Giorgio wrote:Skipjack wrote:Giorgio wrote:Maybe you meant "more than 10% of the F9 first stage"?
Added weight to the first stage does not really affect payload mass as much. It is more relevant for the BFS though, which is a second stage and there every added kg means a kg less payload.
well every added KG would mean 2.7 KG less payload. minor but we understood.what you meant .
The fins were added to add drag and more than controlled flight of the rocket. The rule of thumb is that aerobraking can kill a velocity approximately equal to the escape velocity of the planet where the aerobraking is performed 11 km/s for Terra, 5 km/s for Mars. That equals a lot of fuel. Robert Zubrin says mass of the heat shield and thermal structure should be about 15% of the total mass being braked. Which sounds like a lot, but is often much less that the propelant required to brake with rocket thrust.
Think like the EA6-B speed brake(sort of) or the tail structure of the shuttle.
The deceleron is an aileron that functions normally in flight but can split in half such that the top half goes up as the bottom half goes down to brake.
The use of two flaps per wing on the BFR, with one flap opening upwards and the other opening downwards, allows the most rapid deceleration while maintaining accurate control of the spacecraft. Flaps that open upwards create a downforce in addition to reducing air speed, thus forcing the spacecraft towards the ground; conversely, flaps that open downwards create an upforce which pushes the nose of the spacecraft into the air. Wing-mounted air brakes that open in both directions allow the opposing upward and downward forces to cancel each other out, creating resistance that forces the spacecraft to rapidly decelerate.
The material science behind this method is actually a lot simpler than aero brake/ capture. the downside is a failure would most likely result in a loss of craft.