Saturday, 28 July 2012

Project title “Polymerisation in the Stratosphere”

We are looking for partners to make a stratospheric flight experiment

The aim: The development of polymeric material that is curable in free space environment for use as structural components in large space constructions.

Background: Future space exploration will require large light-weight structures for habitats, greenhouses, space bases, space factories and so on. A new approach enabling large-size constructions in space relies on the use of the technology of the polymerization of fiber-filled composites with a curable polymer matrix applied in the free space environment. For example, a fabric impregnated with a long-life matrix (prepreg) can be prepared in terrestrial conditions and, after folding, can be shipped in a container to orbit and unfolded there by inflating. Then the matrix polymerization reaction is initiated producing a durable composite wall or frame. Using such an approach, there are no restrictions on the frame size and form of the construction in space and the number of deployment missions is kept at a minimum.
In free space the material is exposed to high vacuum, dramatic temperature changes, plasma of free space due to cosmic rays, sun irradiation and atomic oxygen (in low Earth orbit), micrometeorite fluence, electric charging and microgravitation. The development of appropriate polymer matrix composites requires an understanding of the chemical processes of polymer matrix curing under the specific free space conditions to be encountered.

Previous studies: Our preliminary studies of the polymerization process in high vacuum, space plasma and subject to temperature variations indicate that for specific prepeg preparations the polymerization process is likely to be successful in free space and that the composite cured in a free space environment will have satisfactory mechanical properties. However, the curing processes are sensitive to free space factors such as high vacuum, flux of high energy particles and temperature variations encountered.
Particularly pertinent observations from our previous work include:
·      The evaporation of the active components can stop the curing reaction and evaporation can cause bubble formation in the curing polymer matrix and compromise the mechanical properties of the cured matrix.
·      Fluxes of high energy particles in space irradiation can destroy macromolecules and create free radicals, which can accelerate the curing kinetics and strengthen the composite.
·      Temperature variations change dramatically the curing kinetics and evaporation process.

(For details see A. Kondyurin, Curing of composite materials for an inflatable construction on the Moon, chapter in “Moon. Prospective Energy and Material Resources”, Springer-Verlag, Berlin, 2012; A. Kondyurin, M. Bilek, Ion Beam Treatment of Polymers. Application aspects from medicine to space, Elsevier, Oxford, 2008; Kondyurin A., B. Lauke, R. Vogel, Photopolymerisation of composite material in simulated free space environment at low Earth orbital flight, European Polymer Journal 42 (2006) 2703–2714; Kondyurin A., B.Lauke, E.Richter: Polymerization Process of Epoxy Matrix Composites under Simulated Free Space Conditions, High Performance Polymers. 16, 2004, p. 163 – 175; Kondyurin A.V., Building the shells of large space stations by the polymerisation of epoxy composites in open space, Int. Polymer Sci. and Technol., v.25, N4, 1998, p. 78-80).

Our preliminary studies show, that the curing process can proceed and a durable composite material can be polymerized under simulated free space conditions. However in a laboratory environment it is not possible to simulate accurately the combinations of factors observed in space in order to assess how the various influences couple. To develop the appropriate polymer matrix composition for use in a particular free space environment, the effects of the prevailing free space conditions acting together must be taken into account. In 2010 we carried out the flight experiment with uncured composite in stratosphere during NASA balloon mission and showed, that the effect of cosmic rays on crosslinking of the uncured composite is significant and well observed. More detailed investigations of the curing process under real free space conditions, where all these free space factors act simultaneously during the curing process are required.

Scientific goal of the stratospheric flight experiment:
The goal of the experiment is an investigation of the effect of the stratospheric conditions on the polymerization process in the polymer matrix of the composite material. Stratospheric conditions are expected to have a unique impact on chemical processes in polymer materials. The unique combination of low atmospheric pressure, high energy cosmic rays, high intensity UV radiation including short wavelength UV, diurnal temperature variations and other aspects associated with solar irradiation has strong influence on chemical processes in polymeric materials. Since such conditions can not be adequately simulated in the laboratory, it is difficult to predict the impact on curing chemistry which is particularly important in designing polymers which could be shaped and cured in space for large scale structural applications.

Project plan:
The experiment involves expositing a cassette containing polymer samples to the local environment during the stratospheric balloon flights. The samples consist of uncured polymer matrix and carbon/glass fibers. The polymer matrix is activated by stratospheric conditions (temperature and sun irradiation) and the chemical polycondensation reaction is initiated. Control samples, which have been cured or partially reacted prior to the flight will be included in the cassette. After the flight, the samples will be returned to the laboratory and analysed by spectral, chemical and mechanical methods. The concentration of active components, the stage the reaction reached in each composite, structure of the polymer, degradation of polymer macromolecules, crosslinking, oxidation and mechanical properties will be analysed. To help understand how the conditions couple, a parallel set of samples will be exposed to similar vacuum levels, UV light and temperature variations in laboratory experiments. These samples will be analysed in the same way as those exposed in the space flights and the results compared.

The cassette holding samples to be exposed in space has a mass of about 1 kg and dimensions with the cover installed of about 200x100x100 mm3. The total mass of the samples is about 100 g. The samples will be placed into the cassette before the flight and sealed by a cover. The cassette is to be placed and fixed on the external side (outside) of the balloon’s cabin, preferably on the sun irradiated side. The control cassettes with the same samples will remain on Earth in the laboratory.

During launching the cover of the cassette will be opened and the samples will be exposed to the stratospheric environment during the flight. Expected conditions are the following: a pressure of about 1-2 Torr, a temperature on the sunny side in the range of +80…900C (during day light 12-14 hours) and -70…800C (night time), a solar flux of 1300 W/m2. The required flight time is 1 day or more.

The temperature, pressure and UV light intensity at the cassette will be recorded during the mission. For measurement, the cassette will be equipped with a thermistor, manometer, radiometer and a UV sensor. The data of temperature, pressure, radiation and UV light intensity will be recorded and sent to laboratory after landing.

After landing, the cassette with samples and the records of flight conditions are to be sent to the laboratory for analysis.

The chemically active polymer composition corresponds to safety rules for stratospheric flights: non-toxic, non-flammable and non-explosive.

Preferably, the experiment will be repeated during some flights because, the flight conditions may be different in individual flights. The deviation of flight conditions during different flights (temperature, irradiation exposure, pressure) will be used for analysis of kinetics of the chemical reactions. The cassette will be loaded with new samples for each flight.

Managing of the cassette operation and data recording during flight:

The cassette operation (opening and closing of the cover) can be done on command from Earth or automatically triggered by a pressure sensor to correlate with the altitude of the balloon flight.

The temperature, UV light intensity and pressure sensors can be installed in the cassette or data can be used from common sensors installed on the balloon. In the second case, the temperature, UV light intensity and pressure data must be recorded during the whole flight.

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