The LiFiCo project is part of a multi-disciplinary research programme, within the prioritised research area Materials Research at Karlstad University. Scientists from different fields, e.g., chemistry, materials physics, and modelling, investigate molecular interactions under normal and microgravity conditions. LiFiCo aims at a better fundamental understanding and control of the molecular interactions yielding the structures found in the molecular blend thin films of the active layer in an organic solar cell. For an organic solar cell, the coating solution contains donor, acceptor, and sometimes additional compounds. The evaporation of the solvent causes a concentration gradient, leading to an evolving phase separation. Due to the fast evaporation, the phase separation is arrested before it reaches completion. This partial phase separation results in a film structure, the morphology, decisive for the device performance. It is of fundamental and applied interest to control and manipulate the film morphology, as well as developing means of performing wet chemistry preparations under microgravity conditions.
The kinetics of the phase separation is slowed down under microgravity conditions, while the evaporation kinetics is thought to remain unchanged. Microgravity conditions, hence, facilitates to study the initial stages of the morphology formation. By applying microgravity conditions in preparations during parabolic flights, we have found differences in morphology related to the slower phase separation. Unfortunately, the short time-span of microgravity under parabolic flights is not enough to ensure complete drying maintaining microgravity conditions. To ensure that the complete drying process is performed under microgravity conditions, sounding rocket experiments are needed.
To realise the deposition of the coating solution, a new experimental unit was developed in collaboration with ESA and the Swedish Space Corporation. This equipment, relying on flow-coating onto a glass substrate, allows to create a gravitational field aligned with the experiment cell. This field is necessary during filling and retraction of the solution, in order to control the liquid flow. The new equipment’s functionality was tested in October 2023 with drop-tower experiments at ZARM in Bremen. These experiments showed that the equipment works as predicted and yielded valuable information on flow-patterns and wetting.
The LiFiCo project is part of the sounding rocket mission Suborbital Express 4-M16, scheduled for launch at Esrange in April 2024. In this contribution we will summarise the results from the preceding parabolic flight campaigns (70th and 78th ESA PFC), the conclusions from the drop-tower experiments at ZARM, and the preliminary results from the sounding rocket experiments.

Convection in a planetary atmosphere is of particular interest when discussing climate change. The fundamental understanding of large-scale convection in atmospheres relies commonly on observations of
planets such as Earth and Jupiter and celestial bodies or numerical models. Laboratory experiments of
such large-scale flows are mostly limited to experiments in cylindrical or spherical shell configurations that
retain the overall physical meaning. AtmoFlow is one of those experiments composed of two concentric
shells mimicking a planetary atmosphere by equatorial heating and pole-ward cooling. Planetary rotation
is given by spherical shell rotation, and terrestrial gravity is given by an artificial central force field induced by an electric field between both shells. The working fluid is confined between the spherical shells.
However, this configuration is sensitive to buoyancy caused by natural convection. Therefore, the system
will be placed on the International Space Station (ISS), presumably in 2026. The AmoFlow experiment
will replace the former GeoFlow experiment, a spherical shell experiment used to study mantle convection,
served on the ISS from 2008 to 2017.
Here, we present a three-dimensional (3D) Direct Numerical Simulation (DNS) of the AtmoFlow spherical shell experiment and its expected flow patterns for the parameter space in solid body and differential
rotation configurations. The numerical simulation shows distinct regimes for the solid body case, illustrating transitions between convective states. The convective pattern formation for the differential rotating
configuration is classified into distinct regimes concerning the forcing strength. The classification can be
made into time-periodic Taylor vortex flow and irregular convective flow with plume structures for large
rotational and buoyant forcing. Smaller buoyant forcing exhibits distinct time-invariant plume structures
reminiscent of classical Rayleigh-Bénard convection, while intermediate equivalent forcing strength for
rotational and buoyant forcing reveal time periodic fish-bone structures. The numerical study used a
finite volume technique based on OpenFoam and was performed on the HLRN cluster.

The core of any scientific research is to investigate the impact of variable parameters on the obtained result. The amount of independent parameters is high, the possible combinations are nearly endless. If gravity would be a selectable parameter, this would likely be in the top three test conditions to better understand two phase material or multiple component behavior, especially in combination with thermal settings.

It is clear that most lab equipment is not designed to be launched for operation in microgravity, let alone for a human space flight environment. Objectives of scientific research can often be translated into requirement specifications that allow to redesign the lab set-up into a configuration that captures all essential test features and at the same time ensures (astronaut) safety and reliability.

