For Questions That Don't Merit Their Own Thread

[K^2]

2 hours ago, p1t1o said:

What is wrong with a ball joint? Or I could be missing something because I have no idea what a quaternion or a cardanic suspension is...

You lose an input DoF with a ball joint. You can still get any 3DoF orientation you want by combining rotations, but you aren't necessarily going to be able to track an arbitrary curve. In addition, you're going to be limited to less than 180° cone.

4 hours ago, 0111narwhalz said:

But are there any clever ways? Ones which are unnecessarily complex but technically possible?

The other classical solution is many-jointed arm. Again, you typically want at least four, possibly five joints to allow for full tracking, and you'll have to be solving inverse kinematics problem along the way. Of course, that's really just a generalization of gimbal concept, as anything with joints will be. The only other thing I can think of is magnetic suspension which avoids joints entirely.

[peadar1987]

If you want to be really clever you just put two turrets with a half-hemisphere field of fire back-to-back. Same coverage, far less complexity.

[Exploro]

On 8/21/2015 at 11:31 AM, theend3r said:

Q: Would it be possible to create a propulsion using magnets and Earth's natural magnetic field? E.g. using Halbach array with extremely strong magnets. (Or of course using magnetic monopoles if it were possible to make them.)

Electrodynamic tether propulsion system would likely be what you want to use.

Edited May 10, 2017 by Exploro

[magnemoe]

On 9.5.2017 at 7:06 AM, 0111narwhalz said:

Alright. Four gimbals it is.

But are there any clever ways? Ones which are unnecessarily complex but technically possible? Just want to explore possibilities now. I don't think there's any real way to make a quaternion exist in real space without some kind of planar bearing, but I'm almost certain there are other options.

An turret as in an gun or telescope mount can not get gimbal lock you have one rotate and one elevate axis and they will never cross. 
If you have 3 axes or an tilt axis you can get gimbal lock if two axis overlap.

[0111narwhalz]

4 hours ago, magnemoe said:

An turret as in an gun or telescope mount can not get gimbal lock you have one rotate and one elevate axis and they will never cross. 

Take the scenario from the Wikipedia page:

Consider tracking a helicopter flying towards the theodolite from the horizon. The theodolite is a telescope mounted on a tripod so that it can move in azimuth and elevation to track the helicopter. The helicopter flies towards the theodolite and is tracked by the telescope in elevation and azimuth. The helicopter flies immediately above the tripod (i.e. it is at zenith) when it changes direction and flies at 90 degrees to its previous course. The telescope cannot track this maneuver without a discontinuous jump in one or both of the gimbal orientations. There is no continuous motion that allows it to follow the target. It is in gimbal lock.

[magnemoe]

1 hour ago, 0111narwhalz said:

Take the scenario from the Wikipedia page:

You are right, you get it with two axes if you fly straight over the turret and then turn, an graduate turn will also cause this but can be handled with software, probably also electric. 
Gimbal lock is an pain then working in 3d to, pretty often the object enter gimbal lock as you have to move it 90 degree along two axes to fit there you want it. Here you can usualy reset gimbal or parent it to an dummy object you can also rotate. 

[Exploro]

On 9/12/2015 at 3:47 PM, Thomassino said:

Hello

I have just seen a bright flash of light in the night sky. It lasted for a less than half a second and was very bright (I'd say something around -5 magnitude) any idea what it could have been? I was wondering maybe a meteor heading right towards me or a piece of spinning space debris reflected sunlight...

What you likey saw was the a flare from a geostationary satellite. Five or six years ago I recall seeing several similar occurrences while looking towards the constellation Leo in late spring. These short (lasting mere seconds) bright flashes usually about the same time; around 11:30 PM local time and occurred in the same place in the sky. These flashes looked nothing like shooting stars nor of satellites flying overhead. Flybys exhibit a gradual change in the magnitude as a spacecraft passes by; ranging from several seconds to sometime several minutes. But the flashes were extremely brief. Having also seen Iridium Flares before I knew these flashes were not quite the same; as Iridium Flares do have noticable motion to them; where as these aforementioned flashes were seemingly fixed. At the time I was unaware geostationary satellite flares occurred. Thus much like you I thought I was witnessing a star flaring up or some other naturally occurring process rather than a man-made one.

[sevenperforce]

14 hours ago, Exploro said:

14 hours ago, Exploro said:

I have just seen a bright flash of light in the night sky. It lasted for a less than half a second and was very bright (I'd say something around -5 magnitude) any idea what it could have been? I was wondering maybe a meteor heading right towards me or a piece of spinning space debris reflected sunlight...

