&gt; 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><p>If your engines burn out after 5 instead of the planned 55 flights, I damn well hope you&#x27;re going to invest into more R&amp;D on them!<p>&gt; Had a 54 day turnaround time which is not &#x27;great&#x27; still.<p>And the pressure to keep up that break-neck pace directly led to the Challenger disaster.