Mun-trapped! MechJeb can't help you now...

[Galane]

Yup, a reference to this movie, in which a Lunar Lander plays a central role.

Download the quicksave file here

Three Kerbals are in a single stage lander in a low and eccentric Mun orbit. The lander has one full Rockomax X200-16 and one full FL-R1, with a Poodle engine.

The lander is docked nose to nose with a support ship that has one full and one partly full X200-16 and one partly full FL-R1, with a poodle engine. Behind that are three empty tanks, a Rockomax 64, a X200-16 and a X200-8, then a Skipper engine.

Everything in flight is all stock parts except for the control pod mod for MechJeb 2.0.9. Also in orbit are two stations with six full Rockomax 64 tanks with a ship docked to one that is an RCS tanker, but it's mostly empty on fuel.

The kicker is the autopilot has failed. MechJeb finds it impossible to do anything without first completely reversing the orbit direction before executing the desired maneuver, doesn't matter if the inclination is set to 0 or 180, it's reverse gears first, oops, there's no fuel left. There is enough fuel to leave Mun SOI, MechJeb has managed it several times, sending our poor Kerbals on a dutchman towards the outer system with no fuel.

Thus the player has three options.

1. Manually trigger the separator to jettison the empty tanks then fly out of Mun SOI manually, keeping the support ship docked until its tanks are empty. Can't use MechJeb because even though a manual separation leaves the support ship's engine set to inactive, MechJeb will activate it AND throttle up the lander's engine at the same time. Once out of Mun SOI, either make it back to Kerbin with enough fuel to land or do an orbit rendezvous to take on fuel for landing. (Once out of Mun SOI, MechJeb should recover its sanity and be able to do a Hohmann transfer to Kerbin.)

2. Build a rescue vehicle to send out and fill up all the tanks on the support ship, giving the player what should be plenty enough fuel for even the most ham-handed pilot to manually fly out, or for Insane MechJeb to waste on reversing orbit direction before doing anything else. In that case, the empty tanks are a resource to keep.

3. Build a rescue vehicle to dock only fuel tanks to the lander, completely replacing the dead weight parts of the service ship (engine, RCS tank, Rockomax Brand Adapter etc.) Either leave the service ship in Mun orbit to be refueled later or crash it for disposal. Fly out manually or let MechJeb waste some fuel.

A note about the lander. It has no parachutes and no way to cut the crew pod loose. MechJeb has brought it down to Kerbin several times from orbits as high as 200KM and landed with almost 1/2 a tank left. So that's an additional challenge, the lander has to have at least half of a X200-16 full of fuel upon re-entering Kerbin's atmosphere in order to land safely. This landing convinced our engineers that the lander was a robust enough design to upgrade to a manned version. Immediately after, it was updated to the design seen in this scenario and has proved to be reliable in many flights.

If it's not possible to get the lander back to at least a refuel rendezvous so it can land on Kerbin, I'll have to re-think my Mun landing strategy.

If you do manage to figure out how to make MechJeb not burn all the fuel reversing orbit direction I'd love to know how you do it. I've even tried setting it to 180 degree inclination in an attempt to make it use the direction the ship is already going. Seemed logical. If it wants to stop and turn around at 0, 180 *should* make it stay going around the way it already is.

[Stochasty]

Errr... so the challenge is just whether or not you know how to plot a Mun return trajectory without the use of MechJeb?

Unless I'm misunderstanding things, there's not very much to this challenge. It might be a reasonable challenge for new players, but that's about it.

[Galane]

There's a limited amount of fuel to use. The hardest way back home is to not send out any more fuel.

[Liquid]

As a "master-race purist" who's flown hundreds of stock Mün missions, using Mechjeb would probably make this harder!

(disclaimer: though I personally prefer manual flight, Mechjeb is still a great mod and r4m0n is a great programmer)

[Galane]

Right. I got stuck in this situation and MechJeb just can't fly out of it. Doesn't matter what sort of maneuver I try with it, the first thing it insists on doing is reversing the orbit direction, which burns up all the fuel - leaving the poor Kerbals either on a trajectory back to Mun for a crash or drifting off into space.

I'd like to see if someone can manually pilot out of this, get back to Kerbin and land with the fuel available.

