Questions about "The High Frontier"

Mike Combs wrote:

"Hop David" wrote in message
...

Nyrath has mentioned recent research on tolerance to angular velocity. It
indicates humans can tolerate higher rpms if transition is gradual. 4 as
opposed to 1 rpm would mean a sixteen fold difference in radius length.


Seems to suggest that Winkler was being overly-conservative when he insisted
that anything over 1 RPM would be a mistake.


I believe a 1 RPM ceiling is overly-conservative but I acknowledge it is
still not settled. More research needs to be done.

Hop

Damien Valentine wrote:

So. The consensus to the SPS question seems to be that such a project
is technically possible, but economically impossible, in much the same
way that...say...we could theoretically power the whole developed
world with billions of hamsters running around in really big wheels.

I don't see this consensus.

You're ignoring some considerations.

Coal and petroleum put carbon into the atmosphere. There are costs for
these energy sources not shown at the gas pump or in your utility bill.

Coal, petroleum and nuclear are all limited energy sources. Space based
solar also is also limited but the limit is far higher.

The infra structure for making SPS would give us other options. It would
make the rest of the solar system much more accessible.

SPS isn't competitive with conventional power sources in the short term.
But it is a good long term investment, in my opinion.

Hop

Mike Combs wrote:

"Hop David" wrote in message
...

Mike Combs wrote:


... If one's society ultimately fails (or just consistently performs
poorly), it would have to be a result of its underlying philosophy. In a
space habitat, one could hardly blame resource depletion, an energy
crisis, population pressures, a crop failure, or inconvenient location.

I don't agree.

Should the cloud of habs spread through NEAs and the main belt, there will
be a wide spectrum of fortunes. Some colonies may be situated near a two
lobe asteroid, one lobe being nickel-iron rich in platinum group metals,
the other lobe having water, ammonia and lots of hydrocarbons. This could
be a very wealthy hab. Other habs may be eking it out near big chunks of
silicon.


Well, that gets us back to the "inconvenient location" part of what I said.
My point being of course that, unlike nations here on Earth which cannot
change their locations, orbital habitats will be able to adjust their orbit
to something more advantageous.

An orbital habitat would need some delta vee capability for station
keeping. But a hab with enough delta vee capability to leave its
neighborhood for another is a taller order.

Hop

: Erik Max Francis
: That's centripetal/centrifugal acceleration, not force.

In what sense is there any centrifugal acceleration going on?


Wayne Throop http://sheol.org/throopw

Wayne Throop wrote:

: Erik Max Francis
: That's centripetal/centrifugal acceleration, not force.

In what sense is there any centrifugal acceleration going on?

A centrifugal pseudoforce corresponds to a centrifugal
pseudoacceleration, related simply by F = m a. The acceleration was
given as a positive scalar, so it could be viewed as either (he said it
was the "centrifugal force," which is clearly wrong). Only if it were
expressed as a vector would it be clearly a centripetal or centrifugal
acceleration (-omega^2 r r^ or omega^2 r r^, respectively).

I know what you're saying, which is that pseudoforces are usually
expressed in terms of forces, not accelerations, and
pseudoaccelerations/pseudoforces are fictitious anyway. But they're
equivalent, and often you use the centripetal acceleration to figure out
what the centrifugal _pseudoacceleration_ is (they're equal and
opposite), and from that compute the pseudoforce by multiplying it by
the mass of the object in question.

--
Erik Max Francis && && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM, Y!M erikmaxfrancis
Can I walk with you / Through your life
-- India Arie

::: That's centripetal/centrifugal acceleration, not force.

:: In what sense is there any centrifugal acceleration going on?

: Erik Max Francis
: A centrifugal pseudoforce corresponds to a centrifugal
: pseudoacceleration, related simply by F = m a.

But you just got done dismissing the notiono of calling a pseudoforce a
"force", so why are you calling a pseudoacceleration an acceleration.
And of course, no physical objects is undergoing a centrifugal
pseudoacceleration in either the rotating frame, nor centrifugal
acceleration in the inertial frame.

Hm. Possibly you mean, some object *would* undergo a centrifugal
pseudoacceleration if you dropped it? Which is OK. But why
is it OK to call that an acceleration but not OK to call the
thing-related-to-it-by-F=ma a force?

: I know what you're saying, which is that pseudoforces are usually
: expressed in terms of forces, not accelerations, and
: pseudoaccelerations/pseudoforces are fictitious anyway.

Well... no, a smaller nit that that even. I'm just confused
as to what distinction you draw between "accelerating in the
rotating frame" and "force int he rotating frame", such that it's
OK to call the one an "acceleration", but not to call the other
a "force".

: But they're equivalent, and often you use the centripetal acceleration
: to figure out what the centrifugal _pseudoacceleration_ is (they're
: equal and opposite), and from that compute the pseudoforce by
: multiplying it by the mass of the object in question.

Well... the pseudoforce IS pseudo because there's no equal and opposite
reaction to it. It's an artifact of the coordinates. And there never
really was an equal-and-opposite deal with accelerations, so I'm not
following that. In the inertial frame, there's a centripetal force
exterted by the hab on the feet of somebody standing in it, and there's
an equal and opposite centrifugal force exerted by those feet on that
hab. But accelerations? In the inertial frame both feet and hab are
undergoing centripetal acceleration, and neither is undergoing
centrifugal acceleration. In the rotating frame, of course,
neither feet nor hab are accelerating at all.

So anyways... I'm a bit confused as to what you mean by there being
no centrifugal force, but there maybe is a centrifugal acceleration.
I can't make anything come out that way no matter how I look at it.


Wayne Throop http://sheol.org/throopw

Wayne Throop wrote:

But you just got done dismissing the notiono of calling a pseudoforce a
"force", so why are you calling a pseudoacceleration an acceleration.

No, I just got done pointing out that a force isn't the same as an
acceleration. I was pointing to something that was called a force, but
had units of acceleration.

Well... no, a smaller nit that that even. I'm just confused
as to what distinction you draw between "accelerating in the
rotating frame" and "force int he rotating frame", such that it's
OK to call the one an "acceleration", but not to call the other
a "force".

I made no such distinction.

--
Erik Max Francis && && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM, Y!M erikmaxfrancis
Man is a clever animal who behaves like an imbecile.
-- Albert Schweitzer

:: But you just got done dismissing the notiono of calling a pseudoforce
:: a "force",

: Erik Max Francis
: No, I just got done pointing out that a force isn't the same as an
: acceleration. I was pointing to something that was called a force,
: but had units of acceleration.

Ah. You fooled me by beeing too straightforward.
Or alternatively, I didn't see it because it was hidden
right under my nose.

Though... there's still no centrifugal acceleration going on
in circular motion, in either inertial or rotating coordinates.
Ha! So there! Take that!

Unless you're hiding something else under my nose.
Like, an object dropped while in circular motion.


Wayne Throop http://sheol.org/throopw

Wayne Throop wrote:

Ah. You fooled me by beeing too straightforward.
Or alternatively, I didn't see it because it was hidden
right under my nose.

Simplicity is the best trickiness.

--
Erik Max Francis && && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM, Y!M erikmaxfrancis
Man is a clever animal who behaves like an imbecile.
-- Albert Schweitzer

Erik Max Francis wrote:

Hop David wrote:

Agreed. Even more importantly, human tolerance to angular velocity
(revolutions per minute) needs to be determined.

Centrifugal force is w^2 * r, w being angular velocity and r being
radius.


That's centripetal/centrifugal acceleration, not force.


Right you are. It's meters/sec^2, not kg meters/sec^2

Hop