Science Talk

Ken S. Tucker · Guest

On Jul 3, 8:25 pm, david.willi...@bayman.org (David Williams) wrote:

David Williams · Guest

-> We're using a Rotating Coordinate System, connecting
-> the Earth to the Moon, so we reduced the gravitational
-> field effect of the Earth on s/c to nil at the Moon by
-> a centrifugal force expression. That enables us to keep
-> the Earth and Moon on the x-axis.
-> Very cool, a bit of General Relativity in that.

-> Btw, hows that mission to Jupiter going?
-> Regards
-> Ken

Presumably you have also included Coriolis forces, which crop up when
anything moves radially in a rotating frame of reference.

Incidentally, you should enjoy the current (July '0 Cool

issue of
Scientific American magazine. There's a piece in it about simulations
of the structure of spacetime.

dow

David Williams · Guest

-> LOL, Dave thinks Inuits carried Viking stuff from Nfld to E-island!
-> Dave turn OFF the TEEVEE and learn from real experts.
-> Ken

Which real experts? You?! L&L&L&L&LOL

People carry trinkets all over the place. If an Inuit had a nice bit of
Viking jewellery, he might carry it anyplace an Inuit might go,
including to Ellesmere Island.

dow

David Williams · Guest

-> More Red Herrings, read "North star...etc.".

A few thousand years ago, there was no "North Star", i.e. a bright star
close to the North Celestial Pole, just as there is no "South Star"
now.

-> > To "do longitude" at all accurately, you need a timepiece that will
-> > gain or lose very little time over the period you will take to do your
-> > voyage. If your clock is wrong by an hour, your estimate of longitude
-> > will be wrong by 15 degrees. If it is wrong by only a minute, you'll be
-> > wrong by 15 arc-minutes, i.e. about 15 nautical miles.

-> What's 15 miles, nothing, it's a matter that they could
-> predict within a day or so of arrival, close enough.

-> > Since long
-> > voyages took months or years, chronometers were needed that would gain
-> > or lose no more than a few minutes in that much time. The British were
-> > the first to achieve this accuracy, which helped them in their
-> > explorations.

I said that the clock has to be accurate to *a few* minutes, which
would translate to a few tens of nautical miles. Anything much more
inaccurate than that would lead to ships missing islands altogether,
and similar mishaps.

In the early 1700s, I think, the British Admiralty offered a large
prize to anyone who could invent and construct a chronometer of
sufficient accuracy. A lot of people tried developing large machines
with carefully compensated pendulums, and so on. Many of these were
superbly accurate clocks when used on land, but totally failed when
carried on ships that were being tossed in stormy seas. Finlly, a man
named Harrison realized that pendulums were useless, and that a
mechanism much more like that of a pocket watch, with a balance-wheel
as the basic oscillator, would have a much better chance of working. He
constructed several chronometers which were really just oversized
watches and submitted them to the Admiralty. They won him the prize.
Similar mechanisms were the basis for navigational chronometers until
just a few decades ago, when quartz-crystal oscillators came into use.
Now, I am wearing a $10 watch that would have easily won the prize 300
years ago.

-> You have a habit of underestimating the ingenuity of
-> everyone except brits Smile

.
-> Ken

If Galileo, Einstein, the Wright brothers, Tsiolkovsky, Von Braun,
Turing, etc., etc., were all Brits, then I guess you're right. If you
think I underestimate your own ingenuity, you may be right too. But if
you think Newton, Babbage, Stephenson, Watt, Brunell, Hawking, etc.,
are undeserving of respect just because they are or were Brits, then
your judgement is a lot worse than mine.

dow

Ken S. Tucker · Guest

On Jul 3, 8:00 pm, david.willi...@bayman.org (David Williams) wrote:

David Williams · Guest

-> > Presumably you have also included Coriolis forces, which crop up when
-> > anything moves radially in a rotating frame of reference.

-> Not sure I even understand the problem, though I
-> did ponder it when I used the Rotating CS, (RCS).

-> In an Ordinary non-rotating CS, (OCS), I can shoot
-> a missile directly vertical from earth on a perfectly
-> straight *path* and hit the moon....((maybe, better assume
-> lunar gravity is zero to start)), but then one would need
-> to aim the missile to where the moon will be at impact.
-> So relatively to an axis (use lasers) connecting the
-> Earth to the Moon, that straight *path* will be relatively
-> curved, does that make sense to you?

Imagine there's a string stretched between the Earth and Moon, and
your spacecraft is attached to it with some sort of pulleys. If the
co-ordinate system is not rotating, and the moon is somehow stationary
relative to earth, there will be no forces in the pulleys. If the frame
of reference remains stationary, but the moon is in orbit around the
earth, there will have to be some "sideways" force from the string that
accelerates the spacecraft to the moon's transverse speed by the time
it gets there. If the frame of reference rotates to keep pace with the
moon, the force will still exist to make the spacecraft travel in the
straight path. If no string or pulleys exert the force, the spacecraft
will, in the rotating frame of reference, accelerate sideways as if it
were being acted on by a force. This is the Coriolis force. Like
centrifugal force, it appears only in rotating frames of reference. It
is real, and cannot be ignored.

