Former astronaut Dr Buzz Aldrin has cancelled his visit to Cork next week on medical advice.
He was due to speak at the launch of the International Space University's (ISU) 30th Space Studies Program (SSP17) on the 26th of June.
Dr Aldrin, the second person to walk on the moon, said he had made the decision with great regret.
In a statement, the SSP17 organisers said he had said he had been very much looking forward to visiting Ireland.
Dr Aldrin, who is 87, is the Chancellor of the International Space University.
The organisers have wished him a speedy recovery are now looking for alternative options for the lecture on 27 June.
