Impuesto Específico a las Bebidas Alcohólicas

Given the large deployed-to-stored size ratio required for solar sails, linear deployment devices have been the only ones considered here. Hinge deployment devices only work by rotating hardware from one position to another and, therefore, are not suitable for solar sails. Examples of the latter are the type of booms that deploy by unfolding, like Astro Aerospace’s 20 m FlatFolded Tubes used in the Mars Express spacecraft [Mobrem and Adams, 2006, Adams and Mobrem, 2006], or the CFRP deployable booms with tape-spring hinges studied in [Mallikarachchi, 2011]. Also, tape-spring based truss structures like Foster Miller’s 58 g/m Slit-Tape Truss [Jenkins, 2006], and AFRL’s 157 g/m DECSMAR truss [Pollard and Murphey, 2006].

A review of different linear deployment devices that have or could have the potential of being used in solar sails will be presented next. Good reference are found in [Conley et al., 1998] and [Jenkins, 2006]. More recently, as part of an extensive review of large deployable structures technology for the DEPLOYTECH FP7 project, a wide boom technology survey has been carried out [Viquerat et al., 2013a].

Wire deployers

Wire deployers tend to work with the centripetal force generated from a spinning spacecraft. They also rely on the spin-induced tension to keep the wire taut after its full extension. In principle, the wire has a very low bending and torsional stiffness to be used as a rigid boom, so this type of deployers could only be used on spinning sails or helyogyros. In addition, because of their low tension, oscillations and travelling wave phenomena can cause undetermined scenarios. The attitude control and manoeuvring of sail concepts that use them, then, becomes quite complex. There are three main types of wire deployers:

• Yo-Yo De-spin. It is commonly used to slow down the spin rate of a satellite. It uses masses attached to the tip of wires, which are wound around the spacecraft and afterwards pulled away from it using the centripetal force. Nevertheless, a Yo-Yo-like-deployer requires parasitic masses that can reduce the performance of the spinning sail, unless these are small

as for IKAROS. In there the 14 x 14 m2 sail was unfurled and kept tensioned using just 0.5 kg tip masses.

• Drum Deployer. Here the wire is wound onto a drum inside a mechanism. The mechanism is generally used to deploy a wire structure that will have its root attached to the spacecraft. • Tethers. They normally use a drum deployer type of method, where the drum mechanism is the one being extended. However, they tend to rely on gravity gradient forces. They are normally used to extend away from the spacecraft massive pieces of equipment and sensors as shown in Figure 2.17 (left). Also alternative sources of electricity or propulsion by their interaction with Earth’s electromagnetic field. The necessary mass difference to produce the sufficient gravity gradient could potentially contradict solar sail’s design goals.

Figure 2.17: Deployment of the Tethered Satellite System (TSS-1) by Space Shuttle Atlantis in 1992 (left) [Source: NASA]; and lightweight telescopic boom stored and deployed (right) [Source: Northrop-Grumman].

Telescopic Booms

Telescopic booms have a tapered geometry once deployed. They normally consists of several concentric conical tubes that latch when reaching the end of extension of each section. They required a powered deployment actuator, such as a motor-driven lead screw, or a smaller tubular boom running inside them. Telescopic booms are commonly used in applications requiring high strength, stiffness and retraction capability. However, given their large deployed-to-stored size ratio and especially the linear mass compared to other boom options, to date, they have not been considered for solar sail applications. Northrop-Grumman has recently developed a relatively light composite telescopic mast that is driven by one of their STEM booms [Northrop-Grumman, 2010] (see Figure 2.17 (right)). Another lighweight example is the Sula boom proposed in [Humphries et al., 2007].

Coilable Masts

Coilable masts are a type of deployable truss structure that are stowed by coiling the continuous structural members that run along the full length of the mast (longerons), into a tight helix held inside a canister. Once deployed, battens lie in a plane perpendicular to the longerons and diagonals generally criss-cross every face on each side of the mast, providing additional structural support

(see Figure 2.18). Longerons and battens must be made of a material with high strain capability to accommodate the stowage contortions.

There are two deployment methods possible for coilable masts: a free deployment or one using a motor. The first uses the stored strain energy generated during packing of the structural members to drive the propelled mast outwards in an unwinding motion. Using this method the coilable mast can be stowed in less than 2% of its deployed length. To reduce the shock load that occurs at full deployment, a lanyard running down the center of the mast connected to a brake mechanism, or a motor driven drum can be used. The free deployment method has the disadvantage of having a transition region with considerably less stiffness than the deployed section, hence, the mast cannot withstand significant loads during deployment. The motor-driven canister-deployed coilable mast is the alternative choice if the application requires a non-rotating tip payload or a load-bearing mast during deployment.

