airspace vs the vault of heaven

airspace

noun
  • that part of the sky designated for the sole use of aircraft. 

  • The cavity in a cavity wall containing air for insulation. 

  • The portion of an enclosed area which contains air, especially breathable air. 

  • Space (i.e. a few neighboring frequencies) available for broadcasting within a particular frequency band. 

  • A specified portion of the atmosphere, especially that under the technical aviation control and/or jurisdiction of a particular state over which territory (and territorial waters) it lies. 

the vault of heaven

How often have the words airspace and the vault of heaven occurred in a corpus of books? (source: Google Ngram Viewer )