Advanced Question Orbit Decay Question

[thammond]

I have an orbit decay question using the new atmospheric model in 2010P1.

I launched a Sputnik 1 (from Igel's First in Space add on) with the new atmospheric model turned on (in the extras tab). I let the simulation run for quite some time using 10x time compression. I am now up to 1/13/58 and neither the rocket (core A) nor the Sputnik 1 satellite are close to having their orbits decay to the point of reentry (apogee of about 900 km). For reference, the real Sputnik 1 satellite orbit decay date was 1/4/58 while the Core A stage orbit decay date was 12/2/57.

I did not record the initial orbital parameters when I 1st launched the sputnik 1, but it was on the correct date of 10/4/57 and had a apogee of about 960 km and a perigee of about 210 km which is close to the actual Sputnik 1 of (939 x 215).

The orbit decay I have been getting has been about a constant 0.6 km per day off the apogee. Oddly the Core A stage initially was decaying at a slightly faster rate than Sputnik 1 (which seems logical) up until around the last week or so (simulated time) in which the Sputnik 1 is now "catching up" (decaying slightly faster, which does not seem logical) to the core stage. The difference (on a given orbit in time) between the apogee of Core A vs Sputnik grew from zero at the point of satellite separation form the core to about 10 km but now is getting smaller.

A few questions I can think of. Do I have everything setup correctly in orbiter to get an accurate atmospheric drag occurring? Is the atmospheric model not accurate enough to get the Sputnik 1 to orbit decay in roughly the correct time frame? Is the 10x time compression affecting the accuracy? Is the Sputnik1 and Core A stage I am using modeled accurately enough to get them to decay in the correct time frame? Is there something else that I'm not thinking about?

 

[Urwumpe]

A few questions I can think of. Do I have everything setup correctly in orbiter to get an accurate atmospheric drag occurring? Is the atmospheric model not accurate enough to get the Sputnik 1 to orbit decay in roughly the correct time frame? Is the 10x time compression affecting the accuracy? Is the Sputnik1 and Core A stage I am using modeled accurately enough to get them to decay in the correct time frame? Is there something else that I'm not thinking about?

AFAIR, the model is not 100% accurate, it assumes a moderate solar activity index, while in reality, the exosphere density depends on the solar activity.

 

[Lmoy]

Which atmospheric model are you using? Orbiter has a few, with varying degrees of accuracy. Also I do think 10x compression decreases the accuracy. Additionally the aerodynamic parameters of the satellites may not be accurately modeled, which would affect the accuracy.

Now I want to try this out in real time and see how it goes.

 

[Dantassii]

AFAIR, the model is not 100% accurate, it assumes a moderate solar activity index, while in reality, the exosphere density depends on the solar activity.

I think it can be said that the exosphere density depends greatly on the solar activity which is quite difficult to model.

Remember Skylab....

Dantassii
HUMONGOUS IMS shipbuilder

 

[Urwumpe]

I think it can be said that the exosphere density depends greatly on the solar activity which is quite difficult to model.

Remember Skylab....

Dantassii
HUMONGOUS IMS shipbuilder

Well, yes. its a difference of 800 km peak altitude for the boundary between exosphere and interplanetary medium and 1500 km during strong solar activity.

Still, even for Skylab, it only had an effect over a longer time.

 

[Lmoy]

I'm not very familiar with solar activity cycles. You say it's difficult to model; is this because solar activity is unpredictable and/or difficult to measure? If so, would an atmospheric model that randomly increases the boundary between the thermosphere and exosphere over time possibly be somewhat more accurate in regards to the decay of high altitude LEO/MEO orbits?

 

[Urwumpe]

I'm not very familiar with solar activity cycles. You say it's difficult to model; is this because solar activity is unpredictable and/or difficult to measure?

It is still pretty much unpredictable, but reliably measured by observing the 10.3 cm radiation band.

We have learned a lot about the behaviour of the sun in the past years, but even accurately predicting the length of a solar cycle is still beyond our ability. We know its about 11.5 years long. But it can be 9 years to 13 years long in reality.

One day we will have better models.

But our atmosphere model can already handle solar input good enough to fit with recordings of past solar activity.

 

[thammond]

I think it can be said that the exosphere density depends greatly on the solar activity which is quite difficult to model.

Remember Skylab....

Dantassii
HUMONGOUS IMS shipbuilder

I did find some data indicating that the time frame of Sputnik 1 coincides with a peak cycle for solar activity.