Thinking about the no atmosphere caveat here made me think of Venus, which is the opposite of no atmosphere for solid/rocky bodies in our solar system.

Earth's low orbital velocity is about 7.8 km/s. It's common to tack on another 1 to 1.5 km/s for the gravity drag and to ignore atmospheric drag in comparison. It's true that modern vehicles often reduce thrust slightly near max-Q but it's not a huge effect.

But launching from the surface of venus with its 100 times higher atmospheric density and similar scale height poses a substantial penalty.

You could not accelerate at the same rate as Earth launches; you'd hit a brick wall from atmospheric drag, so you have to climb more slowly, and minimize the sum of the losses due to drag and gravity.

Is it possible to estimate how much larger these losses are on Venus compared to the roughly 1 km/s delta-v loss from Earth?

Has anyone already calculated how much slower you'd have to go at max-Q, or the number of extra minutes it would take to reach low Venus orbit (compared to Earth launch)?

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    $\begingroup$ Surely no one would launch from the surface of Venus in a rocket, at least a chemically powered one. Surely you'd use a balloon of some kind to get to the upper atmosphere and launch from there? $\endgroup$ – Steve Linton Sep 27 '19 at 8:54
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    $\begingroup$ @SteveLinton I'm asking because I am serious. And don't call me Shirley $\endgroup$ – uhoh Sep 27 '19 at 10:39
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    $\begingroup$ The dv from surface to low Venus orbit has been estimated at 27000m/s by at least one “solar system subway map” but I don’t know how that was arrived at. I can try it in my sim over the weekend but I suspect it’s going to be very dependent on how much heating you can take. I’ll probably use a Q limiting approach as a proxy for heat limiting. $\endgroup$ – Russell Borogove Sep 27 '19 at 15:57
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    $\begingroup$ @MagicOctopusUrn: driving to the mountains before takeoff is a widely-known trick for shaving delta-V off of Eve ascents in Kerbal Space Program $\endgroup$ – Jacob Krall Sep 28 '19 at 13:42
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    $\begingroup$ You’d need rockets that were not over expanded at 90 bar so your isp is going to be pretty terrible, at least for the first stage $\endgroup$ – Steve Linton Oct 4 '19 at 10:57

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