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I'm building a spaceship in POV-Ray.
I think that, normally, you want to put the maneuvering thrusters at the
cardinal directions of the spaceship so that you can turn most efficiently.
But can you put them at other places too?
I mean, instead of just the top/left/bottom/right, can you place
additional thrusters around the circumference of the ship?
Mike
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Am 09.01.2016 um 00:39 schrieb Mike Horvath:
> I'm building a spaceship in POV-Ray.
>
> I think that, normally, you want to put the maneuvering thrusters at the
> cardinal directions of the spaceship so that you can turn most efficiently.
>
> But can you put them at other places too?
>
> I mean, instead of just the top/left/bottom/right, can you place
> additional thrusters around the circumference of the ship?
Certainly you can -- it'll actually be a bit more effective in terms of
propellant consumption (probably by a factor of about 1.2).
Remember to orient the thrusters tangential to the ship, so that they
can be used not only for translation but also for attitude control.
While flywheel-based mechanisms can /change/ the ship's attitude at no
propellant cost, they are of limited use when it comes to /stabilizing/
the ship.
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On 1/8/2016 10:52 PM, clipka wrote:
> Am 09.01.2016 um 00:39 schrieb Mike Horvath:
>> I'm building a spaceship in POV-Ray.
>>
>> I think that, normally, you want to put the maneuvering thrusters at the
>> cardinal directions of the spaceship so that you can turn most efficiently.
>>
>> But can you put them at other places too?
>>
>> I mean, instead of just the top/left/bottom/right, can you place
>> additional thrusters around the circumference of the ship?
>
> Certainly you can -- it'll actually be a bit more effective in terms of
> propellant consumption (probably by a factor of about 1.2).
>
> Remember to orient the thrusters tangential to the ship, so that they
> can be used not only for translation but also for attitude control.
> While flywheel-based mechanisms can /change/ the ship's attitude at no
> propellant cost, they are of limited use when it comes to /stabilizing/
> the ship.
>
Okay, thanks.
Mike
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Le 2016-01-08 22:52, clipka a écrit :
> Am 09.01.2016 um 00:39 schrieb Mike Horvath:
>> I'm building a spaceship in POV-Ray.
>>
>> I think that, normally, you want to put the maneuvering thrusters at the
>> cardinal directions of the spaceship so that you can turn most efficiently.
>>
>> But can you put them at other places too?
>>
>> I mean, instead of just the top/left/bottom/right, can you place
>> additional thrusters around the circumference of the ship?
>
> Certainly you can -- it'll actually be a bit more effective in terms of
> propellant consumption (probably by a factor of about 1.2).
>
The fuel-saving factor depends on the geometry of your spaceship (more
specifically, its moment of inertia). And you probably need to take the
occupants' well being in consideration as well*, and not just your fuel
mileage.
For example, if the Millenium Falcon wants to turn right, and only fires
the left-side thruster to turn the ship (minimizing fuel consumption),
it will rotate about an axis (called the "instantaneous center of
zero-velocity") that's somewhere between the central turret and the
cockpit - assuming an uniform mass distribution. This means the cockpit
will appear to move backwards. to reduce motion-sickness from the crew,
you would have to fire most thrusters as well, and the left-side ones a
lot more, so that the instantaneous center of zero-velocity is right
undeneath the cockpit, using a lot more fuel.
*Unless, of course, they have Star Trek-like inertial dampers.
--
/*Francois Labreque*/#local a=x+y;#local b=x+a;#local c=a+b;#macro P(F//
/* flabreque */L)polygon{5,F,F+z,L+z,L,F pigment{rgb 9}}#end union
/* @ */{P(0,a)P(a,b)P(b,c)P(2*a,2*b)P(2*b,b+c)P(b+c,<2,3>)
/* gmail.com */}camera{orthographic location<6,1.25,-6>look_at a }
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Attachments:
Download 'millenium.png' (20 KB)
Preview of image 'millenium.png'
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Francois Labreque <fla### [at] videotron ca> wrote:
> Le 2016-01-08 22:52, clipka a écrit :
> > Am 09.01.2016 um 00:39 schrieb Mike Horvath:
> >> I'm building a spaceship in POV-Ray.
> >>
> >> I think that, normally, you want to put the maneuvering thrusters at the
> >> cardinal directions of the spaceship so that you can turn most efficiently.
> >>
> >> But can you put them at other places too?
> >>
> >> I mean, instead of just the top/left/bottom/right, can you place
> >> additional thrusters around the circumference of the ship?
> >
> > Certainly you can -- it'll actually be a bit more effective in terms of
> > propellant consumption (probably by a factor of about 1.2).
> >
>
> The fuel-saving factor depends on the geometry of your spaceship (more
> specifically, its moment of inertia). And you probably need to take the
> occupants' well being in consideration as well*, and not just your fuel
> mileage.