Figure 2.18: CoilABLE mast during deployment (left) and design sketch (right)[Source: ATK/ABLE].

ATK/ABLE Engineering has developed composite coilable masts with linear mass densities of less than 70 g/m making them ideal for solar sail booms. The CoilABLE GR1mast was used in the

ATK/ABLE 20 x 20 m2 sail ground demonstration [Murphy et al., 2006]. An even lighter version of just 35 g/m called the ST8 SAILMAST or CoilABLE GR2 has been produced by ATK/ABLE

for a 40 x 40 m2 scaled-up version of their S4 solar sail subsystem [McEachen, 2008].

The AstroMast boom developed by Northrop-Grumman is based on the same concept as ATK’s CoilABLE booms. There are only minor differences in truss-architecture but the mast has a continuous 120◦ twist over its length [Northrop-Grumman, 2007]. The Solar Sail AstroMast is an untwisted 230 g/m AstroMast with a small sail at its tip and is used to counteract disturbance torques on satellites (e.g., asymmetric solar array alignment). Deployment will also be done by strain-energy, but has to be controlled by using for example a central lanyard.

The TriLok boom developed by ATK consists of three flexible side elements which are locked together at their edges to form a triangular truss-like structure. In stowed configuration each side element is coiled up separately on a cylindrical core. The cores are mounted on a single deployment module which is located at the truss tip and enables full force transmission even in the beginning of the deployment phase [Jenkins, 2006]. The linear mass density of this mast is 140 g/m.

Recently, DLR [Hillebrandt et al., 2012] proposed a high performance coilable triangular truss structure that uses TRAC boom type longerons. It is designed mainly for axial compression loaded applications that require moderate bending strength, such as solar sails. A small packaging ratio is

gained using a two path folding pattern, where the truss is flattened first in cross direction enabled by hinges added to one row of battens. In the second step, the flattened truss is reeled on a small central hub, taking advantage from the high deformation capability of thin-walled carbon tapes.

Articulated Masts

Articulated masts are another type of deployable truss structure. They allow more freedom in choosing the longeron material and cross section as they are stored by folding the longerons at pivot joint/articulations as shown in Figure 2.19 (left). There is so much freedom with this concept that numerous configuration exist. All articulated masts can be manually or motor deployed using a lanyard mechanism or a canister deployment system. Nevertheless, due to their articulated joints, they have worst packaging ratios and are usually heavier than coilable masts for similar mechanical property booms. Hence, no solar sail design has considered them yet. For example, ATK’s masts FAST and ADAM masts reach much higher values in strength and stiffness and are flight proven. However, the higher stiffness results from larger diameters and stiffer components that result in a specific mass above 1 kg/m. Stohlman [Stohlman, 2011] studied the repeatability of extension on these joint-dominated deployable masts.

A new ultralight (20-80 g/m) articulated mast architecture called the Superstring, with a length limit in the order of 100 m, was proposed in [Brown et al., 2009]. Althought the concept is currently at a low TRL. The novelty of this concept comes from the innovative packaging scheme, that allows the square truss structure to collapse into a single plane that can then be wrapped around the spacecraft hub, as if it was a huge articulated tape-spring.

Figure 2.19: ADAM articulated mast (left) [Source: NASA]; and Ultraboom isogrid boom (right) [Jenkins, 2006].

Isogrid Booms

ILC Dover has developed the UltraBoom shown in Figure 2.19 (right). It is an uncured composite isogrid structure that will be deployed by inflation and cured in space. It has a circular cross-section and is made of very long and thin carbon fibre tows impregnated with a shape memory polymer. The tows are directed diagonal and parallel to the centre line with lots of intersection points to from the isogrid shape structure [Jenkins, 2006]. 3 m samples of 70 g/m have been extensively tested [Agnes et al., 2006], but the final specific mass of the booms would be of about 145 g/m.

