality of column members connected at their ends. <CIT> discloses a structure. <CIT> discloses a multi-band, concentric helical antenna operating in a conical mode which produces a uniform radiated flux within a footprint.

We describe an apparatus and method as set forth in the appended claims.

In one aspect, there is provided a deployable structure as recited in claim <NUM>.

In one aspect, there is provided a method of deployment of a deployable as recited in claim <NUM>.

Other features of the invention will be apparent from the drawings, and the description which follows.

<FIG> show a deployable structure <NUM>. The deployable structure <NUM> is suitable for use in deployment of a space structure and subsequently supporting itself and the space structure. <FIG> shows the deployable structure <NUM> in a stowed configuration and <FIG> shows the deployable structure <NUM> in a deployed configuration. The deployable structure <NUM> comprises a deployable element <NUM>, in the form of a lattice, and a deployment mechanism <NUM>. In both the stowed and deployed configurations, the lattice <NUM> is generally cylindrical, being characterised by a length and a radius. <FIG> show how the lattice changes in length and radius on deployment, with an increase in length relative to a datum at an end of the lattice <NUM> and relative decrease in radius from the stowed configuration to the deployed configuration.

This deployment apparatus <NUM> performs well in key design aspects of deployable space structures such as size, packaging ratio, mass and bending stiffness when in the deployed configuration. The deployment apparatus <NUM> operates with high reliability and offers good deployment control, thus reducing the likelihood of damage to attached components. The operation of the deployable structure <NUM>, and features that contribute to its utility are described in more detail below.

<FIG> show a lattice <NUM> corresponding to the deployable element of the deployment apparatus <NUM>. <FIG> shows the lattice <NUM> in a deployed configuration and <FIG> shows the lattice <NUM> in a stowed configuration. In <FIG> part of a deployment mechanism <NUM> is also shown, as described in more detail below. The lattice <NUM> comprises eight pre-stressed strips <NUM>, <NUM>. Half of the strips are arranged in a clockwise helix and the other half of the strips are arranged in an anticlockwise helix. This assembly prevents the strips from uncoiling and enables a stable shape to be lattice shape to be formed. The skilled person will appreciate that more than eight or less than eight strips may be used. The strips <NUM>, <NUM> comprise holes, which are equally distanced from each other along the length of the strips <NUM>, <NUM>. Fasteners <NUM>, in this example in the form of rivets, are inserted into the holes, joining the strips <NUM>, <NUM> to one another at pivoting connections, thereby forming the lattice <NUM>. It will be appreciated that other similar fastening means such as bolts, pins, screws etc. may be used to join the strips <NUM>, <NUM>. The strips <NUM>, <NUM> are made of carbon fibre reinforced plastic material, and have high bending stiffness and low weight. The lattice <NUM> is configured to use stored energy of bending in the strips during the transition from stowed configuration to deployed configuration. In this way, self-deployment action can be achieved, and energy sources such as batteries need not be carried to drive the deployment of the lattice. As the strips in the lattice deform during deployment, by virtue of their deformation and relative movement, the lattice <NUM> changes in length and radius simultaneously.

As will be appreciated from <FIG>, the lattice <NUM> in this example has three stability points. The fully stowed configuration is stable, the fully deployed configuration is stable, and there is a stability point in between these two. Different points of stability may exist at other points of partial deployment. Through the manipulation of the manufacturing parameters, the lattice <NUM> can be configured to be stable from at one or more other positions between the stowed configuration and the deployed configuration. In particular, the bending stiffness of the strips around their three principal axes, the degree of pre-stress/pre-bending applied to the strips, the number and separation of the holes in the strips are relevant.

In this way, the deployment apparatus <NUM> is adaptable to most deployable space applications such as solar arrays or antennas.