>
> For example, if the Millenium Falcon wants to turn right, and only fires
> the left-side thruster to turn the ship (minimizing fuel consumption),
> it will rotate about an axis (called the "instantaneous center of
> zero-velocity") that's somewhere between the central turret and the
> cockpit - assuming an uniform mass distribution. This means the cockpit
> will appear to move backwards. to reduce motion-sickness from the crew,
> you would have to fire most thrusters as well, and the left-side ones a
> lot more, so that the instantaneous center of zero-velocity is right
> undeneath the cockpit, using a lot more fuel.
>
> *Unless, of course, they have Star Trek-like inertial dampers.
>
> --
> /*Francois Labreque*/#local a=x+y;#local b=x+a;#local c=a+b;#macro P(F//
> /* flabreque */L)polygon{5,F,F+z,L+z,L,F pigment{rgb 9}}#end union
> /* @ */{P(0,a)P(a,b)P(b,c)P(2*a,2*b)P(2*b,b+c)P(b+c,<2,3>)
> /* gmail.com */}camera{orthographic location<6,1.25,-6>look_at a }
Keep in mind that they also want to turn gradually, not make a right angle and
fly off in a new direction instantly, because of inertia.
Assuming that they did simply turn the ship at a right angle, they'd still need
to fire the off-side thrusters to control the turn. It makes sense, if you
assume that they're already burning their thrusters, that they simply relax the
thrust on one side and then gradually shift the thrust back to center, so that
the center of pressure is always behind the center of gravity.
Regards,
A.D.B.
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I think it all depends on whether you want hollywood-style space
fighters -- that for some obscure reason are constantly firing their
main engines anyway, and for much more obvious reasons may need to turn
quickly -- or a real-world spaceship.
A real-world spaceship will only occasionally fire /any/ engines of
notable power at all, drifting unaccelerated most of the time, with
plenty of time to change its attitude -- which is done mostly for
thermal management (attitude towards the sun), scientific reasons
(attitude towards a point of interest, though usually scientific
instruments on a manned spacecraft will have their own degrees of
freedom to track a POI), or to prepare for the occasional major course
correction. To save weight there will only be a single set of engines
for such corrections, mounted so that the array points away from the
center of mass, usually at what is perceived as the rear end of the
ship. Attitude changes will be done without haste, allowing for better
fine-tuning as well as preventing any nausea-inducing effects (any that
go significantly beyond the nausea-inducing effect of zero-g anyway).
Actual course corrections /will/ involve notable g forces, but
acceleration will be linear. No attitude changes will be made during
such acceleration burns whatsoever, except possibly to actively
stabilize the attitude(*). Any course correction procedure asking for a
deliberate change in attitude during the acceleration burn would
demonstrably be a waste of propellant.
Docking is another matter; there, attitude is mostly kept unchanged and
maneuvering thrusters are used for acceleration in arbitrary directions.
But even then, such changes will be kept minute, to both keep relative
speed low and -- again -- prevent additional nausea.
For anyone interested in real-spaceflight mechanics, Kerbal Space
Program is a highly recommended piece of software.
(* Spacecraft with continuous-thrust engines like ion drives are an
exception, but their thrust-to-weight ratio is extremely low anyway, so
there's not much acceleration going on that could potentially induce
nausea.)
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clipka <ano### [at] anonymousorg> wrote:
> I think it all depends on whether you want hollywood-style space
> fighters -- that for some obscure reason are constantly firing their
> main engines anyway, and for much more obvious reasons may need to turn
> quickly -- or a real-world spaceship.
>
> A real-world spaceship will only occasionally fire /any/ engines of
> notable power at all, drifting unaccelerated most of the time, with
> plenty of time to change its attitude -- which is done mostly for
> thermal management (attitude towards the sun), scientific reasons
> (attitude towards a point of interest, though usually scientific
> instruments on a manned spacecraft will have their own degrees of
> freedom to track a POI), or to prepare for the occasional major course
> correction. To save weight there will only be a single set of engines
> for such corrections, mounted so that the array points away from the
> center of mass, usually at what is perceived as the rear end of the
> ship. Attitude changes will be done without haste, allowing for better
> fine-tuning as well as preventing any nausea-inducing effects (any that
> go significantly beyond the nausea-inducing effect of zero-g anyway).
> Actual course corrections /will/ involve notable g forces, but
> acceleration will be linear. No attitude changes will be made during
> such acceleration burns whatsoever, except possibly to actively
> stabilize the attitude(*). Any course correction procedure asking for a
> deliberate change in attitude during the acceleration burn would
> demonstrably be a waste of propellant.
>
> Docking is another matter; there, attitude is mostly kept unchanged and
> maneuvering thrusters are used for acceleration in arbitrary directions.
> But even then, such changes will be kept minute, to both keep relative
> speed low and -- again -- prevent additional nausea.
>
> For anyone interested in real-spaceflight mechanics, Kerbal Space
> Program is a highly recommended piece of software.
>
>
> (* Spacecraft with continuous-thrust engines like ion drives are an
> exception, but their thrust-to-weight ratio is extremely low anyway, so
> there's not much acceleration going on that could potentially induce
> nausea.)
