P. Radhakrishan (Nair, Paramaswaran Radhakrishnan) — known sometimes as "Space Radhakrishnan" — is a veteran space scientist, author and speaker from India. He retired from the Indian Space Research Organisation as the Deputy Director of Liquid Propulsion Systems Centre. Radhakrishnan was slated to travel to space in the STS-61-I (Challenger) mission in September 1986 as a Payload Specialist for INSAT-1C, but the flight was cancelled after the Challenger disaster. N.C.Bhat from ISRO Satellite centre was the other Indian space scientist who was trained by NASA for the mission — the plan was to select one of these two for the mission.