Fun fact about #Starship. By doing the flip around 500m vs higher up like 2,000m, the difference in delta V is ~ 500 m/s! That's a 20 tonne fuel saving, which means basically 20 tonnes MORE you can put into orbit. That's more than a F9 has ever launched, just by flipping later!
Except it's crashed every time thus far.
A single Raptor puts out 2200kN of thrust at full throttle. That's enough thrust to provide a greater than 2:1 thrust to weight ratio of a dry Starship at 100 tons. Granted, a dry Starship has no fuel to put through said Raptor, and the engine reportedly burns about 600kg of propellant/oxidizer per second. The current maneuver at 500 meters needs 20 to 24 tons of fuel/ox to accomplish its goal when landing on 2 engines and performing the entire maneuver in a 20 second window.
Every ten seconds added to the burn is an additional 12 tons of fuel for 2 engines, or 6 tons for a single engine.
Starship's terminal velocity in belly flop orientation is about 100 meters/sec. Starting the burn on a single engine at 2000 meters and initiating the orientation change more slowly on a single engine will cost 15-20 seconds of additional burn time. As the engine gimbals to face downwards, it slows descent of the craft so that it is in air that much longer and needs that much more fuel to avoid falling out of the sky.
That single Raptor, working with 40 tons of fuel and a 100 ton Starship, has a TWR of 1.57. It's going to cancel out 5.7 meters/sec of downward velocity, and that number is going to climb every second since the ship gets lighter from burnt fuel. It'll take 17 seconds to cancel out vertical velocity this way, or about 10.2 tons of fuel. That 17 seconds offers lots of opportunity to assess engine health, and possibly spool the remaining engine(s) for an alternate landing solution.
Two Raptors have a TWR of 3.54 (100 ton craft and 24 tons fuel). Every second that two Raptors fire, they cancel out 25.4 meters/sec of downward velocity, and that number climbs every second as the ship gets lighter. Obviously takes a lot less time to hit 0 m/s from 100 m/s this way (4 seconds, or about 5 tons of fuel). But there's no margin for error.
Right now their whole landing maneuver is a sub-20 second burn, with flip. Musk's big talking point on this was redundancy when it comes to human rating this thing. When you need two engines for the TWR of the finished craft loaded with cargo, and you don't have time in your flight profile to spool the 3rd engine at some point in the landing approach, then you don't have redundancy.
I think paying the 10-20 tons of additional fuel penalty for the additional landing contingencies that a higher flip provides is worth it.
