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**Jorge R. Frank**

(Henry Spencer) wrote in
:

In article ,
Jorge R. Frank wrote:
So a dense-propellant SSTO doesn't really need less delta-V to reach
orbit, but you use a smaller delta-V term when modelling one using the
rocket equation.

Depends on whether you think of delta-V as the actual change in
velocity, or as the change the vehicle could achieve in ideal
conditions -- that is, a measure of vehicle performance or required
vehicle performance.

The latter is often the more useful view.

No doubt about it. But it can be confusing - especially to one with an
orbital mechanics background who hasn't worked vehicle ascent-performance
issues - and especially when you don't label your delta-Vs as "actual" or
"ideal". I understood what you were getting at, but can understand why Herb
didn't. I'm not disputing anything you wrote, just disputing Paul Dietz's
assertion that you'd explained the issue completely.

So I would phrase it a bit differently. The dense-propellant SSTO has
to achieve the same orbital velocity, but its gravity losses are lower
(as are its drag losses, although that's less important), so the total
delta-V the vehicle must deliver (equal to the velocity it could
achieve in drag-free gravity-free space) is lower.

That works for me too.

--
JRF

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