NASA hasn&#x27;t developed a new rocket since the space shuttle, so they simply have no relevant experience.  In addition, SpaceX, ULA, and Orbital Sciences have demonstrated an ability to develop space systems much more quickly and reliably than NASA, which usually has cost&#x2F;scope death spirals, largely due to slow schedules, bureacracy and lack of impetus to move forward.  In addition, NASA develops launch systems for a single customer, whereas all the others are trying to develop systems which can be used for a wide variety of customers, meaning that they can amortize development over more launches, as well as offering the opportunity to improve design and manufacturing reliability and cost issues.<p>SLS is only the latest in a series of system designs which have been cancelled&#x2F;drastically redesigned.[1]  Even if SLS were completed (at over 10 times the cost of any other alternative), it is scheduled for less than one launch per year, which means that it will never demonstrate reliability or achieve economy.<p>[1] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Space_Launch_System" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Space_Launch_System</a>