# Tag Info

28

The only satellite I know of that was shaped to have low drag was GOCE, which orbited at 250 km. Since it was vital to ensure that the measurements taken are of true gravity and not influenced by any movement of the satellite, this unique five-metre long arrow-shaped satellite had none of the moving parts often seen in other spacecraft. The satellite, ...

14

I am wondering whether there is a mathematical formula that we can use to calculate the drag force without empirical measurements. Yes, much modern rocket design is done with Computational Fluid Dynamics software instead of in wind tunnel testing. can we simply look at the system of one air molecule and the rocket, calculate the instantaneous change in ...

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 ...

8

It is possible to compute rather than measure the drag on an object. However the answer to the specific technique you suggest: can we simply look at the system of one air molecule and the rocket, calculate the instantaneous change in momentum of the air molecule after collision as the resistive force, and then sum up the forces experienced by all air ...

8

I think there are a few misconceptions to clarify here: Rotating bodies can generate lift. This is known as the Magnus effect. Lift is a hydrodynamical phenomenon: Differences in flow velocity above and below a moving body translate into pressure differences which heave the body up. However in very rarified gases this mechanism stops working. This is ...

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 ...

7

There is a mathematical formula, but it requires knowing the pressure and velocity distribution around the surface of the object: $$D=\int_{S_{upper}}\left[-pcos(\theta)+\tau_wsin(\theta)\right]dA +\int_{S_{lower}}\left[psin(\theta)+\tau_wcos(\theta)\right]dA$$ where $S_{lower}$ and $S_{upper}$ refer to the lower and upper surfaces, respectively, and $\theta$...

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 ...

6

It's some other force. In particular, it's that last approach to Titan on September 11 that will send Cassini deep enough into Saturn's atmosphere so as to make the spacecraft burn up on September 15. Notice that your graph shows that Cassini will make several somewhat close approaches with Titan during the next several months. Some will raise Cassini's ...

4

Some issues with this: Drag is dependent on cross-sectional area, and so is solar radiation pressure. This would mean that different spacecraft would have a different definition of space. We might get around this by designing a "standard spacecraft", but that's exactly what defining the Karman line was for in the first place. The exosphere is complicated ...

3

I'm not a specialist, but here are my guesses: the geocentric equatorial frame makes it easier to express $\mathbf{v}_{rel}$, the spacecraft's velocity relative to the atmosphere, in terms of $\mathbf{r}$ and $\mathbf{v}$: $$\mathbf{v}_{rel} = \mathbf{v} - \boldsymbol{\omega}_E\times \mathbf{r},$$ where $\boldsymbol{\omega}_E$ is the angular velocity of ...

2

Some general code-review. Overall the assumptions look okay, but the how the decay is actually calculated could be clearer. the atmospheric density is taken from the link above and linear interpolated for the altitudes in between. While I agree that this is a perfectly reasonable approach, the table does have some sparse values where linear interpolation ...

2

I don't see the exact equation that is in the question, but it looks like it's derived from equations in Chapter VI Paragraph C "Drag of Streamlined Shapes" in Hoerner 1965 Fluid-Dynamic Drag. At least, there is a marked similarity. I found similar equations (at least the same power law) in a book I own, McCormick 1979 Aerodynamics, Aeronautics, ...

2

While the actual efficiency of this strategy is questionable and involves biomechanics, friction, and many other complicating factors, the most reduced model can indeed be compared to the Oberth effect. What you are "feeling" is the force you are applying. "Hard" is when it takes you a lot of force to move the pedals, "easy" is ...

2

The reason your biking scheme feels easier is, because the power you put into the pedals is applied for a longer time and therefore lower. There is no relation to Oberth effect because the total energy spent is constant. Compare the two cases: Pedal only going up-hill - you have to apply power during the time going uphill. Pedal going up-hill and in the ...

2

The Kármán line definition is not ignorable. Wikipedia: The Kármán line is therefore the highest altitude at which orbital speed provides sufficient aerodynamic lift to fly in a straight line that doesn't follow the curvature of the Earth's surface. If you can remain above the Kármán line you are a spacecraft. Full stop. In fact it's a bit worse. It is ...

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 ...

Only top voted, non community-wiki answers of a minimum length are eligible