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Claytsuk

Jool Mission Experiencs - School Boy Errors

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My expertly planned mission to Jool with a manned landing on Laythe has not gone well… I’m playing stock 0.23.

Have already been to the Mun, Minmus and Duna (and back ) multiple times so I do get this docking, intercept, landing etc.

Plan

- Launch a refuelling station in advance of the manned mission to Jool and get into Orbit

- Launch a manned Jool engine module to refuel in Kerbin Orbit – 2 nuclear engines.

- Launch a manned Laythe lander to doc with the engine module for the trip to Jool

- Aerobrake into Jool orbit and into a stable orbit

- Drop a probe into Jool atmosphere and beam back science and leave a sat in orbit.

- Refuel the engine mod in Jool Orbit and then transfer to Lathye

- Land on Lathye, redock in Laythe orbit and then ditch everything but the engine and capsules for the trip back to Kerbin.

- Get loads of Science. Boom…

Here’s what actually happened, lots of lessons learned here…

- I actually got everything into Jool orbit fine, journey was uneventful and aerobraking worked well for both the refuel station and lander into about a circular 250k orbit. That was the first mistake, way too close to Jool and would take far too much fuel to push out to Laythe’s orbit.

- Also found that in my low circular Jool orbit the inclination of the fuel station and landing module was very different. Would again take a lot of fuel to match up orbits and dock negating the point for refuelling in the first place.

- So I still dropped the probes and sats and got some science but predicted I would not have enough fuel to get to Laythe and then back home.

- So I got impatient and went straight home and burned to Kerbin using all the lander fuel but missed my intercept and my 3 Kerbals are now destined to orbit the sun for ever.

What I would do next time

- When getting into Jool orbit don’t circularise too low. Aerobrake so the orbits intersect Lathye’s orbit and wait for a Laythe intercept. Would save a lot of delta V.

- Is it possible to aim for a equatorial orbit (or other planned orbit) with consistency? How? I need to do this…

- I might not bother with the refuel station but try to take enough fuel in the engine module to get there and back again.

- Stronger/more docking ports so I could time accelerate in a burn with less wobble.

- Slightly redesigned ships.

Questions

- Was I right to aerobrake at Jool and then go to Laythe, should I try to just go direct to Laythe?

- Is it possible to aim for a equatorial orbit with consistency? How? I need to do this… I can to a mid-course burn to hit the right height in the atmosphere fine but not it seems get my inclination matching up.

Sigh, feel despondent…

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It is possible to get a near-equitorial orbit with aerobraking. During a probe-to-eve mission I was doing I got it about 7 degrees inclination, which IMO is pretty good. I had your problem of too-low-for-gilly though, as well.

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and my 3 Kerbals are now destined to orbit the sun for ever.

What makes you say that? It's not that difficult to rendezvous in Sun orbit and bring them back home.

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Questions

- Was I right to aerobrake at Jool and then go to Laythe, should I try to just go direct to Laythe?

- Is it possible to aim for a equatorial orbit with consistency? How? I need to do this… I can to a mid-course burn to hit the right height in the atmosphere fine but not it seems get my inclination matching up.

You can aim for equatorial, no problem.

You are, after all, coming in with an exactly matched orbital plane, right? So you are coming from the right direction.

All you need to do is hit the right altitude, and the right planar angle.

If you are coming from an exact equatorial direction, and you pass through an equatorial inclination, your path after the encounter will *still remain* in the planet's orbital alignment.

If you are entering too far south, your path will curve North after the encounter, and vice-versa. Just correct until your path curves around the planet but remains on the plane, and then finetune your interception altitude. Profit!

Right to aerobrake Jool, not Laythe? the answer to that question is Green. With purple Polka dots!

It is possible, but *hard*. Typically when I try it I waste more fuel than would have been needed to transfer from a Jool-centric Laythe-apogee orbit. You only need about 35m/s, if you can plan far enough ahead!!

Why? easy. When entering Jool system, your navball etc align to the current governing Sphere Of Influence. And that SOI will belong to Jool, not Laythe. So you have to translate references, and planes, and hit a fast-moving small *low gravity* target while being sucked in by the biggest thing in existence, after the Sun. Not the easiest task!

Once i manage to get to Jool, I apply my course-correction burn as soon as I enter the SOI. (Which I enter at the absolute slowest speed I can manage).

This allows a miniscule course correction (usually under 50m/s) to finetune my plane + aerobrake + resultant altitude orbit. Use any of the moons in a distant low-delta-v encounter to circularise your Jool orbit just enough to not aerobrake any more, and you are on Laythe with less than 100m/s spent in Jool system. 5m/s if you are smart/lucky.

P.S.

Whoever said aerobrake is a single event? I use the first air to slow down *just* enough to remain in Jool SOI after the aerobrake. Who cares if it takes another 5 aero-orbits to get the final one you wanted, you can use Jool to trim off even 0.5 m/s if you want.

P.P.S.

unless you use a resources mod. If Jebediah need to breathe, eat, and s&it, disregard all of my above comments.

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I use Precise Node mod - in patched conics mode 3 you can actually see how your orbit around the body will look before intercept. Then you can fiddle with your trajectory until you get satysfying results - very useful :). As for fuel stations: about only place i use them outside of Kerbin system is Duna. Jool gets tankers: probe controlled, highly autonomous ships that are basically fuel tanks with some systems attached.I send them before the main mission and leave in convenient parking orbit. If my manned vessel needs refuelling, usually it's tanker doing rendez-vous.

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What has happened to me multiple times is getting into orbit counter to the direction that jool's moons are. That's not conducive to any mission!

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You really have to nail the plane correction for Jool. If you have something like Engineer Redux, it will help, otherwise you'll end up with an inclined orbit.

If you aerobrake at about 114k, you should end up with an apoapsis somewhere near Laythe's orbit. You can then fine tune your orbit round Jool to get an encounter, and then aerocapture at Laythe, with an altitude of 23-25k.

Don't try and go straight to Laythe from a Kerbin transfer. Even if you get an intercept, your encounter velocity will be absurdly high and you will be unlikely to successfully aerocapture.

Edited by ComradeGoat

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Sending a fuel tanker ahead of your mission might seem like a great plan, but it is always more fuel efficient (but much more tricky) to send all the fuel, landers and other equipment on one ship with one set of engines.

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Frankly, at this point i don't care about efficiency. I want my Kerbals safe while far from home, and with enough fuel to do everything i want while in Jool system. If it means sending three or four tankers, or building kethane refinery somewhere - so be it. Of course it might and probably will change when we'll get proper economy in the game.

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Although it's best to try and correct inclination before capture, if that for some reason can't be done you can use flybys of Jool's moons to correct your inclination for relatively little delta-v (provided you have a suitably large orbit). When I did my grand tour I shaved off a 1500m/s inclination correction by flying over Laythe's north pole. The intercept only cost me 200m/s.

HmUhBXB.jpg

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