On 2/22/2015 2:28 PM, Alain wrote:
> 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


What about within nebulae?

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On 23-2-2015 5:11, Mike Horvath wrote:
> On 2/22/2015 2:34 PM, Alain wrote:
>> The most realistic space fighter I ever saw was the Fury from Babylon 5.
>> NO wings. No profiling. Just bone dry design with a canopy designed only
>> to provide the largest view field as possible.
>
> I thought the corvettes from Independence War were pretty cool.
>
>
http://static.giantbomb.com/uploads/scale_small/4/48222/1130546-independencewaruscoverxt6.jpg
>

Yes, both models exemplify the road taken by more modern (and 
realistic?) design.

-- 
Thomas

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On 22/02/2015 21:09, Doctor John wrote:
> On 22/02/15 19:28, Alain wrote:
>>
>> 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
>
> How the hell did you calculate that? I'm not saying you're wrong -
> you're probably right - but can I see the equations?

Drag force is directly proportional to the fluid density, and velocity 
*squared*. So if the density is 10^14 times lower, the velocity "only" 
needs to be 10^7 times higher to get the same force. I don't know where 
Alain got the 10^16 km/hr from.

But it gets worse, the power (rate of doing work) required to maintain 
the velocity against drag equals the drag force times the velocity. So 
if you want the same *power* requirement as on Earth, the velocity only 
needs to be about 50000 times higher.

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Am 22.02.2015 um 20:34 schrieb Alain:

> The most realistic space fighter I ever saw was the Fury from Babylon 5.
> NO wings. No profiling. Just bone dry design with a canopy designed only
> to provide the largest view field as possible.

Well, the struts for the Fury's engines sort of /look/ like wings, with 
their somewhat horizontal arrangement.

For a space fighter, I guess it would be more reasonable to arrange the 
engines in an orthogonal X shape: Both for safety (if one engine fails 
catastrophically, you want a maximum distance to the nearest other 
engine(s)) and for the sake of being able to effect attitude corrections 
by means of variable engine thrust (with an orthogonal arrangement, both 
pitch and yaw can be affected equally well, while the "flat" X shape 
strongly favors yaw).

Possibly the best compromise between reasonable arrangement and viewer 
expectations would be a 3-engine design with an upside-down Y configuration.

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Am 19.02.2015 um 09:25 schrieb scott:
>> 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.

In an ideal gas, the speed of sound is proportional to the square root 
of the pressure... until relativistic effects kick in, I guess.

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Am 24.02.2015 um 17:31 schrieb clipka:
> Am 19.02.2015 um 09:25 schrieb scott:
>>> 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.
>
> In an ideal gas, the speed of sound is proportional to the square root
> of the pressure... until relativistic effects kick in, I guess.

In numbers: Speed of sound in hydrogen and helium is roughly 10^3 m/s at 
atmospheric pressure. With the pressure in outer space being lower by a 
factor of about 10^14, according to Newtonian mechanics the speed of 
sound in this medium would be about 10^7 times higher, i.e. 10^10 m/s - 
exceeding the speed of light by about 1.5 magnitudes.

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Le 15-02-22 16:09, Doctor John a écrit :
> On 22/02/15 19:28, Alain wrote:
>>
>> 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
>
> How the hell did you calculate that? I'm not saying you're wrong -
> you're probably right - but can I see the equations?
>
> John
>

The speed of light is a little under 300 000 Km/s. Multiply that by 
3600, the number of seconds in an hour, gives about 1 080 000 000 Km/h 
whitch is somewhat larger than the true speed of light in a vacuum, that 
I rounded down: 10^9

Next, I used the appriximative presure ratio between sea level and space 
"vacuum" in Earth vicinity: 10^14 to 1.
Finaly, I multiplied that with a speed of 100 Km/h (about 60 Miles per 
hour), or highway speed: 10^16

That's around 10 000 000 times the speed of light! In StarTreck second 
generation universe, that's warp 7, or a ludicrous warp 10 millions in 
the original.

As I'm only concerned with the order of magnitude, the approximations 
are acceptable.

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Le 15-02-22 23:12, Mike Horvath a écrit :
> On 2/22/2015 2:28 PM, Alain wrote:
>> 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
>
>
> What about within nebulae?

Compared to most nebulaes, the best vacuum attained in the most advanced 
laboratories looks like medium to high presure.

So, when traveling at non-relativistic speed, you can normaly totaly 
ignore their presence.

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Le 15-02-24 11:53, clipka a écrit :
> Am 24.02.2015 um 17:31 schrieb clipka:
>> Am 19.02.2015 um 09:25 schrieb scott:
>>>> 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.
>>
>> In an ideal gas, the speed of sound is proportional to the square root
>> of the pressure... until relativistic effects kick in, I guess.
>
> In numbers: Speed of sound in hydrogen and helium is roughly 10^3 m/s at
> atmospheric pressure. With the pressure in outer space being lower by a
> factor of about 10^14, according to Newtonian mechanics the speed of
> sound in this medium would be about 10^7 times higher, i.e. 10^10 m/s -
> exceeding the speed of light by about 1.5 magnitudes.
>

That would be inversly proportional.

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Am 24.02.2015 um 23:04 schrieb Alain:

>>> In an ideal gas, the speed of sound is proportional to the square root
>>> of the pressure... until relativistic effects kick in, I guess.
>>
>> In numbers: Speed of sound in hydrogen and helium is roughly 10^3 m/s at
>> atmospheric pressure. With the pressure in outer space being lower by a
>> factor of about 10^14, according to Newtonian mechanics the speed of
>> sound in this medium would be about 10^7 times higher, i.e. 10^10 m/s -
>> exceeding the speed of light by about 1.5 magnitudes.
>>
>
> That would be inversly proportional.

Whoops - yes. Consider it a typo.

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