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Altaïr

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From what I've seen the ISP and thrust are correct, it's the fuel consumption that's rounded...
That's what I thought, but I made some tests a while ago, and noticed that all my stages had slightly more delta-V than expected. And I realized that I had a much closer result by considering that the fuel consumption was accurate. That's why we recalculate Isp from thrust and fuel consumption.

Now that only makes a difference about a few m/s in practice. It doesn't drastically change things.
 

Mooncrasher

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I love how the various real life formulae like Kepler's laws and the one for calculating the mass of an object from its surface gravity and radius apply perfectly to SFS. Just with different units.
 

Mooncrasher

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Seriously, the result I got from roughly calculating the orbital period of the SFS Earth based on Kepler's third law agreed with my rough stopwatch measurement by 99.6%. That's a rounding error size deviation.
 

Horus Lupercal

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I love how the various real life formulae like Kepler's laws and the one for calculating the mass of an object from its surface gravity and radius apply perfectly to SFS. Just with different units.
Seriously, the result I got from roughly calculating the orbital period of the SFS Earth based on Kepler's third law agreed with my rough stopwatch measurement by 99.6%. That's a rounding error size deviation.

Yeah, there's been a lil bit of work on that between a few people for a bunch of challenges that came up a few months ago. It works out pretty damn well.
 

Mooncrasher

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Yeah, there's been a lil bit of work on that between a few people for a bunch of challenges that came up a few months ago. It works out pretty damn well.
Oooooh, link?
Currently I'm calculating what the periapsis of a satellite should be for it to get to the Earth-Sun L4/L5 position in one Earth-year after leaving the Earth's SOI.
 

Horus Lupercal

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Oooooh, link?
Currently I'm calculating what the periapsis of a satellite should be for it to get to the Earth-Sun L4/L5 position in one Earth-year after leaving the Earth's SOI.
Head here...

Right, update time for the old headache sheet.
The celestial data page has a resonance orbit calculator on it
 

Mooncrasher

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Oh, thanks.
I'm at the final step where I know what the semi-major axis should be, but I'm stuck at figuring out the periapsis (aka the minor axis) based on knowing what the apoapsis (aka the major axis) and semi-major axis are. The formulae I found depend on knowing the eccentricity or focal points of the ellipse, which I don't know.
 

Mooncrasher

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Oh wait...
Semi-major axis = (Major axis + Minor axis) / 2?
 

Altaïr

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Oh, thanks.
I'm at the final step where I know what the semi-major axis should be, but I'm stuck at figuring out the periapsis (aka the minor axis) based on knowing what the apoapsis (aka the major axis) and semi-major axis are. The formulae I found depend on knowing the eccentricity or focal points of the ellipse, which I don't know.
If you have the semi-major axis, you've done the hardest part, as you have:
Semi-major axis = (periapsis + apoapsis)/2

For an ellipse, the major axis is the line that joins the apoapsis and the periapsis.

Just be careful that under SFS, the periapsis and apoapsis are measured from the Sun's surface, while in the formulas, they are supposed to be measured from the center. For this, you may substract 31.5 km (the Sun's radius) to get the value you should aim in SFS.
 

Mooncrasher

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Head here...
The celestial data page has a resonance orbit calculator on it
I tried downloading the zip file on post #22.
The spreadsheet it gives me has no orbital resonance calculator, and the "last modified" date is from December.
Is there any chance it's a duplicate from the version in the first post?
 

Horus Lupercal

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I tried downloading the zip file on post #22.
The spreadsheet it gives me has no orbital resonance calculator, and the "last modified" date is from December.
Is there any chance it's a duplicate from the version in the first post?
Ooooh, I updated that in March with some extra goodies in there. Hmmmm...
 

Mooncrasher

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Yup, looks like that's the right one now. :)
Now to figure out how it works.
 

Horus Lupercal

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You put your numbers in the green areas and leave the white bits alone.
So, when you want to work out your resonance orbit, you put your required orbit in the green Ra/Rp box, how many satellites you want to upload and how often you want to cross paths with the satellite orbit per rotation when you're delivering. It will spit out the orbit the bus needs to be in and the elliptical orbit speeds of the intended satellite orbit and the bus resonance orbit.
 

Horus Lupercal

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Docking

Is it impossible?

No.

It's necessary
(If you want to progress...)

When docking, the main thing that you need to bear in mind is what is known as orbital speed (how fast you're going around in that circle). Everything in different orbit sizes is moving at a different speed.
That also goes for the speeds at Apoapsis and Periapsis. Just cos you're at the same height orbitally, if the other side of the orbit is different, then your speeds will still be different.

Where as everything in the same orbit is moving at the exact same speed.

So, Imagine we're like this. one section that we're controlling at a slightly lower orbit than than where we want to dock.

Screenshot_2019-03-29-01-00-37.png


Press on the destination section...

Screenshot_2019-03-29-01-07-46.png


And press Set As Target.

