[SPACE] Tidal braking

[Agemegos]

Originally Posted by dataweaver

Note that P is used elsewhere to represent orbital periods; so you should probably choose another letter to represent the mass of the object that the tides are on. I'd be inclined to use a lowercase m.

Fair enough. I just have a paranoid fear of typographers' changing a lowercase m to an uppercase M for appearance's sake. It would be just like them to do so because the editor had declared the style of the work to use capitals in all formulas, and to do so without consulting the author and without realising that it profoundly changed the meaning of the equation.

Traumatic experiences….

You skimmed over the fact that planets generally have axial tilts, and thus the torque applied by tidal forces would tend to fight the axial tilt as well as the rotational speed. Because of this, planets that start with high axial tilts will tend to have their axial rotation slowed less than planets that start with low axial tilts. Also, it means that older systems will tend to have smaller axial tilts than younger systems will.

True, I did. I was thinking of correcting the erroneous formulas in Space rather than of extending its scope.

I don't think they are going to accept a corrigendum that increases the page count.

However, it might be possible to decrease the axial tilt of planets with a high value of A * P/D^5) * S without making the rules on p. 118 too complicated.

Likewise, the same tidal forces that tend to slow a planet's rotation will also tend to drive satellites into higher orbits, eventually letting them break away from the planet. Younger systems will tend to have more satellites and in tighter orbits than older systems will.

True. Perhaps you would like to suggest corrigenda and upgrades for the 'Satellite Orbital Radius' procedures on p 116.

First: Tidal forces don't drive W toward zero.

Indeed they don't. I just felt that the easiest way to right the rules was to calculate a temporary value for W, calculate the implied period, and override it if this implied retrograde rotation. W isn't used subsequently for anything else, so there is no need to correct it.

Rather, solar tides drive W toward 1/(8766 P), where P is the Planetary Orbital Period in years; and lunar tides drive W toward 1/(24 P), where P is the Satellite Orbital Period in days. If W is at or between these values, the various tidal forces will be in competition. In other words, a satellite will end up delaying or preventing a solar tide-lock, depending on how powerful the satellite's tides are.

True. I simply feared that I could not write a rule to sum this up that was sufficiently simple.

Second, a nitpick: Daylength doesn't equal 1/W; Rotational Period equals 1/W. The length of a day is computed from the Rotational Period on page 118, under "Local Calendar".

True. I ought to have used 'S' (sidereal period) rather than 'Daylength'. Which means I shouldn't have used 'S' for that sum of squares value.