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New Flight Gear Terrain Engine

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Re: New Flight Gear Terrain Engine

Postby vitos » Sat May 14, 2011 9:35 pm

Thorsten wrote in Sat May 14, 2011 1:12 pm:I beg to differ. You did not launch and land as it was in reality, you did launch and land as a Flightsimulator would allow you to do it and just didn't notice the difference to reality. There are lots of physics issues which are not in Flightgear, but needed for spaceflight.


I am talking about what I had been tested and know really. Atmosphere on high altitudes in JSB acts exactly as it should and produce very small drag, but drag, and exactly drag what I had awaited. I was even changed reactions a bit to make 100...150km orbital flight more durable, because that small drag was lead to fast deorbit on second or third orbit as it does in reality on that altitudes.

Yes, shield heating issues is still up to You if You make reentry. But those reactions in first approach do not changes nothing but only possibility of craft to burn out if it oriented wrong side too long. I suppose it's not problem. If You thinks what these reactions really changes drag then I could say not so, at least if You are using Datcom calculated data for hypersonic flight.

To be exact, burn on west Africa coast leads exact to landing somewhere in Kasakhstan. I had been tested it.

Maybe some magnetic fields really produces shifts but I suppose not so, at least until You give me formula for that to prove You are right. And if You would give to me formula it would be included in JSBSim fast.

About long term flights I could say what we simply do not need it now. We need only short flights up to number of orbits because no normal man could wait with simulator so long and currently there is not so much of possibility to make a time warps in FG with all that terrain lags.

And, to finish that reasoning, some long way begins from first step. If You do not make it then here will be no long way, at least for You.

Thorsten wrote in Sat May 14, 2011 1:12 pm:Nope - I'm trying to explain to you why there has not been any response on the devel list. However, if you think you know already, then I'll just quit taking here.


People who wants to do something search for means. People who do not, them search for explanations. I want to do, so I do not need explanations. I need "I could help". If You personally could not then much talking is wasting of time for both of us only.
Last edited by vitos on Sat May 14, 2011 10:00 pm, edited 2 times in total.
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Re: New Flight Gear Terrain Engine

Postby vitos » Sat May 14, 2011 9:57 pm

xiii wrote in Sat May 14, 2011 1:31 pm:When it comes to hot weather you both better go water the flowers in the garden, (or at least focus on a funny MDW nasal simulation) until conditions for a fun and friendly collaboration are back.


I do not argue. I search for people who can help. That's all. So if someone thinks "that's not needed" or "that's could not be done" or "better do it other way, do not know when and how" or something similar then there is no reason in conversations simply.

It is _already_done_. Again, it's _already_done_. I had liftoff somewhere near Kasakhstan, all three stages workout, then orbital corrections to make stable orbit, then orbital flight, then deorbit burn, then deorbit with exact 10g, then landing on chute system near Kasakhstan again. I did it twice. It works.

Maybe it's not exact as someone wants, but well, if You want it better then take a part. If not then do Your business.

Look. If it's so hard to find some guy who could include already existed engine in already existed simulator then how You suppose I could find guys to make completely new simulator? A?

I said and had shown it pretty clear, if not then it's impossible to make it clearer. There is _no_other_way_ to make some common open source space flight simulation than improve Flight Gear in that means. At least until You are not some wealthy sponsor who wants to waste 50k$ to simulator itself and 200k$ to promotional campaign in knowing it'll never get back. In other case You would make something as http://www.openorbit.org/home. I mean something what could take a lot of efforts but could not grow to some product really used by people.

Me personally is not a guy who could do brand new simulator currently. If You are one then where Your brand new simulator is?

So, again, if You want some open source space flight then take a part. If not then do Your own stuff.
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Re: New Flight Gear Terrain Engine

Postby jonsberndt » Sat May 14, 2011 10:26 pm

Thorsten wrote in Sat May 14, 2011 1:12 pm:
There is no real difference, nor in physics, nor in stability. Only different accounting of gravity. There is no real difference. JSBSim, what Flight Gear is using already, accounts all needed things at least for low Earth orbit flight. You seems to not had read what I did wrote too. If I write "spaceflight is possible already...I did it number of times" it means what I did it from takeoff to land exactly as it was in reality.


I beg to differ. You did not launch and land as it was in reality, you did launch and land as a Flightsimulator would allow you to do it and just didn't notice the difference to reality. There are lots of physics issues which are not in Flightgear, but needed for spaceflight.

