Although I've seen various discussions about the supposed reasons and requirements for the change from seven seats to four seats in Crew Dragon, this seems to be new definitive information:



December 7, 2019 Stephen Clark writing at Spaceflightnow reports:



Quote A requirement change from NASA also contributed to delays, Shotwell said.



After SpaceX had already designed the interior layout of the Crew Dragon spacecraft, NASA decided to change the specification for the angle of the ships seats due to concerns about the g-forces crew members might experience during splashdown.



The change meant SpaceX had to do away with the companys original seven-seat design for the Crew Dragon.



With this change and the angle of the seats, we could not get seven anymore, Shotwell said. So now we only have four seats. That was kind of a big change for us.

https://spaceflightnow.com/2019/12/07/after-redesigns-the-finish-line-is-in-sight-for-spacexs-crew-dragon/





This is a prime example of how SpaceX has been having trouble to satisfy NASA's changing wishes. When SpaceX was awarded the CCtCAP contract NASA retained the right to change requirements, pretty much at will.NASA got a REALLY good deal with CCtCAP: Firmed Fixed Price yet able to change requirements late into the game.And some of those requirement changes have come to bite SpaceX pretty hard. One famous example is the switch to water landings which indirectly has resulted into the current extended (and costly) parachute testing campaign.Another one is presented here: change the angle of the seats. And thus making it impossible to fly seven folks. Which in turn makes the vehicle unattractive for purely tourist flights.The thermal "issues" that DM-1 had was also the result from a NASA requirement change. You see, on DM-1 there weren't any actual thermal issues. DM-1 had the originally designed thermal control set-up which actually met the original NASA thermal requirements.But you guessed it: NASA changed the thermal requirements. And NASA did so pretty late into the planning cycle for DM-1. Those new requirements could not be met by the DM-1 setup. Which in turn required a waiver to fly DM-1 with the original thermal set-up but also requiring substantial rework to the DM-2 vehicle to meet NASA's new, more stringent thermal requirements.And there have been several more major requirement changes. The result is that SpaceX spent much more money on CCtCAP development effort than originally planned. Elon mentioned hunderds of millions and that's a number that was confirmed to me by several other SpaceX sources. The requirement changes are also mentioned to me as being "substantial contributors to delays in meeting targeted flight dates".In other words: NASA proclaiming that the CCP contractors are delayed "due to working thru technical issues" is only HALF THE STORY.Good thing that Gwynne called this out, albeit it slightly veiled, in recent interviews.SpaceX is not alone in this however. Boeing has had its fair share of requirement changes, and resulting delays, as well.