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Gemini 060615 released!
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Author Topic: Reentry Simulation Development Archive  (Read 7923 times)
Anonymous
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« on: January 28, 2005, 06:29:10 AM »

Hi all

First. This project is amazing: THANK YOU VERY MUCH Movieman, RMaia, Moonwalker and ALL apollo project guys..

Im newbie here and I would like to be help but Im not much coder myself   Rolling Eyes   ....trying figure it out though.  (maybe near future).
 
Heres some ideas for the future projects....I know you guys have hands full... but I cant help it . Here it goes.....

1. FDAI`s 3D shape & markings and their error needles need some work. Something like If you could slave error needles to transX targeting system.( something like Alignplane II MFD) You could use these in midcourse correction, turn progrades, retrogrades etc.

2. Entry Monitor System. Oh! we absolutely need that.  (DeltaV/ VHF Range, 0.5g Treshold ind, Lift vector and of course the Scrolling tape)

With AGS these two are instruments that gives Apollo/CSM the right feeling and "soul"  Though there are many important instruments beside these

Couple questions:
Is it possible to implement  sextant/star tracking systems in Orbiter
at all according to its code?
and can anybody give simplified explanation how those error needles and attitude thumb wheels (ASCP) work or interacts each other?

i couldnt figure it out.

Im so happy to see that Apollo Project is going on fast and strong.

Thanking

Apassi
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Bob7
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« Reply #1 on: January 28, 2005, 11:53:50 PM »

It whould work, as long as someone decides to implement it. The ship's orientation would have to be controlled by the AGC (thats how it was on the real thing). The user would use a set of keys to adjust a special .dll controlled view. They could place a marker in over the apollo guidance stars (they are already marked via the F9 key). The angles of the view would be fed to the AGC and used for it's own guidance calculations (seperate from Orbiter).
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chode
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« Reply #2 on: January 31, 2005, 01:14:57 PM »

I've been trying to figure out what the correct lift model should be for the Apollo command module with the hopes of getting it into NASSP/NCCP at some point. I've found the current lift model in the source code, and I don't think it is very realistic. Also, I tried reentries with different AOAs and verified that it just doesn't behave as I would expect. Does anyone know where that model originated? I have a model that I think is more realistic and would like to see it incorporated into the ongoing development. I sent a more detailed PM to movieman about this, but would also like to see if there is anyone else interested or knowledgable about this.
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movieman
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« Reply #3 on: February 01, 2005, 07:58:16 AM »

The real CM had a CoG offset from the center of pressure, and was controlled by rolling to change the lift. How exactly it worked beyond that, I don't really know.
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chode
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« Reply #4 on: February 02, 2005, 02:53:11 AM »

At this point, I'm very optimistic about creating a realistic re-entry model for Apollo for Orbiter.

movieman: Thanks so much for distributing your latest source code, I was able to get it to compile without TOO much trouble. I was successful in modifying the code to incorporate my new airfoil models.

Using what I've gathered about the lift and drag coefficients for Apollo, I've been able to reproduce a reentry profile (in Orbiter) that very closely matches the real Apollo 8 reentry. I'll post some graphs, if anyone is interested.

However, the flight profile is extremely difficult to fly manually, which is probably why the real Apollo had computers fly the reentry. So, I guess eventually we'll need an autopilot for reentry.

And movieman, your right about rolling to control lift,  they actually rolled 180 degrees to keep themselves from escaping the atmosphere.
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chode
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« Reply #5 on: February 04, 2005, 03:26:27 AM »

Quote from: Anonymous
Hi all


2. Entry Monitor System. Oh! we absolutely need that.  (DeltaV/ VHF Range, 0.5g Treshold ind, Lift vector and of course the Scrolling tape)


Apassi


Well, I'm working on the EMS, scrolling tape and all, and I think you'll be happy with the result.
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Apassi
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« Reply #6 on: February 04, 2005, 06:00:37 AM »

Thanks for replying.

Hey chode: Have you figure it out how the entry trajectory is plotted to the
scrolling tape ?

Apassi
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chode
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« Reply #7 on: February 04, 2005, 11:30:15 AM »

From what I've researched, the scroll was a transparent mylar with the graphics printed on the front side, and an opaque coating on the back,  which was "scratched" by a stylus on the back side. I'm not sure exactly what it looked like in operation. For example: was the entry line black or did it have some color to easily distinguish it from the graphics.
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movieman
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« Reply #8 on: February 05, 2005, 01:01:10 PM »

Good! It will be nice to see that working realistically.
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robertsconley65
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« Reply #9 on: February 07, 2005, 12:00:30 AM »

You code should be interesting to see as gemini has the same type of lifting re-entry as apollo. The method I came up with was simply looking up the different l/d values as you rolled the gemini around using the old lift function. The biggest difficulty was computing the right drag value but hopefully I solved that in Merc 5.0. So Gemini 5.0 will just use the Merc 5.0 airfoils with the addition of lift vectors.

