When you're trying to leave a gravity well (such as Earth's), then thrust deep in the well has a higher effective ISP than equivalent thrust higher up the well.
Doesn't the Oberth effect refer to thrusting while passing near a gravity well (i.e. a Gravity Assist [wikipedia.org]), not accelerating from the bottom of a gravity well from rest? Given that a launching rocket starts with zero velocity, wouldn't ISP be the lowest at the beginning of the ascent, due to the massive amount of propellant needed to being accelerating?
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When you're trying to leave a gravity well (such as Earth's), then thrust deep in the well has a higher effective ISP than equivalent thrust higher up the well.
Doesn't the Oberth effect refer to thrusting while passing near a gravity well (i.e. a Gravity Assist [wikipedia.org]), not accelerating from the bottom of a gravity well from rest? Given that a launching rocket starts with zero velocity, wouldn't ISP be the lowest at the beginning of the ascent, due to the massive amount of propellant needed to being accelerating?