SOFIA gets above most of the water vapor in the atmosphere allowing it to do IR astronomy that ground based telescopes can't. SOFIA is accessible in a way that

SOFIA gets above most of the water vapor in the atmosphere allowing it to do IR astronomy that ground based telescopes can't. SOFIA is accessible in a way that space telescopes aren't. This allows switching instruments, upgrading instruments, and development of new instruments that can't be done in active space telescopes. Its development and maintenance cost to date is a bit over 1/10 the cost of Webb to date. Plus it's really cool to cut a hole in an airplane and stick a telescope out.