The ships used to get there http://partsbyemc.com/pub/AARP-Mun-collection.zip

Edited September 7, 2013 by Galane

[PrivateFlip]

Errr... so the challenge is just whether or not you know how to plot a Mun return trajectory without the use of MechJeb?

Unless I'm misunderstanding things, there's not very much to this challenge. It might be a reasonable challenge for new players, but that's about it.

Got the same feeling. I've jet to be in on of these (in)famous mechjeb discussions and I hope not to get in one by responding to this thread.

I've never used mechjeb so it could be mechjeb flies way more efficient mechjeb than me but somehow I don't think it's an amount which would make the difference. If it was I would definitely want to know what it does what I can't or don't do. (What I do is burn prograde when my ship is "in front" of the Muns orbit around Kerbin until you reach escape velocity and after escaping I just burn retrograde until the orbit dips into the atmosphere.)

[Xeldrak]

Well, there you go - mechjeb vanished while loading the vehicle, but I thankfully I can navigate within the Kerbin-Mun-System by hand....at least a littlebit. I tried to comment each picture...

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By the way - there is quite a lot of fuel in that spaceship, no need to fuel up anyway. Is enough to reach Duna......literally....

(once again showing off my mad powered decent skills)

Edited September 7, 2013 by Xeldrak

[Sirine]

similar to this We are not losing those kerbals!

I believe this is harder?

[Galane]

So, it is possible. Good to know.

[Xeldrak]

Yes, it's definitely possible - you'got loads of fuel and the Poodle is a very efficient engine (for a chemical engine). Basically all you have to do is burn prograde when you are between the Mun and Kerbin. Get rid of this support craft, it just make the whole thing wobblier and the lander has loads of fuel on its own. I strongly suggest to play around with orbital mechanics and rely less on MechJeb

Edited September 7, 2013 by Xeldrak

[Johnno]

I didn't think this challenge seemed hard enough, so I kicked it up a notch. No debug menu, no mechjeb (I've never had it). Do I win?

[ihtoit]

yep. Easy. Offload as much fuel out of the giant tank section as you can (preferably empty it) then dump it. It's a trick question. Move all your fuel to the back of the spacecraft. Burn prograde from the backside of Mun until your orbit track brings you to Kerbin encounter (this is called a free-return trajectory/transfer manoeuvre and describes a figure-8 between the two bodies) (will not take much Delta-V), then burn retrograde at apoapsis until your periapsis starts you to aerobraking altitudes (<70km) (again, will not use a lot of Delta-V), continue to orbit until you're at the stage where periapsis intersects with the ground, then tail land that sucker (this will use the most fuel). No MechJeb required.

[Van Disaster]

Quite possible even with using mechjeb - set your maneuver markers up by hand & have it fly those. People seem to think you either use all the autopilots or nothing.

[aNewHope]

I was able to land on the Mun first, dock with the fuel tank and get back to Kerbin. Sadly I landed in the ocean which ripped the rocket apart (2 m/s surface speed).

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PS.: They are all alive and happy!

[Sirine]

Yeah, the "mechjeb" autopilot only stop your flying skill for improving. I never want to use it. (ATM)

[Galane]

Amazing flights. Landing with the support ship still docked and another with a *second* Mun landing and safe-ish return to Kerbin.

[numerobis]

My reaction is: MechJeb is open source. If it can't fly as well as manual, the real challenge is to improve it.

[Tiron]

Yeah, the "mechjeb" autopilot only stop your flying skill for improving. I never want to use it. (ATM)

There's a reason it includes the capability to disable functions or entire modules via the .cfg.

It does provide some *excellent* informational stuff, though, including one no other mod can do: Atmospheric entry simulation. Unless you have FAR.

[occar]

I guess the OP has now figured out that there are people really good at this game and that MechJeb, while useful, is far from efficient.

[Traches]

I take an "all things in moderation" view of mechjeb. I let it do the easy, boring, day to day maneuvers while doing the tricky ones myself. When I do use the autopilot, 95% of the time it's flying a maneuver node I planned manually, or it's just pointing me at the marker while I control the throttle.

The autopilot is a secondary function of mechjeb; the wonderful part is the information it can give you.