What you likey saw was the a flare from a geostationary satellite. Five or six years ago I recall seeing several similar occurrences while looking towards the constellation Leo in late spring. These short (lasting mere seconds) bright flashes usually about the same time; around 11:30 PM local time and occurred in the same place in the sky. These flashes looked nothing like shooting stars nor of satellites flying overhead. Flybys exhibit a gradual change in the magnitude as a spacecraft passes by; ranging from several seconds to sometime several minutes. But the flashes were extremely brief. Having also seen Iridium Flares before I knew these flashes were not quite the same; as Iridium Flares do have noticable motion to them; where as these aforementioned flashes were seemingly fixed. At the time I was unaware geostationary satellite flares occurred. Thus much like you I thought I was witnessing a star flaring up or some other naturally occurring process rather than a man-made one.

Weirdest thing I ever saw was an old rocket body in an elliptical orbit reflecting the image of the full moon onto a low-lying mostly-transparent cloud layer. I could have sworn it was a UFO.

[Exploro]

4 hours ago, sevenperforce said:

Weirdest thing I ever saw was an old rocket body in an elliptical orbit reflecting the image of the full moon onto a low-lying mostly-transparent cloud layer. I could have sworn it was a UFO.

That is an impressive sight. Out of curiousity was this viewed with unaided eyes or through optics like a telescope or binoculars?

[sevenperforce]

8 minutes ago, Exploro said:

That is an impressive sight. Out of curiousity was this viewed with unaided eyes or through optics like a telescope or binoculars?

Naked eye.

I happened to glance up at the sky and saw a weird triangular glow shooting across the sky at ridiculous speeds. The object was huge, too; from my working knowledge of orbital mechanics, I would have said it was either 10 km across in orbit, or a few hundred feet across at an altitude of 10,000 feet or less. 

I watched it for as long as it took to move across the sky, which was about 15 seconds. As it moved, I noticed that it changed shape, which clued me in that it was a projection rather than an actual object. Of course, its size and speed made me sure it wasn't a real object.

The shape change was due to the slow rotation of the rocket body. I spotted a small glowing speck (the actual rocket body) traveling in lockstep with the projection; that was when I realized it was a reflection. The two merged about 20 degrees above the horizon. I glanced to the other side of the sky and saw the crescent moon (I think I said full moon before; I meant crescent) and realized that's what was being reflected.

[magnemoe]

On 13.5.2017 at 0:50 AM, sevenperforce said:

Naked eye.

I happened to glance up at the sky and saw a weird triangular glow shooting across the sky at ridiculous speeds. The object was huge, too; from my working knowledge of orbital mechanics, I would have said it was either 10 km across in orbit, or a few hundred feet across at an altitude of 10,000 feet or less. 

I watched it for as long as it took to move across the sky, which was about 15 seconds. As it moved, I noticed that it changed shape, which clued me in that it was a projection rather than an actual object. Of course, its size and speed made me sure it wasn't a real object.

The shape change was due to the slow rotation of the rocket body. I spotted a small glowing speck (the actual rocket body) traveling in lockstep with the projection; that was when I realized it was a reflection. The two merged about 20 degrees above the horizon. I glanced to the other side of the sky and saw the crescent moon (I think I said full moon before; I meant crescent) and realized that's what was being reflected.

One guy restored an old WW2 truck with an huge search light on the back, very fun but, police told him to restrict use of it as they got so many ufo reports. 
In dry an clean air, and you have some other light you will not see the beam just the light up in the clouds.

 

 

[Green Baron]

It is incredible and somewhat annoying how frequent and bright satellite trails became over the last years. Sky is rather dark here, slow moving faint objects or fast moving flares from rotating satellites (aka "iridium-flares") or short faint and bright flashes can be seen. Especially when the sun is low under the horizon, but also in the hours around midnight, high in the sky.

You only need a dark sky to realize.

 

... if you see a shooting star, before wishing for something, make sure it's a natural one ;-))

 

Edited May 14, 2017 by Green Baron

[Kryten]

Iridium NEXT are supposed to have much less intense flares than the current design, so shouldn't be as much of a problem for very long. Current ones are to be deorbited after NEXT constellation is fully built up.

[Camacha]

On 14/05/2017 at 2:41 PM, Green Baron said:

It is incredible and somewhat annoying how frequent and bright satellite trails became over the last years. Sky is rather dark here, slow moving faint objects or fast moving flares from rotating satellites (aka "iridium-flares") or short faint and bright flashes can be seen. Especially when the sun is low under the horizon, but also in the hours around midnight, high in the sky.