<FIG> shows a stepper motor <NUM> which acts as the deployment mechanism <NUM>. The motor <NUM> cooperates with sliders <NUM> that attach to the lattice. The lattice <NUM> is attached, at its far end, to the motor <NUM> by a tension element, in this example a cable. The sliders <NUM> are small and serve to anchor the lattice <NUM> to the deployment mechanism in a way that accounts for the reduction in radius of the lattice <NUM> as the lattice moves from the stowed configuration to the deployed configuration. Bearings or any other similar component may be used instead of the sliders <NUM>. The motor <NUM> is also small, and in use fits inside the lattice <NUM>. As a result, the stowed volume is not increased by the stepper motor <NUM>. The stepper motor <NUM> is configured to regulate deployment speed of the lattice <NUM>, by resisting extension of the lattice <NUM> by tension in the tension element. The motor <NUM> releases the tension element by controlled unwinding, resisting the elastic extension of the lattice <NUM>, thereby allowing the deployable structure to change from the stowed configuration to the deployed configuration in a regulated manner. This is advantageous because a quick release of the lattice <NUM> could create a shock wave that might potentially damage components attached thereto. Thus, the deployment of the lattice <NUM> is simple and reliable. Magnets may be used to lock the lattice <NUM> in the deployed configuration.

In example embodiments where a deployment mechanism as described is used to control the deployment of a deployable structure including a lattice <NUM>, there may be unused empty volume inside of the lattice when arranged in the stowed configuration. That is, with typical stepper motors of generally cubic geometry, there may additional space within the deployable structure in the stowed configuration, either radially to the side or around the deployment mechanism, or axially adjacent to or along from the deployment mechanism.

<FIG> shows another example of a deployable structure <NUM>. The deployable structure <NUM> comprises a first lattice <NUM> and a second lattice <NUM>. To achieve higher packaging ratios, the first and the second lattices <NUM>, <NUM> can operate together to deploy to a greater length than would be easily achieved with a single larger lattice.

The first lattice and the second lattice <NUM>, <NUM> have the same properties as the above-described lattices of <FIG> or <FIG>. The first lattice and the second lattice <NUM>, <NUM>, are axially aligned with one another. The first lattice and second lattice <NUM>, <NUM> are operable to deploy in series. The first lattice and second lattice <NUM>, <NUM> are connected together end to end. The second lattice <NUM> has a smaller radius than the first lattice <NUM>. Thus, it is possible to nest the second lattice <NUM> inside the first lattice <NUM> when the deployable structure is in the stowed configuration. In this way, the deployed length may be significantly increased while maintaining the same stowed volume. A deployment mechanism (e.g. a stepper motor as described above) may be mounted inside the lattices and operate to regulate the deployment of the lattices in the deployable structure.

<FIG> shows another example of a deployable structure <NUM>. The deployable structure <NUM> comprises a first lattice <NUM>, a second lattice <NUM> and a third lattice <NUM>. To achieve higher packaging ratios, the first, second and third lattices <NUM>, <NUM>, <NUM> can operate together to deploy to a greater length than would be easily achieved with a single larger lattice.

The first lattice, second lattice and third lattice <NUM>, <NUM>, <NUM> may have the same properties as the above-described lattices of <FIG> or <FIG>. The first lattice, second lattice and third lattice <NUM>, <NUM>, <NUM> are axially aligned with one another. The first lattice, second lattice and third lattice <NUM>, <NUM>, <NUM> are operable to deploy in series. The first lattice, second lattice and third lattice <NUM>, <NUM>, <NUM> are connected together end to end. The second lattice <NUM> has a smaller radius than the first lattice <NUM>, with the third lattice <NUM> having a smaller radius than the second lattice <NUM>. Thus, it is possible to nest the second lattice <NUM> inside the first lattice <NUM> when the deployable structure is in the stowed configuration, and further to nest the third lattice <NUM> in the second lattice <NUM>. In this way, the deployed length may be significantly increased while maintaining the same stowed volume. A deployment mechanism (e.g. a stepper motor as described above) may be mounted inside the lattices and operate to regulate the deployment of the lattices in the deployable structure.

In one example, rigid steel joints connect the first lattice <NUM> and the second lattice <NUM> in end to end arrangement, and correspondingly connect the second lattice <NUM> and the third lattice <NUM>. The second lattice <NUM> has a smaller radius by <NUM> than the first lattice <NUM> in the stowed configuration. The third lattice <NUM> has a smaller radius by <NUM> than the second lattice <NUM> when in the stowed configuration.

