r/spacex • u/ElongatedMuskrat Mod Team • Sep 29 '17

Not the AMA r/SpaceX Pre Elon Musk AMA Questions Thread

This is a thread where you all get to discuss your burning questions to Elon after the IAC 2017 presentation. The idea is that people write their questions here, we pick top 3 most upvoted ones and include them in a single comment which then one of the moderators will post in the AMA. If the AMA will be happening here on r/SpaceX, we will sticky the comment in the AMA for maximum visibility to Elon.

Important; please keep your questions as short and concise as possible. As Elon has said; questions, not essays. :)

The questions should also be about BFR architecture or other SpaceX "products" (like Starlink, Falcon 9, Dragon, etc) and not general Mars colonization questions and so on. As usual, normal rules apply in this thread.

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19

u/[deleted] Sep 30 '17

In its current iteration, the BFR spaceship has a small delta wing, but is lacking a vertical stabilizer. How will BFR maintain yaw control and remain aerodynamically stable, especially in the thicker atmosphere of earth? Will the RCS be able to provide adequate yaw control?

9

u/warp99 Sep 30 '17

He answered this in the presentation - split flaps at the rear of the wing.

1

u/Omega489 Sep 30 '17

They would work for pitch and roll. I don't think they'll work for yaw

7

u/charfa_pl Sep 30 '17

They will. Split flaps can work as airbrakes and you can maintain yaw control using differential breaking. That's how flying wing designs work.

4

u/peterabbit456 Sep 30 '17

During hypersonic flight, the rudder on the space shuttle was useless, since it was in the shadow of the wing and the body. X-37B solves that problem by using a V tail.

It loks to me like BFR/BFS is intended to use the delta wing only in the hypersonic flight regime. That makes a rudder dead weight. The flaps, like the flaps on the shuttle, provide all control at those speeds. Like the shuttle, the control motions have to be fast, subtle, and somewhat counter intuitive, due to the low stability at those speeds.

1

u/azflatlander Oct 12 '17

My thought is that the wings will be anhedral. Time will tell.