I fail to see how Flightgear could possibly get re-entry physics right for starters. Re-entry creates super-hot plasma shockwaves, and here actually chemistry matters, because there's a lot of reactions going on which alter atmospheric properties. Doesn't occur for flight simulations. Re-entry has been and still is a tough problem to simulate. But orbital flight requires not only to simulate gravity vs. centrifugal force - there's drag from upper atmosphere, magnetic fields and these sort of thing.


Thorsten,

Actually, yes, in fact we are very close to being able to simulate all aspects of spaceflight from liftoff to touchdown. As far as orbital flight goes, we are spot on. For ascent, we are spot on - as far as the available data will take us. For entry, we can get very, very close. Neither JSBSim - nor many other 6DoF simulators that I have worked with in the field of spaceflight for many years - care at all about the chemistry. They only care about the forces and moments, which come from the coefficients, which can be estimated with some degree of finesse and give pretty nice results. Spaceflight with JSBSim and FlightGear is in fact right now absolutely possible from a 6DoF flight dynamics perspective. The graphical engine is not quite there yet, though.

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Re: New Flight Gear Terrain Engine

Postby vitos » Sat May 14, 2011 10:41 pm

jonsberndt wrote in Sat May 14, 2011 10:26 pm:For entry, we can get very, very close.


BTW, is it possible to add some default heating calculations? I already have a formulas for stagnation and surface temperatures:

Code: Select all
      <fcs_function name="aero/temperature/stagnation-mach-c">
      <function>
         <description>
            Stagnation temperature due to Mach number and altitude
         </description>
         <product>
            <difference>
               <product>
                  <sum>
                     <value>273</value>   <!-- Celsius to Kelvin -->
                     <value>15</value>   <!-- Standart mean temperature -->
                  </sum>
                  <sum>
                     <value>1</value>
                     <product>
                        <quotient>
                           <difference>
                              <value>1.4</value>   <!-- Cp/Cv coefficient for twoatomic gases -->
                              <value>1</value>
                           </difference>
                           <value>2</value>
                        </quotient>
                        <pow>
                           <property>velocities/mach</property>
                           <value>2</value>
                        </pow>
                     </product>
                  </sum>
               </product>
               <value>273</value>
            </difference>
         </product>
      </function>
      </fcs_function>

      <fcs_function name="aero/temperature/surface-mach-c">
      <function>
         <description>
            Surface temperature due to Mach number and altitude
         </description>
         <product>
            <difference>
               <property>aero/temperature/recovery-mach-c</property>
               <product>
                  <quotient>
                     <value>0.5</value>
                     <value>50</value>   <!-- Mean air heat transfer coefficient-->
                  </quotient>
                  <quotient>
                     <property>atmosphere/P-psf</property>
                     <product>
                        <value>0.3048</value>   <!--  Feets/sec to meters/sec-->
                        <value>0.3048</value>   <!--  Feets/sec to meters/sec-->
                     </product>
                  </quotient>
                  <pow>
                     <product>
                        <property>velocities/vt-fps</property>
                        <value>0.3048</value>   <!--  Feets/sec to meters/sec-->
                     </product>
                     <value>3</value>
                  </pow>
               </product>
            </difference>
         </product>
      </function>
      </fcs_function>


Nearly sure about first, do not sure about second. And there is needing of adding some glowing color calculations on base of temperature and other factors. Already have some, but not exact. Maybe someone could check this out.

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Re: New Flight Gear Terrain Engine

Postby Thorsten » Sun May 15, 2011 10:54 am

So, let me be more precise, since I think we're talking two different issues here:

1)Short, low orbit flights: Here I believe that the issues are reasonably well under control. I believe that if you have the right table of coefficients, you will get reasonable answers. The issue is that the atmosphere is, as in a Flightsim, the dominant dissipative force and any deviation from constant gravity is small, gravity is dominated by Earth and you require stability of orbits on relatively small timescales, because an orbit in the upper atmosphere is probably physically unstable before it becomes numerically unstable.

I remain skeptical about the re-entry physics though, especially if it handles deviations from the default profile correctly. But I'll let myself be convinced by results - so once I have more time, I'll have a look how the Vostok behaves on re-entry.

