Maui wrote:Pathological skepticism is great! I think everyone could use more skepticism.
I am comforted that you all are not concerned by this design change, though no one has really addressed how such a large surface area can be reliably/safely actuated at hypersonic speeds.
In all fairness I don't think anyone here can address that point as that type of verification is generally handled by advanced fluid dynamic software that few companies in the world can afford and that should run on computers that even less companies can afford.
But I believe we can be pretty confident that SpaceX engineering team did have the resources to verify the structural integrity of this solution.
Maui wrote:As an aside, why would separate legs mean hanging trusswork? Existing F9 extendable legs would certainly be the better model if separate legs were to be used, yes?
Actually no. If you look at the existing F9 landing legs "extended" you will notice that they are already in the form of a triangular strut
. The folding legs set up was good to experiment and learn how to land a rocket, but a similar system on a BFR that has an empty weight of 4 times the F9 would have needed a much bigger, thicker and heavier hydraulic equipment. And when you start to increase the size in these hydraulic systems the total weight grows faster than you can imagine.
Let's not forget that F9 legs seems small but they are already quite big
when you observe them from near.
Edited to add:
A quick google disclosed that the weight of the 4 landing legs of the F9 is around 2500 Kg which is a little bit more than 10% of the empty weight of the F9 rocket and 20% of LEO/ 50% of GTO payload.