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Reach Jool or Eeloo and return


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The big hurdle in the game I'm trying to overcome right now is to reach the further out planets like Eeloo or Jool and it's moons and return. I can get ship out there no problem and land but I don't have enough fuel to return home. I try and add more fuel tanks to be jettisoned along the way, but it seems the weight penalty of the added mass of these extra fuel tanks just means longer burns to get there, longer burns to get into orbit and then I'm still left without enough fuel for the return trip. So then I add even more fuel tanks, which means more mass which means longer burns which means more fuel consumption which again leaves me without enough fuel to get home. It seems to me like adding more fuel tanks just adds a weight penalty that just cancels out most of the additional range that fuel would give you.

I've seen people doing return trips from Jool and Eeloo and doing it in tiny crafts with a single small fuel tank. How is this possible?

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Well, there is the option of manipulating the KSP files to add extra thrust, or provide infinite fuel, as a first.

I have no experience going to Jool, but you could send a second (and a third, depending on how much delta-V you'll be needing) spacecraft over to Jool, and combine the fuel of both to give one of them enough fuel to return home, then either dump your tankers into Jool's atmosphere or just leave them floating, and return home. Also, check if you have enough fuel to make it to Dres or Duna - it should be easier to get fuel for the return trip there. Perhaps you already have a station orbiting Duna.

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I haven't returned from Jool or Eeloo yet.

But I have successfully returned from Duna with a tiny probe.

Important for interplanetry travel is the transfer window which offers the most fuel efficient trajectory.

I use Kerbal Alarm Clock for telling me when a transfer window opens.

Also an aerocapture maneuver around Jool saves a lot of fuel.

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So then I add even more fuel tanks, which means more mass which means longer burns which means more fuel consumption which again leaves me without enough fuel to get home. It seems to me like adding more fuel tanks just adds a weight penalty that just cancels out most of the additional range that fuel would give you.

That's the exponential nature of the rocket equation!

Tiny craft = less weight = more delta V. But seeing your craft in that other thread, looks like you've got that already. Are you using the fuel in that for your kerbin orbit burn, and-or your transfer burn?

You could pretty easily add an extra transfer or Kerbin orbit stage to that, and still have something that you can launch without too much trouble.

Sometimes it's better to have a longish burn, and save delta V by not adding extra engines, sometimes you need that Delta V.

Or perhaps it's time to consider a flight with a lander that docks to a return module , or re-docks with a service module left in orbit.

That module could just be a fuel tanker with enough to return home.

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Just remember Einstein: E = mc²

So the thing is... build it lightweight (may only use 1 nuclear engine, not 10) and build it so you can throw away "dead mass" like empty fueltanks.

Cheers!

StainX

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The big hurdle in the game I'm trying to overcome right now is to reach the further out planets like Eeloo or Jool and it's moons and return. I can get ship out there no problem and land but I don't have enough fuel to return home.

Try putting a tanker in orbit at your destination. Then your manned mission can refuel once it gets there.

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1. rocket design

From the delta-v map here we see that using aerobraking it wil take 3510 to get to Jool orbit and back. 50% extra seems a sensible precaution to take on a first mission so we will aim for 5250

for the payload (pod for 1 kerbal, solar panels, parachutes, decouplers etc) we shall say 1.5 tonnes

We will use an lv-n engine(2.25t ISP 800) and a ftl-800 tank (4.5t full and .5 empty).

The mass full =8.25t

empty = 4.25

from the rocket equation that gives delta v= 5200

If you can get that basic rocket full into LKO then it should have plenty of fuel to make it all the way if flown correctly.

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Use the delta v map and work backwards. Build a lander that has enough delta v to get back from where you're going.

Then add on an interplanetary stage that will get the lander from a Kerbin orbit to your destination.

Then build the big stage to get that into orbit around Kerbin.

(Also allow a decent margin of error)

I've done missions like this to Moho, Laythe and Eeloo.

The lander and IP stage should use nuclear engines, unless you land somewhere big and need more thrust, like Laythe.

