Title of Invention

A DEPLOYABLE SOLAR SAIL ASSEMBLY FOR SATELLITES AND A METHOD OF MAKING IT

Abstract

The invention relates to a deployable solar sail assembly for satellites. It comprises of a deployable solar sail with a hold down mechanism, a release mechanism and a deployment mechanism. Solar sail i~ attached to a coilable lattice boom through a turn table and housed in a canister. The solar sail comprises a top cone, middle cone and bottom cone. The top cone and the middle cone is made of plurality of thin film segments of a space compatible material joined to one another and fixed to an assembly of a top cone inner ring and top cone outer ring. The bottom cone is made of at least two segments of relatively thicker film of a space compatible material and fixed to an assembly of a bottom cone inner ring, bottom cone middle ring and bottom cone outer ring. The upper and lower edges of the middle cone is attached to the top cone outer ring and to the bottom outer ring respectively

Full Text

The invention relates to a deployable solar sail assembly for satellites and a method of making it. A solar sail is required in a spacecraft with one sided solar array to counterbalance the solar radiation torques on the solar array. Such deployable solar sail and associated mechanisms should meet the following requirements. 1. It should be stowable so as to fit within the launch vehicle envelope. 2. The configuration has to ensure a minimum unbalance torque variation over all seasons. 3. The solar sail has to be deployed sufficiently away from the spacecraft, to minimize thermal inputs into the coolers of the meteorological payload. 4. The deployed sail assembly should meet the natural frequency requirements of the system. 5. Thermal and optical properties of sail should be stable through out the mission life. 6. The sail should have provisions for grounding to the space craft. The deployable solar sail assembly according to the invention is made to satisfy all the above mentioned requirements. The invention provides a deployable solar sail assembly for satellites, comprising of a deployable solar sail with a hold down mechanism, a release mechanism and a deployment mechanism, said solar sail being attached to a coilable lattice boom through a turn table and housed in a canister characterised in that said solar sail comprises a top cone, middle cone and bottom cone, the said top cone and the said middle cone being made of plurality of thin film segments of a space compatible material joined to one another and fixed to an assembly of a top cone inner ring and top cone outer ring, the said bottom cone being made of at least two segments of relatively thicker film of a space compatible material and fixed to an assembly of a bottom cone inner ring, bottom cone middle ring and bottom cone outer ring, the upper and lower edges of the middle cone being attached to the top cone outer ring and to the bottom outer ring respectively. The invention also provides a method of making the deployable solar sail assembly for satellites as described herein above, comprising the step of cutting accurately the segments of top cone, middle cone and bottom cone with notch free edges using templates, fabricating top cone inner ring, top cone outer ring, bottom cone outer ring, bottom cone middle ring and bottom cone inner ring, bonding and curing the segments of the cone using fixtures to ensure wrinkle free joints, joining the top cone to middle cone and the middle cone to bottom cone by adhesive, providing a grounding tab by a conductive path from sail for attaching to spacecraft, folding the solar sail systematically using templates, attaching the sail to a coilable lattice boom and stowing the boom and sail in a canister and provided with hold down mechanism, release mechanism and deployment mechanism. The deployable solar sail assembly according to the invention will now be described with reference to the accompanying drawings. Figure 1 (a): shows the stowed deployable solar sail with drive mechanism. Figure 1 (b): shows the deployed solar sail with drive mechanism. Figure 2 : shows the solar sail. Figure 3 : shows the top view of the top cone. Figure 4 : shows the middle cone. Figure 5 : shows the bottom cone. Figure 6 : shows the top cone ring assembly. Figure 7 : shows the bottom cone ring assembly. Figure 8 : shows the solar sail being stowed. Figure 9 : shows the folds pattern of the solar sail. Figure 10 : shows the base end drive mechanism for boom straightening. The solar sail comprises a top cone (7) assembled on a top cone ring assembly, a bottom cone (9) assembled on a bottom ring assembly and a middle cone (8) attached to both top cone (7) and bottom cone (9). The top cone ring assembly consists of a top cone inner ring (13) and a top cone outer ring (14) with spokes (16) connecting the top cone outer ring and top cone inner ring. The spokes are preferably made of glass fibre reinforced plastic. The bottom cone ring