Solitudines Vastae Celeste

I am begging for more help with my Latin from my kind and helpful readers. I am trying to name a starship ‘Wastlands of Heaven’ in Latin. I know from studying old maps that the poetical term for an empty area on the map filled with dragons is Solitudines Vastae (3 1 NOM P F). But I cannot figure out the proper declension for the adjective ‘celestial’. Would it be Solitudines Vastae Celeste ? or Solitudines Vastae Celestissimus ?

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