Witold Sokolowski

Potential biomedical and commercial applications of cold hibernated elastic memory (CHEM) self-deployable foam structures

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.

Long-term and thermal instability of carbon/carbon composite

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/

Dimensional stability of high-purity Invar 36

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.

Erosion of carbon/carbon by solar wind charged particle radiation during a solar probe mission

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 cameras 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.

Cold hibernated elastic memory (CHEM) self-deployable structures

The possible erosion of a carbon/carbon thermal shield by solar wind-charged particle radiation is reviewed. The present knowledge of erosion data for carbon and/or graphite is surveyed, and an explanation of erosion mechanisms under different charged particle environments is discussed. The highest erosion is expected at four solar radii. Erosion rates are analytically estimated under several conservative assumptions for a normal quiet and worst case solar wind storm conditions. Mass loss analyses and comparison studies surprisingly indicate that the predicted erosion rate by solar wind could be greater than by nominal free sublimation during solar wind storm conditions at four solar radii. The predicted overall mass loss of a carbon/carbon shield material during the critical four solar radii flyby can still meet the mass loss mission requirement of less than 0.0025 g/sec.