I just sent the 3 man capsule to Eeloo and back. It had 2 nuclear engines on the lander and another 2 on the IP stage. All 4 fired during IP manoeuvres with fuel lines to the lander to keep it full.

Let me know if you still have problems and I'll post some pics.

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2. Launch windows

using launch window planner/ ( a tool I wish I cold create) we can see that there is a good launch window on day 61 of a brand new game arriving on year 2 day 188.

A couple of days before the launch day launch the rocket into a nice circular equatorial orbit

On d day add a maneuver node at about the trailing side of kerbin, adjust it prograde to about 2000m/s then pull the node around until the projected path leaves Kerbin as close as parallel to Kerbin's orbit as possible. do some fine tuning to try to get as close as possible to a Jool intercept

The burn will take about 4 minutes so 2 minutes before the node you should start burning in the node's direction

At the ascending/descending node of the transfer place a maneuver node and achieve your intercept.

On the way back do the same thing, the best return date appears to be year 2 day 262

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  • 4 weeks later...

It's quite impractical to try and do this all with one vehicle. Even with nuke engines, if I need to carry a sizeable lander beyond Duna I bring an interplanetary cruise stage, the lander itself, and a refueling tanker. The cruise stage carries the lander and uses up the vast majority of its fuel getting to Jool and then getting into orbit. Then the lander goes and lands. In the meantime, the refueling tanker (flown separately from the other two) arrives with about half of its fuel or more still remaining and docks with the cruise vehicle in orbit, transfers all of its fuel and then deorbits with RCS. The lander returns to the now partially-fueled cruise stage, the crew transfers and the lander is ditched before burning back for Kerbin. By doing this I have plenty of fuel left upon my return to Kerbin to circularize my orbit and rendezvous and dock with my space station so I can reuse the interplanetary stage.

Here is a breakdown of my standard deep-space mission design so that you can see what kind of infrastructure you're going to need to bring:

Cruise stage:

1 big orange tank, four nuke engines (mounted radially on some structural parts), four 1-m RCS tanks and RCS thrusters for docking, one hab module, one 2-kerbal lander can, and senior docking ports on the front and back (plus extras like solar panels, lights, batteries, antennae, etc. for utility/show). I have a second version which has landing legs and can land on the Mun pretty easily, so it has decent thrust leading to not intolerably long burns.

Lander:

Varies, I estimate the landing dV beforehand and then give myself a margin, then I make the lightest vehicle that I can with the requisite dV and TWR. My Vall lander had two nuke engines, but the Dres version only used 2 LV-909s, it turns out that the extra fuel required by the chemical engines weighed less than the difference in mass between the nukes and the chems. It's important that you minimize the mass of this because it will cost you loads of fuel to get it out to your target!

Refueling tanker:

One big orange tank, two nuke engines mounted radially on structural parts, two 1m RCS tanks (for replenishing supplies on the cruise stage, if necessary), one of the big probe cores (it's not the lightest but it looks better) and some small solar panels tacked to the sides. There is a single senior docking port on the front. This is a flying fuel can and should be able to get anywhere in the kerbolar system with plenty of fuel left to get your cruise stage home, especially if you aerobrake at Kerbin.

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Given how the rocketry fuel use equation works, to get a big payload somewhere it's often simpler to, instead of making one massive rocket, send it in smaller parts in multiple separate ships and then dock the parts together when they get there. One of the types of separate "ship" you can send is one in which the payload is just an unburned full fuel tank with docking ports. Put it in orbit around Jool and then ships trying to get back home can dock with it and take fuel from it.

Also, get a refueling station in low orbit around Kerbin. Send lots of fuel tank payloads to it and make them contain docking rings so they can be attached to other ships. Then send your ship to the station first, pick up full fuel tanks there, and then from there go on to Jool. This is sort of just another application of the idea of sending your payload in separate launches and attaching them later.

Just a warning though - a ship with lots of modules connected by docking rings in space (and therefore modules cannot be strutted to each other because they weren't built in the VAB that way) tends to wobble a bit and you'll have to make all your rotations gentle and slow. But then again, if you're going all the way to the outer planets, you've got plenty of time to wait for very slow rotations to line up your burns.

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