Elon hatte gestern auf Reddit eine AMA session. Ama steht für "ask me anything". Dies wurde erst wenige Stunden davor angekündigt per Twitter. Die Reddit-jünger haben auch diesmal viele interessante Fragen bereitgehabt die dann von den Moderatoren weitergeleitet wurden. Achtung, vieles ist höchst technisch.
https://www.reddit.com/r/space/comments ... about_bfr/Sehr unterhaltsam, eine meiner Lieblingsstellen:
Why was Raptor thrust reduced from ~300 tons-force to ~170 tons-force?
One would think that for (full-flow staged combustion...) rocket engines bigger is usually better: better surface-to-volume ratio, less friction, less heat flow to handle at boundaries, etc., which, combined with the target wet mass of the rocket defines a distinct 'optimum size' sweet spot where the sum of engines reaches the best thrust-to-weight ratio.
Yet Raptor's s/l thrust was reduced from last year's ~300 tons-force to ~170 tons-force, which change appears to be too large of a reduction to be solely dictated by optimum single engine TWR considerations.
What were the main factors that led to this change?
Darauf antwortete Elon:
[–]ElonMuskElon Musk (Official)[S] 22.3k Punkte vor 10 Stundenx2
We chickened out
Um dann doch noch eine richtige Erklärung nachzuliefern.
[–]ElonMuskElon Musk (Official)[S] 13.2k Punkte vor 10 Stunden
The engine thrust dropped roughly in proportion to the vehicle mass reduction from the first IAC talk. In order to be able to land the BF Ship with an engine failure at the worst possible moment, you have to have multiple engines. The difficulty of deep throttling an engine increases in a non-linear way, so 2:1 is fairly easy, but a deep 5:1 is very hard. Granularity is also a big factor. If you just have two engines that do everything, the engine complexity is much higher and, if one fails, you've lost half your power. Btw, we modified the BFS design since IAC to add a third medium area ratio Raptor engine partly for that reason (lose only 1/3 thrust in engine out) and allow landings with higher payload mass for the Earth to Earth transport function.
, es wird ca. 6 Monate noch dauern bis es ankommt, also genug Zeit, um den Mars zu "Grüne Umweltzone" zu machen 
