Madsen participated in the design and analysis of the five Danish magnetic properties experiments flown on the 1997 Mars Pathfinder mission.
[4] The results from the magnetic properties experiments showed that there had not been liquid water on the surface of mars for the last 2 billion years.
[7] The results from the magnet experiment was considered a success in that they helped the understanding of how the dust on Mars was composed and built up.
[7] Members of the team, including Madsen, were at the control center at the Jet Propulsion Laboratory in Pasadena during the rovers' landing and the first three months of initial data collection.
[8][9] In 2007, Madsen's team was invited by NASA to design the three radiometric calibration targets for the Phoenix mission called "Improved Sweep Magnet Experiment" (ISWEEP).