Packaging and Deployment of Solar Arrays and Antennas

Researchers

Manan Arya
Nicolas Lee
Christophe Leclerc
Alan Truong
Antonio Pedivellano
Fabien Royer
Andrew Lee
Alexander Wen
Wolfgang Klimm
Maximilian Braun
Terry Gdoutos
Sergio Pellegrino

Description

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Many space missions need structures with large planar surfaces such as antenna arrays, photovoltaic arrays, drag sails, sunshields, and solar sails. We have introduced a novel deployable structure and packaging concept which enable tight packaging and ultralight mass density.

The packaging concept, called slip wrapping, utilizes slipping folds, which allow for rotation about and translation along a fold line. There are two compaction steps, each compacting the membrane along a single dimension. First, the membrane is z-folded. Then, the resulting stack of n strips is wrapped in a rotationally symmetric fashion. The slipping folds accommodate the incompatibility created by wrapping the thick membrane strips around different radii. The symmetric wrapping scheme ensures that the ends of the strips need not slip, and can therefore remain connected. The video below demonstrates a controlled, two-stage deployment of a membrane packaged according to this scheme.

This packaging scheme can be generalized to many other fold-and-wrap patterns, such as the 4-fold-symmetric packaged model shown below. It can also be used to package structures that are not just membranes, but have some out-of-plane bending stiffness. We are using such structures, where the edges of the strips are reinforced with deployable longerons, in the development of large space solar power spacecraft.

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From 2018, we have developed 4 generations of 2 m-scale structural prototypes based on a 4-fold-symmetric architecture. Using the “fold-and-wrap” packaging concept shown above, these structures can be safely stowed in a cylindrical configuration with a 200 mm diameter and 300 mm height. Our space solar power structural architecture is not only the first engineering scale demonstration of the slip-wrapping packaging concept, but it is also the first example to date of a large-area bending-stiff deployable structure. The bending stiffness provided by the deployable longerons allows the space structure to maintain its planar shape in space with minimal external support, reducing the overall mass of the spacecraft and making this architecture more scalable.

Coilable Thin Shell Structures

The deployable longerons used in the space structure above have been the object of extensive research. Their thin-walled curved cross-section provides high bending stiffness when deployed, while also withstanding large elastic deformations, allowing packaging by folding or coiling.

Most of our research has focused on Triangular Rollable And Collapsible (TRAC) longerons. This type of structure consists of two tape measure-like sections that are bonded together on one edge. Using ultra-thin ply composites, we manufacture TRAC longerons that can be as thin as 80 m and achieve a linear density of 8 g/m.

Coiling thin shell structures can be challenging, and requires a deployment mechanism to control their behavior. Due to their high bending stiffness, these structures store elastic strain energy during packaging, and spontaneously self-deploy if unconstrained. They are also prone to instabilities when coiled around a cylindrical hub. In some cases, the coiled structure does not conform to the radius of the hub, but uniformly increases its coiling radius, leading to a blossoming instability. In other cases, the shell structure undergoes buckling, forming multiple localized folds with high curvature. Both types of instability are shown in the figure below.

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These instabilities can potentially damage the deployable structure or jam the deployment mechanism. Hence, appropriate constraints are required to achieve the desired packaging behavior. A simple solution consists in using radial springs to push the deployable structure against the hub: this effectively suppresses blossoming instabilities, but it still allows buckling. Applying tension to one end of the shell structure (and a counter torque on the hub of the mechanism) results in a more uniform loading. An alternative solution is to co-coil a thin membrane with the deployable structure, and apply tension to the membrane using a second spool. In this case, the tensioned membrane applies a distributed pressure on the structure, conforming it to the hub. 

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Using tension stabilization, we have successfully coiled TRAC longerons to a radius of 12.4 mm. However, extending this coiling concept (or any of the others shown above) from individual shell components to large-area space structures introduces new challenges, and requires the development of novel deployment mechanism architectures.

Deployment Mechanism Concepts

Deployment mechanisms and test fixtures have been built to demonstrate packaging schemes and coiling concepts. Simple coiling test fixtures are used to study the behavior and survivability of structural elements, such as TRAC longerons, with respect to different radii of curvature. The results of these studies feed into the design and geometry of more advanced mechanisms.

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Early prototypes of deployment mechanisms were small-scale models used to study the effectiveness of various tensioning architectures in preventing coiling defects. At the end of these studies, the pressure stabilized coiling scheme was selected for further development.

