He was selected for spaceflight training in 1978 as a part of the Intercosmos Program. Having obtained the highest marks during three years of preparation, he was then selected for a joint space flight with the Russian cosmonaut Leonid Popov. In May 1981 they completed an eight-day space mission on board Soyuz 40 and the Salyut 6 space laboratory where they completed scientific experiments in the fields of astrophysics, space radiation, space technology, space medicine and biology.
Since 1978 Prunariu was an active officer of the Romanian Air Force. For different periods of time Prunariu was detached within other ministries to perform civil functions. In 2007 he completely retired from the Air Force with the military rank of major general, continuing his professional activity as a civil servant. At the end of 2015, by a decree of the President of Romania, Prunariu received the 3rd star, becoming a lieutenant-general (ret.).