2) Leaving LEO (i.e. Apollo, pictures from Mars,...): Here, you have a multibody gravitational problem - on a trajectory to Mars, there is the gravity of Earth on leaving with a correction by the Moon, of Sun during most of the trajectory, and of Mars on capture. In this complicated gravitational field which varies over time, you need to have your trajectory stable over a time period of 3 months (!) or so while users go fast-forward with simulation time. At the same time, you can do the math how far 0.1 degree deviation in your trajectory simulation by numerical errors would displace you 250.000.000 km later on arrival. That's a problem that's simply not there in a Flightsim. Even tiny forces accumulate to substantial effects over long times with no dissipative effects around - magnetic fields, light pressure, solar wind.

That's in contrast to a Flightsim where you have forces acting now - it doesn't matter for aerodynamical flight if a gust hit you 10 minutes ago, the plane doesn't remember and the code doesn't need to keep track of tiny forces. It matters in space. Are you truly telling me that JSBSim is able to handle these issues correctly?
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Re: New Flight Gear Terrain Engine

Postby jonsberndt » Sun May 15, 2011 12:38 pm

Thorsten wrote in Sun May 15, 2011 10:54 am:So, let me be more precise, since I think we're talking two different issues here:

1)Short, low orbit flights: Here I believe that the issues are reasonably well under control. I believe that if you have the right table of coefficients, you will get reasonable answers. The issue is that the atmosphere is, as in a Flightsim, the dominant dissipative force and any deviation from constant gravity is small, gravity is dominated by Earth and you require stability of orbits on relatively small timescales, because an orbit in the upper atmosphere is probably physically unstable before it becomes numerically unstable.

I remain skeptical about the re-entry physics though, especially if it handles deviations from the default profile correctly. But I'll let myself be convinced by results - so once I have more time, I'll have a look how the Vostok behaves on re-entry.

2) Leaving LEO (i.e. Apollo, pictures from Mars,...):

...

That's in contrast to a Flightsim where you have forces acting now - it doesn't matter for aerodynamical flight if a gust hit you 10 minutes ago, the plane doesn't remember and the code doesn't need to keep track of tiny forces. It matters in space. Are you truly telling me that JSBSim is able to handle these issues correctly?


Thorsten,

No, there's no intention that JSBSim would handle interplanetary flight - that's not our domain (at least right now ;-) ). I have been referring only to operating only in the vicinity of a single planetary body, such as Earth, Moon, Mars, etc.

Regarding entry, a better high altitude atmosphere model would help a lot. Right now we use the standard atmosphere, and as I recall we have sort of extended that at high altitude. Our current default atmosphere model is not relevant to any kind of real research. We do have another atmosphere model that might be a lot better, but I have not yet tried it in this application. It's the MSIS atmosphere model, and it is in our atmosphere/ subdirectory.

Also, regarding orbital flight, I recently did a comparison between JSBSim and STK (Satellite Toolkit) for a highly elliptical orbit over a 24 hour period. The results were very close. See the JSBSim Facebook page for the details. ( http://www.facebook.com/jsbsim ).

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Re: New Flight Gear Terrain Engine

Postby vitos » Sun May 15, 2011 3:49 pm

jonsberndt wrote in Sun May 15, 2011 12:38 pm:No, there's no intention that JSBSim would handle interplanetary flight - that's not our domain (at least right now ;-) ). I have been referring only to operating only in the vicinity of a single planetary body, such as Earth, Moon, Mars, etc.


To me it's not big problem since Soviets did not get to Moon in manned flight. It`s eight years to times of Apollo 50x celebration, I suppose it will be solved in JSB to that time. If not then here will be some other solution. Eight years is comparatively long story.

jonsberndt wrote in Sun May 15, 2011 12:38 pm:Regarding entry, a better high altitude atmosphere model would help a lot. Right now we use the standard atmosphere, and as I recall we have sort of extended that at high altitude. Our current default atmosphere model is not relevant to any kind of real research. We do have another atmosphere model that might be a lot better, but I have not yet tried it in this application. It's the MSIS atmosphere model, and it is in our atmosphere/ subdirectory.


Actually current atmosphere have a void layer on ~50km altitude so g force on reentry grows to 6, then drops to 0, then grows to 10 again. How to switch to other atmosphere model in JSB? Is it possible to make switch by some property in runtime to not affect current users, or that better model will be better for any craft and it possible to make it default?

jonsberndt wrote in Sun May 15, 2011 12:38 pm:Also, regarding orbital flight, I recently did a comparison between JSBSim and STK (Satellite Toolkit) for a highly elliptical orbit over a 24 hour period. The results were very close. See the JSBSim Facebook page for the details. ( http://www.facebook.com/jsbsim ).


