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Old 05-14-2017, 07:53 AM   #796
jacquesmomo
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Originally Posted by fred18 View Post
 In the meantime I'm starting to think about the multiple vessels docked as multistage rocket seriously. It's actually the most realistic thing possible...

A very good idea...

And now, just to show you my new ELA-2 crawler (with your help ) : the Ariane 4 can stand on the crawler and It is fully functional !

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Old 05-15-2017, 05:45 PM   #797
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Originally Posted by boogabooga View Post
 Well, what is the advantage of docked vessels?
Well for now there is no immediate advantage, the scope would be to have the very same functionality of current multistage2015.

What I like about the idea is that anyway:
1) it would be much more realistic in this way, since it will be exactly as it happens in real life.
2) point 1 means also from programming point of view, which is probably fun only for my side, but still it's a point
3) it would be much easier to code: once the rocket is created it won't be needed to update it, to save or restore it or whatever it is, orbiter will take care about it automatically since each vessel will live its own life
4) point 3 means also an easiest portability for the future. Updates and changes may be implemented easier than now which is a huge code, bigger part of it consisting in building and setting the rocket
5) I'm also thinking about a "kerbalisation" when you can load your stages into the sim, assemble your rocket and fly. Not that I like it much, I don't even have KSP installed, but how much this is liked around?
6) last but not least: the actual way of detaching stages which basically delete the original mesh and spawns a stage module in its place still gives to me a sense of miscontinuity, even graphically. I don't know if that's like knowing where the magic trick is, so from then on you always see it even if the magician do it perfectly....

There are many downsides anyway I know. Also beacuse Docking is not meant to be used for this kind of activities. But it's also a bit of fun to test it. My target for now is to just create the SLS example with this new method and launch it with the orbit program, put Ms2015 SLS next to this and see if there is an advantage, if it's more beautiful, if it's more realistic, or if it's way worse.

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Originally Posted by boogabooga View Post
 It might be nice to have payloads docked together. Perhaps for live vessel payloads, you undock rather than detach?
yes. My idea is to simulate the jettison by deleting the docking port of the rocket on J press by the user.
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Old 05-15-2017, 09:48 PM   #798
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Originally Posted by fred18 View Post
 5) I'm also thinking about a "kerbalisation" when you can load your stages into the sim, assemble your rocket and fly. Not that I like it much, I don't even have KSP installed, but how much this is liked around?


That was exactly what I was thinking with a previous post I wrote here !
And about my wish to integrate in the "guidance_file"a command like "= Undock (123)"
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Old 05-16-2017, 10:26 PM   #799
boogabooga
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Okay, after about two years I've upgraded my multistage 2015 to the latest version. Some thoughts/bug reports:

First of all, since apparently the SLS test scenario is my responsibility , I should say that the boosters are facing the wrong way. In the SLS ini, it should be angle =180 instead of angle = 3.14. IIRC, last fall the code was changed from radians to degrees but it appears that the ini file was not changed to match.

It seems that for some reason, since Oct. 2015, the default fairing jettison velocity has changed from +3X to -3Y. Not necessarily a bug, but it's something to be aware of since my old scenarios now look weird.

Orbiter 2010 only:
The camera vessel is not working properly for me. (Default SLS test scenario.) I can't see any terrain or vessels through the camera unless I pause the scenario. Only the horizon. Also, many CTDs when I switch to camera vessel. Everything works fine in Orbiter 2016.

Orbiter 2016 only:
It seems that the "GLimit" guidance command is only being respected if the complex flight is on and not when it is off. Or perhaps vice versa (memory fuzzy). I might test this some more and get back to you. But I did notice an issue in my Atlas V.
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Old 05-17-2017, 01:09 AM   #800
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Originally Posted by boogabooga View Post
 First of all, since apparently the SLS test scenario is my responsibility , I should say that the boosters are facing the wrong way. In the SLS ini, it should be angle =180 instead of angle = 3.14. IIRC, last fall the code was changed from radians to degrees but it appears that the ini file was not changed to match.

