This website claims to be an excerpt from NAS9-17779 about exploring
Phobos:

http://fti.neep.wisc.edu/neep602/LEC16/neal.html7

But it says stuff like:

"(2) Crew vehicle tethered to surface from 30 - 50 m height (3-point
tether system for energy conservation)"

How is a mass supposed to just hang up there 30 - 50 m off the
surface of Phobos? Why? Is this really a NASA document?

Flymuffins wrote:

>"(2) Crew vehicle tethered to surface from 30 - 50 m height (3-point
tether system for energy conservation)"

It does sound a bit weird. This caught my eye:

"Given the decay of the Phobos orbit, will landing, EVA, or spiking
significantly perturb it?"

Hmmm...Phobos masses about 1.08*10^16 kg. Say four billion loaded
supertankers, or one and a half million Great Pyramids of Cheops. ;-)
There's no way anything "significant" could be done to Phobos orbit,
short of NASA taking the world's nuclear arsenal, Bruce Willis and some
dodgy Hollywood effects there. ;-)

>How is a mass supposed to just hang up there 30 - 50 m off the
surface of Phobos? Why? Is this really a NASA document?

If the mass is tethered on the far side of Phobos, and forced to
co-orbit (in a higher-but-slower track round Mars), then there would be
a net tension on the cable(s), just like there would be on an asteroid
tethered at the "far" end of an Earth orbital tower, beyond the
geosynchronous point. At some altitude the tension on the tether will
balance the local gravitational attraction of Phobos...but my (early
morning) spreadsheet for this case suggests that altitude is nearer
3.2km above the surface of Phobos and not lower.

Is it a NASA document? Don't know. It's a very poor summary if it is.

Regards,

Andy G

> >How is a mass supposed to just hang up there 30 - 50 m off the
> surface of Phobos? Why? Is this really a NASA document?
>
> If the mass is tethered on the far side of Phobos, and forced to
> co-orbit (in a higher-but-slower track round Mars), then there would be
> a net tension on the cable(s), just like there would be on an asteroid
> tethered at the "far" end of an Earth orbital tower, beyond the
> geosynchronous point. At some altitude the tension on the tether will
> balance the local gravitational attraction of Phobos...but my (early
> morning) spreadsheet for this case suggests that altitude is nearer
> 3.2km above the surface of Phobos and not lower.
>

Is Phobos tidally locked to Mars, or does it rotate on its axis? If it
rotates, maybe a 50-meter cable would be all that is needed to float the observatory.

Steve

Hi Steve!

>Is Phobos tidally locked to Mars, or does it rotate on its axis? If it
rotates, maybe a 50-meter cable would be all that is needed to float the
observatory.

It's tidally locked, long end towards Mars.

Andy G

I've been looking around for awhile for good information about
working on asteroids, but all I ever find is stuff like this.
Without any decent research material, and no real, out-of-world
experience, how will any equipment ever get designed?

I wish there was some way to do something like the MIT student
competitions in robotics. But where would the competition be held?
Would 20 seconds in a vomit comet be enough time to test student
designs? Or would they all compete against each other in a computer
simulation? Or should they all just be launched to an asteroid?!

Well, if I'm the next NASA administrator, I'll set up a competition
with some combination of these!

--- In spacesettlers@yahoogroups.com, "Andrew Goddard"
wrote:
> Flymuffins wrote:
>
> >"(2) Crew vehicle tethered to surface from 30 - 50 m height (3-
point
> tether system for energy conservation)"
>
> It does sound a bit weird. This caught my eye:
>
> "Given the decay of the Phobos orbit, will landing, EVA, or spiking
> significantly perturb it?"
>
> Hmmm...Phobos masses about 1.08*10^16 kg. Say four billion loaded
> supertankers, or one and a half million Great Pyramids of
Cheops. ;-)
> There's no way anything "significant" could be done to Phobos
orbit,
> short of NASA taking the world's nuclear arsenal, Bruce Willis and
some
> dodgy Hollywood effects there. ;-)
>
> >How is a mass supposed to just hang up there 30 - 50 m off the
> surface of Phobos? Why? Is this really a NASA document?
>
> If the mass is tethered on the far side of Phobos, and forced to
> co-orbit (in a higher-but-slower track round Mars), then there
would be
> a net tension on the cable(s), just like there would be on an
asteroid
> tethered at the "far" end of an Earth orbital tower, beyond the
> geosynchronous point. At some altitude the tension on the tether
will
> balance the local gravitational attraction of Phobos...but my
(early
> morning) spreadsheet for this case suggests that altitude is nearer
> 3.2km above the surface of Phobos and not lower.
>
> Is it a NASA document? Don't know. It's a very poor summary if it
is.