asembly consists of bottom cone inner ring (11), bottom cone middle ring (25) and bottom cone outer ring (21). The bottom cone inner ring and the bottom cone outer ring are attached with a lacing thread (24). The solar sail is attached to a coilable lattice boom (1) in a canister (C) through a turn table (10). The bottom or inboard end of the solar sail is attached to the coilable lattice boom (CLB) through pivots through interface blocks (47). A launch restraint assembly (S) holds down the stowed, systematically folded sail (12). A tie rod (3) passing through the canister (C) and a launch restraint assembly (5) holds the stowed lattice boom assembly (1). The stowable lattice boom (1) is provided with a drive (2) and a bolt cutter (4) for releasing and deploying the boom and sail. A boom straightening mechanism (6) is also associated with solar sail drive mechanism. The top cone (7) and middle cone (8) are made from segments (17) of kapton film with one side aluminised wherein the aluminised side of the segments are kept towards the inside of the top cone and middle cone and the non aluminised side of the kapton film is kept towards the outside of the top cone and middle cone. The bottom cone is also made of atleast two segments of one side aluminised kapton film relatively thicker than the thin aluminised kapton film of the top cone and middle cone. The aluminised side of the kapton film is kept towards the outside of the bottom cone. The slant straight edges of the segments of middle cone and bottom cone are bonded with adhesive joints (18,23). The inner and outer edges of the bottom cone are joined to bottom cone inner ring (11) and bottom cone outer ring (21) respectively using attachment means (24). The bottom cone middle ring (25) is attached to bottom cone, by adhesive. The segments of the cone can be made of any suitable space compatible material which satisfies the required thermal and optical properties, the environmental requirements, and capability of compact stowage and low weight. For ensuring a compact stowage of the solar sail during the launch, and to fit well within the launch vehicle envelope, the solar sail (12) is systematically folded and held down to the spacecraft interface (28). Compact folding of the solar sail (12) is similar to the camera bellows and the flipping back of the bottom cone is aided by a stand off (30). The plurality of joints (18) of the segments (17) of middle cone (8) are used as folding reference. The folding pattern comprises of radial folds (32) and tangential folds (31) and templates (33) are used for guiding and locating the folds. The templates (33) have a smooth surface and have no sharp corners. The bottom cone (9) is supported by a supporting fixture (29) and the middle cone (8) is folded in the form of a bellow. In order to ensure that the said folds do not interfere with deploying CLB, a minimum gap (X) is provided between the folded film and the top cone inner ring (11). To avoid sliding of the folds during launch, a maximum peep out length (Y) of the folded film from the top cone outer ring (14) and bottom cone middle ring (26) is provided. The deployment mechanism comprises a coilable lattice boom (1) housed in a canister (C) with a lanyard for control drive (2). The CLB (1) consists of continuous longeron (34) which are interconnected to a triangular battens (35) through hinge assemblies at regular intervels throughout the length. Three pairs of diagonals (36) at each bay provide the necessary shear and torsional rigidity to the boom (1) which is self deployable. The boom (1) provides the necessary stiffness to the deployed sail. A pre-twist feature is provided in the boom throughout its length to avoid thermal distortion of the boom. Since the available self deployment force at the start of the deployment in a fully stowed boom is small, a spring drive mechanism (6) is provided to give additional force to the longerons (34) at the baseend thus ensuring an early boom strightening. The CLB (1) compactly stowed in the canister (C) and the folded sail (12) are attached to the spacecraft (28). The launch restraint assembly (5) holds down the stowed sail (12). A tie rod (3) passing through the canister (C) holds down the CLB (1) and the launch restraint assembly (5). The release of the sail (12) is achieved by cutting the tie rod (3) with a bolt cutter (4) provided for it. The control drive (2) achieves the controlled deployment. The spring drive mechanism (6) attached to the bottom plate (37) of the canister (C) comprises a spring (38) connected to the CLB longeron end fitting (39) through a swaged terminal (40), wire rope (41) and a tab (42). The spring (38) is guided by a mandrel (43) and supported by an end cap (44) provided on the mandrel (43). A microswitch (45) connected to a bracket (46) monitors the straightening of the CLB (1). The deployable solar sail assembly according to the invention is made in the following manner. Segments of top cone (7), middle cone (8) and bottom cone (9) are cut accurately with notch free edges using templates. The top cone inner ring (13), the top cone outer ring (14), the bottom cone middle ring (25) and the bottom cone inner ring (11) are fabricated in a known manner. The segments of the cone are bonded and cured using fixture to make wrinkle free joints. The top cone (7) is joined to middle cone (8) and the middle cone is joined to bottom cone (9) by adhesive. A grounding scheme comprising of conductive tabs and a conductive path from sail to the space craft is provided. The fabrication, and folding procedures, for solar sail according to this invention can be adopted to manufacture sail of various sizes and geometry depending on requirements. The drive mechanism along with novel early straightening feature for the boom is simple, reliable and can be adopted to deploy solar sails of various sizes. WE CLAIM: A deployable solar sail assembly for satellites comprising a deployable solar sail with a hold down mechanism, a release mechanism and a deployment mechanism, said solar sail being attached to a coilable lattice boom (1) through a turn table (10) and housed in a cannister (C) characterised in that said solar sail comprises a top cone (7), middle cone (8) and bottom cone (9), the said top cone (7) and the said middle cone (8) being made of plurality of thin film segments (17) of a space compatible material joined to one another and fixed to an assembly of a top cone inner ring (13) and top cone outer ring (14), the said bottom cone (9) being made of at least two segments (22) of relatively thicker film of a space compatible material and fixed to an assembly of a bottom cone inner ring (11), bottom cone middle ring (25) and bottom cone outer ring (21), the upper and lower edges (19, 20) of the middle cone (8) being attached to the top cone outer ring (14) and to the bottom outer ring (21) respectively. The deployable solar sail assembly as claimed in claim 1, wherein the said space compatible material is a film of aluminised kapton with the aluminised side being in the inner side of the top cone and middle cone and kapton side being the outer side of the top cone and middle cone and the aluminised side being the outer side of the bottom cone and kapton side being the inner side of the bottom cone. The deployable solar sail assembly as claimed in claim 1 or 2, wherein the turn table (10) is connected to the top cone inner ring (13) and top cone outer ring (14) through a set of radial spokes (16). The deployable solar sail assembly as claimed in claim 3, wherein the said radial spokes (16) are made of glass fibre reinforced plastic. The deployable solar sail assembly as claimed in any one of the claims 1 to 4, wherein the thin film segments (17) of the cone are bonded along the slant side with adhesive joints (18). The deployable solar sail assembly as claimed in any one of the claims 1 to 5, wherein the inner and outer edges of the cone are attached to the bottom cone inner ring (11) and bottom cone outer ring (21) respectively by fixing means (24). A method of making the deployable solar sail assembly for satellites as claimed in claim 1, comprising the step of cutting accurately the segments of top cone (7), middle cone (8) and bottom cone (9) with notch free edges using templates, fabricating top cone inner ring (13), top cone outer ring (14), bottom cone outer ring (2IX bottom cone middle ring (25) and bottom cone inner ring (11), bonding and curing the segments of the cone using fixtures to ensure wrinkle free joints, joining the top cone (7) to middle cone (8) and the middle cone (8) to bottom cone (9) by adhesive, providing a grounding tab by a conductive path from sail for attaching to spacecraft, folding the solar sail systematically using templates (33). attachinc the sail to a coilable lattice boom (1) and stowing the boom and sail in a canister (C) and provide with hold down mechanism, release mechanism and deployment mechanism. 8. The method as claimed in claim 7, wherein the segments of top cone, middle cone and bottom cone are made of aluminised kapton and the top cone and middle cone are made with aluminised side facing inwards and bottom cone is made with aluminised side facing outwards. 9. A deployable solar sail assembly for satellites, substantially as hereinabove described and illustrated with reference to the accompanying drawings. 10. A method of making the deployable solar sail assembly for satellites, substantially as hereinabove described and illustrated with reference to the accompanying drawings

Documents:

951-mas-2000-abstract.pdf

951-mas-2000-claims filed.pdf

951-mas-2000-claims granted.pdf

951-mas-2000-correspondnece-others.pdf

951-mas-2000-correspondnece-po.pdf

951-mas-2000-description(complete)filed.pdf

951-mas-2000-description(complete)granted.pdf

951-mas-2000-drawings.pdf

951-mas-2000-form 1.pdf

951-mas-2000-form 19.pdf

951-mas-2000-form 26.pdf

951-mas-2000-form 3.pdf