Joolean tour question

[Sleepy_Steve]

So I'm planning a joolean grand tour. Woo!!

I'm going to be using 3 different partially reusable landers, and a central interplanetary tug for the mission. The goal is to hit all 5 moons. But when I look at the deltaV map I get something like 14km/sec deltaV needed on the tug to go there, visit all the moons, and come back.

That strikes me as a bit excessive, is that even in the right ball park?

Edited August 29, 2014 by Sleepy_Steve

[Laie]

First off, in case of a Jool-5 mission, using a single delta-V figure makes no sense.

It is entirely possible to move from one moon to the next on a budget of 500m/s (often less). The key is that the bulk of your vessel never gets into a low, circular orbit. Only the lander needs to get down there, after all -- the "mothership" or however you call it can remain in whatever orbit it first enters, with a very high apoapsis. Rendezvous doesn't become much more difficult that way, but after you docked again, with your apoapsis already pretty high, it takes only a little nudge to leave the moon and fly on to the next. Most of the 500m/s is spent on being captured by the next moon.

[Red Iron Crown]

You should check out this delta-V map instead of the usual ones if you're puttering around the Jool system.

[Himynameisjake]

Like has been said here before, you do not need to attack this the way you're thinking of doing it. I'll get back to you in a while with an obnoxiously over-done way to do it, but for now, take a look at the Ulitimate Jool-5 challenge or my grand tour (both in my signature) for examples.

You should check out this delta-V map instead of the usual ones if you're puttering around the Jool system.

Well now, that's just pretty

[Red Iron Crown]

Well now, that's just pretty

For all the maps and planning I've used, I still haven't strung together a successful Jool-5 mission. Maybe the third time will be the charm.

[Sleepy_Steve]

That's a good point about the non low circular orbit for the main craft. And if I split off landers relatively early, I don't have to move the WHOLE monstrosity around to each moon.

That's also a very pretty delta-V map.

The plan is to base the mothership around the ship on the left of this image:

Initial changes are less RCS, and no science module to save payload. Additionally, two of the LV-N nacelles will be detachable tugs with probe bodies and RCS to help the landers get where they need to be without moving the whole thing around. Tylo lander would dock to the back of that ship, and the configuration would allow me to drop any number of the landers once I'm done with them and up to two of the four nukes. The two other landers would attach to docking ports at the end of the detachable nacells.

Edited August 29, 2014 by Sleepy_Steve

[Sleepy_Steve]

Now just to figure out total payload mass in the landers...

[Laie]

Now just to figure out total payload mass in the landers...

The best way is to plan this backwards. Assemble the vessel you expect to return to Kerbin and give it the fuel it needs for the trip. Then add the gear and fuel for the last landing. Then add the fuel needed to get to the last moon. And so on.

Not visiting every single moon with your big ship is a good idea. But from my own very recent experience, I suggest that you don't try to reach Vall before you've been to either Laythe or Tylo first.

Edited August 29, 2014 by Laie

[Sleepy_Steve]

Tylo is first, it's lander is by far the most massive... This is the untested design I came up with below. I didn't have the large docking ports yet for the big interplanetary stage (not outlined in a square) to be 100% reusable, and I don't have the large RCS tanks so I expect a pretty ugly addition to the nose of the large capsule before too long.

Single launch because I'm lazy. 239 parts and 109 tons so far... Now I just have to get Bill and Jeb back from other missions, slap on a bit more RCS, and add.... 7300 liquid fuel and however much oxidizer that needs.

[Empiro]

I did a tour of Jool not too long ago. I only had a single 20-25 ton 3-stage lander that had 6800 m/s DV for landing on Tylo, the core had 2300 m/s which is more than enough to land on Vall, Bop and Pol, and I refueled it from the main ship. For Laythe, I had a 10.5 ton space plane which was pretty fun to use. It let me choose where I wanted to land more easily. Hopefully you don't have too much issue touching the lander down on to solid ground.

Like others suggest, you don't need to get into a low orbit. I put myself into an elliptical orbit around most of the moons so that I could get low orbit science (I only had a single Science Jr and Single Goo to save on mass in the Tylo lander). It takes some patience to rendezvous and dock with an elliptical orbit though.

[SRV Ron]

Based upon another player's design, this 3 kerbal Jool explorer was tested. It is design to do fly by of the system after aerobraking in the Jool atmosphere to slow to orbital speed. Slingshot manuvers are used to advance to the system moons and eventual escape to Kerbal return. Probes are then released during the flyby to drop into Jool or land on the system's moons.

The modified launcher;

Test launch on SRBs

In orbit ready for the Jool insertion burn

Jool aerobraking

The aerobraking place me into a slingshot orbit ready for fine tuning to the destination of my choice.

[Sleepy_Steve]

ok, so to update this... how do I estimate my burn time needed for my 1900m/s transfer burn? 190 tons, 240 thrust from the four nukes...

My rough guesstimate is somewhere between a 20 and 30 minute burn. If I raise the apoapsis of the orbit to near the mun that reduces the required burn length by 42%... but that still means a 10-15 minute burn, and that still seems overly long.

How accurate are my estimates? And what else can I do to make it work better? Raise my periapsis higher to give more time to do the burn? Give the ship a brief kick on the final transfer burn to Jool by turning on the Skipper and two Rockomax 48-7s for a little bit?

[Laie]

"simple" way: just fiddle with the fuel levels in the VAB until you know your weight before and after the burn. One Nerva expells about 7.62kg of fuel+oxidizer per second. So divide the mass difference by (number of nervas * 7.62) and you know your burn time in seconds.

Of course, you can just calculate it from scratch -- but I find that looking up the formulae and typing them into the calculator takes me much longer than switching to VAB.

Incdentally, 7.62mm^H^H kg isn't quite right, but close enough and easy to remember.

[Sleepy_Steve]

Well, I think I made it... at least the main burn was done. I increased my apoapsis in the wrong angle, and had to do some odd radial stuff to get the ejection angle right. Hopefully a plane change at the AN and an encounter tweak can get me an encounter. This is a lot harder than my probes or the ship I sent to duna. Maybe it's the low TWR?

[Sleepy_Steve]

Mission Update:

^ Ejection burn was not as smooth as I'd hoped. ~300m/s for plane change. Then I needed about 1500 m/s of burning negative radial to get an encounter with a 500km periaps at Jool. More burns are needed later to tweak into aerobreaking.

So... burning radial on ejection + massive radial correction = I goofed the pre-burns and possibly missed the ideal point in my transfer window... I've noticed Alarm Clock and MechJeb have different estimations of transfer windows. MechJeb normally coming before alarm clock.

Cross feed in the docking ports caused me to drain all my landers without realizing it. Now my center core is down to about a third of a jumbo-64 tank. I'm not sure how much deltaV the thing has left any more. I will not scrap any mission objectives.