It seems that for some reason, since Oct. 2015, the default fairing jettison velocity has changed from +3X to -3Y. Not necessarily a bug, but it's something to be aware of since my old scenarios now look weird.
oh , I have to say that I had been using the SLS example also for testing purpose for the DMD and all the other stuff, so it's easy to guess that I messed up something at the time and never got back to fix it. I'll take what you provided at the time again and I'll fix it!

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Originally Posted by boogabooga View Post
 Orbiter 2010 only:
The camera vessel is not working properly for me. (Default SLS test scenario.) I can't see any terrain or vessels through the camera unless I pause the scenario. Only the horizon. Also, many CTDs when I switch to camera vessel. Everything works fine in Orbiter 2016.
seems like I put the wrong dll in the package or I compiled the MS_Camera vessel using wrong properties. I have to check this soon!

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Orbiter 2016 only:
It seems that the "GLimit" guidance command is only being respected if the complex flight is on and not when it is off. Or perhaps vice versa (memory fuzzy). I might test this some more and get back to you. But I did notice an issue in my Atlas V.
That's interesting, I can't remember a relation among this two options. I'll go to check the code there.

Thanks for beta testing and bug report!! it's fundamental to have a working addon for everybody!!

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Old 05-17-2017, 11:39 AM   #801
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So, it seems that "Glimit" is not working properly in Orbiter 2016, and it has nothing to do with complex flight. Tested again and not working either way. Perhaps it works randomly and that's how I got confused?
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Old 05-19-2017, 05:36 PM   #802
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Originally Posted by boogabooga View Post
 So, it seems that "Glimit" is not working properly in Orbiter 2016, and it has nothing to do with complex flight. Tested again and not working either way. Perhaps it works randomly and that's how I got confused?
Will you please check if this works better?
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Old 05-19-2017, 11:05 PM   #803
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Seems to have fixed it, but as always the actual G is about 0.2 above the limit.
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Old 05-20-2017, 12:29 AM   #804
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 Seems to have fixed it,
the reason of the bug then is that in the new orbiter the velocity vector function has more than one frame to be chosen and I chose not the best one for this use.

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 but as always the actual G is about 0.2 above the limit.
0.2 Gs or 0.2 m/s2 ? how do you measure your acceleration or your G-load?

it's important to say that:
1) the value of G0, general gravity acceleration is computed and not given, and the result for earth is 9.82.
2) the acceleration is computed as the projection of the acceleration on the velocity vector (just like the surface mfd works).
3) The result could be FPS driven. Today during my test it was very precise, but in my new pc I get some 600 FPS so it's difficult to say .

I added here a patched module which will show you in the debug string when glimit command is active the Current G of the rocket (as calculated by the program) so we can see if that's an FPS issue or if simply we are doing two different calculations.
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Old 05-20-2017, 12:32 AM   #805
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I use a load MFD and it always seems to read about 0.1-0.2 Gs above the limit I set.

I will check.

Any word on the camera in Orbier 2010?
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Old 05-20-2017, 12:34 AM   #806
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 Any word on the camera in Orbier 2010?
Did not have the time to check it yet, too much real life in this days. I'll have a look at it this weekend.
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Old 05-20-2017, 01:46 AM   #807
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There is a bug in the way that Multistage 2015 is calculating G load. I suspect that you are not properly taking into account gravity.

Here we are a few seconds after ignition with the launch vehicle accelerating upward vertically:



Notice that Launch MFD is giving a very sensible value of 1.63G all directed along the Z axis.

Multistage is showing 0.63G, which is wrong, since the launch vehicle is clearly accelerating upward. I know that my rocket has a >1 thrust/weight ratio...


Quote:
Originally Posted by fred18 View Post
 Did not have the time to check it yet, too much real life in this days. I'll have a look at it this weekend.
Be sure to make time to spend with your new bride...

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Originally Posted by fred18 View Post
 2) the acceleration is computed as the projection of the acceleration on the velocity vector (just like the surface mfd works).
Why projections? You don't really care about how much the velocity is changing for this, just the G force.
Just find the instantaneous total thrust force and divide by the instantaneous total stack mass, then normalize by 9.8...
I think that by the time a Glimit calc is needed, most users will be well above the atmosphere, so neglect drag.

