Don&#x27;t they sometimes use compressed nitrogen to pressurize a fuel tank?  Nitrogen is pretty much air without the O2.<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Monopropellant_rocket" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Monopropellant_rocket</a>