<story><title>SLS vs. Starship</title><url>https://everydayastronaut.com/sls-vs-starship/</url></story><parent_chain><item><author>bryanlarsen</author><text>The reasoning behind SLS sort of made sense 10 years ago.   We didn&amp;#x27;t know that Starship, New Glenn and Falcon Heavy were coming down the pipe.  We decided that the US &amp;amp; NASA needed super-heavy lift capability.   Previous attempts to design a heavy lift vehicle were lost to political regime change and congress in-fighting.   Previous attempts to design a single-stage-to-orbit vehicle were cancelled due to its virtual impossibility.&lt;p&gt;So NASA &amp;amp; Congress designed a program that was unkillable.   It greased too many wheels and lined too many pockets to make it easy to kill.   It was also designed ultra-conservatively using mostly existing designs so there was no technical risk.&lt;p&gt;So now when we complain that it&amp;#x27;s a pork-filled boondoggle that&amp;#x27;s impossible to kill, that was the plan, and there was a certain logic behind it.   It makes no sense in a world with Falcon Heavy, Starship &amp;amp; New Glenn, but who would have predicted that with confidence in 2010?</text></item></parent_chain><comment><author>OnlyOneCannolo</author><text>It made sense as an institutional flywheel.&lt;p&gt;The Constellation Program [1] that preceded SLS had two vehicles - Ares I for ISS crew and supplies after Shuttle was retired, and Ares V for occupying the moon. The missions gave some justification for needing vehicles. Their design was primarily a means to preserve existing contracts and jobs. Additional wheel greasing made it happen.&lt;p&gt;That stuff about re-using parts to reduce risk is just what people say because it sounds good, but isn&amp;#x27;t inherently true. Kind of like how &amp;quot;drug delivery&amp;quot; and &amp;quot;machine learning application&amp;quot; are go-to pseudo-justifications for many research proposals.&lt;p&gt;Constellation was eventually canceled when ISS resupply went to the Commercial Crew Program [2]. Ares V was stripped down and reimagined as the mission-less SLS. SLS is not really intended to do much more than exist for the time being.&lt;p&gt;There are a lot of factors that will go into canceling SLS - infighting between NASA centers, preserving jobs and contracts with Old Space companies, even more wheel greasing. I&amp;#x27;m interested to see how it plays out.&lt;p&gt;[1] &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Constellation_program&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Constellation_program&lt;/a&gt;&lt;p&gt;[2] &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Commercial_Crew_Program&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Commercial_Crew_Program&lt;/a&gt;</text></comment>
<story><title>SLS vs. Starship</title><url>https://everydayastronaut.com/sls-vs-starship/</url></story><parent_chain><item><author>bryanlarsen</author><text>The reasoning behind SLS sort of made sense 10 years ago.   We didn&amp;#x27;t know that Starship, New Glenn and Falcon Heavy were coming down the pipe.  We decided that the US &amp;amp; NASA needed super-heavy lift capability.   Previous attempts to design a heavy lift vehicle were lost to political regime change and congress in-fighting.   Previous attempts to design a single-stage-to-orbit vehicle were cancelled due to its virtual impossibility.&lt;p&gt;So NASA &amp;amp; Congress designed a program that was unkillable.   It greased too many wheels and lined too many pockets to make it easy to kill.   It was also designed ultra-conservatively using mostly existing designs so there was no technical risk.&lt;p&gt;So now when we complain that it&amp;#x27;s a pork-filled boondoggle that&amp;#x27;s impossible to kill, that was the plan, and there was a certain logic behind it.   It makes no sense in a world with Falcon Heavy, Starship &amp;amp; New Glenn, but who would have predicted that with confidence in 2010?</text></item></parent_chain><comment><author>mlindner</author><text>I think you&amp;#x27;re misrepresenting the past.&lt;p&gt;&amp;gt; It was also designed ultra-conservatively using mostly existing designs so there was no technical risk.&lt;p&gt;Politicians can&amp;#x27;t design a rocket and cannot get what is &amp;quot;ultra-conservative&amp;quot;. Rockets are not Lego blocks that you can just mix and match. They&amp;#x27;re explicitly designed a certain way to support a certain load profile. Even if the parts of the SLS _look_ like they have low risk, they do not and that&amp;#x27;s why the vehicle has taken so long to develop.&lt;p&gt;One example, if the shuttle boosters were could actually have been used directly they wouldn&amp;#x27;t have needed to extend the number of segments from 4 to 5, redesign the liner between the segments, and completely redesign the nozzle. It&amp;#x27;s a new booster.&lt;p&gt;Second example, even though the shuttle external tank looks like it&amp;#x27;s being used, in previous iterations the shuttle external tank did not support any axial loads, it was simply held on to the bottom of the Orbiter. Now the external tank has to withstand the entire axial load of the rocket so it&amp;#x27;s basically redesigned from scratch.</text></comment>