To regulate deployment of the deployable structure <NUM>, a deployment mechanism is provided is attached to the top of the inner lattice (i.e. the third lattice <NUM>). In the example of <FIG>, the deployment mechanism comprises a stepper motor and a spool of cable. The stepper motor is still small enough to be placed inside the lattices. In this way, a multi-stage deployment can be regulated by a single deployment mechanism.

Although the example embodiment of <FIG> comprises three lattices, two lattices only may be nested in alternative embodiments, and likewise, four or more lattices may be nested in still further embodiments.

The skilled person will appreciate that increasing the stiffness of the strips in the lattice will produce a smoother deployment. The bending stiffness of the deployable structure, when deployed, is increased by increasing the number of strips in the lattice to three, four or more. Use of three, four or more strips in the lattice helps to hold the lattice in the deployed configuration, resisting bending.

In the example shown in <FIG>, each lattice <NUM>, <NUM>, <NUM> has six strips. The deployment mechanism provides a sufficient amount of force to regulate deployment of the deployable structure but is still small enough to fit inside the lattices <NUM>, <NUM>, <NUM>. The stowed height of the deployable structure of <FIG> and <FIG> is <NUM> and the deployed height is <NUM> which gives the packaging ratio of <NUM>.

<FIG> shows a method of manufacturing of a lattice. The manufactured lattice can be used in any of the deployable structures described herein. The method relates to manufacture from components that comprise a composite material, for example a fibre reinforced plastic material such as CFRP.

At step S730, the method comprises determining required lattice characteristics. At steps S732 to S738 strips are formed, and then assembled to form a lattice at step S740. <FIG> shows example sub-steps of the method for forming the strips for assembly, which starts with step S732 of forming pre-stressing material strips. At step S734, the method comprises curing the strips. At step S736, the method comprises a step of finishing the post-cured strips, for example including trimming. At step S738, the method comprises forming holes in the post-cured strips to enable the strips to be joined to one another, for example by drilling. At step S740, the method comprises assembling the strips into the lattice, coupling the strips to one another.

Referring to step S730, the method comprises determining required lattice characteristics. A mathematical model has been developed that discussed relevant design parameters, published as <NPL>. Once the lattice characteristics have been decided, based on its application, manufacturing can begin.

At step in S732, the method comprises a step of pre-stressing strips. <FIG> shows a finite element model which shows the application of pre-stress through the change in radius from manufactured shape to being part of a lattice. Pre-stressing of the strips in the lattice is achieved by laying up the strips on a curved mould with a radius larger than that of the desired lattice. The increase in the radius of the mould results in the increased pre-stress on the strips.

At step S734, the method comprises a step of curing the strips. The strips are cured in the autoclave. For example, the strips may be cured at <NUM> degrees Celsius and <NUM> bar pressure. For example, the strips may be made of fibre reinforced polymer material.

At steps S736 and S738, the post-cured strips are trimmed, and holes formed in the strips to allow the strips to be joined to one another. The holes are drilled at equal distances from each other in lattices which are to deploy in a rectilinear manner.

Finally, the strips may be assembled into the lattice at step S740. Half of the plurality of pre-stressed strips is arranged in a clockwise helix and the other half of the plurality of pre-stressed strips is arranged in an anticlockwise helix. This assembly resists uncoiling and improves the overall stability of the structure. Fasteners are used to couple the pre-stressed strips in the lattice.

The holes which are formed in the strips, either by the particular step of drilling post-cured strips, or by other methods. In examples not covered by the scope of the claims, the holes may be arranged at unequal distances from each other. This allows the lattice formed of the strips to be deployed in a non-linear manner.

In examples not covered by the scope of the claims, the fasteners may be provided at unequal spacings along the length of the strips such that on deployment the lattice element bends to a curved deployed configuration.

