GECKO (Gecko Adhesives for Space Applications)

Project Description:

The first objective is to analyse how so-called gecko adhesives perform under the influence of the space environment. Gecko adhesives are synthetic dry adhesives inspired by geckos. The technology of dry adhesion mimics the feet of geckos. As the gecko feet, dry adhesives feature millions of small microstructures that get in contact with a counterpart surface. The resulting van der Waals forces allow high adhesion to several targets. These gecko materials are usually manufactured out of materials that are either easily manageable in a laboratory environment or show high expected adhesion in a laboratory environment. As the idea of applying gecko adhesives to space flight technology is quite new, the materials commonly used (for example PDMS or PU) have to be analysed in terms of performance under space conditions. Some expected behaviour includes for example outgassing of PU in vacuum or an embrittlement of the fine microstructures due to low temperatures.

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Thus, to fulfil the first objective, tests of gecko adhesives need to be performed in a laboratory environment as reference and under space conditions as well. The second kind of tests requires the simulation of for example, vacuum, thermal cycling or radiation.

Illustration of a gecko’s foot with increasing scale

After achieving the first objective by gaining substantial knowledge on gecko adhesives performance under space conditions, the second objective is to optimise gecko adhesives for a space application. A docking/grappling mechanism shall be developed that can dock to or grapple space debris. The gecko adhesives shall be optimised to be used in such a mechanism. Since gecko adhesives are synthetically produced, many design parameters can be varied to improve adhesion. However, not only adhesion shall be maximized, but also applicability to space conditions. A material that exhibits higher adhesion might still be unusable if it outgasses too much in vacuum. The parameters that may contribute to the optimization of the gecko adhesives to space application include:

• Microstructures aspect ratio
• Microstructure spacing
• Microstructure cross section
• Microstructure material
• Base/ backing layer material

The optimization shall not only be performed with respect to space applicability, but also regarding usability in a docking/grappling mechanism. For application to such a mechanism, additional parameters for optimisation apply, such as:

• Manageability (clean room required, do not touch, etc.)
• Attachability of base/ backing layer
• Number of re-use cycles

Finally, the third objective is the design and test of a docking or grappling mechanism for which the gecko adhesives have been optimised in the scope of the second objective. The design of a suitable mechanism requires an analysis of potential targets with a particular focus on target geometries and materials, so that the mechanism can dock to or grapple those targets and the adhesives adhere to target materials. Potential targets can be evaluated using so-called priority lists, which rank space debris according to their criticality. It can be defined in several ways, but generally criticality is the impact of a space debris fragmentation on the (global) collision probability of the entire population. High-ranked target objects include several Zenit 2 and Ariane 4 upper stages, as well as Envisat or Metop satellites.

After an analysis of target geometries and materials, the mechanism needs to be designed so that it can bear/absorb maximum loads. The development process may include rapid prototyping techniques, as those allow to easily build a low priced prototype, perform tests, and subsequently conduct iterations to improve performance. The final design of the mechanism can then be manufactured with space qualified or at least more durable materials and tested both in a laboratory environment and under simulated space conditions.

To summarize, the main technical objectives include a thorough analysis of gecko adhesives applicability to space use in general and especially their applicability to a docking/grappling mechanism to target space debris. The gecko adhesives shall be optimised for the use in a docking/grappling mechanism. Furthermore, the objective is to develop and test such a mechanism in a laboratory environment and under simulated space conditions. Thus, by the end of the work, the gecko adhesive based mechanism may have reached a Technology Readiness Level (TRL) of 5.

Test setups to analyse performance of small gecko adhesive pads (left) and mechanism performance on different curvatures (right).

Project Term:

March 2017 – May 2018

Partner:

The project is carried out as a part of the General Support Technology Programme (GSTP) (funded by the European Space Agency) in cooperation with the following partners:

• Leibniz Institut für Neue Materialien, Germany
• Institut für Mikrotechnik, TU Braunschweig, Germany
• Aerospace & Advanced Composites GmbH, Austria

Publications:

• Journal
• Proceeding