Accross the globe, numerous test habitats have already been developed for research by scientists. However, these are only designed for use on Earth and to investigate organizational and psychological issues of an astronautic crew. There is still no habitat design that could actually withstand the extreme conditions on Moon or Mars.

In the MaMBA (Moon and Mars Base Analog) project at ZARM, scientists designed and constructed a habitat for long-term stays on Moon and Mars. The concept consists of six living and working spaces, called modules, each of which fulfils different functions. The laboratory module is a central place where people work together during the day. For this module a full-size mock-up has already been constructed at ZARM, with complete laboratory equipment, exactly as it could be used within the habitat on Moon and Mars. 

Similar to a Tiny House, the aim is to adapt the equipment as best as possible to the limited space available. After all, the more compact the construction, the lower the significant costs of transporting the components from Earth to the Moon or Mars. The mock-up of the laboratory module has already been used for several simulations in which scientists have worked on their current research projects for a week at a time.

The two-storey laboratory module is the heart of the habitat. The scientists will spend a lot of time there to advance their research. On the lower level of the laboratory module, the scientists can do their research and on the upper level, there is space for storing material or equipment. 

Modular equipment, designed for maximum flexibility, allows the scientists to work comfortably within the limited working space. Integrated into the outer wall of the module is a tank for the propagation of cyanobacteria, which, among other things, produce oxygen and are thus part of the life-support system.

In the Laboratory for Applied Space Microbiology (LASM) at ZARM, research is being conducted into which atmospheric conditions optimally promote the growth of these microorganisms. For this purpose, Atmos (Atmosphere Tester for Mars-bound Organic Systems) - an atmosphere-controlled vacuum photobioreactor - has been developed here, with which microorganisms can be cultivated and propagated outside their natural environment.

With the help of Atmos, the research team has been working to determine what atmospheric conditions would support the growth of cyanobacteria, while also improving technical feasibility on Mars. In Atmos, the proportions of the gases and the atmospheric pressure were changed in various runs and the corresponding development of the bacteria was observed. The goal of the investigations was to get as close as possible to the Martian atmosphere while still maintaining strong growth of the cyanobacteria.

We are used to the phenomena that in less than a second, natural photosynthesis in plants magically transforms carbon dioxide and water into glucose and oxygen using sunlight – with oxygen being only a ‘waste product’ of this biological process.

It is easy to imagine that we need to solve a key problem for all space missions to the International Space Station (ISS), Mars or Moon: how do we produce sustainably and efficiently oxygen (and an artificial atmosphere) for long periods of time? How do we recycle carbon dioxide exhaled by astronauts? Currently, oxygen and hydrogen are produced through water electrolysis in the so-called “oxygen generator assembly” (OGA) on the ISS. The energy required for the reaction is fed into the reactor from incoming sunlight via solar panels outside the space station. That sounds great – it sounds like everything works already! 

Not quite. The near-absence of buoyancy caused by microgravitation on the ISS hinders the detachment of gas bubbles from electrodes in the electrolyser and the produced gases (oxygen and hydrogen) can only be detached and utilised through rotation. This requires a lot of energy: 1.5 kW out of the 4.6 kW used by the entire Environmental Control and Life Support System (ECLSS) on the ISS is used by the OGA to produce oxygen for crew members. For long-term missions to the Moon or Mars, life-support systems that must rely on sunlight as their sole energy source must become much more efficient.

A fire on board a spacecraft is one of the most dangerous scenarios in space missions. There are hardly any options for getting to a safe place on board or escaping from a spacecraft. It is therefore crucial to understand the behavior of fires under these special conditions.

ZARM researchers has been conducting experiments on the propagation of fires in weightlessness since 2016. In their experiments the environmental conditions are similar to those on the ISS – with an oxygen level in the breathing air and an ambient pressure similar to that on Earth, as well as forced air circulation. These experiments have shown that flames behave completely differently in weightlessness than on Earth: A fire burns with a smaller flame and spreads more slowly, which means it can go unnoticed for a long time. However, it burns hotter and can therefore also ignite materials that are basically non-flammable on Earth. In addition, incomplete combustion can produce more toxic gases. And most suprisingly, a flame tends to spread in the opposite direction to the air flow. Accordingly, trying to blow out a flame on a spaceship would be a very bad idea!

Why do flames behave differently in weightlessness?

On Earth, the layers of air surrounding a flame flow upwards. Gravity takes care of this: the layers of air heat up and expand, thus they become lighter and rise. As new air flows in from below, oxygen is permanently supplied to the flame.

In 2021, a team of 25 international scientists used the Northrop Grumman CYGNUS supply vehicle for the ISS to study the behavior of fires in space. During the SAFFIRE (Spacecraft Fire Safety Demonstration) experiment, the team collected data material, and took thousands of individual photos, documenting the combustion of a five-centimeter-wide, one-centimeter-thick Plexiglas sample.

A current series of experiments with very thin plexiglass foils is being carried out under weightlessness in the Drop Tower Bremen. Here, ZARM scientists are observing the propagation of flames after igniting the samples to investigate how the fire reacts when one of the three parameters – ambient pressure, oxygen content and flow velocity – is changed in different proportions. The reason for this is that future space missions are currently being planned with modified atmospheric conditions, e.g. lower pressure and higher proportions of oxygen in the breathing air for the crew. This can have dangerous consequences in the event of a fire.

In general, missions with an astronautic crew are always designed for an outward and return flight. Therefore, the spacecraft may only move so far away that it can return with the fuel it has on board. This makes it impossible to jump too deep into space. But refuelling stations or fuel depots in space could extend the flight range of spacecraft into deep space.

However, refueling in space is also relevant for non-astronautic missions. If you want to launch a fully fueled spacecraft into space, the rocket launch – the moment to escape the Earth's gravitational pull – alone consumes enormous amounts of fuel, depending on the weight of this payload. An alternative would be to launch the spacecraft designed for long exploration missions with an empty tank and refuel it in space. The empty tank saves weight and thus fuel for the launch vehicle. The transport of the fuel depot on the one hand and of the fuel to the depot on the other hand can be accomplished with pure cargo rockets (i.e. without crew). These rockets are subject to lower safety requirements than rockets that are approved for passenger transport and are therefore allowed to transport larger amounts of fuel. This is more efficient and saves costs.

On Earth, we have a dense network of fuel stations to ensure the availability of fuel almost everywhere. Similarly, installing refueling stations in orbit or on the surface of Moon or Mars could significantly increase our range of motion.