The fasteners may be provided at unequal spacings along a part of the length of the strips such that on deployment the lattice element bends to a curved deployed configuration along a part of the length thereof, and further provided at equal spacings along a part of the length of the strips such that on deployment the lattice element bends to a rectilinear deployed configuration along a part of the length thereof.

The fasteners may be provided at generally decreasing spacings along a part of the length of the strips such that on deployment the lattice element bends to a curved deployed configuration along a part of the length thereof with a decreasing radius of curvature. Alternatively, the fasteners may be provided at generally increasing spacings along a part of the length of the strips such that on deployment the lattice element bends to a curved deployed configuration along a part of the length thereof with an increasing radius of curvature.

Referring to step S730, the method comprises determining required lattice characteristics. The analytical model developed for the related deployable structures which deploys in a straight line can be used to estimate the location of the stable points and the general characteristics of the deployable structure with variable curvature. The determination of the characteristics of a deployable structure with variable curvature is described in more detail in relation to <FIG>.

An important aspect of a deployable structure with a variable curvature is its radius of curvature. The radius of curvature, and corresponding curve is controlled by two factors. The first factor is the spacing of the connections between the strips that form the lattice (i.e. the spacing of the holes). The second factor that determines the curve of the lattice is its stable position considering the amount of pre-stress in the strips and their bending characteristics generally.

It is desirable to have the spacing of the connections on the inside of the curve closer together than the ones on the outside. This spacing may be determined, for example, through computer-aided design (CAD) modelling. The curve and length of the lattice are determined simply by a line as shown in <FIG>. The radius of curvature of the lattice is then controlled by a horizontal line that is connected to the bottom of this curve. In order to create the helical shape of the lattice, a surface sweep of this horizontal line is created along the first curve. Here, the number of revolutions the strips have in the lattice is decided.

<FIG> shows a single sweep lattice with <NUM> revolutions. This process is repeated three more times, sweeping different lines at different angles to the original curved line. This produces four clockwise strips of the lattice. This process may be repeated more than three times or less than three times. The process is repeated by sweeping the lines in the anti-clockwise direction to create all eight strips of the lattice. This is shown in <FIG>.

As will be appreciated, according to design requirements more or less than eight strips may be made. The locations of the connections of the lattices are located where the sweeps of the lines cross paths. The spacings on the strips increase as the helix moves from the inside of the curve to the outside and vice versa. In order to accurately measure these spacings, the lattice is reduced in size and revolutions, to the location of the first connection, as shown in <FIG>. Then the length <NUM> of each of the line sweeps is recorded. Next, the lattice is increased in length and revolutions to the next connection. This is shown in <FIG>. Lengths <NUM> are recorded and the process is repeated. The recorded lengths <NUM> may be, for example, one or more lengths of the arc(s). After one full helix revolution, the spacings in each of the strips repeat.

As above, the second factor that is relevant to determining the curve of the lattice is its stable position. As the curved lattice deploys, the curve of the structure increases. Therefore, a lattice that only deploys a little can only have a relatively slight curve, and a lattice that can deploy to greater lengths can curve relatively more. The stable position can be determined by mathematically modelling the strain energy to accurately predict the stability positions. This may be achieved by, for example, finite element modelling. An example of a finite element model is shown in <FIG>.

<FIG> shows a method <NUM>, not covered by the appended claims, of determining required lattice characteristics for a deployable structure with variable curvature. As stated above, the curve and stable points of the lattice. The method <NUM> comprises a step of determining spacing of holes in a lattice S931. The method <NUM> further comprises a step of determining the curve and length of the lattice S933. The method <NUM> further comprises a step of determining the radius of the lattice S935. The method <NUM> further comprises a step of creating a helical shape of the lattice S937. The method <NUM> furthers comprise a step of determining a stable position of the lattice S939. The method <NUM> of <FIG> may be used at step S730 in <FIG> to manufacture a deployable structure with variable curvature.

