Satellite Hardware: Stow-and-Go for Space Travel

Man-made satellites have to fit a lot into a compact package. Protected inside a rocket while blasted through the atmosphere, a satellite is launched into Earth orbit, or beyond, to continue its unmanned mission alone. It uses gyroscopes, altitude thrusters, and magnets to regulate sun exposure and stay pointed in the right direction. Once stable, the satellite depends on solar panels to recharge its internal batteries, mirrors, and lenses for data capture, and antennas for communication back to Earth. Whether it is a bread-loaf-sized nano, or the school bus sized Hubble Telescope, every satellite is susceptible to static electricity buildup from solar wind, the very cold temperatures the Earth’s shadow (or deep space), and tiny asteroids along the route

Systematically Creased Thin-Film Membrane Structures

This paper presents a study of a square membrane, creased according to the Miura-ori folding pattern. When the membrane is allowed to expand from its packaged configuration, it initially expands elastically under zero corner forces. Starting from this naturally expanded configuration, the paper investigates the stress distribution and the load-displacement relationship when in-plane, diagonal loads are applied at the corners. It is found that out-of-plane bending is the main load-carrying mode and, for stress magnitudes typical of current solar-sail designs, the behavior of the membrane remains linear elastic. A simple analytical model, originally proposed for randomly creased membranes, is shown to predict with good accuracy the load-displacement relationship of the corners. It uses physically based and hence directly measurable membrane parameters

Shape correction of thin mirrors in a reconfigurable modular space telescope

In order to facilitate the construction of future large space telescopes, the development of low cost, low mass mirrors is necessary. However, such mirrors suffer from a lack of structural stability, stiffness, and shape accuracy. Active materials and actuators can be used to alleviate this deficiency. For observations in the visible wavelengths, the mirror surface must be controlled to an accuracy on the order of tens of nanometers. This paper presents an exploration of several mirror design concepts and compares their effectiveness at providing accurate shape control. The comparison test is the adjustment of a generic mirror from its manufactured spherical shape to the shape required by various off-axis mirrors in a segmented primary mirror array. A study of thermal effects is also presented and, from these results, a recommended design is chosen

Shape Correction of Thin Mirrors

Future large space observatories will require large apertures to provide better resolution and greater light gathering power; thin mirror technologies provide one possible route for addressing this need. This paper presents a study of a 10 m diameter sparse aperture based on a collection of thin, active mirror segments with identical initial shapes. A preliminary design for a 1 m diameter mirror segment is proposed and an investigation into the performance of this design is carried out utilizing finite element modeling tools. The results indicate that it is possible to adapt the generic segment shapes to fit the local mirror shape, and achieve near diffraction-limited performance through the use of lightweight, surface-parallel actuators. These actuators may also be used for thermal compensation. Additionally, a design for a scaled 10 cm diameter prototype mirror to test and validate the envisioned scheme is presented

Concept and Design of a Multistable Plate Structure

A concept is presented for a compliant plate structure that deforms elastically into a variety of cylindrical shapes and is able to maintain such shapes due to the presence of bistable components within the structure. The whole structure may be fabricated as a monolithic entity using low-cost manufacturing techniques such as injection molding. The key steps in the analysis of this novel concept are presented, and a functional model is designed and constructed to demonstrate the concept and validate the analysis

Ultralight Ladder-type Coilable Space Structures

We describe the concept of an ultralight ladder-type coilable strip used as the main element to build large planar deployable space solar power spacecrafts. It is composed of TRAC longerons connected with lenticular cross-section rods which enables it to fully flatten and thus be packaged efficiently. The design is tackled here as well as the manufacturing of a scaled version of this new type of structures. Finite element analyses are used to understand the underlying behavior of such structures. Experimental model testing is then used as a way of validating this computational framework. Finally a simulation framework enabling simulation at the spacecraft scale is presented and preliminary results obtained with shows how such structures behave while integrated into a larger spacecraft

Phenomenological model for coupled multi-axial piezoelectricity

A quantitative calibration of an existing phenomenological model for polycrystalline ferroelectric ceramics is presented. The model relies on remnant strain and polarization as independent variables. Innovative experimental and numerical model identification procedures are developed for the characterization of the coupled electro-mechanical, multi-axial nonlinear constitutive law. Experiments were conducted on thin PZT-5A4E plates subjected to cross-thickness electric field. Unimorph structures with different thickness ratios between PZT-5A4E plate and substrate were tested, to subject the piezo plates to coupled electro-mechanical fields. Material state histories in electric field-strain-polarization space and stress-strain-polarization space were recorded. An optimization procedure is employed for the determination of the model parameters, and the calibrated constitutive law predicts both the uncoupled and coupled experimental observations accurately

Viscoelastic effects in tape-springs

Following recent interest in constructing large self-deployable structures made of reinforced polymer materials, this paper presents a detailed study of viscoelastic effects in folding, stowage, and deployment of tape-springs which often act as deployment actuators in space structures. Folding and stowage behavior at different temperatures and rates are studied. It is found that the peak load increases with the folding rate but reduces with temperature. It is also shown that a load reduction of as much as 60% is possible during stowage due to relaxation behavior. Deployment behavior after significant load relaxation demonstrates features distinct from elastic tape-springs. It starts with a short dynamic response, followed by a quasi-static deployment, and ends with a slow creep recovery process. A key feature is that the localized fold stays stationary throughout deployment. Finite element simulations that incorporate an experimentally characterized viscoelastic material model are presented and found to capture the folding and stowage behavior accurately. The general features of deployment response are also predicted, but with larger discrepancy