Costs where not only based on refurbishing costs, as they included R&amp;D and ongoing capital costs.  See: upgrades <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Space_Shuttle_main_engine" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Space_Shuttle_main_engine</a>  Not to mention building but never using an extra engine,  Ground crew etc.<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;STS-61-B" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;STS-61-B</a> Had a 54 day turnaround time which is not &#x27;great&#x27; still.  That&#x27;s 6+ short missions per year per orbiter call it 5 including missions and some unscheduled down time.<p>They started with 6 orbiters * 5 missions a year ~= 30 missions per year.  The shuttle actually did 135 over 30 years or 4.5 per year * (~0.75 per orbiter per year).<p>PS: At even 1&#x2F;2 that 30 mission per year rate they would have finished 135 missions in under 10 years.