Last edited by boogabooga; 05-20-2017 at 03:27 AM.
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Old 05-20-2017, 10:47 AM   #808
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All right, I've made a couple of tests and this is becoming a bit tricky:
in orbiter you can obtain easily the total force vector acting on the vessel so my idea was quite simple: get the total force vector, get its length, divide it by rocket mass and that's the acceleration right?

What's happening with the rocket just climbing is a bit counterintuitive to me, I have to think about it: when the rocekt fire its engines and starts to climb we have the gravity force which is downward and the thrust force which is upward (neglecting the rest now, for simplicity). the resulting force therefore is the difference between weight and thrust, so the acceleration I get is just the difference between acceleration due to thrust and acceleration due to gravity, that's why you see 0.63. Now, as we know they should sum to get the G value, not the opposite, even though the total force vector is calculated in the right way. It's a bit of a mind trick.

And then there is another point, which is connected to the velocity vector projection: while in orbit without firing any engine the only force acting on the vessel is weight right? then you should feel 1g (a little less due to the height, but for now it's not important). well in reality due to the centrifugal apparent force you feel 0G, then how to account the G load properly?

Surely I can for simplicity take the thrust, divide it by the mass to obtain the acceleration, but then sitting on the ground it would be 0g, while it should be 1g, right? I was just thinking how to get the overall correct result. I've made a new function to calculate Gs, which gives exactly 1G on the ground, but still I get the difference between thrust and weight while climbing.
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Old 05-20-2017, 10:39 PM   #809
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Fred, I think you are confused over contact forces vs. body forces. I recommend that you read up on that. You "feel" contact forces, but not body forces. And what you "feel" is not the same as your actual time derivative of velocity.

A freefall is 0G. You "feel" weightless, but really you are accelerating downward via a body force. Whether you have enough horizontal velocity to orbit is inconsequential to the issue here.

A hover at constant altitude is 1G. You feel the 1G via the contact force of the rocket engine, but in reality your velocity is not changing relative to the ground.

A rocket accelerating upward with a thrust/weight of 2 is 2G. The cargo inside feels 2G of force due to contact forces, but the actual change in velocity relative to the ground is 9.8 m/s/s.

---------- Post added at 06:39 PM ---------- Previous post was at 06:09 PM ----------

Quote:
Originally Posted by fred18 View Post
 All right, I've made a couple of tests and this is becoming a bit tricky:
in orbiter you can obtain easily the total force vector acting on the vessel so my idea was quite simple: get the total force vector, get its length, divide it by rocket mass and that's the acceleration right?
Not going to give the informtion that you need.

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Originally Posted by fred18 View Post
 when the rocekt fire its engines and starts to climb we have the gravity force which is downward and the thrust force which is upward (neglecting the rest now, for simplicity). the resulting force therefore is the difference between weight and thrust, so the acceleration I get is just the difference between acceleration due to thrust and acceleration due to gravity, that's why you see 0.63. Now, as we know they should sum to get the G value, not the opposite, even though the total force vector is calculated in the right way. It's a bit of a mind trick.
Yes, the actual acceleration will be 0.63* 9.8 m/s/s, but that does not matter to what we are doing here. The cargo inside the rocket will only "feel" the contact force of the firing rocket engine, and that is going to be 1.63G. To the cargo, it is being pushed back with the force of gravity plus some extra.

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 And then there is another point, which is connected to the velocity vector projection: while in orbit without firing any engine the only force acting on the vessel is weight right?
No, the only force acting on the vessel is gravity.

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Originally Posted by fred18 View Post
 then you should feel 1g (a little less due to the height, but for now it's not important).
No, you feel 0G, because gravity is a body force and not "felt".

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Originally Posted by fred18 View Post
 well in reality due to the centrifugal apparent force you feel 0G, then how to account the G load properly?
No. You feel 0G because gravity is a body force and is not felt. You still feel 0G if you are in space on a suborbital trajectory. (People are going to be paying good money to do that with Virgin Galactic, and Blue Origin and the rest, so it better be true. ) Or an escape trajectory. Or any kind of dragless freefall.

