Write in your own simple words what the following expression conveys in the context they occur in the text.
But there was a major roadblock.
It means there was an obstacle in getting the possession of the site for Space Research Centre because that site was actually the fishing grounds of Thumba's fishermen. Moreover, it had an old church of St Mary Magdalene, a bishop's house, and a school, which was under the administration of the church. So the officials thought that it was difficult to shift so many people with their religious place.