Kerbin day -51 seconds

[mstrfalco]

My question regarding the shortened day is.. will this be a change in the way the timepieces work, meaning units will roll over at a different increment, or is the rotation of Kerbin actually different?

If the rotational rate was changed this could have some side effects.

It could cause a few 3rd party tools to break which calculate when to launch into particular orbits from KSC. If the rotational rate is changed then half a year into game-play Kerbin would be facing near opposite direction from what would be the case in 23.5. Also if this were the case Geostationary orbit would be at a different altitude. (just slightly)

Edited July 17, 2014 by mstrfalco

[Pecan]

Have you read the release notes?

No; why not?

Because they're not out yet; so how would we know?

[psyper]

Have you read the release notes?

No; why not?

Because they're not out yet; so how would we know?

wow jaded much?

From what I can gleam from the thread with people who have the early release of the game:

Apparently it's a difference between the time it takes the planet to rotate and the length of the day (which is slightly different due to Kerbin orbiting the sun). Currently (according to the wiki), the rotation is 6 hours, but the "day" is actually 6 hours 51 seconds. So they changed the day to be 6 hours, which means the rotation will probably be something like 5 hours 59 minutes and 9 seconds. Which will make inserting geosynch satellites a little bit more fun.

Edit:

Or maybe it's a result of Mun and Minmus slowing down Kerbin's rotation due to tidal forces

Where did they announce that the day will be shorter?

The Kerbin sidereal day WAS 6 hours. You're saying they've sped up Kerbin's rotation such that the solar day will be 6 hours instead.

According to the wiki, this WAS:

length solar day = 21600s / (1 - 21600s / 9203544.6s) = 21650.8s = 6 hours 50.6 seconds

Assuming Kerbin's orbital period is the same, now we have:

length of sidreal day = 21600s / (1 + 21600s / 9203544.6s) = 21549.4s = 5 hours 59 min 9.4 seconds

The difference in-game is the switch to solar time- so the sun will always be overhead at "noon" (3:00:00?) on Kerbin. Before, the sun would gradually be lower in the sky every day until it becomes "midnight" at "noon". With the switch to "Kerbal time", I think the switch away from sidereal would make sense. Why would Kerbals count off their days relative to the stars and not their own sun?

So.. This is definitely going to be a thing in 0.24?

I'm curious what this means for the Kerbal year... Did they change Kerbin's orbital velocity to make 1 revolution = 1 year, or, if not, exactly how long do they arbitrarily define a year? The year used to flip over every time Kerbin completed a revolution (skipping over however many hours/minutes/seconds were left over and starting from 0:00:00 for the new year. But if the time is relative to the sun you can't just set the clock to 0 like this.

Not sure if this is what you're after but I hope it helps.

Edited July 15, 2014 by psyper

[Hacktech]

Geeeeeeks!!

[Red Iron Crown]

This was confirmed by HarvesteR a while back. Day length has been changed in 0.24 by speeding Kerbin's rotation ever so slightly.

I did tweak the Kerbin day slightly here so that 6h is now the length of a solar day, not a sidereal one. As a result, the sidereal days are now 51 seconds shorter, and you may get an eastward launch velocity boost of around 0.01 m/s.

However, over many days, the time of 'noon' still drifts. I suspect that this is related to the year not really being an integer number of days, and there being no accounting for leap years...

Anyhow, 6h for solar or sidereal doesn't really matter in any case, becuase the UT clock doens't measure local time. It measures time elapsed since game start, which is the only solid epoch really, in a game where you not only have a planetful of timezones, you have several planets, each with different day/year lengths...

Really, it's much much easier to just measure local time at your position as a function of sun angle. UT time is useful though, not because it relates to any particular natural cycle, but because it is consistent.

Cheers

[TrooperCooper]

Does that mean no more Launch Window Planner untill its updated?

[Red Iron Crown]

Just use Earth days in the planner and in game and it should be fine.

[TrooperCooper]

Just use Earth days in the planner and in game and it should be fine.

Genious.

[NecroBones]

Does that mean no more Launch Window Planner untill its updated?

No, I would think that this will still function normally. The universal time since epoch, is still consistent. The planet's rotation has sped up slightly, but its orbit has not changed.

Unless you're talking about launch time of day, rather than window dates. Then yeah. It might be out of whack.

[problemecium]

On a semi-unrelated note, why would Kerbals count their days relative to the stars? Because they love space, of course. To them, Kerbol is just another celestial object that happens to make Kerbin really well-lit for three hours.

/tangent

[Blind Dead McJones]

Launch windows are going to be the same no matter what the rotation of Kerbin is. Same phase angle, intercept angle, etc. so the method won't change, just the calculation. The difficult part is that you might have to do the calculation that way rather than using dates... or just wait until Kerbal Alarm Clock updates.

Just use Earth days in the planner and in game and it should be fine.

That might work also. I've been meaning to investigate that function anyway.

[LethalDose]

I think the length of the day was intitially changed FROM 6 hrs to 6 and change. I think it was done so that it was a synodic day (Sun being over head to sun being overhead) instead of a sidereal day (360 degrees rotation).

It's probably being changed back so it's easier to adjust synchronous orbits (it's easier to precisely set a 6 hr orbit than a 6 hr 52 s orbit).

[Tw1]

On a semi-unrelated note, why would Kerbals count their days relative to the stars? Because they love space, of course. To them, Kerbol is just another celestial object that happens to make Kerbin really well-lit for three hours.

/tangent

I was quite happy with them counting one day as several passes of Kerbol. It made life on kerbin interesting to imagine.

[DerekL1963]

It's probably being changed back so it's easier to adjust synchronous orbits (it's easier to precisely set a 6 hr orbit than a 6 hr 52 s orbit).

Huh? Setting an orbit to a particular time is just as easy regardless of whether it's 3 hrs, 6 hrs, or 6 hr 53.17 seconds. You read the appropriate display, compare your current orbit to your desired one, and burn as needed.

[cpast]

Kerbosynchronous orbits have to be the same period as the sidereal day, not the solar day. They are now a bit under 6 hours, as opposed to before when they were precisely 6 hours.

[ArmchairGravy]

After reading this thread I'm more confused than before. Are we moving from sidereal days to solar days, or solar to sidereal?

[Red Iron Crown]

After reading this thread I'm more confused than before. Are we moving from sidereal days to solar days, or solar to sidereal?

Neither. Kerbin's rotational speed has changed.

[TrooperCooper]

All of Kerbalkind united in an effort to help rocket launches. Thus they all faced east while standing on solid ground. Then they all farted once, which did speed up the rotational speed of the planet a little bit. And now our rockets will need a little less dV to get into orbit.

[LethalDose]

Huh? Setting an orbit to a particular time is just as easy regardless of whether it's 3 hrs, 6 hrs, or 6 hr 53.17 seconds. You read the appropriate display, compare your current orbit to your desired one, and burn as needed.

round numbers are easier to remember and shoot for.

[mstrfalco]

To address a few of you. I was not referring to launch windows between planets being affected, I was referring to launch windows for launching into certain orbits around Kerbin that have inclinations not equal to zero. These look like they will be affected as now the UT for launching into particular ones will be changing. (This will affect the time for launching into an obit with a certain LAN specifically)

On a side note... how might I change the thread from unanswered to answered? I feel this question has been satisfied.

[Red Iron Crown]

On a side note... how might I change the thread from unanswered to answered? I feel this question has been satisfied.

Edit the OP, go advanced, change the thread prefix.