To check out if JSBSim solving problems what Thorsten mean You may to do that thing:

Take that graph of ISS altitude:
Image

Get any straight line cut. From beginning to end it's ISS altitude changing with time without correction burn.

Make some body of ISS character area, and of ISS 415tonns mass, You may count area by that sample picture:

Image

To make it short, ISS have 4 solar arrays, 34x12m each, and whole ISS active area gotta be ~5*solar array area=5*34*12=2040m^2.

And put that body on circular orbit with that initial altitude for that amount of time.

Actually, for short flight, and, to be honest, for some end user space flight simulation at all, it's all not problem, as atmosphere "breathing" because of sun activity cycle, which, as You may see, can change drag up to two times, and other similar things. So if someone interested in that then that someone can check this out. Me personally not so.
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Re: New Flight Gear Terrain Engine

Postby Thorsten » Mon May 16, 2011 7:04 am

Actually, for short flight, and, to be honest, for some end user space flight simulation at all, it's all not problem, as atmosphere "breathing" because of sun activity cycle, which, as You may see, can change drag up to two times, and other similar things. So if someone interested in that then that someone can check this out. Me personally not so.


Right... I think that's a more honest statement than what you previously said:

There is no real difference, nor in physics, nor in stability. Only different accounting of gravity. There is no real difference. JSBSim, what Flight Gear is using already, accounts all needed things at least for low Earth orbit flight. You seems to not had read what I did wrote too. If I write "spaceflight is possible already...I did it number of times" it means what I did it from takeoff to land exactly as it was in reality.


So we can agree that there are currently unrealistic issues (like an empty layer of atmosphere) and not everything is 'as it was in reality', that we don't know at this point because you haven't tested it if orbit deterioration due to drag is addressed correctly, that you actually don't care too much about accurate implementation of some effects because you already know that there are others like atmosphere breathing which you haven't taken into account and that there is actually more quite different physics coming in once you leave a low orbit and that accounting for gravity isn't the only difference?

You know, I think there's nothing wrong with spaceflight in Flightgear - if it doesn't lead to a project state in which just more open issues pile up (which is a question of organization), then I even think it's a great idea. But I'd like a honest list of what issues need to be addressed to do what amount of spaceflight on the table up front, so that people can have a realistic picture of what making it work amounts to. And I think it's fair to state that going to moon is not just a question of a different terrain rendering engine.

So if you are interested in short orbital hops in real time, the deorbiting, then I agree with you that this seems quite in reach with a different atmosphere, a rendering engine and some testing of things like orbital drag forces and so on. But an implementation of the whole solar system (as your post can be understood) is something different entirely.
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Re: New Flight Gear Terrain Engine

Postby vitos » Mon May 16, 2011 10:42 am

Thorsten wrote in Mon May 16, 2011 7:04 am:Right... I think that's a more honest statement than what you previously said:


Man, ease a bit. Who are You to claim me unhonest?

Thorsten wrote in Mon May 16, 2011 7:04 am:You know, I think there's nothing wrong with spaceflight in Flightgear - if it doesn't lead to a project state in which just more open issues pile up (which is a question of organization), then I even think it's a great idea. But I'd like a honest list of what issues need to be addressed to do what amount of spaceflight on the table up front, so that people can have a realistic picture of what making it work amounts to. And I think it's fair to state that going to moon is not just a question of a different terrain rendering engine.


You simply want to bite some too big piece at once. It's useless to make big list of tasks until we can not solve one vital task what blocks solving of any next problem in that list entirely. And it seems You do not understand structure of most Open Source projects at all. You talk as if there was some group of people for whom I could address some wish list and who would implement it, and implement it instead of me myself. Of course man who would ask so could be unhonest. But mostly people who are as that _pays_ for doing what them want. We have completely different story.

Firstly, there is no such group. There is different people, each solve problems in what he or she interested.

Secondly, I want to take part in it by solving problems what me personally wants to solve. I have no wish to "ask and get". Simply there is some problem on the way what blocks my path, which I could solve alone personally but it would take too much not interesting efforts, and what someone else who interested exactly in it could help me to solve fast and easy for that someone.

So I am asking no whole "community" what unexisted really. I am searching for concrete guy or girl who could be interested in helping me to solve that concrete task. If that task will be solved then we, in case that guy or girl would want to solve next problem with me, could make next step. In other case I will make that step alone, and if that would become too hard for me then there could not be that step at all, I simply would go someplace else. But it's final and last option which I wish to avoid.