In the earth's atmosphere, if there is low pressure to the north and
high pressure to the south, the wind does *not* blow from south to
north! In the northern hemisphere, it blows roughly from west to east.
This is the result of the Coriolis force produced by the earth's
rotation.

-> Thanks, I'll see if it's online, I haven't renewed sciam,
-> no time for pop mags anymore.

I don't subscribe to it, but sometimes I pick up a copy from a store if
the headlines look interesting. This month's did.

dow

Ken S. Tucker · Guest

On Jul 4, 5:16 pm, david.willi...@bayman.org (David Williams) wrote:

Ken S. Tucker · Guest

On Jul 6, 8:19 am, david.willi...@bayman.org (David Williams) wrote:

David Williams · Guest

-> Well perhaps you culd recommend the appropriate
-> algorithm we could employ to keep Earth and Moon
-> on the x-axis.
-> We're pretty excited about Project Constellation and
-> we want to review it via sim.
-> Next we're going to sim Earth Orbit Rendevous.
-> Ken

If I were you, I think I'd do all the calculations in a non-rotating
frame of reference, and have an output routine that would present
everything so earth and moon are on the x-axis. The output routine
would look at the positions of earth and moon in the non-rotating frame,
figure out the transformation (rotation and maybe translation) that
would have to be done to put them both on the x-axis, and do the same
transformation on the position of the spacecraft to display it. But
this would just be an output procedure (a separate SUB), which would
not affect the computed positions of the objects in the non-rotating
frame of reference.

This would avoid all complications with centrifugal and Coriolis
effects.

dow

David Williams · Guest

-> That's a good idea. Recall I wrote a program for us
-> using the sun and 9 planets all grav interlinked that
-> permitted choosing anyone as the center and then
-> locking in an axis between any two planets, but I
-> can't find the darn thing right now. Did I give you a
-> copy?
-> There is no evidence of complications from Coriolis,
-> but centrifugal is inevitable and has been perfectly
-> accounted for....onward!
-> Ken

If you're doing it in two dimensions, all you need is a couple of
routines that will convert polar coordinates to Cartesian and vice
versa. You may already have them in your program to handle the
acceleration vectors. Then, to make your display, just convert the
moon's and spacecraft's coordinates to polar, subtract the angles, so
the moon's is zero, then convert back to Cartesian and plot the point
for the spacecraft. Very easy. In three dimensions, it's only slightly
more complicated. There are 3D conversion routines in the "Sunalign"
program I posted here a while back.

When you launch your craft toward the moon, on the rotating display its
path will curve markedly to the right, if you're looking from the
north. That's the result of the Coriolis effect. But you don't have to
calculate this, or the centrifugal one. Using a non-rotating frame for
your calculations and just making the display rotate will handle all
the details for you.

dow

P.S. No. I don't have a copy of your earlier program.

Harri Tavaila · Guest

david.williams@bayman.org (David Williams) wrote in
news:1215140762.873.1215133298@bayman.org:

Ken S. Tucker · Guest

On Jul 9, 12:13 am, Harri Tavaila <en.s...@roskat.fi> wrote:

David Williams · Guest

On 07/09/2008 12:24 PM, dynamics@vianet.on.ca wrote to All:

-> What we need to do is dig up a dead Viking off E-island.
-> But according to DOW, that could have been carried from
-> NFLD, so there is no point in introducing evidence and
-> confusing people whose minds are made up.
-> Been there, tried it.
-> Ken
-> "you can't teach pigs to sing"

It´s wonderful how Ken invents other people´s reactions to events which
have not happened and, in all probability, never will happen.

He lives in a dream world.

dow

Ken S. Tucker · Guest

On Jul 10, 2:46 pm, david.willi...@bayman.org (David Williams) wrote:

David Williams · Guest

On 07/11/2008 6:24 AM, dynamics@vianet.on.ca wrote to All:

-> On Jul 10, 2:46 pm, david.willi...@bayman.org (David Williams) wrote:
-> > On 07/09/2008 12:24 PM, dynam...@vianet.on.ca wrote to All:
-> >
-> > -> What we need to do is dig up a dead Viking off E-island.
-> > -> But according to DOW, that could have been carried from
-> > -> NFLD, so there is no point in introducing evidence and
-> > -> confusing people whose minds are made up.
-> > -> Been there, tried it.
-> > -> Ken
-> > -> "you can't teach pigs to sing"
-> >
-> > It´s wonderful how Ken invents other people´s reactions to events which
-> > have not happened and, in all probability, never will happen.
-> > He lives in a dream world.
->
-> Dave if you have a "bias" to green technology,
-> financially or otherwise then your objectivity is
-> excluded, do you?
-> If so you want to believe any pop-TEEVEE
-> show that favors your investment above actual
-> science that you conviently marginalize, don't
-> be ashamed that's a typical human property Smile

.
->
-> I happen to hold investments in Green technology,
-> however that has nothing to do with Global warming,
-> so I'm unbiased.
-> Ken

What pop-TV show are you imagining?

I have some investments in nuclear technology. I that green or not?

dow