According to astronomical calculation, along with the polestar there is another star, which is called Sisumara, where Lord Visnu, who is in charge of the maintenance of this material world, resides
SB Canto 4
O immortal one, this unique airplane has been sent by the Supreme Personality of Godhead, who is worshiped by selected prayers and who is the chief of all living entities. You are quite worthy to board such a plane.
According to astronomical calculation, along with the polestar there is another star, which is called Śiśumāra, where Lord Viṣṇu, who is in charge of the maintenance of this material world, resides. Śiśumāra or Dhruvaloka can never be reached by anyone but the Vaiṣṇavas, as will be described by the following ślokas. The associates of Lord Viṣṇu brought the special airplane for Dhruva Mahārāja and then informed him that Lord Viṣṇu had especially sent this airplane.
The Vaikuṇṭha airplane does not move by mechanical arrangement. There are three processes for moving in outer space. One of the processes is known to the modern scientist. It is called ka-pota-vāyu. Ka means "outer space," and pota means "ship." There is a second process also called kapota-vāyu. Kapota means "pigeon." One can train pigeons to carry one into outer space. The third process is very subtle. It is called ākāśa-patana. This ākāśa-patana system is also material. Just as the mind can fly anywhere one likes without mechanical arrangement, so the ākāśa-patana airplane can fly at the speed of mind. Beyond this ākāśa-patana system is the Vaikuṇṭha process, which is completely spiritual. The airplane sent by Lord Viṣṇu to carry Dhruva Mahārāja to Śiśumāra was a completely spiritual, transcendental airplane. Material scientists can neither see such vehicles nor imagine how they fly in the air. The material scientist has no information about the spiritual sky, although it is mentioned in the Bhagavad-gītā (paras tasmāt tu bhāvo 'nyaḥ (BG 8.20)).