SB 4.12.35
tri-lokim deva-yanena
so ’tivrajya munin api
parastad yad dhruva-gatir
visnoh padam athabhyagat
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Dhruva Maharaja thus surpassed the seven planetary systems of the great sages who are known as saptarsi. Beyond that region, he achieved the transcendental situation of permanent life in the planet where Lord Visnu lives.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The airplane was piloted by the two chief associates of Lord Visnu, namely Sunanda and Nanda. Only such spiritual astronauts can pilot their airplane beyond the seven planets and arrive in the region of eternal, blissful life. It is confirmed in the Bhagavad-gita also (paras tasmat tu bhavo ’nyah) that beyond this planetary system begins the spiritual sky, where everything is permanent and blissful. The planets there are known as Visnuloka or Vaikunthaloka. Only there can one get an eternal, blissful life of knowledge. Below Vaikunthaloka is the material universe, where Lord Brahma and others in Brahmaloka can live until the annihilation of this universe; but that life is not permanent. That is also confirmed in the Bhagavad-gita (abrahma-bhuvanal lokah). Even if one goes to the topmost planet, one cannot achieve eternal life. Only by arriving in Vaikunthaloka can one live an eternally blissful life.