Re: starship-design: Deceleration scheme

[Steve VanDevender <stevev@efn.org>]

Timothy van der Linden writes:
 > Steve,
 > 
 > > > I'm not sure what you mean with "things" but it simply is not true that
 > > > higher exhaust velocities are best.
 > >
 > >This is really very simple.
 > 
 > No, it is not, otherwise you'd have acknowledged my approach. I'm starting
 > to doubt if you've looked at what I did.
 > 
 > I've seen your calculations over and over, and know they are right, but only
 > if you care for a total energy (including restmass). We only care about
 > normal energy (like the kind you store in a battery, which excludes restmass).
 > The latter is what I minimized.
 > 
 > Ken has done a good job in displaying our diffence of approach. I can't tell
 > it more clear.
 > 
 > I'd which you'd just tell me that I'm wrong or right.

I've been meaning to get back to you on this.  I think you and Ken have
finally gotten me to see what you were talking about, and at least
intuitively I'm willing to accept that yes, you can minimize total
energy expenditure if you have a fuel with a low mass-energy conversion
ratio by using lower exhaust velocities and more reaction mass. This may
mean a much higher fuel-to-payload ratio but, as we all agree, high
conversion ratio fuels like matter-antimatter have their own
difficulties.  So I'll stop bugging you about that one, unless when I
get around to doing the math I can't duplicate your results.