Inflatable Booms

Inflatable technology has been widely researched because it can offer the lightest solution possible for large space structures [Jenkins, 2001]. Current focus on inflatable booms have used an inflation system that will provide an internal pressure which will sustain the structural load until the external boom composite membrane is rigidised, i.e. by ultraviolet or infrared radiation [Cadogan and Scarborough, 2001, Allred et al., 2002]. The inflatability of the structure is strongly determined by the boom stowage method, which in turn will depend on the packaging method of the sail connected membrane. For example, in a wrapped membrane the embedded deployable booms will either be coiled or z-folded [Katsumata et al., 2009].

There are three main types of boom stowage methods: rolling [Steele and Fay, 2000]; conical- telescopic; and origami folding patterns. The latter method has produced a wide range of folding methods, such as the Z-fold/concertina folding, with a new modified z-fold proposed by [Katsumata et al., 2011] to alleviate the normal instability found during inflation of these z-folded booms; Yoshimura pattern [Tarnai, 1994]; inverse/bellows/accordion folding used in EADS Astrium’s in- flatable boom [Dupuy and Le Couls, 2010, Guenat and Benedic, 2011]; helically triangulated cylin- ders analysed in [Guest, 1994a, Guest, 1994b, Guest, 1996]; Miura-ori cylinders based on Miura-ori fold patterns like the one proposed by [Sogame and Furuya, 2000] and [Senda et al., 2006]; and the rigid-foldable patterns introduced by [Tachi, 2009].

An important challenge of this technology is to ensure a controlled deployment and avoid instabil- ities during inflation of the boom. An overview of existing strategies by [Grahne and Cadogan, 2000] include compartmentalisation, retardation, columnation, and propagating instability. A detailed review on different packing approaches and rigidisation methods for inflatable booms is available in [Schenk et al., 2014]. The rigidisation methods proposed to date use UV-setting resins, ther- mosetting resins, glass transition resins, stretched/yielded metal laminates, gas and vapour cured resins, solvent boil-off structures, foams, and photolysable structures [Cadogan and Scarborough, 2001]. However, inflatable boom technology is still under examination to reduce leak issues, deploy- ment and rigidisation risk, and the chance of micro-meteorites puncturing the membrane before it is completely hardened.

Figure 2.20: L’Garde’s inflatable boom stowed (left) and deployed (right) [Source: NASA]. L’Garde has developed an isogrid inflatable boom with a conical-telescopic stowage/deployment method [Lichodziejewski et al., 2003] as shown in Figure 2.20 (left). Nitrogen gas is used un- til rigidisation. The boom consists of a thin Kapton bladder reinforced with longitudinal and spiral wrapped Kevlar fibres impregnated with a sub-Tg resin. Continuously attached along the

string longerons and battens. This provides the inflatable boom with additional bending stiffness against out-of-plane solar radiation loads. The inflatable booms were successfully demonstrated in L’Garde’s 20 x 20 m2 sail ground demonstrator [Lichodziejewski et al., 2006] as shown in Fig- ure 2.20. A 25 m long version will soon be utilised as the deployable and supporting structures of the upcoming Sunjammer solar sail mission [Barnes et al., 2014]. The Cibola experiment launched in 2007 [Caffrey, 2009] demonstrated in orbit the deployment of a 2.4 m long Kevlar fabric version of this sub-Tg inflatable-rigidisable booms. However, only one of the three masts, used in RF

antennae, inflated correctly. Flexible Shell Booms

Flexible shells booms are thin-walled structures of various cross-section shapes, that can be elastically flattened and rolled-up on a reel, like a carpenter’s tape-measure. They obtain their stiffness during deployment by transitioning from a flat to a curved geometry [Pellegrino, 2002]. These booms are usually motor-driven or have a brake/speed-damper mechanism, rather than self-deployed, so as to provide retraction capability [Trexler, 1968], and especially to control the extension speed. This occurs because the coiled configuration holds a large amount of strain energy that, uncontrollably released, would produce fairly fast chaotic deployments. They also require an external mechanism that provides the final boom shape, consisting of guides and/or rollers as in [Weir and al., 1964, Aguirre-Martinez et al., 1987]. Another control option is to use a pneumatic actuator with, for example, a small inflatable bladder running inside the boom, as shown in [Fernandez and Lappas, 2012]. The many designs of flexible shell booms proposed over the years can be classified in the following groups:

