shouldn't orbital vehicles be tide locked?

[Chris_C]

Now I could be entirely wrong about this...

I'd always thought that a vehicle should be rotated by tidal forces such that the same surface of the vehicle is facing the planet...

so for instance if you have a cupola on the "bottom" of your vessel is should always have a view of the planet and the planet should not appear as if its rotating round the vessel (relative to the vessel)

OR

am I completely wrong and does the ISS use its gyros to spin the station at one revolution every 90ish mins?

[Tex_NL]

...

am I completely wrong and does the ISS use its gyros to spin the station at one revolution every 90ish mins?

You just answered your own question.

[Nibb31]

Spacecraft (even the ISS) are too small and too balanced to be tidally locked. The Moon is tidally locked to the Earth because it is large, heavy, and one side is heavier than the other.

[Chris_C]

Spacecraft (even the ISS) are too small and too balanced to be tidally locked. The Moon is tidally locked to the Earth because it is large, heavy, and one side is heavier than the other.

So the ISS is actively rotated all the time then ?

[Brotoro]

Satellites CAN use tidal forces to stabilize them... It's called gravity-gradient stabilization. The satellite must be sufficiently long and thin for this to work (or have two parts tethered together).

[andrewas]

So the ISS is actively rotated all the time then ?

Yes. Its actually almost perpendicular to the orientation it would be in if tidally locked, so theres a constant load on the gyros to keep it in the correct orientation.

Shuttle used to use tidal locking to hold orientation, engines down, nose up. This was done during experiments that needed near-perfect microgravity since any other orientation would need occasional thruster usage to hold.

[ThreeKelvin]

Spacecraft (even the ISS) are too small and too balanced to be tidally locked. The Moon is tidally locked to the Earth because it is large, heavy, and one side is heavier than the other.

Wether a satellite is tidally locked has nothing to do with the mass of the object. In order to have an object locked it must:

1) Have an atraction attitude, i.e., an attitude that, due to the gravitational gradient, is accelerated towards, and

2) A way to dissipated energy, e.g. a flexible structure that transforms some of the work done on it by the gravity gradient into heat, which is then radiated away from the spacecraft. (Otherwise 1 just gives you a pendulum.)

Since no satellite is completely rigid they'll all become tidally locked given enough time. Some satellites even rely on the gravitational gradient for attitude control. (see e.g. http://en.wikipedia.org/wiki/%C3%98rsted_%28satellite%29)

[magnemoe]

An satelite become tidal locked if the same part point towards earth all the time. It would rotate once every orbit. If you set up an rotation like this it would be tidal locked in practice, you might even want to design it long with heavy parts in the ends to let nature help you pointing the antenna against earth.

[Dunbaratu]

Technically you could still have tidally locked orbits when doing things on-rails. (You just make sure that the rotational position of the object is always hardcoded to be with its longest axis pointing toward the primary's center. Just like the game makes a time-parameterized equation for the linear position of the ship (at time=t it will have x=f(t), y=g(t) and z=h(t), for some functions f,g, and h), it could make a time-parameterized equation for the rotational position of the ship: at time=t it will have theta=F(t), rho=G(t), and phi=H(t), for some F,G,and H functions. But the hard part would be deciding whether or not you should set up equations that preserve existing constant rotation, or set up ones that cause tidal locking, when first going onto rails. The decision would be largely arbitrary since in reality any object would become tidally locked EVENTUALLY since there's no such thing as a 100% radially symmetrical object - imperfections will make there be *something* for the tide to act upon, and also they would make there be *something* to dampen the oscillations a little bit. It's just that this "EVENTUALLY" might be longer than the duration of the solar system so it becomes a moot point. Trying to decide if an object is "elongated enough" to put it on tide-lock rails instead of constant-rotation rails would be a sort of made up arbitrary decision.

[The Scientific Moustache]

but it is impossible to achieve in KSP no matter how long and uneven your mass is. any satellite get s approximated as its mass at CoM

[OtherDalfite]

but it is impossible to achieve in KSP no matter how long and uneven your mass is. any satellite get s approximated as its mass at CoM

If you were to leave a very long, unbalanced craft up and you stayed focus on it at 1x timewarp for a very long while, you would eventually see this effect come into play. The slightest tap of control however, and you would have to wait for it to regain it's orientation.