Screenshot_2019-03-29-01-07-50.png


And the screen should look roughly like this. Notice, there's no transfer window, just a direct line (The closest approach line) from you to the closest you'll get to that object in this particular orbit cycle you're on. See how it's roughly diagonal as well? That's bad.

To alter that, you need to time warp so your craft orbits around the Earth along with your target. Now, because they're moving at different speeds, one will catch up to the other. What will happen before that is the closest approach line will line up straight and stop moving. How long that takes depends on the difference in orbit sizes. If they're 150 odd Km apart, then the speed difference is huge and one will catch the other a lot quicker. If the orbits are very close together (like, 15-20km) then the orbital speed difference is a lot less and it can take a while to get them to line up properly.

Anyway, eventually this will happen...

Screenshot_2019-03-29-01-09-01.png


At the bottom left corner of the orbit, there is a very short line. That is the closest approach line from earlier, but as close as the orbits allow, and it will be static as you orbit.

If you zoom in there, it'll look like this...

Screenshot_2019-03-29-01-08-10.png


Now, for a tiny bit more orbiting. What needs to happen now is keep going around until the orbit before you actually catch up to the target section.

Then, once in that rotation and at the exact opposite side of the orbit to the Closest Approach line, burn prograde slowly until the orbits meet.

The Closest Approach line will move again. Don't worry about that, let it move until the orbits meet and overlap slightly. The Approach line will then jump to either one of the overlap points and become very small.

Zoom in...

Screenshot_2019-03-29-01-09-44.png


And your closest approach is now in metres rather than km.

Throttle down even more and burn very gently prograde and watch that number shrink...

Screenshot_2019-03-29-01-10-13.png


To distance a few hundred metres or so. Less than 500m is good, between 100-200m is better. Too far and you may miss completely. Too close, and if you burn to0 late for slow down you could risk just crashing straight into your target.

If the number starts getting bigger, then you're burning in the wrong direction. Switch to retrograde and try again.

The earlier you get this sorted, the less Dv it costs.

Then, once you've got that nice and close, now time for more orbiting. It never goes straight in that first time, so don't panic if it misses by miles that first rotation.

On the second rotation, they will get very close and start roughly flying close. Press on your craft and select Follow to make this part easier.

Zoom right in so you can see both craft and sack the time warp if you're still doing it.

It should look roughly like this.

Screenshot_2019-03-29-01-11-07.png


Now, we're close, but we're facing in the wrong direction for the speed matching burn. Rotate the craft so that the incoming object is approaching from the tail end.

Screenshot_2019-03-29-01-11-23.png


Now, when it comes in relative to you, you can burn away, thus slowing your approach down.

Keep zooming in as they get closer and closer. Then, switch to normal view and zoom out so you can just about see your craft as a dot. Eventually, a second dot will appear moving in.

Screenshot_2019-03-29-01-12-00.png


Hard to spot? Zoom in a little bit more as it approaches. It will pass 177m away from you so you can afford not to worry yet

Screenshot_2019-03-29-01-12-11.png


Like this. Once you're pretty close, but before it passes, you burn hard away from it to equalise your closing speeds.

Remember to bear in mind how much speed you need to catch up when doing this. I've come from pretty close with a light rocket armed with a pokey engine so a very short stab of throttle was enough to sort it.

If however you're coming up from 31km to 150km direct and you've only got 4 Ions decelerating your 1500t 3rd stage, then you're gonna be in for a shocker as it screams past you laughing.

What you're actually doing is making your orbit exactly the same as his, at the same place as he is, so you fall around the Earth at the same speed but are static relative to each other.
Also, ignore the direction arrow and the speed gauge. They are relative to the body you are orbiting, not the target you've selected. All of this is done by dead reckoning and judgement.

Screenshot_2019-03-29-01-13-10.png


Now, to make contact. This is pretty easy with RCS, as you just press an arrow and the craft moves in that direction. I've gone full hard core (cos I forgot to fit it with RCS...) and am docking old school with main engine inputs.

Screenshot_2019-03-29-01-14-47.png


With a wee bit of arsing about, you get your docking ports as close as possible. They're 'magnetic' and will not only lock as they pass but have a slight attraction to each other as well so will pull you in if you are close enough.

Screenshot_2019-03-29-01-14-47.png


And docked. You can now transfer fuel an whatever you wish to do with both of them. They are now one ship for all intents and purposes until you separate them.
 
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Horus Lupercal

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What if I have the glitch where the closest approach line keeps spasmijg out around the orbit of an object you want to dock to?
Its not so much a glitch, its the way the system works out where you're going. It usually happens if you're in one SOI and have an orbit going into another (like going from Earth to Mars). Once you leave Earth SOI and are in solar orbit, it'll straighten out.

It also goes a but wavy if you're zoomed in too far as well
 

Altaïr

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What if I have the glitch where the closest approach line keeps spasmijg out around the orbit of an object you want to dock to?
That's probably due to numerical imprecision in the internal calculations. But it generally doesn't make a big difference. Even if you "miss" your encounter by 200 meters (or even more) because of this, you'll still be able to manually navigate towards your target.