Control during re-entry of the capsule was done through rolling only.

Rob Conley
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chode
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« Reply #10 on: February 07, 2005, 01:09:04 AM »

Well, if you're interested, here's the code:

CreateAirfoil(LIFT_VERTICAL, _V(-0.014,0.107,0.75), CoeffFunc, 3.5 ,11.95, 1.0);

with the callback function:

void CoeffFunc (double aoa, double M, double Re, double *cl, double *cm, double *cd){
   const int nlift = 11;
   const double factor=0.0;
   static const double AOA[nlift] =
      {-180*RAD,-160*RAD,-150*RAD,-120*RAD,-90*RAD,0*RAD,90*RAD,120*RAD,150*RAD,160*RAD,180*RAD};
   static const double CL[nlift]  = {0.0,-0.3,-0.425,-0.215,0.0,0.0,0.0,0.215,0.425,0.3,0.0};
   static const double CM[nlift]  = {0.0,0.004,0.006,0.012,0.015,0.0,-0.015,-0.012,-0.006,-0.004,0.};
   static const double CD[nlift]  = {1.6,1.4,1.0,0.6,0.75,0,0.75,0.6,1.0,1.4,1.6};
   static double SCL[nlift-1];
   static double SCM[nlift-1];
   static double SCD[nlift-1];
   for(int j = 0; j < nlift-1; j++){
      SCL[j]= (CL[j+1]-CL[j])/(AOA[j+1]-AOA[j]);
      SCM[j]= (CM[j+1]-CM[j])/(AOA[j+1]-AOA[j]);
      SCD[j]= (CD[j+1]-CD[j])/(AOA[j+1]-AOA[j]);
   }
   for (int i = 0; i < nlift-1 && AOA[i+1] < aoa; i++);
   *cl = (CL + (aoa-AOA)*SCL);
   *cm = factor*(CM + (aoa-AOA)*SCM);
   *cd = (CD + (aoa-AOA)*SCD);
}

The functions for the coefficients of lift, drag, and pitching moment are taken directly from a study I found on the aerodynamics of a re-entry capsule not unlike the Apollo.

The key to the whole scheme is the "center of lift offset": (-0.014, 0.107, 0.75) in CreateAirfoil, which locates the center of lift and drag back from the center of mass and slightly offset from the vertical axis. This combination gives the body a "stability angle" of 160 degrees AOA. So, as you roll the capsule around, it automatically stays at the proper AOA, making control rather easy; you only need to roll it during re-entry, and the aerodynamic forces keep the AOA close to 160.

[EDIT] My earlier comment about this reentry being extremely difficult was made before I discovered how to create a "stability angle". So the reentry should be quite easy to fly when this gets into the project.
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RMaia
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« Reply #11 on: February 08, 2005, 08:24:25 AM »

That's a great contribution. Actually a reentry auto-pilot may not be too far from reality, as after I finish work on the LM ascent auto-pilot V4, my plans are to start working on one. This will be of much help.

BTW, Chode, could you send me the modified airfoil code so I can try it out? I don't know if it's my computer (which for sure is not working as I wished) or the forum, but I'm not able to copy and paste it... Crying or Very sad
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Rodrigo Merce Maia

- Sometimes, simplicity is the best answer to complexity.

Physics is FUN!
robertsconley65
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« Reply #12 on: February 08, 2005, 09:43:57 AM »

Quote from: chode
Well, if you're interested, here's the code:


The functions for the coefficients of lift, drag, and pitching moment are taken directly from a study I found on the aerodynamics of a re-entry capsule not unlike the Apollo.



You have a copy of that study and how you translated the values from that to what orbiter expects?  I some studies of Gemini so this would help a lot. This is great stuff thanks.

Rob Conley
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chode
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« Reply #13 on: February 08, 2005, 02:16:27 PM »

The study I used is here:

http://techreports.larc.nasa.gov/ltrs/PDF/NASA-aiaa-96-0316.pdf

There are a lot of reports on that site that may be worth looking at.  I haven't had a chance to look at many yet.

This doesn't tell how to create a stability angle by offsetting the center of pressure from the center of gravity. I had to figure that out myself, and the final values were arrived at by trial and error.

Can you send me or point me to the stuff you have on Gemini?
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robertsconley65
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« Reply #14 on: February 14, 2005, 10:18:54 PM »

Quote from: chode


Can you send me or point me to the stuff you have on Gemini?


Opps I never replied to this. All my Gemini docs are at
https://sourceforge.net/project/showfiles.php?group_id=55046&package_id=68567&release_id=172017

Rob Conley
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