The chemical use of water in ISRU

Equitable and sustainable access to fresh water is a major challenge of the 21st century on Earth. The presence of water is also a key challenge in space. It is a major condition of human settlement in outer space and the presence of carbon based alien life. In space, water is the most precious element.

Why is it so important to have water on Mars?

For a trip to Mars, a large amount of water is required. Water is useful for daily life: drinking, growing food (see our article about algae), hygiene, thermal control, protection against radiation. Launching one kilogram of water from Earth to space is very costly regarding money, power, and storage.

North polar ice cap on Mars - Mars Reconnaissance Orbiter- Credit NASA-JPL

North polar ice cap on Mars – Mars Reconnaissance Orbiter- Credit: NASA-JPL

Ice was discovered on Mars by the Phoenix Mars lander in 2008. The presence of water on Mars is a great opportunity. This offers astronauts the chance to mine regolith and extract water directly from the ground.  The success of human space exploration depends on the control and the access of water in ISRU (In-Situ Resource Utilization).

The chemistry of water

Water can also be seen as H20, a combination of hydrogen and oxygen. This is a simple molecule that can be broken into H2 and O2 through, for example, a process named electrolysis.

2H2O + ENERGY = 2H2 + O2

In this case, an electric current goes through water; resulting in separation of water into hydrogen and oxygen. This is an endothermic reaction, the system absorbs energy. In order to be efficient, a catalyst must be added to speed-up the process. On Mars, oxygen and hydrogen could be separated using electrical power generated through solar panels.

Electrolysis of water - Credits: Instructables

Electrolysis of water – Credits: Instructables

Additionally, it also possible to convert hydrogen and oxygen into water. This is an exothermic reaction, also known as combustion reaction where the system releases energy.

2H2 + O2 = 2H2O + ENERGY

If the chemistry of water still remains obscure to you, please find more details here.

Applications in ISRU

Water, hydrogen, oxygen, energy…. have many applications in ISRU. Actually, the chemistry of water has two main advantages in ISRU; it could store power and produce fuel.

During sunlight, solar panels would provide power to space vehicles, devices and habitats while storing power produced by the electrolysis of water. During dark periods, oxygen and hydrogen would be recombined to generate electrical power. That would be a continuous supply of energy for the crew and equipment on Mars.

Plus, the reconstitution of hydrogen and oxygen into water produce a high amount of energy rather quickly. It is also a very powerful chemical propellant that rockets use. The fuel obtained in ISRU is a mass that doesn’t need to be carried from Earth. This allows the spacecraft to carry more valuable payload.


Many problems must be solved before these technics can be used on a large scale. The process of electrolysis to separate oxygen and hydrogen is not optimal yet and requires more research, mainly on the catalyst, before being ideal. The storage of hydrogen is also challenging. This gas is extremely volatile and its liquid form requires cryogenic temperatures (–252.87 °C). Finally, the overall process must be fully controlled to insure the safety of the method. Due to the amount of energy involved and the presence of hydrogen, any uncontrolled combustion reaction would lead to tragic events.

More about mining water on the Air&Space Blog.

Because we are all Born For Space !