Of course there is a huge list. Much more real You want it, much bigger that list become. For example, real heating/cooling -150...250c difference implementation it's a huge problem what asks for craft twisting in real life and not solved in any space simulator what I heard of until now. But if You scared of that list then it's simply not Yours. If not then You do not care much about it at all and solve only one current problem what blocks path.That's what I am doing.

Boris Elyseyevitch Chertok, who had and have essential role in real Russian Space Program, and particularly in Vostok program, had said many times: "If today someone would put before us Vostok and ask us for permission to let it fly then no one of us would vote for that. That day we all had vote for it without a doubt."

We would never get somewhere in case we would though about distant future problems. Those problems does not matter because it unexisted until we not solve current.

Actually, I can not understand what makes You talks so long here. My interest is known. I want to make _comfortable_ spaceflight _in_Flight_Gear_. In case You want it You help me, by deeds, not talks. In case You do not care You keep silence and avoid that topic as most of guys do. It seems You do _not_ want it. Why?
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Re: New Flight Gear Terrain Engine

Postby jonsberndt » Mon May 16, 2011 11:08 am

Thorsten wrote in Mon May 16, 2011 7:04 am:
Actually, for short flight, and, to be honest, for some end user space flight simulation at all, it's all not problem, as atmosphere "breathing" because of sun activity cycle, which, as You may see, can change drag up to two times, and other similar things. So if someone interested in that then that someone can check this out. Me personally not so.


Right... I think that's a more honest statement than what you previously said:

There is no real difference, nor in physics, nor in stability. Only different accounting of gravity. There is no real difference. JSBSim, what Flight Gear is using already, accounts all needed things at least for low Earth orbit flight. You seems to not had read what I did wrote too. If I write "spaceflight is possible already...I did it number of times" it means what I did it from takeoff to land exactly as it was in reality.


So we can agree that there are currently unrealistic issues (like an empty layer of atmosphere) and not everything is 'as it was in reality', that we don't know at this point because you haven't tested it if orbit deterioration due to drag is addressed correctly, that you actually don't care too much about accurate implementation of some effects because you already know that there are others like atmosphere breathing which you haven't taken into account and that there is actually more quite different physics coming in once you leave a low orbit and that accounting for gravity isn't the only difference?

You know, I think there's nothing wrong with spaceflight in Flightgear - if it doesn't lead to a project state in which just more open issues pile up (which is a question of organization), then I even think it's a great idea. But I'd like a honest list of what issues need to be addressed to do what amount of spaceflight on the table up front, so that people can have a realistic picture of what making it work amounts to. And I think it's fair to state that going to moon is not just a question of a different terrain rendering engine.

So if you are interested in short orbital hops in real time, the deorbiting, then I agree with you that this seems quite in reach with a different atmosphere, a rendering engine and some testing of things like orbital drag forces and so on. But an implementation of the whole solar system (as your post can be understood) is something different entirely.


I didn't read it that way at all, and it's certainly not my intention to model anything outside of flight near a single planetary body.

Anyhow, I forgot to mention one thing for the experiment on orbital flight: I had no drag coefficient defined, so there was no drag at all. The intention was to test orbits over a single day - not over ten years. With some tweaks on the atmosphere model, I think we'll be in even better shape. I had not seen the void area in the atmospheric properties. Will be interested to look into that.

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Re: New Flight Gear Terrain Engine

Postby vitos » Mon May 16, 2011 11:24 am

jonsberndt wrote in Mon May 16, 2011 11:08 am:I didn't read it that way at all, and it's certainly not my intention to model anything outside of flight near a single planetary body.


Someone else will implement celestial mechanics then. From JSBSim will be needed no essential additions I suppose, and from Flight Gear will be needed possibility to switch between JSB and that celestial engine on altitudes what higher when hight elliptical orbit but lower then significant part of path to the Moon.

jonsberndt wrote in Mon May 16, 2011 11:08 am:Anyhow, I forgot to mention one thing for the experiment on orbital flight: I had no drag coefficient defined, so there was no drag at all. The intention was to test orbits over a single day - not over ten years. With some tweaks on the atmosphere model, I think we'll be in even better shape. I had not seen the void area in the atmospheric properties. Will be interested to look into that.


I had tested drag on orbit of course. Yes, I suppose it will not ask much, only slight tweaks. Maybe there is no void layer in other better atmosphere engine. Could You tell, how to switch on it?

