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Q. Aerodynamics in 0 atmosphere ?



 
 
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  #1  
Old August 3rd 03, 08:08 AM
Bob Weber
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Default Q. Aerodynamics in 0 atmosphere ?

Pointy objects generally have less drag (resistance to moving) than barns
when propelled thru air. Drag is proportional to the size and shape of the
object, proportional to the density of the air and proportional to the
square of the velocity of the air stream. In outer space there is no air so
the density is zero, hence, no drag so the shape doesn't matter.

"Jim" wrote in message
...
Hi.

I want to know if a pointy projectile in outer space does or does NOT
have an advantage over let's say a barn, as far as being propelled in
outer space ( or anywhere above, where there is no atmosphere).

I think I read recently that it makes no difference. But I have a hard
time digesting that.

Can someone shed some light on that ?

Thanks again, for your all your most excellent answers,

Jim



  #2  
Old August 3rd 03, 08:30 AM
Odysseus
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Default Q. Aerodynamics in 0 atmosphere ?

Jim wrote:

I want to know if a pointy projectile in outer space does or does NOT
have an advantage over let's say a barn, as far as being propelled in
outer space ( or anywhere above, where there is no atmosphere).

I think I read recently that it makes no difference. But I have a hard
time digesting that.

Can someone shed some light on that ?


The subject of your message is something of a contradiction in terms:
without "air" there's no "aero"dynamics.

A "pointy" or streamlined projectile works better than others in the
atmosphere because it pushes air aside in such a way as to minimize
the drag caused by friction and turbulence. But with no atmosphere
there's nothing to cause drag no matter what the shape of the
projectile or spacecraft. The LEM used by the Apollo missions is a
good example; its ungainly shape would be hopeless for an aircraft
intended to fly in an atmosphere, but was not the slightest
impediment to manoeuvres in the near-vacuum of space. Likewise a
falling leaf or feather would drop just like a stone without air to
make it 'float'.

--
Odysseus
  #3  
Old August 3rd 03, 12:50 PM
Jim Jones
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Default Q. Aerodynamics in 0 atmosphere ?

On Sun, 03 Aug 2003 08:45:18 +0100, Andrew McKay
wrote:

On Sun, 03 Aug 2003 05:25:42 GMT, (Jim)
wrote:

Thanks again, for your all your most excellent answers,


Are you having a problem with your school studies or something?

Andrew


Andrew,

Good question. The fact is, I've only recently taken a keen interest
in astronomy - something which I regret not having done much earlier.
I have recently purchased some nice books with text/illustrations on
the subject. These books, which I can't put down, simply help me
generate more questions, which I bring here. No doubt that in my
books or internet research, my fundamental questions are answered, but
I find this newsgroup the best way to answer those questions of mine,
the subjects of which I'm not sure how to ponder.

My threads' responders like Starford, Impmon, Vancil, Ruskai, Weber
and others are no doubt Scientists, PHDs, Mathematicians, Astronauts
and others who kindly impart with the knowledge they've gained through
training and experience. For that I'm grateful.

They may have been in the middle of an experiment, and forgot a flask
heating on their bunsen burner, to answer my question.
Another may have answered a question and risked a brand new comet
flying past their unattended telescope.

So, to answer your question, yes, I am having some trouble with some
concepts, but am most sincere in my questions, and hope I've despelled
any suspicion of lack of integrity in my search for knowledge.

Thanks,
Jim




..
  #4  
Old August 3rd 03, 08:03 PM
G=EMC^2 Glazier
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Default Q. Aerodynamics in 0 atmosphere ?

Hi oc and Odysseus Always best to keep in mind bouyancy is an up force
and gravity is a down force and here on earth gravity is the weakest
force. Still it has to be reality that a dumb bell one end a hydrogen
balloon,and the other end a lead object the same size as the hydrogen
balloon when drooped from a great height will hit the moons surface lead
first. Greater gravity creates faster acceleration. Density increases
greater gravity. Bert Ps hydrogen was only use to make the dumb bell
size,and had nothing to do with bouyancy. The force of bouyancy
naturally does not exist on the moon. On the moon its mass density that
can create greater acceleration on the moon. On the moon
the same stuff taken there from the earth will fall 6 times slower(mass
for mass) that stays the same. Bert

  #5  
Old August 3rd 03, 09:05 PM
Odysseus
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Default Q. Aerodynamics in 0 atmosphere ?

