Zubrin citisism

Lol, it makes much more sense if I read it right. Turns out we're
saying essentially the same thing as far as I can tell. The only
difference is that you're implicitly assuming the impulse is small
relative to the momentum of the habitat, as in the case of an actual
colony launching any realistic payloads, whereas I'm interested in
allowing for the possibility of a small station that catches and
relaunces large payloads.

--- In spacesettlers@yahoogroups.com, Ian Woollard
wrote:
>
> No, no. I meant you fire the *projectile* at 90 degrees to the
orbital
> plane of the habitat!
>
> The idea of trying to make a habitat do a 90 degree turn... that
> wouldn't work at all in any short timescale.
>
> On 11/7/05, Dan Wylie-Sears wrote:
> > Good site. But a transfer orbit isn't relevant, because I'm
> > precisely trying *not* to change the apogee and perigee. I want
to
> > launch payloads from a station while keeping the same orbit. Or
to
> > catch payloads launched from somewhere else, again without
messing
> > up your orbit.
> >
> > What I'm talking about is illustrated nicely on that page, if you
> > scroll down slightly to the heading "Orbit Plane Changes". I'm
> > saying you can make a plane change, go around half an orbit, and
> > make another plane change back to the plane you started in. Ian
> > mentioned out that you can do it for a ninety-degree plane
change,
> > and I'm trying to argue that you can do it for any angle.
> >
> > --- In spacesettlers@yahoogroups.com, Ryan Z wrote:
> > >
> > > Dan,
> > >
> > > Your making this way to complicated. A quick
> > > tutorial on orbital mechanics should clear things up.
> > > Here is a decnt one:
> > > http://www.braeunig.us/space/orbmech.htm#maneuver
> > >
> > > Basically, to do an orbital change to a higher
> > > orbit, you do a delta-v change putting you at the
> > > perigee of the new orbit which has an apogee of the
> > > orbit you wish to be at. You then do a delta-v change
> > > at the apogee of the orbit and you are now in the new
> > > orbit. Switch apogee and perigee around and that is
> > > how you move to a lower orbit.
> > >
> > > Hope that helps!
> > >
> > > Ryan
> > >
> > > --- Dan Wylie-Sears wrote:
> > >
> > > > Me:
> > > > >> it shouldn't depend on the angle being 90
> > > > degrees.
> > > >
> > > > Ian Woollard:
> > > > > No, it sort of does.
> > > >
> > > > Ok, you well may be right, given the number of
> > > > mistakes I've been
> > > > making lately. But where does the following
> > > > reasoning go wrong?
> > > >
> > > > (1) Given any orbit and any point on that orbit, you
> > > > can draw a line
> > > > through that point and the center of the
> > > > primary.
> > > >
> > > > (2) That line intersects the orbit again an equal
> > > > distance from the
> > > > primary on the other side (call it point two).
> > > >
> > > > (3) Given any angle, there's a plane intersecting
> > > > the plane of the
> > > > original orbit with that dihedral ange.
> > > >
> > > > (4) In that plane, there's an orbit just like the
> > > > original orbit
> > > > except for being in a different plane.
> > > >
> > > > (5) That orbit (call it orbit two) also passes
> > > > through point two.
> > > >
> > > > (6) A body in orbit one at point one has a
> > > > particular momentum (call
> > > > it m1). A body of the same mass in orbit two at
> > > > point one has a
> > > > momentum (call it m2). The difference m2 minus
> > > > m1 specifies an
> > > > impulse such that if that impulse is exerted at
> > > > that point the
> > > > body will go from orbit one to orbit two.
> > > > Because m1 and m2
> > > > have the same magnitude, this impulse is in the
> > > > plane that
> > > > bisects the dihedral angle. It's also
> > > > perpendicular to the line
> > > > through the primary.
> > > >
> > > > (7) Likewise at point two.
> > > >
> > > > (8) The two impulses do not in general have the same
> > > > magnitude, but
> > > > they're in the same plane and perpendicular to
> > > > the same line,
> > > > and hence have the same direction.
> > > >
> > > > > You also have to be careful to put the projectile
> > > > into escape-
> > > > > otherwise it often comes back at you an orbit
> > > > later- and at the
> > > > > same speed you fired it at!
> > > >
> > > > This is true when you're launching from a fixed
> > > > location like the
> > > > lunar poles (although in that case it will hit the
> > > > surface somewhere
> > > > else first unless you're launching horizontally).
> > > > But otherwise it
> > > > will come back to where you were and you won't be
> > > > there any more.
> > > > Still, it's a hazard because the orbital periods may
> > > > have a small-
> > > > integer ratio, or close enough that your size makes
> > > > up the
> > > > difference.
> > > >
> > > > --- In spacesettlers@yahoogroups.com, Ian Woollard
> > > > wrote:
> > > > >
> > > > > On 11/5/05, Dan Wylie-Sears wrote:
> > > > > > If I'm visualizing right (this time, for a
> > > > change) it shouldn't
> > > > > > depend on the angle being 90 degrees.
> > > > >
> > > > > No, it sort of does. If you angle it with the
> > > > orbit too much you
> > > > end
> > > > > up changing apogee or perigee of your orbit-
> > > > you're trying not to
> > > > do
> > > > > that I think.
> > > > >
> > > > > You also have to be careful to put the projectile
> > > > into escape-
> > > > > otherwise it often comes back at you an orbit
> > > > later- and at the
> > > > same
> > > > > speed you fired it at!
> > > > >
> > > > > Me, I don't like punching holes in my windows, for
> > > > one thing they
> > > > keep
> > > > > the suction out of the habitat. I'm funny like
> > > > that.
> > > > >
> > > > > --
> > > > > -Ian Woollard
> > > > >
> > > > > "People are brilliantly stupid, and stupidly
> > > > brilliant"-Robin
> > > > Abrahams
> > > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > >
> --
> -Ian Woollard
>
> "People are brilliantly stupid, and stupidly brilliant"-Robin
Abrahams