Redwire has microgravity equipment heritage in this field that has been highly successful:
• SODI has been (intermittently) operational from 2009 till 2023, imaging liquid mixtures under thermal gradients while exposed to controlled vibrations. Every test campaign only required the upload of a cell array that contained 2 experiments to be tested consecutively.
• The Transparent Alloys instrument is operational since 2017 and is really a lab-in-a-box. The core element is a Bridgman Furnace with two microscopes to image the adiabatic zone. Glass cartridges with different dimensions can be translated to investigate directional solidification in a very wide temperature range. Materials with toxic hazard level (THL) 2 have been safely uploaded and tested.
• COLIS is ready to be launched in September 2024 and will investigate the origin, formation and dynamics of colloidal crystals, glasses and gels. The optical diagnostics in 6 different orientations combine various lab set-ups in one configuration. The crew replaceable Cell Module has its own thermal control and a stirrer to ‘reset’ the experiment liquids.

Miniaturization of different scientific lab setups - adding robustness for launch and ensuring crew safety - is confirmed to be feasible with comparable test results to ground based lab set-ups. The flexibility towards the on-orbit experiment protocols is provided by making scientific data available in (almost) real time, so the science teams are able to fine tune the scientific parameters of their experiment on orbit, thus optimizing the science return.
The development of a new space instrument takes a few years, but the re-use capability allows relative fast iterations to boost science to new levels.

An uttermost priority of human space exploration is the sustainable fabrication and recycling of materials, mitigating the consequences of an impossible resupply of resources from Earth. Moreover, the long-term missions to Moon and Mars will require in-situ resource utilization (ISRU) technologies to synthesise materials in harsh environments and reduced gravitation. This opens a path for research on the fabrication and synthesis of materials that have potential for being utilised in energy conversion technologies in these environments.
Photoelectrochemical (PEC) energy conversion is currently investigated for space applications, due to its potential in converting water and carbon dioxide using sunlight into oxygen, hydrogen, and useful carbon compounds. Further, the monolithic design of PEC devices, which include integrated semiconductor-electrocatalyst systems, offers significant advantages for long-term space missions, such as a compact and lightweight payload. Particularly important is hereby the choice of electrocatalyst material (metals or metal oxides) for the respective anticipated redox reaction to minimize activation polarization overpotentials of the device.
Since microgravity is known to affect the synthesis of nanomaterials by inducing increased crystallinity and increased porosity - which are attractive qualities in a catalyst material - the present study investigates the effect of this environment on the synthesis of metal and metal oxide nanoelectrocatalysts via photoelectrodeposition. Further on, the performance of the synthesized catalyst materials is assessed in photoelectrochemical water splitting in the Bremen Drop Tower, Germany, as well as terrestrially. The starting metals are chosen with respect to their availability in extraterrestrial environments for future ISRU (e.g. ruthenium).

Introduction

Motivated by emerging environmental awareness, the use of PCMs as thermal control and energy storage devices has notably increased in recent years. Thermal control in buildings is arguably one of the most widespread applications, where PCMs are incorporated into building walls to absorb/release energy in the form of latent heat and compensate for energy imbalances.

This concept is explored in space habitats, where extreme temperatures fluctuations are a common issue. PCM performance is analyzed considering only conduction, a scenario with practical interest in reduced gravity environments.


Method

As sketched in the figure, the habitat consists of a semi-spherical construction. The PCM is placed within the habitat wall — between its exterior and interior boundaries — and acts isolating the internal habitat environment from the cyclic variation of the external solar flux. Such habitat design can be obtained by co-axial 3D printing, where the inner and outer nozzles print PCM and regolith geopolymer, respectively. The wall, of thickness L, displays absorptivity (α) and emissivity (ε) values on its exterior boundary. Note that the selection of (α,ε) can be done by design, using appropriate paintings or coatings.

The system dynamics are explored numerically for a wide range of parameters, including L, (α,ε), and eclipse/illumination fractions, among others.


Result

Balancing the heat absorbed and released by the PCM during illumination and eclipse, one can estimate the optimal (α/ε) and the minimum PCM thickness, which depend on the solar flux, the melting temperature, the mission period and illumination fraction, and the density and latent heat of the PCM. From a design perspective, simple expressions can be used to select the external painting of the wall, given a PCM and mission environment.

In the figure, the optimal system response is shown, demonstrating that, under repeated cycles of illumination and eclipse, the PCM can maintain the internal temperature of the habitat at the melting point.


Conclusions

Nowadays, PCMs are widely used in different applications. Here, we have examined their capability to thermally control a space habitat: the design integrates the PCM within the habitat walls, reducing the fluctuations of the interior temperature that result from cyclic variations in solar radiation. We find that the ratio α/ε play a key role and largely define the optimal design of the habitat.

Space Forge is an in-space manufacturing company growing advanced materials in the microgravity and vacuum environment of low earth orbit.

To achieve this, we have been developing the world’s first returnable and reusable microgravity platform - the ForgeStar. With high-power density and frequent launch cadence, we are offering ForgeStars as a new research platform as an alternative to the ISS. We anticipate research related to biological studies, pharmacology and metallurgy - amongst others - and for researchers working on materials growth, we can offer additional facilities.

In this talk, we will outline the capabilities of the platform and explain how researchers can access it via our “Microgravity as a Service” process.