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.
