In 1773 the Society of Jesus was suppressed by Pope Clement XIV and Calandrelli was posted as a professor of mathematics at the Collegio Romano.

Along with Ruggero Boscovich another observatory was considered at the Collegio Romano on the rooftop of the Church of St. Ignazio but found to be too expensive.

After Boscovich's death, Calandrelli, with the help of Cardinal Zelada established a 67-meter observation tower in 1787 from which he examined the positions of stars and planets.

Calandrelli favoured the repulsion theory and assumed that all the cometary material including its vapour are attracted to the centre of the comet.

In 1815 Calandrelli was relieved from his teaching duties and he was fully involved in his studies and retired in 1824 to the seminary of Saint Apollinaire where he died and was buried in the church cemetery.