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Re: New Flight Gear Terrain Engine

Postby Sealbhach » Mon May 16, 2011 11:32 am

Don't forget about the new scenery tiles needed, to get a nice view while burning up on re-entry. :D

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Re: New Flight Gear Terrain Engine

Postby Thorsten » Mon May 16, 2011 11:37 am

Man, ease a bit. Who are You to claim me unhonest?


I just called your statement 'honest', didn't I? :-) I don't remember calling you dishonest.

Actually, I can not understand what makes You talks so long here. My interest is known.


I'm chiefly not talking to you (I'd do that by PN if needed), I'm talking to the same people you'd like to address - gathering a picture of what actually needs to be done before starting to do something. I actually consider that useful. You don't own this tread, so you'll have to put up with my opinion for the time being.

You simply want to bite some too big piece at once. It's useless to make big list of tasks until we can not solve one vital task what blocks solving of any next problem in that list entirely.


Who are you to tell me what is useless and what not? It seems you don't understand the structure of project management at all, ... (I'm kidding you a bit).

I found it always useful to see and define the big picture first, then outline what needs to be done, and then work with purpose towards the big picture goal. Saves lots of double work. I was thinking about dynamical evolution of clouds long before I had ever a decent solution for a single cloud - because I wanted to have all items in place once I arrived there, and not being stuck in some old code which limits me unless I redo everything. So - it's called brainstorming.

Kindly accept that there are different work philosophies around and that Boris Elyseyevitch Chertok is not the measure of all things.

In case You want it You help me, by deeds, not talks. In case You do not care You keep silence and avoid that topic as most of guys do. It seems You do _not_ want it. Why?


First, you may want to remember your own reaction to my question Hm, if you are happy with the Wiki system, then why don't you simply continue to use it? Nobody wants to take it away. But others (such as myself) feel that they are not happy with it, and would like to have different information - so we try to implement something else in addition - why do you see the need to argue against it just because it is not the information you consider useful? in this thread. Why did you get involved and continued to discuss?

My answer here is obvious. Spaceflight interests me, I'd like to see it, and I'd like to see it done well. So according to my (and others (not your and yet others) philosophy of what's useful to begin a project, I start by assembling a bigger and hopefully realistic picture of what is needed for what. That got admittedly a bit derailed by you doing away with my points that spaceflight and aerodynamical flight have different requirements and by your claim that you could do things 'as in reality' which made me somewhat angry. Do you think you can understand why?

I may not be behaving as expected in your philosophy how to run a project - but hey, this is open source - my philosophy is as valid as yours, and I believe talk can contribute to a project if it contains information. As I believe my points do.
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Re: New Flight Gear Terrain Engine

Postby vitos » Mon May 16, 2011 11:43 am

Sealbhach wrote in Mon May 16, 2011 11:32 am:Don't forget about the new scenery tiles needed, to get a nice view while burning up on re-entry. :D

.


osgEarth, what I had talked about here previously, allows more exact tiles on some places and less exact on others. Since liftoff and deorbit paths for spaceflights is defined there is possibility to make it without additional midlayer. Guys who take other paths than normal may not need nice views until they come on >25km altitude where current FG engine could take a part, because they for sure would be more interested in question will craft burn out or not and will it land on some solid ground or not than cool looking views.

Actually tiles, for both high altitude layer and orbit/deorbit midlayer, could be counted automatically on base of current FG tiles. It's another task, but not first in list. Firstly we need _any_ Earth ground view on altitudes >25km what not slows FG to zero. Until that problem is not solved it's not needed to get deep into other tasks.
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Re: New Flight Gear Terrain Engine

Postby jonsberndt » Mon May 16, 2011 12:17 pm

jonsberndt wrote in Mon May 16, 2011 11:08 am:
...

Anyhow, I forgot to mention one thing for the experiment on orbital flight: I had no drag coefficient defined, so there was no drag at all. The intention was to test orbits over a single day - not over ten years. With some tweaks on the atmosphere model, I think we'll be in even better shape. I had not seen the void area in the atmospheric properties. Will be interested to look into that.

Jon


This might be a good article to look at if the upper atmosphere model is to be improved:

"Jacchia-Lineberry Upper Atmosphere Density Model"
http://ntrs.nasa.gov/archive/nasa/casi. ... 012203.pdf

Also, take a look at this survey of atmosphere models:
http://www.spacewx.com/Docs/AIAA_G_003C_2010_9-10.pdf

Jon
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