SpaceBok is tested on an extremely flat floor to simulate reduced gravity.
The Mars Curiosity Rover has been remotely exploring the Red Planet for the last eight years and although it remains operational, the rugged terrain has caused significant damage to its wheels. Could a more flexible rover design lead to a longer-lasting and deeper exploration? Enter the world of legged robots with SpaceBok, a project led by the Eidgenössische Technische Hochschule (ETH) Zurich with the goal of designing and creating a legged robot capable of walking and jumping in low gravity conditions. After all, that’s how Neil Armstrong moved after the first Moon landing – by hopping and jumping.
“The motivation for developing the SpaceBok originated from the thought that future missions to the Moon or Mars could advance into increasingly difficult and steep terrain, and for this, versatile exploration robots would be needed,” says Hendrik Kolvenbach, supervisor of the SpaceBok project. “Particularly the exploration of craters is interesting, as these could potentially hold water and other resources which could for example be used as fuel for rockets or as habitats, and would therefore be useful to humans.”
The SpaceBok may be a little wider than the springbok that serves as its inspiration and only reach to about knee-height, but with a little imagination you can recognise the similarities in the prototype – especially when it comes to the jumping motion. Some might also be reminded of the models produced by Boston Dynamics, but the SpaceBok is distinguished by a design specifically intended for energy-efficient movement in low-gravity conditions and so- called dynamic walking.
Hendrik Kolvenbach, supervisor of the project, prepares the robot for a test.
“Dynamic walking is characterised by its capability to momentarily put itself in an unstable position (just like humans and animals do) to increase the efficiency of the movement at higher speeds," Kolvenbach continues. "This would be interesting on the Moon, as you can leverage he low gravity to progress, for example, in a jumping motion.”
3D printing is an obvious aid for a prototype such as the SpaceBok and the ETH team directed the printing in the most part towards the robot’s torso.
“As it is a prototype, a lot of parts were changed even during construction, and 3D printing allowed us to make changes flexibly and at short notice,” Kolvenbach explains. “In addition, many of these parts feature complex geometries, which in this way could be achieved quickly and at low cost. For the most part, we used plastics, which have the additional bene t of being lightweight and ultimately allow the robot to jump higher.”
The project team mainly uses MakerBot and Ultimaker FDM printers. They are currently working on different versions of the robot's feet, and the speed and low cost of additive manufacturing means iterations for sole textures can be produced and tested quickly. For parts which need to withstand forces during jumps and landings, a HP Multi Jet Fusion printer and Nylon materials were employed.
The jump sequence of the SpaceBok.
Having constructed a functioning prototype, the project moved to its next phase, with the SpaceBok and its behaviour in different gravity conditions being tested at ESTEC, the European Space Agency’s Space Research and Technology Centre.
At ESTEC’s facilities, both zero gravity as well as generally reduced gravity can be simulated. The SpaceBok tests were conducted with the help of an extremely flat floor and air bearing platforms. Although these tests are somewhat limited, as they do not take place in a completely three- dimensional space, they did allow the team to test and adjust the orientation of the robot during its flight phase, to ensure that the robot lands safely after each jump.
This leaves only one question: Will this jumping robot actually be sent into space one day, to aid in exploratory missions on the Moon or on Mars? Kolvenbach is hopeful: “Since the opportunities are apparent, we hope that the chances [of a space mission] will increase with each successful test. There is an increased research interest in legged robots here on earth, for example for parcel delivery, rescue missions or autonomous inspection. Ultimately, all these developments contribute to making the technology more robust and efficient, and therefore also make them interesting for space exploration.”
