A cold-hibernated elastic memory (CHEM) structures technology is one of the most recent results of the quest for
simple, reliable and low-cost self-deployable structures. The CHEM technology utilizes shape-memory polymers in
open-cell foam structures or sandwich structures made of shape-memory-polymer foam cores and polymeric
laminated-composite skins. It takes advantage of a polymer's shape memory and the corresponding internal elastic
recovery forces to self-deploy a compacted structure. This paper describes these structures and their major
advantages over other expandable and deployable structures presently used.
Previous preliminary investigations and experiments have confirmed the feasibility of certain CHEM structures for
space applications. Further improvements in CHEM technology and structure design widen potential space
applications, including advanced solar sail structural concepts that are revealed and described in this paper.
A new class of simple, reliable, lightweight, low packaging volume and cost, self-deployable structures has been developed for use in space and commercial applications. This technology called "cold hibernated elastic memory" (CHEM) utilizes shape memory polymers (SMP) in open cellular (foam) structure or sandwich structures made of shape memory polymer foam cores and polymeric composite skins. Some of many potential CHEM space applications require a high precision deployment and surface accuracy during operation. However, a CHEM structure could be slightly distorted by the thermo-mechanical processing as well as by thermal space environment. Therefore, the sensor system is desirable to monitor and correct the potential surface imperfection.
During these studies, the surface control of CHEM smart structures was demonstrated using a Macro-Fiber Composite (MFC) actuator developed by the NASA LaRC and US Army ARL. The test results indicate that the MFC actuator performed well before and after processing cycles. It reduced some residue compressive strain that in turn corrected very small shape distortion after each processing cycle. The integrated precision strain gages were detecting only a small flat shape imperfection indicating a good recoverability of original shape of the CHEM test structure.
A cold hibernated elastic memory (CHEM) foam structure is one of the most recent results of the quest for simple, reliable and low-cost expandable space structures. The CHEM technology utilizes shape memory polymers in open cellular (foam) structure or sandwich structures made of shape memory polymer foam cores and polymeric composite skins. It takes advantage of the polymer’s heat activated shape memory in addition to the foam’s elastic recovery to deploy a compacted structure. The glass transition temperature Tg is tailored to rigidize the structure in the fully deployed configuration.
Previous experimental and analytical results were very encouraging and indicated that the CHEM foam technology can perform robustly in space as well as in the Earth environment. CHEM structures are described here and their major advantages are identified over other expandable/deployable structures. Although the space community is the original major beneficiary, a number of potential applications are also anticipated for the “earth environment”. CHEM developers strongly believe that this technology has great promise for a host of commercial and bio-medical applications. Some of these potential and already investigated CHEM applications are described in this paper.
Experiments and analyses have confirmed the feasibility of an innovative, new class of very simple, reliable, low mass, low packaging volume, and low-cost self-deployable structures for space and commercial applications. The material technology called "cold hibernated elastic memory" (CHEM) utilizes shape memory polymers in open cellular (foam) structures. The CHEM foams are self-deployable and are using the foam's elastic recovery plus their shape memory to erect structures. These structures are under development by the NASA's Jet Propulsion Laboratory (JPL) and Mitsubishi Heavy Industries (MHI). Currently, the CHEM structure concept is well formulated, with clear space and commercial applications. The CHEM structures are described here and their major advantages are identified over other expandable/deployable structures. Previous experimental results were very encouraging and indicated that the CHEM foam technology can perform robustly in the Earth environment as well as in space. Some potential space applications were studied under various programs at JPL with promising results. Although the space community will be the major beneficiary, a lot of potential commercial applications are also foreseen for the "Earth environment" and described in this paper as well.
KEYWORDS: Foam, Shape memory polymers, Space operations, Polymers, Packaging, Control systems, Aerospace engineering, Mars, Space robots, Temperature metrology
Experiments have confirmed the feasibility of an innovative, new class of very simple, reliable, low mass, low packaging volume, and low-cost self-deployable structures for space and commercial applications. The concept called 'cold hibernated elastic memory' (CHEM) utilizes shape memory polymers (SMP) in open cellular (foam) structures. The SMP foam materials are under development by the Jet Propulsion Laboratory (JPL) and Mitsubishi Heavy Industries (MHI). The CHEM structures are described here and their major advantages are identified over other expandable/deployable structures. In preliminary proof- of-concept investigation conducted on SMP foams, all evaluation/test results were very encouraging and confirmed the basic characteristics of CHEM structures. The main objective of this program is to develop and validate the CHEM structure technology for most promising space applications. However, possible terrestrial commercial applications are also anticipated and described in this paper as well.
Very stringent dimensional stability requirements for metering rods of the NASA/Jet Propulsion Laboratory Cassini spacecraft NAC (Narrow Angle Camera) were the driving forces to select and conduct dimensional stability tests of several dimensionally stable materials. Carbon/carbon composite samples, among the other selected materials, were tested at the University of Arizona Dimensional Stability Laboratory. Fabry-Perot laser- interferometric techniques were used to measure dimensional changes to accuracies in the 0.01 ppm range. Coefficient of thermal expansion (CTE), thermal hysteresis and temporal stability test results at 27.5 degree(s)C and 38 degree(s)C are reported here. The test results indicate that this carbon/carbon composite material, made from 2D fabric and pitch base fiber, appears to be the best among all tested nonmagnetic materials. A CTE of -1.5 ppm/$DEGC over the temperature range of -48 degree(s)C to +52 degree(s)C is reported here along with a temporal stability <EQ 1 ppm/year. However, demonstration of a relatively high thermal hysteresis within the temperature range of -48 degree(s)C to +52 degree(s)C was unexpected and a cause for further evaluation. A possible procedure to resolve this issue and an alternate carbon/carbon material design are also suggested here.
High performance requirements for the Imaging Science Subsystem/Narrow Angle Camera (NAC) instrument on the NASA/Jet Propulsion Laboratory (JPL) Cassini spacecraft impose very stringent demands for dimensional stability of metering rods in the camera's athermalizing system. Invar 36 was chosen as a baseline material because it possibly could meet these requirements through high purity control and appropriate thermomechanical processes. A powder metallurgy process appears to be the manufacturing method to ensure high purity and cleanliness of this material. Therefore, a powder metallurgy manufacturer was contacted and high purity (HP) Invar 36 was produced per JPL engineering requirements. Several heat treatments were established and heat treated HP Invar 36 samples were evaluated. Coefficient of thermal expansion (CTE), thermal hysteresis and temporal stability test results are reported here. The test results indicate that JPL has succeeded in obtaining possibly the most dimensionally stable (lowest CTE plus lowest temporal change) Invar 36 material ever produced. CTE < 1 ppm/ degree(s)C are reported here along with temporal stability < 1 ppm/year. These dimensional stability properties will meet the requirements for metering rods on the NAC.
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