Lunar elevators

--- In spacesettlers@yahoogroups.com, Ian Woollard

> Maybe, although there are complications with a lunar rotovator that
> aren't present with a beanstalk to the same degree or at all.

Indeed there are :)

> For example, a rotovator stretches every time it goes down to the
> surface which can make for a wild ride,

IIRC, Hoyt compensates for this by the use of replaceable tethers.

> it's highly orbitally unstable ("MASCONS"), and you probably need to
> expend propellent just to keep it going.

This is where Hoyt proposes to have the the tether shift its mass in
orbit. He offers a treatment in the link I provided.

> Beanstalks are probably safer. There are concerns with
> micrometeorites cutting it, but hoytether concepts probably help
> with that. And beanstalks are nearer the state of the art.

As you point out, the micrometeorite threat of a beanstalk is
increased by its larger cross sectional area. The rotating tether
reels in and out and thus is at less risk.

By state of the art would you be referring to the engineering of a
static tower versus a dynamic system?

> > Lunavator = getting bases set up, delivering equipment, delivering
> > staff and supplies.

> > Mass Driver = getting tonnes of material into orbit

> Mass Driver == complicated, dangerous, expensive, one way, *small*
> payloads
> Beanstalk == cheap, passive, bidirectional, *big payloads*

Cheap versus expensive, well I'm not so sure about that. I'd need to
see more of your rationale for making the comparison to gauge whether
I buy into it or not. Big vs small payloads is dependent on design
criteria for both have capacity to increase payload size. Which is
easier to scale-up? Which has greater redundancy, one massive
beanstalk or multiple small payload mass drivers? The biggest omission
from your list is payload frequency:

Mass driver = 1/10th of a second or so.
Beanstalk = time for elevator to travel to orbit or beyond (weeks
according to the author).

> But the world isn't necessarily either-or. A beanstalk might be a
> good way to lower mass driver components to the moon for example. It
> enables mass drivers if they turn out to be a good idea.

I'm with you 100% on this statement. Mass drivers aren't practical for
delivering material to the surface. I actually favor, and have for the
last few years, a dual approach, each to their own strengths, and
drastically reducing rocket reliance.

I am, however, still very interested in the beanstalk vs rotating
lunavator trade-offs analysis. Does anyone have access to technical
reports on the beanstalk idea?

One thing that troubles me is that the author states the beanstalk
wouldn't be ideal for human transport because of the weeks long
journey. The lunavator center of mass orbits closer to the the moon
and only has to travel a few hundred km to get to the surface.

TangoMan