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The finalized mechanism design architecture consists of:

  • A central spool driven by a rotation actuator, which coils the structure

  • Secondary roller spools that supply a wrapping membrane that is co-coiled with the structure

The spool/rollers operate in a leader/follower configuration respectively. A unique aspect of this approach is that tension is not applied directly to coiled structure, but to the wrapping membrane.

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Subsequent full scale versions of the coiling mechanism were sized to support the packaging and deployment of the 2m -scale structure. The current version of the mechanism has been designed to undergo environmental qualification testing in preparation for an upcoming demonstration mission of the packaging/deployment of the SSPP structure and deployment mechanism in LEO.

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Structural Architectures for Deployable Spacecraft

Deployable spacecraft concepts can be categorized into structural architectures that are defined according to the way loads are carried. These concepts are designed to maintain stability against both internal and external loading while achieving high mass efficiency.

Many classical concepts are based on the bending architecture which relies on flexural stiffness that is derived from structural depth. An example is a deployable solar array composed of hinged composite sandwich plates. An alternative is the tensioned architecture which consist of a tensioned membrane that is supported by deployable boom(s) that react in compression. Flexible blanket solar arrays and square solar sails adopt this architecture. The cable-stayed architecture is a variation which includes a vertical column at the root that shares the effective loading with horizontal structural members through tensioned cables.    

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The broad research objective is to develop a methodology for comparing the load carrying performance between these architectures for large space structures. This involves comparing the loads that cause buckling, material failure, and excessive deflection while imposing identical material, mass, and maximum deflection between architectures.

Publications

  • Wilson L., Gdoutos E.E., and Pellegrino S. (2020). Tension-Stabilized Coiling of Isotropic Tape Springs. International Journal of Solids and Structures. 2020 Apr 1;188:103-17.

  • Pedivellano A., Gdoutos E.E., and Pellegrino S. (2020). Sequentially controlled dynamic deployment of ultra-thin shell structures. In AIAA Scitech 2020 Forum 2020-0690.

  • Gdoutos E.E., Truong A., Pedivellano A., Royer F., and Pellegrino S. (2020). Ultralight Deployable Space Structure Prototype. In AIAA SciTech 2020 Forum, 2020-0692.

  • Lee, A.J. and Pellegrino, S. (2021). Cable-stayed architectures for large deployable spacecraft. SciTech 2021, AIAA.

  • Gdoutos E.E., Leclerc C., Royer F., Türk D.A., and Pellegrino S. (2019). Ultralight spacecraft structure prototype. In AIAA Scitech 2019 Forum, 2019-1749.

  • Leclerc C., and Pellegrino S.(2019). Reducing Stress Concentration in the Transition Region of Coilable Ultra-Thin-Shell Booms. In AIAA Scitech 2019 Forum, 2019-1522.

  • Pedivellano, A. and Pellegrino, S. (2019). Stability Analysis of Coiled Tape Springs. In AIAA Scitech 2019 Forum, 2019-1523.

  • Royer F., and Pellegrino S. (2018). Ultralight ladder-type coilable space structures. In 2018 AIAA Spacecraft Structures Conference, 2018-1200.

  • Leclerc C., Pedivellano A., and Pellegrino S. (2018). Stress concentration and material failure during coiling of ultra-thin TRAC booms. In 2018 AIAA Spacecraft Structures Conference, 2018-0690.

  • Leclerc C., Wilson L.L., Bessa M.A., and Pellegrino S. (2017). Characterization of ultra-thin composite triangular rollable and collapsible booms. In 4th AIAA Spacecraft Structures Conference, 2017-0172.

  • Arya, M., Lee, N. and Pellegrino, S. (2016). Ultralight Structures for Space Solar Power Satellites. SciTech 2016, San Diego, AIAA-2016-1950 (pdf).

  • Arya, M., Lee, N., and Pellegrino, S. (2015). Wrapping thick membranes with slipping folds. 2nd AIAA Spacecraft Structures Conference, 5-8 January 2015, Kissimmee, FL. AIAA 2015-0682 (pdf).

Patents

  • Pellegrino S., Gdoutos E.E., Pedivellano A., inventors; California Institute of Technology, assignee. Actively Controlled Spacecraft Deployment Mechanism. United States patent application US 16/670,941. 2020 Apr 30.

  • Pellegrino S., Atwater H.A., Hajimiri S.A., Gdoutos E.E., Leclerc C., Royer F.A., Pedivellano A., inventors; California Institute of Technology, assignee. Coilable Thin-Walled Longerons and Coilable Structures Implementing Longerons and Methods for Their Manufacture and Coiling. United States patent application US 16/514,793. 2020 Jan 23.