Ahead of the launch of India's maiden human spaceflight venture 'Gaganyaan' in December 2021, the Indian Space Research Organisation will undertake two unmanned missions in December 2020 and June 2021, ISRO chairman K.Sivan said on Wednesday. Sivan said the Gaganyaan mission not only aims at India's maiden human flight to space but also setting up a new space station for 'continuous space human presence'.