67
votes
Accepted
Why not increase contact surface when reentering the atmosphere?
I've done a lot of work on this subject with researchers and engineers at JPL, NASA Langley, and NASA Ames. There are some interesting things that come out of high-fidelity CFM (Computational Fluid ...
- 18.3k
33
votes
Accepted
What causes a satellite's orbit to decay?
If satellites are truly far beyond the atmosphere, their orbits do not decay, except for very small perturbation effects like solar radiation pressure from the Sun or tidal forces from the Moon.
But ...
31
votes
Are rockets faster than airplanes?
Rockets are much faster than airplanes for most of their flight.
Here's a graph of a Space Shuttle launch:
The red line is speed. It's in ft/s, 1000 ft/s is 1097 km/h. So At about 45 seconds, the ...
- 128k
24
votes
Accepted
Earth re-entry from orbit by a sequence of upper-atmosphere dips to reduce kinetic energy?
Unpowered re-entry into an atmosphere is about trading orbital energy for heat. If the planet being orbited has radius $R$, then the additional specific energy of an elliptic orbit compared to being ...
- 8,188
21
votes
Are rockets faster than airplanes?
A rocket isn't automatically fast - a small firework rocket may be no faster than a car. The important point is that rockets carry their own oxidiser and aren't limited by the need to interact with ...
- 537
21
votes
Accepted
Can Maglev trains ever reach escape velocity?
What you are proposing is known as a mass driver, and the concept goes back at least to the 1960s. It was discussed by Gerard O'Neill in the 1970's as part of a method to build space colonies, and ...
- 11.4k
19
votes
Accepted
How can an *increase* in atmospheric temperature cause an *increase* in the atmospheric mass density?
The key concept is that for a satellite at a fixed altitude, when the atmospheric temperatures below its altitude increase, atmospheric expansion pushes more atmosphere up above the satellite! At the ...
- 18.3k
19
votes
What is the density of the earth's atmosphere at an altitude of four hundred kilometers?
What is the density of the earth's atmosphere at an altitude of four hundred kilometers?
Variation with solar activity
It can vary by a factor of 50 depending on solar activity (and the model that ...
- 149k
16
votes
Accepted
How can a meteor gain energy in an encounter with the Earth even though these answers say it can't?
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. ...
- 431
15
votes
Accepted
Where can I find data for Atmospheric density vs. altitude?
In the Shuttle Mission Simulator we used the Jacchia Reference Atmosphere, it's good to 2500 km. IIRC it's not good low down so we used a standard atmosphere model for atmospheric flight regimes and ...
- 187k
15
votes
What is the density of the earth's atmosphere at an altitude of four hundred kilometers?
The MSISE-90 model is available in digital form at http://www.braeunig.us/space/atmos.htm. A copy of the table is reproduced below. Note the dependence on solar activity, which imparts particlesto ...
- 8,615
13
votes
What causes a satellite's orbit to decay?
The Wikipedia article on orbital decay lists a number of reasons, in addition to atmospheric drag:
Tidal effects
An orbit can also decay by negative tidal acceleration when the orbiting body is large ...
- 179
12
votes
ISS achieving lift by using it's solar panels
I can see your reasoning, however it's not going to work. Aerodynamically the byproduct of lift is drag, meaning when you create lift you also create drag as well. An efficient wing creates less drag ...
- 20.3k
12
votes
Accepted
Can dust be in orbit around a spacecraft which orbits the Earth or Moon?
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 ...
12
votes
Earth re-entry from orbit by a sequence of upper-atmosphere dips to reduce kinetic energy?
When Does an Orbit Stop Being an Orbit
Low Earth Orbit is (rough) 7.8 km/s. This is the lowest amount of energy you can have in an orbit of the Earth. If you try to create a lower energy orbit, you ...
- 1,733
11
votes
Accepted
Why does in-flight mission abort often ends in ballistic high-g reentry?
When you're in orbit you have velocity roughly parallel to the atmosphere, a flat-ish shape angled properly can "fly" across it in a lifting entry where you can dissipate energy in the thinner upper ...
- 20.3k
11
votes
Accepted
How hard does atmospheric drag push on the ISS? Is it more than one pound?
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
$$
Fv=\frac{dE}{...
- 2,080
10
votes
How can an *increase* in atmospheric temperature cause an *increase* in the atmospheric mass density?
The scale height is proportional to temperature. As the scale height increases, the density above about one scale height increases. (The density below that decreases.) This is what you'd expect if the ...
- 58.3k
10
votes
Why not increase contact surface when reentering the atmosphere?
There is a fixed amount of energy which has to be dissipated. You can, to some extent, choose how fast this is done -- more air resistance (either by getting into thicker air or having a bigger ...
- 19.6k
10
votes
Are rockets faster than airplanes?
Rockets don't actually mostly go up, they try quite hard to go up as little as possible.
While flying, gravity is always accelerating you downwards at 9.8 m/s^2. This means that any fuel spent ...
- 109
10
votes
Accepted
Why does a satellite with a higher mass fall slower?
That's a great software-based experiment!
What is this about?
It's about drag and Newton's 2nd law of motion!
$$F = \frac{dp}{dt} = ma$$
but in the context of orbital mechanics.
We can re-arrange ...
- 149k
10
votes
Exactly how "Ferrari-like" was GOCE? Was its drag coefficient as low as the car's?
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...
- 15.1k
9
votes
Accepted
What is typical lifetime of GTO rocket stages before reentry?
The typical lifetime of an upper stage rocket body (in GTO) varies from few weeks to few decades. This large variation is due to the sensitivity of the orbital evolution to the initial launch ...
- 390
9
votes
Accepted
Could SpaceX's Starship's landing and restart process work on Titan?
Getting There:
In general there is "the quick way" and "the efficient way" to get to the outer planets. The trade-off is between the capability of the launch vehicle and the time-...
- 10.1k
9
votes
Why does a satellite with a higher mass fall slower?
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 ...
- 23.4k
9
votes
Would it be possible to avoid the heat-from-friction problem when re-entering the atmosphere by performing (vertical) "U-turns"?
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 ...
- 20.3k
8
votes
Accepted
Shear forces between Shuttle, tank, and boosters - what pushes what?
The three SSMEs provide 568 tons of thrust, the Orbiter has a weight in the region of 100 tons incl payload. The Orbiter always exerts a positive force on the tank from liftoff to MECO, no matter what ...
- 128k
8
votes
Where can I find data for Atmospheric density vs. altitude?
We recently had a similar requirement and created a RESTful web API that wraps the original code of the NRLMSISE00 and the JB2008 models. The API is open and available here for anyone who needs it.
...
- 171
8
votes
Accepted
Is aerodynamic lift ever useful in rocket flight?
Angling to get lift is going to increase the atmospheric cross-section of the rocket and so increase drag. For any reasonable angle of attack, the drag force is going to be much larger than the lift ...
- 170k
8
votes
Why does Earth's atmospheric density have a big "knee" around 100 km? Is there a good analytical approximation?
update: @SergeiOzerov's answer is excellent and so is @DavidHammen's answer. But I believe this answer is not without merit either.
Q: Why does Earth's atmospheric density have a big “knee” around ...
- 149k
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