The MIDAS AFM - modelling and calibration of a space-born atomic force microscope

Short Description

The MIDAS Atomic Force Microscope (AFM) is a unique instrument designed to collect and analyse cometary dust, producing 3D images of individual dust grains and aggregates with nanometre-scale resolution. The data collected will address a variety of key questions about the formation environment of the early Solar System and the nature of cometary material.

MIDAS was designed and built by a consortium led by the Institut für Weltraumforschung der Österreichischen Akademie der Wissenschaften and is the only Austrian Principal Investigator instrument on-board the Rosetta mission. Launched in 2004, Rosetta is currently in hibernation and will wake up and complete final rendezvous manoeuvres in summer 2014. Understanding how an AFM behaves in the space and cometary environment, and how control of such an inherently "hands on" instrument can be automated, are critical both for the Rosetta mission, but are also important to facilitate the development of future space AFM instruments and to maintain the Austrian expertise gained with MIDAS.

This proposal addresses these key issues, including how best to deal with image distortion induced by a variety of factors. A series of tests is planned to determine the sensitivity of the instrument to these effects and devise a strategy (operational or by updating on-board software) to mitigate them. Originally some of these effects should have been reduced by a closed loop capacitive feedback system, however one of two channels was damaged during launch. Another challenge is thus to find the optimal way to use the remaining channel.

In the laboratory an AFM is a very interactive instrument. Tips are worn down over time and frequently replaced and the best images are obtained by a trained operator who adapts the operating parameters to the sample at hand. The first of these problems is mitigated on MIDAS by carrying sixteen tips for redundancy. Even so, the quality of these tips is a major limiting factor to both the quality of the science and the instrument lifetime.

As such, minimising the tip-sample force is critical. This can only be done by numerical modelling, taking into account the unique way in which MIDAS operates. The open source VEDA AFM simulation tool will be modified here to model a MIDAS approach (cantilever amplitude versus distance) curve, first deriving a procedure to measure all of the necessary input parameters from instrument telemetry alone. Once validated, this model will be used to explore the operating parameters space (cantilever amplitude, working and set points etc.) to determine which setting results in the minimum tip-sample force and maximum tip lifetime.

Operating MIDAS is also a challenge due to the large one-way light time at the start of the project, and the large lead-in times for planning operations and instrument commanding. These mean that novel strategies must be developed both by developing suitable ground-based planning tools and also by using on-board autonomy as much as possible.

Taken together all of these steps should ensure that MIDAS is operated in a way returns high quality raw data, which can then be calibrated and artefacts removed to eventually yield an optical science data set for archiving and delivery to the science team.

Project Partners


Austrian Academy of Sciences

Contact Address

Austrian Academy of Sciences
Dr. Ignaz Seipel-Platz 2
A-1010 Vienna
Web: www.oeaw.ac.at