There's a lot of work being done just now on continuous low-thrust
interplanetary trajectory mechanics. I've read some of it, written by
Tadashi Sakai at Georgia Tech. But I prefer transfer orbits that use
"instantaneous" pulse delta-vees. The math is prettier, even with a course
correction or two.

http://sdebug.org/posts/transca.html
http://sdebug.org/posts/trans3.html

But I guess if you don't MIND waiting more than a year to get to where you
might have gone in less than a week, then it doesn't MATTER.

Not only do the more common high-thrust rockets use the instantaneous pulse
transfer orbit math, so do "mass drivers" which shoot metal jacketed loads
from magnetic induction catapults. Aside from science missions that must
sacrifice time because of extremely tight budgetary requirements, I think
that the "billiards" style of celestial mechanics will dominate the "race
car" style for a very long time yet.

Jerry Abbott


"Ugo" wrote in message
...
The ion engine used on the spacecraft is said to be 5-10 times more
efficient than an ordinary chemical booster. That is to say, it can
provide
5-10 times more thrust than a regular engine, with the same amount of
fuel.
The downside of the ion engine is that its thrust is _very_ gentle, so you
can't change your velocity very fast. While an ordinary booster can expend
all its fuel in a matter of seconds/minutes (which can be regarded as
instantaneous, compared to orbital periods in question here), an ion
booster
can take months to spend its fuel and accomplish the desired velocity
change. So, in contrast to sending a spacecraft to the target via a
standard
Hohmann transfer orbit (when you fire all your booster fuel at launch from
Earth parking orbit, aiming the apogee at the Moon's orbit), you have to
keep the ion engine running a long time and you basically end up with a
very
long spiraling orbit to the Moon, which starts at Earth parking orbit and
ends at the Moon's orbit. That's pretty much the whole idea, though in
reality things get more complicated by the Moon's gravitational
perturbations...

--
The butler did it.