Sampling Mars Surface???

G=EMC^2 Glazier wrote:

Now lets take that same steel wheel and put
weight on it(say 40 LB) Now that you have figured out how little area
is pressing "up" against this wheel you must conceive it will be pushed
down into dust,and fine sand(YES) A turning wheel can only make
conditions worse,for it digs a hole for itself.

The main reason a wheel will dig itself into sand is uncontrolled
spinning. With independent drive motors for each wheel and some kind
of computerized 'traction control system' the risk of getting stuck
is low in comparison to that with a conventional drive-train
arrangement. As you pointed out, the rovers aren't in a race; each
manoeuvre can be planned in advance and monitored during execution.

--
Odysseus

Hi Odysseus Well we both agree that wheels will dig into sand if they
are spinning in place. You also say since the rover is moving
very slow and we can see where it is going we can do the steering.At a
distance that creates a big time lapse(especially for controlling the
rovers) Steering means making choices. What if the rover is
surrounded by rocks when it lands(pictures of Mars surface makes this
likely) Now we pick a direction that looks best,and the rover moves ,
but a half hidden rock with a bad shape(bad angle to it) stops the rover
from moving. We see the wheels are digging in. Form the time we see
this,and want the wheels to stop spinning,and back the rover away from
this rock "how long well this take?" Moby likens this to the Titanic
He told that ship was going at 35 knots and even if the captain saw the
iceberg from a half mile away he could not stop the ship in time.
Moby is an expert on inertia. Bert

Bert posted:

Now we pick a direction that looks best,and the rover moves ,
but a half hidden rock with a bad shape(bad angle to it) stops the rover
from moving. We see the wheels are digging in. Form the time we see
this,and want the wheels to stop spinning,and back the rover away from
this rock "how long well this take?"

Bert, the rover has software in it to monitor whether things are slipping or
when the rover isn't moving properly. It can change the way the power is
being distributed to the various motors on each wheel or change their
direction. If it keeps having a problem, it will stop and radio home for
instructions. I strongly doubt that the wheels will spin enough to "dig" the
rover in.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 10th Annual NEBRASKA STAR PARTY *
* July 27-Aug. 1st, 2003, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

David That sounds like my $19.95 plus tax toy train. I know the rovers
had a lot of built in safety features. Time lapses have killed a lot of
people. Did I not prove by my fast pictures that inertia creates a time
lapse. It takes 3 minutes to see what direction the rover is going,it
will take another 3 minutes to change the direction. Well that means
6 minutes. Good thing it is not on Neptune. Bert

G=EMC^2 Glazier wrote:

It takes 3 minutes to see what direction the rover is going,it
will take another 3 minutes to change the direction. Well that means
6 minutes. Good thing it is not on Neptune. Bert

There's no time-lapse for the on-board computer, though. Electric
motors are extremely responsive, so a wheel that's losing traction
can be 'locked' within milliseconds of the computer's detecting a
problem. Once mission control tells the rover where to go -- maybe a
point just a few metres away -- it should be able to proceed on its
own or, as David says, stop and wait for instructions if the
manoeuvre isn't going according to plan. OTOH if there's a sudden
change in circumstances, perhaps a landslide on an unstable slope,
the six-minute reaction time could be a problem. Let's hope the
controllers are good enough at reading the terrain to keep the
vehicles away from dangerous areas.

--
Odysseus

Odysseus and David We seemed to have gone from a micro wave oven size
rovers to a size of a golf cart. I have thoughts that this might not
been to wise,since we are novices. I'm not only worried about size I'm
worried about weight. I don't like all that volcanic ash(like
talcum powder) Sand that has been abrased down to the size of dust.
Still I'm a gambler and would have had one of the rovers land smack in
the middle of the North Pole. I wonder if dry ice is slipery? If it
is(most likely) than we would not have to argue about tracks or
wheels,for skates would be best. I would go however with the engineering
of a toboggan,and David who has Mar's water on his brain would go with
pontoons Bert

Bert posted:

I'm not only worried about size I'm
worried about weight.

The weight isn't excessive. Again, if the mock-up rover can drive around on
the obstacle course that JPL set up for it, it will have little trouble moving
about on Mars.

I don't like all that volcanic ash(like
talcum powder) Sand that has been abrased down to the size of dust.

For the last time, IT ISN'T VOLCANIC ASH!!! It is fine dust weathered down
from smaller rock particles.

I would go however with the engineering
of a toboggan,and David who has Mar's water on his brain would go with
pontoons

Water on the brain eh? Do you even USE your brain Bert? It doesn't look like it.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 10th Annual NEBRASKA STAR PARTY *
* July 27-Aug. 1st, 2003, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

David Don't shout. I can see small letters. The Earth's Volcanoes give
out ash. Mars we know has volcanoes. Ash is rather heavy. Why are you so
mad that it could be on the ground? I'm sure some might have been blown
into space,and here on Earth we see it as shooting stars (why not?)
Billion times better chance of that than picking up a Mars rock.
David I always liked smaller and lighter for space. It goes with the
bigger they are the harder they fall. That is why a cockroach can be
thrown from a plane at 35,000 ft and hit the ground running. Bert

David Don't shout. I can see small letters. The Earth's Volcanoes give
out ash. Mars we know has volcanoes. Ash is rather heavy. Why are you so
mad that it could be on the ground? I'm sure some might have been blown
into space,and here on Earth we see it as shooting stars (why not?)
Billion times better chance of that than picking up a Mars rock.
David I always liked smaller and lighter for space. It goes with the
bigger they are the harder they fall. That is why a cockroach can be
thrown from a plane at 35,000 ft and hit the ground running. Bert

Bert blurted out:

Why are you so
mad that it could be on the ground?

Because *you* keep getting it wrong!! Mars does not have volcanoes all over
its surface. The dust is not volcanic ash (unless you are talking about the
volcano and the area immediately around it. The dust is weathered rock
(created mostly by impacts, wind, temperature variations and water). Volcanic
ash is *different* from the Martian dust, just as dust and sand here on Earth
are different from volcanic ash. You just can't seem to get that right. Go
read a book on geology and you might learn the difference (but somehow, I
don't think you will do this).
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 10th Annual NEBRASKA STAR PARTY *
* July 27-Aug. 1st, 2003, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************