dhanson865
Well-Known Member
Can someone please explain what 'hot landing' means?
It takes less fuel to brake at the last possible instant before landing (the term involved in that math is "gravity losses"). Because of this the faster the booster is traveling at altitude the faster it'll be 1 second before landing and or the less fuel they have left the faster it'll come in for landing. They'll burn as hard as necessary the last possible moment to conserve fuel.
Softer landings have lots a fuel leftover from the lighter payload for that mission and use one engine for a longer burn and come in slower. Less risk, less stress, more likely to be able to reuse that first stage.
Harder landings have less fuel leftover from a heavier payload to orbit (or a payload to a higher orbit) and use 3 engines to burn less time but put out more thrust (3 times the engines at more than minimal thrust means more than 3 times the heat). The engines can be run at a wide throttle range so there is a big difference in exhaust flames/temperature of the engine bell depending on throttle amount and length of the burn in time.
It's not just an expression there literally is more stuff burning / more flames at the last second if the booster is "coming in hot". It also puts more stress on the rocket in terms of heat, vibration, G force during burn, and possibly at time of impact (when it actually touches down).
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