Immediately after his degree, Knudsen received a job invitation to MIT where he spent the next two years as a guest teacher.

[citation needed] During 1966-1967 he taught physics at Middle East Technical University in Ankara Turkey.

One morning Knudsen had sat down at the morning table at the workshop and started an enthusiastic conversation about why Mars exploration is especially important with two people unknown to him; it turned out that they were Agustin Chicarro, who was ESA's Solar System Research Project Scientist and leading and George Scoon, the chief designer of ESA's orbiter probes.

Both were thrilled about Knudsen's rhetoric and invited him to join a science team for a European probe to Mars.

[citation needed] In later years he became known as "Marsmanden" (the Martian) on account of his great enthusiasm towards recent missions to the planet Mars.

In 2000 Knudsen was awarded the Order of the Dannebrog In 2002 he was appointed Honorary Professor of Planetary science at the University of Aarhus.