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 Surely I can for simplicity take the thrust, divide it by the mass to obtain the acceleration,
Yes, do that. That is the contact force that matters.

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 but then sitting on the ground it would be 0g, while it should be 1g, right?
What happens on the ground is that the ground imparts an upward contact force of 1G to cancel the acceleration of gravity. You feel the upward contact force but not the downward body force of gravity. So net is 1G "felt".

Once you leave the ground, the engines (and air drag) will provide all of the contact forces. So just do thrust/mass and just perhaps do a check that you are not on the ground or in the atmosphere or document that the command is not applicable on the ground or in heavy atmosphere.

Nobody needs a throttle back command on the ground, do they?

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Originally Posted by fred18 View Post
 I was just thinking how to get the overall correct result. I've made a new function to calculate Gs, which gives exactly 1G on the ground, but still I get the difference between thrust and weight while climbing.
Only use contact forces in your G force calculation.
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Old 05-21-2017, 10:52 AM   #810
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All right, I'd say that I agree with part of what you said but not entirely.

surely the only thing that matters here is thrust/mass (drag can be considered, it's easy to add it). So I'll make it that way and that's it.

I was trying to reach a good math solution for a bit of purism, and about it the (very easy) solution just came to my mind: The point is that the rocket system is not an inertial system, so apparent forces will arise for the bodies belonging to this system.



Quote:
Originally Posted by boogabooga View Post
 A freefall is 0G. You "feel" weightless, but really you are accelerating downward via a body force. Whether you have enough horizontal velocity to orbit is inconsequential to the issue here.

A hover at constant altitude is 1G. You feel the 1G via the contact force of the rocket engine, but in reality your velocity is not changing relative to the ground.

A rocket accelerating upward with a thrust/weight of 2 is 2G. The cargo inside feels 2G of force due to contact forces, but the actual change in velocity relative to the ground is 9.8 m/s/s.
this is all correct

Quote:
Originally Posted by boogabooga View Post
 Yes, the actual acceleration will be 0.63* 9.8 m/s/s, but that does not matter to what we are doing here. The cargo inside the rocket will only "feel" the contact force of the firing rocket engine, and that is going to be 1.63G. To the cargo, it is being pushed back with the force of gravity plus some extra.
the cargo will feel gravity and the apparent non inertial force due to the rocket accelerating.

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Originally Posted by boogabooga View Post
 No, the only force acting on the vessel is gravity.
well weight is the force acting on a body due to gravity field

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Originally Posted by boogabooga View Post
 No, you feel 0G, because gravity is a body force and not "felt".
No. You feel 0G because gravity is a body force and is not felt. You still feel 0G if you are in space on a suborbital trajectory. (People are going to be paying good money to do that with Virgin Galactic, and Blue Origin and the rest, so it better be true. ) Or an escape trajectory. Or any kind of dragless freefall.
no, the point is that the orbiting vessel is not an inertial system, so centrifugal apparent force will apply. This is due to the fact that the system is constantly accelerated by gravity and the resulting apparent centrifugal force will be equal to F=m*v^2 / r. That's why orbital velocity has an impact to 0g feeling of the orbiting astronauts. Virgin Galactic will use free fall, which applies the same concept, as the vomit comet airplan.
I've made tons of calculations about this in the past (both for real life work and for orbiter), that was silly of me not remembering this immediatly.

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Originally Posted by boogabooga View Post
 What happens on the ground is that the ground imparts an upward contact force of 1G to cancel the acceleration of gravity. You feel the upward contact force but not the downward body force of gravity. So net is 1G "felt".
well I'm not so sure with what you mean with contact and body, in reality it works like this:

if we consider a body into gravity field and we take it as our reference system this will be a non inertial system, since bodies are accelerated towards the bigger mass. The forces acting on a body sitting on the ground are its weight and the constraint reaction of the soil, equal and opposite to the weight force, as Newton said. Then the body is not moving since the resulting force is 0. However the system is not inertial so the body will feel the apparent force due to gravity acceleration, and that's 1G.

Anyway I'll make thrust over mass, that is relevant to the use we want to make here.

Last edited by fred18; 05-21-2017 at 02:44 PM.
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