[meteorite-list] MIND BLOWING

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sun, 15 Jul 2007 00:39:18 -0500
Message-ID: <00e601c7c6a2$7e1e1210$ac2ee146_at_ATARIENGINE>

Hi, Chris, Michael, Pete, List,
    and any interested Martians...


The mass of the air collected by the vane or the
mechanical collecting element of any wind-driven
device is a function of the area A of the collector
times the velocity V of the wind bringing the air
to the vane times the density D of the atmosphere, or

M = A x V x D

The kinetic energy of any moving mass is

E = ( M x V x V ) / 2.

Substituting in the above equation, we see

E = (A x D x V x V x V ) / 2

Yes, the energy scales as the cube of the velocity
AND directly as the area of the collector AND
directly as the density of the atmosphere. Since
the effective density of the Martian atmosphere is
1/81 of the Earth's, IF we made the collector vane area
81 times bigger than we would on Earth, the device
would have the SAME power available at the SAME
wind velocity on both Mars and the Earth.

This was essentially Michael's point, which I will
summarize as "Just make the sucker bigger!" All we
have to do is design the Mars Walker to be suitable
for Mars, but it's just engineering adjustments, no
big deal.

As for the actual wind speeds on Mars, guess what,
not much in the way of measurement has been made:
"The landers based on flat areas observed normal
light 'night time' winds of 2m/s, and stronger noon
winds of 6-8 m/s, but they are nothing compared
with quite common winds generated near mountain
slopes, at maximum these can reach 20 m/s speeds.
However, during dust- devils and storms an exposed
surface on Mars can really be sand blasted: Viking
lander 1 saw a local dust storm with peak wind speed
values of 20-30m/s, and other observations have
found speeds up to 50 m/s." However Pathfinder
experienced strong winds only at night and very light
winds in the daytime.

Here's a discussion of the LACK of windspeed data
from the Phoenix Mars Mission Blog:
http://foreleast.lpl.arizona.edu/blogsPost.php?bID=54
In a word, we don't know by direct measurement what
the wind speeds are, but we do know the dust storms
are nasty. The Mars Walker had better be tough. However,
it can protect itself from high winds by re-positioning its
wind collectors to minimum resistance positions and then
hunkering down on its multitude of legs to reduce its
cross section.

The Walkers in the video are very well-engineered for
"art devices" but I suspect the use of high-tech materials
and lots (a couple of hundred) of localized microprocessors
for each leg and each collector and steering and searching
would produce an awesome machine. These machines walk
"with the wind," but they could easily be made to go against
the wind or in any direction, to maneuver.

It could look for Martian meteorites, among the long list
of things to look for on Mars.


Sterling K. Webb
----------------------------------------------------------
----- Original Message -----
From: "Chris Peterson" <clp at alumni.caltech.edu>
To: <meteorite-list at meteoritecentral.com>
Sent: Saturday, July 14, 2007 10:26 PM
Subject: Re: [meteorite-list] MIND BLOWING


Hi Sterling-

If you give it some more thought, you'll probably figure out that the
potential energy of wind scales as the cube of velocity, not the square.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


----- Original Message -----
From: "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>
To: "Pete Pete" <rsvp321 at hotmail.com>; <mlblood at cox.net>;
<meteorite-list at meteoritecentral.com>
Sent: Saturday, July 14, 2007 6:28 PM
Subject: Re: [meteorite-list] MIND BLOWING


> Hi, Pete, Michael, List,
>
> The first thing I thought of was... Mars, just like
> you. But the air thereabouts is awful thin. I guess
> it's calculator time.
> The density (or pressure) of the Mars atmosphere
> is only about 1/100 of the Earth's. How a wind "feels"
> to an object in its path is dependent on the density of
> the wind (the number of molecules per unit volume)
> and the velocity of the wind. The momentum of the
> wind is the density (really the mass of the molecules in
> the wind added together) times the velocity of the wind.
> So, an object on Mars will encounter wind with 1/100
> the momentum of wind on the Earth traveling at the
> same velocity. That means the wind on Mars has to be
> traveling a 100 times faster than the wind on Earth to
> have the same momentum.
> However, the kinetic energy content of the wind is
> dependent on the velocity of the wind squared (or
> E = (M x V x V)/2, so the wind on Mars only has
> to travel about 10 times as fast to make up for the
> difference in density.
> Mars atmosphere is mostly CO2, a heavy molecule.
> It's not the same as the Earth's atmosphere. The details
> are the density of the atmosphere at the surface of Mars
> is only 81 times smaller than Earth's. Therefore, to "feel"
> the force of a breeze on Mars of the same force as on Earth,
> we would require 9 times the wind velocity (square root
> of 81). For example, to "feel" a light breeze of about 10
> miles/hr on Earth, would require "hurricane speed" winds on
> Mars of 90 miles/hr.
> It's obvious from the video that these walkers require
> as much wind as they can get, here on Earth, or they wouldn't
> be walking on a windy beaches! Here's another complication.
> The gravity on Mars is only 38% of Earth's, so it only takes
> 38% of the force to lift a "foot" up. The walker only "weighs"
> 38% of what it would on Earth. Maybe a "Mars Walker" would
> only require a wind about 5.5 times faster than an Earth wind
> to get the same motive force. [The "mass" is the same but
> the force of Martian gravity only resists its motion 38% as
> much as Earth's gravity does. However, the inertia is the
> same on both planets, something to remember when you
> go for a walk on Mars.]
> The gravity may be less, but a Mars Walker would need
> to carry a lot of extra mass: solar panels for the cameras,
> radios, experiments, and other instruments, and weigh means
> more force and energy is needed. My guess is that a Mars
> Walker is a difficult and marginal thing. What I need now is
> a long term weather report on Martian wind speeds... from
> all over the planet.
>
>
> Sterling K. Webb

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Received on Sun 15 Jul 2007 01:39:18 AM PDT