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martins martins is online now
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Exclamation New atmospheric model for Earth
by martins 02-14-2009, 10:26 PM

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.
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Old 02-14-2009, 10:29 PM   #2
myles
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Sweet! Does this also mean we'll get EI higher also?
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Old 02-14-2009, 10:33 PM   #3
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.
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Old 02-14-2009, 10:36 PM   #4
Arrowstar
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Sounds great to me!
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Old 02-14-2009, 10:39 PM   #5
T.Neo
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Sounds like a new challenge, and room for many new developments.
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Old 02-14-2009, 11:04 PM   #6
martins
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Originally Posted by myles View Post
 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.
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Old 02-14-2009, 11:06 PM   #7
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.
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Old 02-14-2009, 11:07 PM   #8
liber
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And maybe add DTM Digital Terrain Mapping for 3D terrain...that would be great.
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Old 02-14-2009, 11:12 PM   #9
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?
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Old 02-14-2009, 11:16 PM   #10
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 What does that have to do with the atmosphere exactly?
Nothing but it would be nice to have...
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Old 02-14-2009, 11:20 PM   #11
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.
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Old 02-14-2009, 11:25 PM   #12
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.
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Old 02-14-2009, 11:33 PM   #13
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.
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Old 02-14-2009, 11:40 PM   #14
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.
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Old 02-14-2009, 11:52 PM   #15
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
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