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I'm building a bubble around my spaceship to protect from "drag" at
interstellar velocities. This site says that for subsonic craft a
parabola is a better shape for the nose. However, an ogive is better at
supersonic speeds.
http://www.aerospaceweb.org/question/aerodynamics/q0151.shtml
Which applies in outer space? Or, should I not use either and use a
teardrop shape instead?
And, is the piriform shape a good one to use? See here:
http://csi.chemie.tu-darmstadt.de/ak/immel/script/redirect.cgi?filename=http://csi.chemie.tu-darmstadt.de/ak/immel/graphics/povray35/teardrop.html
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Le 19/02/2015 03:53, Mike Horvath a écrit :
> I'm building a bubble around my spaceship to protect from "drag" at
> interstellar velocities. This site says that for subsonic craft a
> parabola is a better shape for the nose. However, an ogive is better at
> supersonic speeds.
>
> http://www.aerospaceweb.org/question/aerodynamics/q0151.shtml
>
> Which applies in outer space? Or, should I not use either and use a
> teardrop shape instead?
Imho, the shape is proportionally relevant to the pressure and its
differential (between front and rear). if the spaceship never has to
experience an atmosphere, the shape is irrelevant, only the
cross-section might give a resistance to the solar-wind: it can be a
brick or a sphere, the difference would be in the generated torque, and
hopefully the engine(s) have far enough power to make that influence
negligible.
The density of hydrogen atom in outer space is variable, but the
pressure is in the nano-pascal ( 10^-9 ) range, and we live in
kilohecto-pascal ( 10^5 ), so the influence of the drag is to be
corrected by at least something like a 10^-14 factor.
The far more concerning problem is the difference of temperature between
sunlighted and non-sunlighted surfaces. Ask a comet about it.
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On 19/02/15 02:53, Mike Horvath wrote:
> I'm building a bubble around my spaceship to protect from "drag" at
> interstellar velocities. This site says that for subsonic craft a
> parabola is a better shape for the nose. However, an ogive is better at
> supersonic speeds.
>
> http://www.aerospaceweb.org/question/aerodynamics/q0151.shtml
>
> Which applies in outer space? Or, should I not use either and use a
> teardrop shape instead?
>
> And, is the piriform shape a good one to use? See here:
>
>
http://csi.chemie.tu-darmstadt.de/ak/immel/script/redirect.cgi?filename=http://csi.chemie.tu-darmstadt.de/ak/immel/graphics/povray35/teardrop.html
>
My immediate reaction is none of the above ;-)
We are not talking aerodynamics here - take a look at the ISS [pretty
picture here
http://www.blogcdn.com/www.engadget.com/media/2011/03/nasa-iss-03-10-2011.jpg].
It is not travelling in interstellar space but neither is it travelling
in (what we define as) an atmosphere.
I would suggest that you concentrate on protecting your craft from
particles travelling with a relative kinetic energy large enough to
cause significant damage.
John
--
Protect the Earth
It was not given to you by your parents
You hold it in trust for your children
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> The density of hydrogen atom in outer space is variable, but the
> pressure is in the nano-pascal ( 10^-9 ) range, and we live in
> kilohecto-pascal ( 10^5 ), so the influence of the drag is to be
> corrected by at least something like a 10^-14 factor.
Drag depends on velocity squared, so that would mean if your velocity
was 10^7 times higher than on earth, you would experience a similar
level of drag.
I have no idea what "interstellar velocities are" though, 10^7 or more? :-)
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> I'm building a bubble around my spaceship to protect from "drag" at
> interstellar velocities. This site says that for subsonic craft a
> parabola is a better shape for the nose. However, an ogive is better at
> supersonic speeds.
>
> http://www.aerospaceweb.org/question/aerodynamics/q0151.shtml
>
> Which applies in outer space? Or, should I not use either and use a
> teardrop shape instead?
What is the speed of sound in space... I don't think any "supersonic"
designs are necessary.
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On 19-2-2015 6:48, Doctor John wrote:
>
> We are not talking aerodynamics here - take a look at the ISS [pretty
> picture here
> http://www.blogcdn.com/www.engadget.com/media/2011/03/nasa-iss-03-10-2011.jpg].
> It is not travelling in interstellar space but neither is it travelling
> in (what we define as) an atmosphere.
And consider Voyager 1 & 2. They are (almost). Their speed is far
superior to ISS's and yet have no protection of any kind.
in addition to John's comment, remember that what we are shown in SF
films are constructions that have very little to do with the necessities
of interstellar space. They need to appeal to (and be recognised by) the
average public which is used to airplanes in daily life ;-)
--
Thomas
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scott wrote:
>
> I have no idea what "interstellar velocities are" though, 10^7 or more?
> :-)
The speed of light times a whole lot if you wanna get anywhere in a
reasonable amount of time
--
Ger
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>> I have no idea what "interstellar velocities are" though, 10^7 or more?
>> :-)
>
> The speed of light times a whole lot if you wanna get anywhere in a
> reasonable amount of time
So we should be talking about superluminal designs, not supersonic. Now
let me go and dig out my text book on superluminal design to see what it
says...
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On 19-2-2015 11:19, scott wrote:
>>> I have no idea what "interstellar velocities are" though, 10^7 or more?
>>> :-)
>>
>> The speed of light times a whole lot if you wanna get anywhere in a
>> reasonable amount of time
>
> So we should be talking about superluminal designs, not supersonic. Now
> let me go and dig out my text book on superluminal design to see what it
> says...
>
According to the Lensmen textbooks of the Galactic Patrol, a teardrop
design is favourite with the habitants of Tellus, while Velantians may
use different shapes; needle shapes for instance. It should be noted
that Boskone had a preference for teardrop shapes until their final
demise. Possibly, those textbooks are obsolete by now ;-)
--
Thomas
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Le 15-02-19 03:22, scott a écrit :
>> The density of hydrogen atom in outer space is variable, but the
>> pressure is in the nano-pascal ( 10^-9 ) range, and we live in
>> kilohecto-pascal ( 10^5 ), so the influence of the drag is to be
>> corrected by at least something like a 10^-14 factor.
>
> Drag depends on velocity squared, so that would mean if your velocity
> was 10^7 times higher than on earth, you would experience a similar
> level of drag.
>
> I have no idea what "interstellar velocities are" though, 10^7 or more? :-)
>
The 10^-9 range is for our spacial neigourhood, or relatively close to a
star. As you travel farther, it drops conciderably. Between the Sun and
Proxima Centaury, the vacuum around the moon looks like high pressure.
In space, to have a drag equivalent to 100 Km/h on a road, using the
10^14 factor for Earth region, you would need to travel at over 100 000
000 000 000 Km/h (10^16 Km/h). That's /way/ faster than the speed of
light ! (about 10^9 Km/h)
Alain
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