# Tag Info

15

I am Patrick Shober (the lead author of the study). Thanks so much for checking it out! If you check out Figure 10 in the paper, I have plotted the specific angular momentum in the Sun-centered frame. So this shows how the meteoroid (the rock) gained energy during the close encounter but then lost a fraction of it due to the atmospheric passage. This can ...

10

A starting point for checking orbital stability is the Sphere of Influence for short term stability (or rather, to select a suitable frame a reference in the patched conic approximation), and the Hill sphere for more long term stability (satellites). $$r_{SOI} \approx a\left(\frac{m_{satellite}}{m_{parent}}\right)^{2/5}$$ For a reference spacecraft, I'm ...

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

Here’s a “real case” simulation, in the sense that I read the ISS initial state from a TLE+SGP4, then I propagate that TLE forward in time until I find a point 1 km away from the initial state (that point is the astronaut and he is exactly along the ISS orbit). The ISS ballistic coefficient is obtained from a best fit of the ISS position during two reboosts;...

4

As you correctly noted, the S he's using is a combination of effective surface area and drag coefficient. All literature I've come across uses S for surface area and expresses drag as $D = C_D\frac{1}{2}\rho V^2S$ where $C_D$ is the drag coefficient and S is the effective surface area. Combining these two into one parameter makes sense to me however. $C_D$ ...

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 ...

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

Because it's using Earth's magnetic field to create drag. It's one of several passive deorbiting systems. An electromagnetic tether uses a conductive tether to generate an electromagnetic force as the tether system moves relative to Earth’s magnetic field. NASA: State of the Art of Small Spacecraft Technology, 12. Passive Deorbit Systems In-Space ...

3

Here’s what I get from all the TLEs currently available at www.space-track.org processed with the SGP4 library freely downloadable from the same site. Definitions T: orbital period. 1-orbit mean radius vector: numerically integrated radius vector against the eccentric anomaly (it’s the semi-major axis). The integration starts from –T/2 and ends to T/2 ...

3

41332 is staying pretty steady, although it is currently listed as "operational" in the databases I'm seeing. It is getting to be a bit lower, although I wouldn't expect it to reenter anytime soon, maybe 3-4 years left (I guess my original prediction was wrong...). Thus far the altitude has gone down about 20 km in 4 years, so 5 km/ year, although the rate ...

3

Some starting numbers here would be that the leading hypersonic projectile will be scooping up a cylinder of atmosphere equal to the frontal area and it's traveled path. The first approximation of the distance that will halve the projectile speed will be the point at which the mass of that block of atmosphere equals the mass of the projectile. Mass of ...

3

Drag has a lot of more complex factors that would require some simulation to determine exact values, but the simplification that is often used shows drag increasing linearly with air density and with the square of velocity. Density at the Karman line is 1/2,200,000 that of ground level, so an increase from 0.5 mach to 7 km/s will feel roughly $\frac{(7000/... 2 [I add another answer to avoid too much mess.] Here are the graphs that show the differences in distance and speed with and w/o the atmosphere: Distance with the atmosphere: 1008.3116 m Distance w/o the atmosphere: 999.7882 m ||Vast|| - ||Viss|| with the atmosphere: 2.2493 mm/s ||Vast|| - ||Viss|| w/o the atmosphere: 0.6093 mm/s Your procedure Since the ... 2 well, its called a gravity assist. the asteroid took a small amount of earth's velocity and used it to speed up. this is different than skipping off a atmosphere think about skipping a rock on a lake, does it speed up? No. With a gravity assist it's like stealing a bit of energy from the planet to propel your much smaller ship, asteroid whatever it is. ... 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 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

In the linked AIAA article, the bottom of page 4 (excerpted below) estimates numbers for a 250 m x 0.28 m tape. When 700 km high, electrodynamic drag and aerodynamic drag are both about 15 μN. Higher up, electrodynamic drag dominates. To generalize this, into equation (4) plug in values for tape width w, a bunch of numbers ∆V me mi that I don't know how ...

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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, ...

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