# Tag Info

Accepted

### Using a fidget spinner to rotate in outer space

This is exactly how it works and how the orientation of many satellites is controlled. For example, the Hubble telescope has 4 fidget spinners installed, pointing in different directions - although ...
• 15.1k
Accepted

### How come we don’t put a huge windmill-like machine in space?

As far as I understand you want the "windmill" to drive a dynamo. Have you ever tried turning a dynamo? It takes some force to do so, and that force is then (partially) turned into electricity. So the ...
• 12.5k

### Qualitative differences between gravity and a spinning habitat

First, I'll adopt terminology from Ringworld: "spinward" is in the direction of spin, and "antispinward" is opposite the direction of spin. And I'll say a bit about the Coriolis equation, but then go ...
• 18.3k
Accepted

### How do the roll-rings at the ISS work?

The ISS Utility Transfer Assemblies (UTAs) are located in the center of the Solar Alpha Rotary Joints (SARJs) - the continuously rotating interface between the outer truss segments that support the ...
• 183k

### How to calculate the speed of rotation of a given point on the Earth's WGS84 ellipsoid, about its axis?

NOTE: This answer was provided for a different, very basic question which didn't specify the WGS84 ellipsoid; it's illustrative of the basic principle as applied to a spherical Earth. Still, not bad ...
• 169k

### How come we don’t put a huge windmill-like machine in space?

Consider the windmill as a system. If there is no wind blowing on the windmill, there is no energy being input into the system. If you pull power out of the windmill, energy is being output from the ...
• 183k

### Would a Foucault pendulum work on the Moon and on the Galilean moons?

tl;dr As long as the pendulum can oscillate reliably, the Foucault Pendulum rotation is independent of the strength of gravity. If your question is about a normal pendulum and you didn't actually mean ...
• 149k
Accepted

### How much energy is lost by damping yaw from a SpinLaunch?

The rotational energy is not removed by aerodynamics, it's probably removed by the precise and accurate timing of the release mechanisms. A bit of digging and analysis shows that most of the ...
• 9,805
Accepted

### Does a change in the rotational speed of something on its own axis (rpm) affect its orbit?

In brief "no", at least not unless the objects are so dense, massive or rapidly rotating, or you measure the orbit with such extreme precision, that general relativity becomes a significant factor. ...
• 19.6k

### At what altitude would I have to go in a lighter than air balloon to be above all wind and just have the earth rotate underneath me?

The question contains a misconception - wind is the movement of the atmosphere relative to the surface. So if you are at an altitude with no wind, you'll be stationary relative to the surface - the ...
• 10.1k

### How does Spinlaunch manage the counterweight right after launch?

Spinlaunch releases the counterweight at the same time as the vehicle. Their patent says: The launch vehicle 105 may be released from the launch vehicle tether... Simultaneously, the counterweight ...
• 12.2k

### Would the Dzhanibekov effect be a problem for Von Braun Wheels?

No... a Von Braun wheel would not ever 'flip' from Dzhanibekov effect. The effect comes from spinning something about its intermediate (and inherently unstable) axis. A Von Braun station is spinning ...
• 3,292
Accepted

### Could a satellite levitate above the magenetic fields of Earth?

The basic calculation we need is set out here. The force that would need to counteract gravity is given by equation 17 $f = \nabla(\mu.B)$ where $\mu$ is the dipole moment of the magnet and $B$ the ...
• 19.6k
Accepted

### How much does the rotation of the Earth affect re-entry and could we go against it?

I was wondering if anyone could explain why the re-entry retrograde would be more delta-v, and by how much. The Earth rotates eastward, carrying the atmosphere with it. For prograde reentry, you're ...
• 169k

### Can an orbit rotate around a non-orthogonal axis?

Sort of. They rely on additional forces to move the orbit around/create points of stability. Sun synchronous orbits (SSO) use the oblateness of the Earth around the equator to change the satellites ...
• 4,211
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### Moment of Inertia of a planet

In this case L is not constant. Its magnitude is, but its direction isn't: it's precessing. Torque is the derivative of angular momentum with respect to time, so if you know the precession rate, you ...
• 18.3k

### Does a change in the rotational speed of something on its own axis (rpm) affect its orbit?

If the question is making implicit reference to the conservation of angular momentum, then, as so often the case, "it depends". The source of the change in rotation cannot strictly come from "energy ...

### At what altitude would I have to go in a lighter than air balloon to be above all wind and just have the earth rotate underneath me?

A balloon cannot ascend above the entire atmosphere. The balloon's buoyancy decreases with height until you're at an equilibrium. The current record is 53 km. At that altitude, you still get wind: ...
• 128k

### How to calculate the speed of rotation of a given point on the Earth's WGS84 ellipsoid, about its axis?

According to Wikipedia's Geographic_coordinate_conversion#From_geodetic_to_ECEF_coordinates The 3D cartesian coordinates $X, Y, Z$ in Earth-centered, Earth-fixed coordinates assuming an ellipsoidal ...
• 149k
Accepted

### Qualitative differences between gravity and a spinning habitat

Depending on how close you are to the habitat's center of rotation, you'll feel anything from zero-g to the maximum the habitat is designed to offer - so while homes may be located in a one-gee zone, ...
• 623

### Can an orbit rotate around a non-orthogonal axis?

If your elliptical orbits are around realistic rotating bodies like the Earth or Jupiter or anything with an equatorial bulge, then it will precess. The most common kind of precession we hear about is ...
• 149k
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### Could the Galilean moons tidally lock Jupiter?

Every action is accompanied by equal and opposite reaction. Specifically, the braking of spin of a planet due to tidal forces exerted by a moon is accompanied by the planet's tidal bulging ...
• 55k

### Does a change in the rotational speed of something on its own axis (rpm) affect its orbit?

In most cases, yes. Spinning a satellite up will not immediately change its orbit, but tidal forces will slowly transfer energy from the satellite to its orbit until it becomes tidally locked with its ...
• 361

### Qualitative differences between gravity and a spinning habitat

Below this answer there is a discussion about driving a car (generalizable to any vehicle) around the inside of a rotating cylinder. If you drove fast relative to the cylinder in the retrograde ...
• 149k
Accepted

### Did the manned NASA capsules rotate during descent?

I can't speak for Mercury or Gemini missions, but the Apollo parachute system is documented in NASA Technical Note D-7437, Apollo Experience Report: Earth Landing System. It appears that they ...
• 48k