From: flymuffins [mailto:flyingmuffins@...]

"I've been looking around for awhile for good information about
working on asteroids..."

`Mining the Sky', by John S. Lewis, is a good layman's book on the subject.
If you want something more technical, there's `Resources of Near-Earth
Space', published by the University of Arizona Press of Tucson. (Prof. Lewis
is one of the authors here, also.) And, there's a multi-volume book set
titled `Space Resources', by Mary Fae McKay, David S. McKay, and Michael B.
Duke. It's available on-line at:
http://lifesci3.arc.nasa.gov/SpaceSettlements/ along with several other
books. If you want it in hard copy, you'll find it at amazon.com. There's
another book by the same title -- yet another John Lewis book -- but since
it was published in `87, I suspect his titles I listed above would be better
choices.

Dave

"Washington D.C., a delightful city that combines the best of southern
efficiency and northern hospitality" -- John S. Lewis

> is one of the authors here, also.)<

You're at UofA?

I've have 'Mining the Sky'. As far as I remember, it has lots of
info about asteroids and the types of resources that are there and
such, but it left me wondering how machines were going to be
designed and tested for the job at hand. As far as I can tell, no
one has ever built any type of machine that can gather ore from an
asteroid.

--- In spacesettlers@yahoogroups.com, "Dave Logsdon"
> From: flymuffins [mailto:flyingmuffins@y...]
>
> "I've been looking around for awhile for good information about
> working on asteroids..."
>
> `Mining the Sky', by John S. Lewis, is a good layman's book on the
subject.
> If you want something more technical, there's `Resources of Near-
Earth
> Space', published by the University of Arizona Press of Tucson.
(Prof. Lewis
> is one of the authors here, also.) And, there's a multi-volume
book set
> titled `Space Resources', by Mary Fae McKay, David S. McKay, and
Michael B.
> Duke. It's available on-line at:
> http://lifesci3.arc.nasa.gov/SpaceSettlements/ along with several
other
> books. If you want it in hard copy, you'll find it at amazon.com.
There's
> another book by the same title -- yet another John Lewis book --
but since
> it was published in `87, I suspect his titles I listed above would
be better
> choices.
>
> Dave
>
> "Washington D.C., a delightful city that combines the best of
southern

> At some altitude the tension on the tether will
> balance the local gravitational attraction of Phobos...but my
(early
> morning) spreadsheet for this case suggests that altitude is nearer
> 3.2km above the surface of Phobos and not lower.
>

3.2km? Wow! That's not as far as I thought. I knew Phobos was
close to breaking up, but not that close.

AND, one of the good points made in this paper was that the Mars
facing side was the comfortable side to explore.

Hopefully with NASA's new mission, some better papers will come out.

From: flymuffins [mailto:flyingmuffins@...]

> is one of the authors here, also.)<

"You're at UofA? "

Nope. The "here" in my post was referring to `another book here in the
post', not my location. Sorry for the confusion.

"I've have 'Mining the Sky'. As far as I remember, it has lots of info
about asteroids and the types of resources that are there and such, but it
left me wondering how machines were going to be designed and tested for the
job at hand. "

Although Chapter Six gives some general ideas about what's needed, you're
correct that there aren't any real details of specific equipment designs.

Dave

> Although Chapter Six gives some general ideas about what's needed,
you're
> correct that there aren't any real details of specific equipment
designs.
>

Well then, the time is now! How are these things going to be
designed and tested?

Even flying them on vomit comet would be expensive for me. I just
saw on TV you can rent a flight for $70K. And then you need a
simulated surface for the robot to work on, but that's a big unknown
too.

Or would a computer simulation be a good first step? Dirt is a
strange thing to simulate though...

From: flymuffins [mailto:flyingmuffins@...]

"Well then, the time is now! How are these things going to be
designed and tested? ... Or would a computer simulation be a good first
step? Dirt is a strange thing to simulate though... "

Practically everything gets designed on computer these days so I'd
say that'll be one of the first steps. Since mining and construction
equipment is also designed that way, I'd be surprised if there weren't
simulations to accommodate quite a variety of soils/regoliths/rock etc. Your
point about the `vomit comet' is well taken; I suspect the micro-gravity
issue will be the biggest design problem.

Dave