• Overlap thin-wall tubes (OTW). They are also known as the Storable Tubular Extendible Member (STEM), [Rimrott, 1965], shown in Figure 2.21 (left). Normally, the cylindrical wall tube subtends an arc of 515◦, so that the overlap increases the strength and stiffness of the tube, and there is no coupling between bending and torsion [Rimrott, 1966, Rimrott and Draisey, 1984]. Their drawback is to have a long transition region, known as the ploy region, from the coiled state to the extended tubular one [Jain and Rimrott, 1971]. Three types of deployment methods have been developed for STEMs: the root drum model, where the reel is fixed to the spacecraft and the boom is reeled out [Mar and Garrett, 1969]; the tip drum model, where the boom tip is fixed and the drum is the one deployed [Warden, 1995]; and the Jack-in-the-box model, where the boom is a flat helical spring that deploys spirally [Rimrott, 1967]. A single STEM can also be designed with sawtooth edges that would interlock upon extension creating a semi-closed stiffer structure [Weir and al., 1964]. In the early stages of space flight, the family of STEM tubes were the most widely used type of space deployable structure [Herzl, 1971].

• Multi-element thin-wall tubes (MTW). They are essentially two OTW tubes that are either nested, as in the Bi-STEM boom, or interlocked, as in the Interlocking Bi-STEM shown in Figure 2.21 (left). This yields torsionally stiffer booms that have a more symmetric

response, and require less ploy lengths than single STEMs. For the interlocked version, friction under torsional loads is further reduced [Rimrott and Elliott, 1966]. However, for these options the deployment mechanisms generally becomes more complex and bulkier.

Figure 2.21: STEM boom family (left) [Source: NASA]; lenticular CFRP boom (centre) [Source: DLR]; and metal TRAC boom (right) [Source: AFRL].

• Lenticular-shaped closed-section booms. As shown in Figure 2.21 (centre), they have a lenticular cross-section shape once deployed. For this, two omega-shaped sections are bonded or welded at the flat edges to form the closed tube. The closed section provides excellent structural properties compared to the rest of the open-section flexible shell booms. However, drawbacks are their manufacturing difficulty and the relatively large minimum coiling radius required, as a result of the high shear stresses developed in the bonded regions. Some examples of this type of booms are the Collapsible Tubular Mast (CTM) family [Aguirre-Martinez, 1985, Aguirre-Martinez et al., 1987] and DLR’s CFRP booms [Sickinger and Herbeck, 2002, Sickinger et al., 2006, Straubel et al., 2011].

The boom proposed in [Adeli, 2010b, Lappas et al., 2011] has also a lenticular shape, formed by butting up front-to-front two independent tape-springs. However, since it has no bonded areas, the structure is only semi-closed, and thus, has a much lower torsional stiffness than closed booms. Its main advantage is the reduction in shear stresses when stowed, that allows a small coiling radius.

• Triangular Rollable And Collapsible (TRAC) booms. They were developed by AFRL researchers [Murphey and Banik, 2011, Roybal et al., 2007] to maximize the boom bending stiffness for a required coiled height. The TRAC boom consists of two tape-springs bonded or welded back-to-back at one of their edges to form a triangular-shaped boom as shown in Figure 2.21 (right). Since they have a large ratio of cross-section area to coiled-height, they are ideal for cubesat applications. Nevertheless, as in lenticular booms, their permissible coiling radii is limited by the shear stresses of the bonded area. A Stainless steel version of the TRAC booms were first used for NanoSail-D [Johnson et al., 2010], an Elgiloy version will be used for LightSail-1 [Biddy and Svitek, 2012], and a CFRP version for the FURL sail [Banik et al., 2008, Banik and Murphey, 2010].

Depending on the solar sail configuration and size, and therefore the structural requirements, some of the aforementioned linear deployment options are more suitable than others. Wire deployers hold considerable promise for spinning-sails and helyogiros as they tend to work with the centripetal force generated from a rotating spacecraft. For three-axis stabilised solar sails: flexible shell booms provide excellent packaging efficiencies, and are thus particularly suitable for sail designs with highly restrictive volume constraints, such as those found in small to medium size sail concepts. However, their mass efficiency is generally worst than the rest of the boom options and thus, in principle, they are not a promising option for large size sails; coilable masts, can require notable size deployment mechanisms and will require complex deployment control systems for very large lengths. They are thus suitable for medium to large sails of up to several hundred meters in size; and inflatable booms, which are the type with less flight heritage and thus require more development effort, can be considered for any size range if the packaging efficiency can be minised with methods such as the ones reviewed in [Schenk et al., 2014]. They are the most mass efficient boom type, so if the many challenges they face are surmounted, it is believed that inflatable technology will enable efficient ultralarge sails of characteristic lengths in the order of kilometers.