11

Here is a rough estimate. The ISS's height drops at the rate around 10 meters per day. The energy of a body of mass $m$ in a circular orbit of radius $r$ is $E=-\frac{\mu m}{2r}$, so $$ Fv=\frac{dE}{dt}= \frac{\mu m}{2r^2}\frac{dr}{dt}. $$ Since $v=\sqrt{\frac{\mu}{r}}$, $$ F=\frac{m v}{2r}\frac{dr}{dt}. $$ Substituting $m=4\cdot 10^5$ kg, $v=7800$ m/s, $r=6....


10

That's a great software-based experiment! What is this about? It's about drag and Newton's 2nd law of motion! $$F = \frac{dp}{dt} = ma$$ but in the context of orbital mechanics. We can re-arrange Newton's law as $a = F_D/m$ where $F_D$ is the drag force, and the drag equation is $$F_D = \frac{1}{2} \rho v^2 C_D A$$ where $\rho$ is the density at that ...


9

The ion propulsion was run continuously to compensate for drag immediately. The drag force varied strongly during each orbit (i.e. changing from night to day), typically between 4 and 12 mN on its 1 m² surface. Absolutely not. The drag coefficient was about 10 times higher. The low $c_W$ that can be reached in a dense atmosphere mostly comes from flow ...


9

From Force=Mass*Acceleration for a given starting drag force (from the constant drag area, altitude and velocity) increasing the mass will reduce the acceleration (deceleration in this case) slowing the satellite and causing the perihelion to lower. So being heavier does not directly make the satellite fall slower, but does change how quickly atmospheric ...


7

There is an outline of the design here: Each probe weighs 16 grams and consist of three 98 mm diameter aluminum sheets at 90 degrees to each other, effectively forming a sphere. The intent is to be lightweight and have a constant cross section, independent of orientation to the velocity direction so that atmospheric drag can be measured in-situ. RF modeling ...


6

Roughly how much lower was GOCE's drag compared to a typical spacecraft, or to a sphere of the same mass. Did it have a drag coefficient as low as a real Ferrari? GOCE's drag coefficient was higher than that of a typical spacecraft. From Geul, J., E. Mooij, and R. Noomen. "GOCE statistical re-entry predictions." Proceedings of 7th European ...


5

It isn't possible to avoid heat from friction in re-entry, you have to deal with it in some way. What you are describing is called a skip-reentry, and it doesn't require wings. This technique was used by the soviet Zond spacecraft and Apollo spacecraft. The Zonds used the technique to alter trajectory, Apollo used it to avoid heat loads by extending re-entry....


4

One of the problem with drag models is that most are not very precise. The few which are precise are usually written in FORTRAN, and lots of tools just interface with the FORTRAN code instead of rewriting and re-validating the algorithm. The typical high fidelity drag models are the Jacchia Roberts models and the more recent NRLMSISE00 model. The former is ...


4

What you're suggesting is an aerodynamic reentry, where aerodynamic surfaces are used to slow the rate of descent into the lower atmosphere. In the real world, heat shields are often shaped in such a way as to generate lift. But wings are almost never used. That's because it's very hard to make an aero-spacecraft that's able to maintain level flight at hyper ...


3

I add this here just for completeness: The General Mission Analysis Tool (GMAT) also can model the spacecrat drag. GMAT doesn't belong to commercial software, but it is available. GMAT has two atmospheric models in its stock distributive: Jacchia Roberts, which can be used for altitudes more than 100 km only, and MSISE90 (for any altitudes). Copernicus ...


3

My understanding is that the "Direct Simulation" part refers to the fact that rather than solving equations governing the flow (as in Computational Fluid Dynamics) it directly simulates the particles interacting with the surfaces. Rather than modelling each atom, they are grouped into "molecules" representing a large number of atoms, and ...


2

Here's an update to the answer by @PearsonArtPhoto with data from other periods. In that answer, the drop rate during the last solar cycle (#24) is used. In the current (2020) minimum of solar activity, the drop rate is substantially lower: (source: https://heavens-above.com/OrbitHeight.aspx?satid=25544 ) That's a mere 200 meter per month, 7 m/day and a ...


2

Combining a couple comments into an answer -- community wiki as none of this is my contribution. Per user OrganicMarble, who worked in training for the shuttle: The words 'ionosphere' or 'charging' don't appear in the Shuttle Crew Training Catalog. The phrase 'space weather' appears once, in the description of a class the crew got on the Tissue Equivalent ...


2

So, I just gave it a try and have reconstructed the orbit with a numerical propagator. Using a state vector converted from the TLE-Data from the 20th Aug, 18:05:26.676 (yes, I know, not exact, but have to be sufficient*) and a BC I choose so the final re-entry epoch matches (just quick and dirty get a reentry 2h later for a 8 day propagation...). Then I ...


1

Any planet or moon that has an atmosphere that is sufficiently dense at some point to support turbulent mixing will have a density knee above which the atmosphere fails to be dense to support turbulent mixing. This density knee is the object's turbopause. The Earth's atmosphere has a turbopause, as do the atmospheres of Venus, Mars, the giant planets, and ...


1

The main commercial competitor to STK is FreeFlyer. They're actually having a users conference right now, which you could join at https://ai-solutions.com/ffuc2020/ Another free tool to consider is Orekit, from https://www.orekit.org/ Drag modeling is seriously hampered by the lack of attitude information. "High-fidelity" only applies to modeling ...


1

Intuitively, the velocity impulse at periapsis is $$\Delta v = \int_{t_{p} - \Delta{t}}^{t_p + \Delta{t}} a_\text{drag} \mathrm{d}t$$ where $\Delta{t}$ is the duration of the periapsis pass. When the eccentricity is high enough, the periapsis pass happens very quickly and $\Delta{t}$ is small; therefore, the $\Delta{v}$ is small and is not sufficient to ...


1

This is not always the case. Suppose the satellite with the higher mass has, say, the form of a sphere, and the lighter one that of a long massive spear with a sharp point gradually extending to the small diameter of the spear, which has a higher mass at the front than at the back. On entering the atmosphere, the spherical satellite will experience more ...


1

Drag is a resultant vector that accumulates from integrating all forces in contact with the body over the entire surface. For the most part, this comes in two forms: pressure (normal to the surface) and shear stress (tangent to the surface). The key thing to obtain drag is to extract the components of these forces aligned with the direction of the flow. ...


1

Progress thrusters would be used the most as the vehicle eventually leaves ISS after few months. That being said, based on the location of thrusters, you can see that roll and pitch have a larger moment arm than roll thrusters. Therefore, roll thrusters work the hardest. https://www.nasa.gov/pdf/167129main_Systems.pdf To reference the comment by uhoh, ...


1

My answer is contrary to the A2A response from over a year ago. The reason for that knee is that that altitude, the turbopause, is where the atmosphere changes from acting like a gas (below the turbopause) to acting more like a diffuse collection of rarely interacting particles (above the turbopause). Rather than looking at ions, look at the noble gases, ...


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