Nasa’s Artemis programme aims to build a space station on the moon. Robots will be an essential work force in its construction and will also play vital supporting roles to the astronauts based at the space station. Development is underway to design and test the joints, based on compact motor technology, that will drive these lunar robots. Andrew Gibson, maxon UK & Ireland’s Head of Space Applications, explains what is required.  

maxon has provided drive systems to every Nasa Mars mission, including the current Perseverance rover. Image: Nasa.

The world is waiting for the launch of Nasa’s Artemis II mission, due this April, which is set to make a 10-day manned mission around the moon. Following the 2022 launch of the unmanned Artemis I, which tested Nasa’s new Space Launch System rocket and the Orion shuttle, this sequel will prove the live operation of Orion’s life-support systems, navigation, propulsion, and deep-space communications.

Artemis II will be the first time humankind has left low earth orbit to reach or circle the moon since the Apollo 17 moon landing in 1972. But for the future of space exploration, the upcoming mission means much more as Artemis II will be an essential stepping stone towards sending a crew to the lunar surface once again, possibly within the next two or three years.

The wider Artemis programme represents humankind’s onward journey into space from the giant leap made by the first moon landing on July 20, 1969. The aim is to develop Artemis Base Camp, a manned lunar surface habitat planned by Nasa to take shape within the next 10 years.

Significantly, Artemis III plans to land on the Moon’s South Pole as ice identified in the region could be melted to make drinking water, used as a source of oxygen, and it could even be split into hydrogen and oxygen to make rocket fuel.

Building lunar stations

There are also plans to support Artemis Base Camp with Nasa Gateway, a lunar orbital station that will eventually be used for docking, logistics, and orbital operations. Together, the moon-based and lunar orbital stations will present a live environment to develop and test the technology needed to send a crewed mission beyond the Moon for the first time, and a manned Mars mission is the ultimate objective.

While spaceflight capabilities are the essential priority, once on the Moon or in its orbit, construction must take shape to enable long-term human survival and create an effective environment to use, develop and test new technology required for further exploration. To achieve this, robots will be key. Robots can deal with the lunar environment in a way that humans can’t, and they are far more adept at providing precision over repeated tasks – especially compared to an astronaut wearing a spacesuit.

The deployment of robotics technology will start with Nasa’s VIPER rover that will explore the Moon for water ice before Artemis crews arrive, just as the Perseverance rover is already doing on Mars. Then, robots will be required to construct modules while in orbit, as well as engaging in construction on the Moon’s surface. This could include tasks such as assembling modules, deploying solar arrays, setting up landing pads, as well as preparing habitats where astronauts will live and the infrastructure they will rely on.

Robots and their joints

When Gateway and Artemis Base Camp have been built, robots will also be crucial to support and assist astronauts with tasks ranging from equipment handling through to scientific experimentation. Already on the International Space Station, robots have been used for a number of years for purposes such as maintenance inspection and moving loads, and even robotic surgery that can be remotely controlled from Earth, both supported by maxon drive systems. 

maxon’s SpaceLab team is currently adapting maxon’s robot joints for use in space.

Within these robots, sensors enable them to detect and measure their environment in combination with a central controller that acts as a brain, interpreting information and making decisions. In addition, it’s the robot joints that are vital as the muscles that drive and locally control robotic limbs and end effectors.

Housed as a single unit, robot joints comprise an electric motor plus a gear that matches the required torque and speed of motion. Inside, encoders report on the speed and position of the motor, and an integrated controller manages its position, speed, and torque. A brake can also be incorporated to hold the movement. 

For a robot joint to achieve the level of control required for delicate tasks, which could range from human surgery through to welding, micron-level precision over motion is required, with accuracy repeated every time. Operating in a space station where electrical power is closely monitored, energy efficiency is also vital. And of course, to help propel the equipment into space, low mass is also crucial.

Space R&D

The robot joint also needs to be extremely strong and protected from impact and vibration, and durable for use over several years. Even on Earth, these attributes are crucial to many robotics applications. However, there are striking differences in the operating conditions in space. As a result, maxon’s SpaceLab, the R&D team dedicated to space projects, is currently adapting and testing maxon’s existing robot joints for use in space environments.

Lacking Earth’s atmosphere, the temperature on the Moon varies greatly, with highs of +120°C and lows of –125°C. While electronic components used in space applications are often protected within thermally controlled enclosures, the SpaceLab team has adapted the design and is testing the robot joints to withstand these temperature extremes.

Another important aspect of thermal testing is the coefficient of linear expansion and the compatibility of different metals in the design of a motor and gear drive system. As metals expand at different rates, designing for this potential is crucial to avoid performance challenges such as introducing backlash to a gearbox or impacting reliability over time.  

The lack of atmosphere on the Moon also contributes to much higher radiation, and in particular this can damage plastic-based components. The plastic supports of electronic components such as PCBs and motor sensors need to be protected and prevented from moving, which can occur through radiation-induced weakness.

To prevent this degradation, standard polymers susceptible to radiation damage can be replaced with PEEK (polyether ether ketone). Cable insulation should also be replaced with PTFE (Polytetrafluoroethylene), or even the higher rated Kapton material.

Dealing with vacuum is another key challenge of designing robot joints and drive systems for space. The central problem this presents is lubrication outgassing, the release of volatile substances trapped within lubrication when exposed to a vacuum. This can result in lubrication loss, leading to faster wear or failure of moving parts, and outgassing can also cause condensation that can damage wider components, especially sensitive items such as sensors or optical equipment. As a result, it’s essential to test a vacuum-compatible grease for space use.

Testing and operation in space

Before a robot joint is deployed in space within its host, the rigorous testing process being conducted by maxon’s SpaceLab team is vital to know that it will, according to the data, work for real. While testing is vital, in the lab it’s not possible to test for ‘unknowns’, and this is where experience in real space missions becomes invaluable.

As well as providing drive systems for every Nasa Mars rover mission, including the Ingenuity helicopter, maxon has designed electric motor-based systems for the International Space Station, the European Space Agency, JAXA (Japan Aerospace Exploration Agency), and SpaceX. Using drive systems in space not only proves that they work as planned over the duration of a mission, but this experience also uncovers the ‘unknown’ criteria that enable design refinement for future progress.   

While we await the progress of Nasa’s Artemis programme, and even the potential of finally sending a manned craft to Mars, what we do know is that robotics and the systems that drive them will play an essential role in the future of space exploration. In the decades ahead, the success of lunar and Martian programs will depend as much on these systems as it will on human ingenuity.