G=EMC^2 Glazier wrote:

Hi oc and Odysseus Always best to keep in mind bouyancy is an up force
and gravity is a down force and here on earth gravity is the weakest
force.


Buoyancy is in a sense just a side-effect of gravity. We tend to
focus on the 'floating' object that seems to experience a lifting
force, but the cause of this force is gravity pulling the displaced
medium downwards. In this way it's a little like "centrifugal force",
which can be regarded as a side-effect of inertia.

--
Odysseus
  #6  
Old August 3rd 03, 10:02 PM
Andrew McKay
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Default Q. Aerodynamics in 0 atmosphere ?

On Sun, 03 Aug 2003 12:50:57 +0100, Jim Jones
wrote:

So, to answer your question, yes, I am having some trouble with some
concepts, but am most sincere in my questions, and hope I've despelled
any suspicion of lack of integrity in my search for knowledge.


Sorry, I was a bit unfair on you

Andrew

Do you need a handyman service? Check out our
web site at http://www.handymac.co.uk
  #7  
Old August 6th 03, 05:00 AM
G=EMC^2 Glazier
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Default Q. Aerodynamics in 0 atmosphere ?

Hi Barry The same object dropped 3ft from the earth's surface has to
be dropped 18Ft up from the moon's surface to hit at the same speed.
Reason moon has one six the gravity force. Bert

  #8  
Old August 15th 03, 09:38 PM
Jonathan Silverlight
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Default

In message , Peter Hodges
writes

On Sun, 03 Aug 2003 05:25:42 GMT, (Jim)
wrote:


I want to know if a pointy projectile in outer space does or does NOT
have an advantage over let's say a barn, as far as being propelled in
outer space ( or anywhere above, where there is no atmosphere).

I think I read recently that it makes no difference. But I have a hard
time digesting that.

Can someone shed some light on that ?

Thanks again, for your all your most excellent answers,

Jim


It's true; in zero atmosphere there's no point in having a "pointy"
end - that's why such things are referred to as AEROdynamic. In fact,
a sphere is possibly the best design for a spacecraft, as you get the
maximum volume for minimumsurface area (and therefore won't lose heat
the crew might want). In practice it wouldn't be a sphe you'd have
things like antennae, navigation 'scopes & so forth pointing in all
directions, & landers attached, and so forth.


For some reason the original didn't appear, but I'll just add that the
biggest constraint is how you return to Earth (as opposed to a true
space craft like the Lunar Module, which can be almost any convenient
shape) You _want_ something that is big and flat like a barn (or the
underside of a space shuttle or capsule) to act as a brake.
The Russians have gone for a more spherical design but it can't be a
true sphere; the centre of gravity must be offset so it doesn't tumble.
--
"Roads in space for rockets to travel....four-dimensional roads, curving with
relativity"
Mail to jsilverlight AT merseia.fsnet.co.uk is welcome.
Or visit Jonathan's Space Site
http://www.merseia.fsnet.co.uk
  #9  
Old August 16th 03, 01:52 AM
Ugo
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Default

"Peter Hodges" wrote in message
...
It's true; in zero atmosphere there's no point in having a "pointy"
end - that's why such things are referred to as AEROdynamic. In fact,
a sphere is possibly the best design for a spacecraft, as you get the
maximum volume for minimumsurface area (and therefore won't lose heat
the crew might want).


AFAIK, keeping heat in space is not an issue at all, as a matter of fact
engineers building probes tend to have trouble dealing with it! You
basically want your own heat source which could easily be regulated and then
you'd need a system to remove excessive heat (radiators). Remember that in
space the only way to lose heat is by blackbody radiation, and that's not
nearly as effective (I'm talking 'normal' temperatures here) as is heat
conductance in contact with air and other stuff.
Someone correct me if I'm mistaken?


 




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