I don't know that it's the acceleration that's causing the nausia in the MF
example above, as much as it's the dissonance between the physically percieved
motion of the ship and the motion as relayed to the brain by the eyes.
Like when you stand on a bridge, watching the water flow benieth you, and you
get the feeling that the bridge is moving the opposite direction, except in that
case, your standing still, while on the Falcon, you'd actually be in motion, but
not in the way your eyes tell you.
For the actual physics, I'll have to trust the experts.
Regards,
A.D.B.
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Am 17.01.2016 um 07:23 schrieb Anthony D. Baye:
> I don't know that it's the acceleration that's causing the nausia in the MF
> example above, as much as it's the dissonance between the physically percieved
> motion of the ship and the motion as relayed to the brain by the eyes.
Not exactly -- it's not so much a dissonance in perceived motion as it
is a dissonance in perceived acceleration (primarily in the absence or
direction thereof) and/or perceived change in attitude. Your eyes
constitute your only sense that can perceive motion, so there cannot be
any dissonance in that, whereas acceleration and changes in attitude are
detected by both your eyes and your vestibular system (a part of the
inner ear).
> Like when you stand on a bridge, watching the water flow benieth you, and you
> get the feeling that the bridge is moving the opposite direction, except in that
> case, your standing still, while on the Falcon, you'd actually be in motion, but
> not in the way your eyes tell you.
But that just causes a weird feeling, not nausea. Your eyes may be at
dissonance with reason, but reason is presumably the highest-level
function of the brain, whereas nausea is among the most fundamental
functions, that there is no such thing as nausea from a dissonance
between perception and reason.
> For the actual physics, I'll have to trust the experts.
And who would that be?
I would have serious doubts about the "expert" status of anyone claiming
that real-world space pilots "want to turn gradually, not make a right
angle and fly off in a new direction instantly". It is certainly
well-advised to avoid excessive g forces, and there may be reasons to
avoid fast changes in attitude in preparation for a turn, but barring
that, there are in fact at least two compelling reasons to make any
actual changes in trajectory pretty sharp: (1) There is (almost) always
a single ideal point in time where the change in trajectory is least
expensive in terms of propellant use; and (2) computing the parameters
for an engine burn required to transit from one particular trajectory to
another is quite easy for sufficiently short burn times, but gets more
complicated the longer the burn takes.
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clipka <ano### [at] anonymousorg> wrote:
> Am 17.01.2016 um 07:23 schrieb Anthony D. Baye:
>
> > I don't know that it's the acceleration that's causing the nausia in the MF
> > example above, as much as it's the dissonance between the physically percieved
> > motion of the ship and the motion as relayed to the brain by the eyes.
>
> Not exactly -- it's not so much a dissonance in perceived motion as it
> is a dissonance in perceived acceleration (primarily in the absence or
> direction thereof) and/or perceived change in attitude. Your eyes
> constitute your only sense that can perceive motion, so there cannot be
> any dissonance in that, whereas acceleration and changes in attitude are
> detected by both your eyes and your vestibular system (a part of the
> inner ear).
>
> > Like when you stand on a bridge, watching the water flow benieth you, and you
> > get the feeling that the bridge is moving the opposite direction, except in that
> > case, your standing still, while on the Falcon, you'd actually be in motion, but
> > not in the way your eyes tell you.
>
> But that just causes a weird feeling, not nausea. Your eyes may be at
> dissonance with reason, but reason is presumably the highest-level
> function of the brain, whereas nausea is among the most fundamental
> functions, that there is no such thing as nausea from a dissonance
> between perception and reason.
>
>
> > For the actual physics, I'll have to trust the experts.
>
> And who would that be?
>
> I would have serious doubts about the "expert" status of anyone claiming
> that real-world space pilots "want to turn gradually, not make a right
> angle and fly off in a new direction instantly". It is certainly
> well-advised to avoid excessive g forces, and there may be reasons to
> avoid fast changes in attitude in preparation for a turn, but barring
> that, there are in fact at least two compelling reasons to make any
> actual changes in trajectory pretty sharp: (1) There is (almost) always
> a single ideal point in time where the change in trajectory is least
> expensive in terms of propellant use; and (2) computing the parameters
> for an engine burn required to transit from one particular trajectory to
> another is quite easy for sufficiently short burn times, but gets more
> complicated the longer the burn takes.
I was not claiming to have expert information on the issue. I was simply
stating that I was not the person who would know. What came before was simply
my perception, based more on intuition than anything else.
my apologies for my unscientific input.
Regards,
A.D.B.
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Am 17.01.2016 um 21:33 schrieb Anthony D. Baye:
> clipka <ano### [at] anonymousorg> wrote:
>>> For the actual physics, I'll have to trust the experts.
>>
>> And who would that be?
...
> I was not claiming to have expert information on the issue. I was simply
> stating that I was not the person who would know. What came before was simply
> my perception, based more on intuition than anything else.
>
> my apologies for my unscientific input.
If anyone has to apologize it's me. I was under the wrong impression
that by "the experts" you meant someone who had backed your earlier ideas.
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