New atmospheric model for Earth

martins

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Since Orbiter's atmosphere model has been discussed quite a bit recently, I finally decided to revisit and rewrite the Earth atmosphere model. I have selected a moderately complex model (L. G. Jacchia, Thermospheric Temperature, Density, and Composition: New Models, Smithson. Astrophys. Obs. Spec. Rept. No. 375, 1977) which covers the range from 90 to 2500km (using a static standard atmosphere model below 90km). The only model parameter (apart from altitude) is the exospheric temperature. I found a plausible model for the diurnal exosphere temperature variations (Montenbruck, Satellite Orbits), but I won't include any dynamic parameters that depend on observation data (geomagnetic activity, solar flux).

Once I've written up the details I'll present them here for disucssion. Also, once implemented, I will upload a new public beta.

In any case, the new model will be substantially different from the current one. Not only will it extend to more than 10x the current altitude, it will also be far denser in the range from ~120 to 200km. This is because the current model seriously underestimates the high-altitude temperature. As a result, long-term stability of LEO (physical and numerical) will become more of a challenge, so I thought I should drop an early warning. Possible problems include

- Launch autopilots. Anything that relies on the current atmosphere model may need to be rewritten. Increased drag will eat into the Delta-V budget, so reaching a given orbit will require tighter planning. Also, since the atmosphere has a diurnal oscillation, the autopilots will need to be adaptive, or take the time of day and season into account.

- Stations and satellites in LEO. They will either require autopilots with orbit boost capacities, or, in the worst case, fudge the drag effects (zero drag coefficients). However, ignoring drag could lead to other problems (pseudo-forces messing up docking operations).

Numerical stability at high time compression will be even more of a headache, but I guess this will be mostly my problem to solve.

So in short, operations in low orbit are bound to become more interesting.
 

myles

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Sweet! Does this also mean we'll get EI higher also?
 

SlyCoopersButt

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I really like the plan. Atmosphere is really an important factor in real life and to see a new model enhancing that realism will be wonderful. It's worth paying the price in time accell and station up-keep. After all, that is more realistic.
 

T.Neo

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Sounds like a new challenge, and room for many new developments. :speakcool:
 

martins

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Sweet! Does this also mean we'll get EI higher also?
EI? I guess this is an acronym I should recognise, but I don't - sorry. Unless you meant extraterrestial intelligence. Sadly, this won't be increased in any way by the new model. It might increase terrestial intelligence, however, if enough people are forced to come up with new orbit solutions.
 

DaveS

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EI = Entry Interface. NASA has defined EI as when the craft passess 400 000 ft(120 km). This is when temperatures start to build up on the craft that is above what you experience on-orbit and a TPS required.
 

liber

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And maybe add DTM Digital Terrain Mapping for 3D terrain...that would be great.
 

T.Neo

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And maybe add DTM Digital Terrain Mapping for 3D terrain...that would be great.

What does that have to do with the atmosphere exactly?
 

martins

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EI = Entry Interface. NASA has defined EI as when the craft passess 400 000 ft(120 km).
Thanks for the clarification. In that case, the answer is no - since EI is a definition rather than a physical property, it won't be affected by the new model. 120km will remain fixed at exactly 120km, even in the new model.
 

myles

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Thanks for the clarification. In that case, the answer is no - since EI is a definition rather than a physical property, it won't be affected by the new model. 120km will remain fixed at exactly 120km, even in the new model.

Sorry, I guess I should have clarified. What I meant was, will we see plasma flames at an altitude higher than 60km? I think it should be around 110-130km where it starts.
 

martins

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Sorry, I guess I should have clarified. What I meant was, will we see plasma flames at an altitude higher than 60km? I think it should be around 110-130km where it starts.
Probably no significant difference. The two models are fairly similar below 120km.
 

Zatnikitelman

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THIS WILL BE AWESOME!! THANKS MARTIN!!
I can see this leading to better aerobraking solutions. With a higher atmosphere, you can slow down faster further from the planet.
 

Quick_Nick

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Wouldn't an 'On/Off' switch be a simple useful solution to either use the 'new and improved' atmosphere or use the current/old addon-compatible atmosphere? If not for the old addons, then for more ease in orbital manevuering, I think an option for using the Orbiter 2006 atmosphere should be available in the next Orbiter. (right next to Nonspherical gravity and Damage Simulation ;))

Also, THANK YOU GREAT DOCTOR! :D
 

SlyCoopersButt

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Now what will this really mean for the stock Mir and ISS which are in orbit with the lack of atmosphere in mind to keep in orbit forever? Far as I know they were never meant to keep up in real life without the help of other ships to keep them boosted. I think left as is they would make a neat challenge to keep up if you cared about them in the sessions. Did Mir have it's own attitude system? If so it would be good to add in order for ships to boost it.
 

jarmonik

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Now what will this really mean for the stock Mir and ISS which are in orbit with the lack of atmosphere in mind to keep in orbit forever? Far as I know they were never meant to keep up in real life without the help of other ships to keep them boosted. I think left as is they would make a neat challenge to keep up if you cared about them in the sessions. Did Mir have it's own attitude system? If so it would be good to add in order for ships to boost it.

I found interesting article about this.

http://science.nasa.gov/headlines/y2000/ast30may_1m.htm

"The ISS will sink a couple of kilometers per year in the future because of atmospheric drag - in its current configuration," says Larry Kos, a NASA/Marshall Space Flight Center
 

V8Li

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One step closer to reality :cheers: , THANKS!
It will be nice to have to plan "orbit boosts" due to orbit decay produced by drag but may become tireing so I'd suggest not an option to turn it ON/OFF but a way to modify the impact (maybe density?) on orbits. So if the parameter (availabel in the LaunchPad too) at 100% will lead to a reentry in 2 years, at 50% could lead to a reentry in 4 years.
 

MajorTom

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This is a very welcome development, Martin.

The boundary between space and the atmosphere is one of my favorite areas to explore. Improving this model in Orbiter will give us better understanding of orbital decay, the long term future of "space junk," more realistic launch vehicle flights, the list goes on...

Thank you!:cheers:
 
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