You only need a dark sky to realize.

Sounds like a luxury problem to me. The sky is so light polluted here that this would be a treat.

 

On 10/05/2017 at 5:05 PM, 0111narwhalz said:

Take the scenario from the Wikipedia page:

So it is basically a non-issue. A helicopter cannot instantly change direction, therefore the gimble will have time to rotate and adjust.

[Grand Ship Builder]

Why doesn't KSP simulate sonic booms and their effects?

[Steel]

15 hours ago, Grand Ship Builder said:

Why doesn't KSP simulate sonic booms and their effects?

Mainly because KSP doesn't really simulate aerodynamics. What you get in the game are a series of models that give you behavior somewhat like real life, but they're not actually modeling the physics properly. Also from the point of view of an aircraft there's not really all that much to simulate, sonic booms affect things around the aircraft much more than the aircraft itself.

Edited May 21, 2017 by Steel

[0111narwhalz]

Speaking of sonic booms: Do they work both ways? That is, if something really loud were on the surface, would an aircraft passing by it hear something like a sonic boom from it? I'd say yes, but the presence of a medium casts doubt.

[p1t1o]

9 hours ago, 0111narwhalz said:

Speaking of sonic booms: Do they work both ways? That is, if something really loud were on the surface, would an aircraft passing by it hear something like a sonic boom from it? I'd say yes, but the presence of a medium casts doubt.

Not sure if this makes sense. For starters, if you are on a supersonic aircraft, there is no "boom" for you at all.

What is the reverse of a sonic boom? Im not sure, something like a shaped charge? - emit a planar shockwave from the inner surface of a giant cone, shockwaves meet at the axis and propel an object to the speed of sound at the shock apex?

[0111narwhalz]

Just now, p1t1o said:

Not sure if this makes sense. For starters, if you are on a supersonic aircraft, there is no "boom" for you at all.

So the motion through the medium is essential to a boom? Makes sense.

[p1t1o]

Just now, 0111narwhalz said:

So the motion through the medium is essential to a boom? Makes sense.

Precisely

[shynung]

If two supersonic planes pass each other too closely (i.e. plane A goes north, B goes south, 100 m distance at closest approach), would the pilots hear each other's sonic booms? Would the planes sustain damage from such an encounter?

[peadar1987]

13 minutes ago, shynung said:

If two supersonic planes pass each other too closely (i.e. plane A goes north, B goes south, 100 m distance at closest approach), would the pilots hear each other's sonic booms? Would the planes sustain damage from such an encounter?

Yup, they'd hear the booms alright. As to whether it would damage the planes or not, I would say no, my gut says the force from a sonic boom at that range would be less than the forces the aircraft is designed to withstand in normal operation. Although I think then wake turbulence could become an issue for both aircraft after passing each other

[p1t1o]

@shynung @peadar1987 Agreed, I dont think that there would be much in the way of structural damage - as a plane travelling at supersonic speeds already must withstand some pretty impressive forces anyway, those forces arising from the wave some distance from the aircraft must be less.

Though the aerodynamic effects could be considerable and loss of control at supersonic speeds can be catastrophic.

All in all, I'd say that the mass and strength of an average supersonic airframe far outstrips the energy of a sonic boom from similar.

Of course not all shockwaves are the same. The sonic boom from a 2km-wide meteor travelling at mach 25 is one heck of a lot stronger than the one that comes of a 5.56mmm rifle round.

For reference, I cant remember if it was mythbusters or what, but I saw online somewhere some footage of a .50-caliber rifle firing between two closely spaced (maybe 6 inches?) rows of wine glasses. The shockwave of the projectile passing made a few of them them wobble slightly, but otherwise nothing at all happened.

Edited May 22, 2017 by p1t1o

[sevenperforce]

7 hours ago, p1t1o said:

For reference, I cant remember if it was mythbusters or what, but I saw online somewhere some footage of a .50-caliber rifle firing between two closely spaced (maybe 6 inches?) rows of wine glasses. The shockwave of the projectile passing made a few of them them wobble slightly, but otherwise nothing at all happened.

I've seen video of a fifty-cal firing through a house of cards without knocking it down. 

One relevant note is that supersonic jets are designed with the equal-area rule in mind, which reduces the size of the sonic boom. A less streamlined object will produce a much more violent sonic boom. Also, the energy in a sonic boom is a function of the speed, so Mach 1.5 is many times less violent than Mach 3.

[Grand Ship Builder]

Now, how hard is it to get to C in Kerbal Space Program without glitches?