<FIG> shows an example of a deployable structure <NUM> not covered by the scope of the claims with variable curvature in a stowed configuration, mid-deployment configuration and deployed configuration. The difference between the deployable structure <NUM> and the above-described deployable structures of the present disclosure is that the fasteners of the deployable structure <NUM> may be provided at unequal spacings along the length of the strips such that on deployment the deployable structure <NUM> bends to a curved deployed configuration. Other properties of the deployable structure <NUM> may be the same as the properties of the above-described lattices of <FIG>, <FIG>, <FIG> and <FIG>. The deployable structure <NUM> may also be connected with other deployable structures <NUM> in series as described in relation to <FIG>. The deployable structure <NUM> may also be deployed in a manner as described herein, such as by the above-described stepper motor.

<FIG> shows a deployable structure, not covered by the appended claims, with a variable curvature <NUM>. <FIG> shows another example of a deployable structure with variable curvature <NUM>. The deployable structure <NUM> may be the same as the deployable structure <NUM> described above. <FIG> highlight that the curved lattice <NUM> may go from straight-line deployment to <NUM> degrees curvature and back. The curvature may also exceed <NUM> degrees.

<FIG> shows a roll-out solar array in a deployed configuration <NUM> and in a stowed configuration <NUM>. This configuration <NUM>, <NUM> uses four curved lattices as the structural members of the reflector and two straight lattices to hold the feed antenna. The design may use more or less than four curved lattices and more or less than two straight lattices.

Multiple lattices can be used in series to produce the dish shape of an antenna. When paired with lattice nesting, the size of this antenna can be increased while maintaining a small stowed size. In the stowed state <NUM>, the curved lattice still has a cylindrical shape which is ideal for nesting. The rigidity of the lattice can be controlled through its composite lay-up allowing it to be tailored to different types of antennae. The deployable structure with variable curvature can be also combined in series with the deployable structure which deploys in a straight line. Thus, any shape of deployment may be achieved. The deployable structure with variable curvature can be referred to as "curved lattice" and the deployable structure which deploys in a straight line can be referred to as "straight lattice".

<FIG> shows an application, not covered by the appended claims, of the deployable structure with variable curvature <NUM>. The deployable structure <NUM> may be used, for example, for steering in a hydrofoil catamaran. <FIG> shows another application of the deployable structure with variable curvature <NUM>. The deployable structure <NUM> may be used, for example, as an artificial elbow joint. However, the uses the deployable structure <NUM> are not limited thereto. <FIG> shows another application of the deployable structure with variable curvature <NUM>. The deployable structure <NUM> may be used, for example, as a deployable robotic arm on spacecraft. However, the uses the deployable structure <NUM> are not limited to such example applications.

Throughout this specification, the term "comprising" or "comprises" means including the component(s) specified but not to the exclusion of the presence of others.

Claim 1:
A deployable structure (<NUM>) comprising:
a first helical lattice (<NUM>) and a second helical lattice (<NUM>), wherein each helical lattice (<NUM>,<NUM>) comprises:
pre-stressed strips (<NUM>,<NUM>) comprising carbon fibre reinforced plastic material, wherein half of the pre-stressed strips (<NUM>) are arranged in a clockwise helix, and the other half of the pre-stressed strips (<NUM>) are arranged in an anti-clockwise helix (<NUM>); and
wherein the strips (<NUM>,<NUM>), comprise holes which are equally distanced from each other along the length of the strips (<NUM>,<NUM>); and
fasteners (<NUM>) inserted into the holes to join the strips (<NUM>,<NUM>) at pivoting connections, thereby forming the lattice,
wherein the first helical lattice (<NUM>) is arrangeable in a stowed configuration and a deployed configuration and the second helical lattice (<NUM>) is arrangeable in a stowed configuration and a deployed configuration, wherein the helical lattices (<NUM>, <NUM>) are configured to deploy using stored energy of bending in the helical lattice elements (<NUM>,<NUM>),
wherein with the helical lattices (<NUM>,<NUM>) arranged in the stowed configuration the second helical lattice (<NUM>) nests in the first helical lattice (<NUM>), wherein the helical latices (<NUM>,<NUM>) are axially aligned, and
wherein the first helical lattice (<NUM>) and second helical lattice (<NUM>) change in length and radius simultaneously during deployment.