# Tag Info

36

Is any of the following true about what is needed to achieve this: continuous change in its rotation, once and for all giving it the right spin to begin with, it happens naturally. The answer is "yes" to all three questions. If a vehicle is shaped right and is given the right rotation to start with, torques that naturally occur such as ...

28

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 they are commonly referred to as "reaction wheels". Unfortunately a typical fidget spinner is a bit too light to be really useful: We have to compare ...

27

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 dynamo is braking your windmill and unless there is some power input to the windmill (wind), it will eventually come to stop. But there is no wind so your ...

27

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 into qualitative effects. Basically, anything that involves "up", "down", spinward or antispinward motion (which captures the fraternity-party activities in ...

26

Although this has indeed "worked to bits" on the Physics and other SE sites it's worth looking at, for the sake of Space Exploration, the interesting history behind the analysis of the falling cat. For the fully rigorous description of the cat's righting reflex - perfectly in keeping with conservation of angular momentum - only came about because it was ...

24

This video published on YouTube on Zero-G: "Movement in Microgravity: Skylab to Space Shuttle" 1988 NASA Weightlessness Footage, starting at 2:10 into it, shows a Skylab astronaut doing a front roll and a spiral roll in the Skylab Orbital Workshop without touching anything to push against to change his orientation. And the same video from 5:45 to 6:00 shows ...

21

Nobody really knows for sure. And there's two, nay three more odd things about it's rotation on its own axis, namely: It is the only planet in the Solar system that rotates retrograde, i.e. clockwise, when all other planets rotate prograde, or anticlockwise, on their axes, Latest findings (merely a good month ago as of writing this answer) revealed that ...

17

One of your instincts was correct; it is indeed the influence of the Moon. Wikipedia notes: Over millions of years, the rotation is significantly slowed by gravitational interactions with the Moon; both rotational energy and angular momentum are being slowly transferred to the Moon: see tidal acceleration. And here is the general case of a satellite ...

17

The power and data part is easy. The Galileo spacecraft that went to Jupiter was a "dual spinner", which had spun and stationary sections. The rotating joint had 48 slip-rings over which power and data were transmitted between the sections. As for connecting pressure vessels with a rotating joint, there are similar industrial applications ...

15

Keeping the Same Face "Down" There's a term for this when it naturally occurs: Tidelocking. Natural orientation One can make use of tidal stress to keep an orientation naturally. When an object of significant length is placed into orbit, the side closer to the center of gravity receives somewhat more "pull" than the far end, and it ...

15

The best way to keep an antenna always pointed at Earth, if you can manage it, is to stick a large weight at the tip of your antenna. The weight will receive more pull, and naturally keep the antenna pointed at that direction. Short of having something like that to help passively, the next best solution is to spin stabilize. By spinning around an axis, you ...

14

The key thing to doing this is to accelerate some of the mass of Venus outside of the planet, or alternatively bringing in some mass. Thus, there are 2 main things that could be done to alter the rotation speed. These ideas are explained in Wikipedia. Carefully plan a series of asteroid impacts in a direction where they can increase the rotational energy of ...

14

NASA did research on Feasibility of liquid-metal vacuum seals, the article was published in 1963 and is accessible here (please look up section B, page 29). Here is quote of the articles conclusion sections. A procedure was found for using a liquid-metal seal in an ultrahigh-vacuum system. Leak reates through a $5.5$ inch-diameter seal were so small that, ...

13

At any latitude, the Earth completes one rotation per day. At the equator, the circumference of the Earth is about 40000 km, so the speed of rotation is 40000 km/day or 463 m/s. If you pick a line of higher latitude and look at it on a globe, you will see that the line of latitude is smaller than the equator. One rotation completed in a day is therefore a ...

12

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 system. With an output and no input, whatever energy is in the system will be drained and not renewed.

11

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 to talk about the Foucault Pendulum phenomenon, then a normal pendulum will still work even in very weak gravity in a reasonable way, as long as the length of ...

10

A satellite can naturally remain aligned to the local vertical. In orbit are two forces to consider: force of gravity and centrifugal force. Centrifugal force is actually inertia in a rotating frame. But if you happen to be on the merry-go-round it feels like a force. Centrifugal force is $\omega^2r$ and gravity is $GM/r^2$ To portray these up and down ...

10

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 earth won't be rotating underneath you. However, if the objective is to go up, move around the world and come back close to where you started, you might be ...

10

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. The centre of mass of the satellite (or of the Earth) follows its elliptic or circular orbit regardless of how the rest of the satellite (or planet) is rotating ...

9

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 Earth's magnetic field. Now a good neodymium permanent magnet has a moment equal to its volume times about 875 $kA/m$ (as discussed here) and a density of 7400 \$...

8

According to a follow-up question in the comments to this ISRO's announcement on Facebook: Rajesh B Nataraja: Basic question? The forward rotation is to alter the thrusters in the right direction for the sling shot? ISRO's Mars Orbiter Mission: You are absolutely right! So this maneuver was about positioning the spacecraft in the direction for the ...

8

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 moving "with the wind" so to speak, so the relative speed between you and the atmosphere is lessened; for retrograde reentry you're going into a headwind; the ...

7

I will try to answer your general question with application to NASA's New Horizons spacecraft. The AOCS/GNC (Attitude and Orbital Control System / Guidance Navigation and Control) subsystem takes care that a spacecraft points to a specific point in space, determines the s/c attitude, and does trajectory corrections. So in simple terms, an AOCS system is ...

7

If the artificial gravity station is monolithic, it could also be hubless. It could have one "runway" on the inside of the ring. Docking ports don't need any complicated rotating seals. Matching rotation speed is made by "landing" the spacecraft on the station, and basically braking on its inner surface until full stop, and then taxi to the closest docking ...

7

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 inside the satellite". The satellite can make its exterior rotate faster by means of an internal gyro rotating in the opposite direction. This case would not ...

6

I have an arts degree and am not an engineer, but I work in technical communications and have an aptitude for problem solving, so I'll give it a go. Marek makes a good point about the acceptable leak rate. I've seen comments from others posted elsewhere that suggest that the seals have to cause friction, or the crew must be in suits to transfer between ...

6

According to the NASA New Horizon's site New Horizons has operated mostly in a spin-stabilized mode while cruising between planets, and also in a three-axis “pointing” mode that allows for pointing or scanning instruments during calibrations and planetary encounters (like the Jupiter flyby and, of course, at Pluto). There are no reaction wheels on the ...

6

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: The wind speeds at 50 km are low, indicating that at that altitude, the atmosphere still corotates with the surface. This means your balloon will stay near your ...

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