Mun Troubles

[FloatingGrass]

No matter how hard I try, something always goes wrong when I try to go to the Mün.

Just today I was on a sub-orbital trajectory around Kerbin when I aimed at the Mün. Until then, everything had gone perfectly well. As I reached my node, I throttled up to 100% and in a few seconds the flight went from completely stable to spinning uncontrollably. I checked everything; nothing was unsymmetrical, all engines produced the same thrust, all tanks were crossfeeding fine.

Nothing ever works out for me, and I wonder how I'll even get to Minmus at this rate.

Please help!

[Vanamonde]

A screenshot of your ship with the UI showing might help diagonose the problem. In the meantime, is it possible your joystick is sending unintentional attitude commands?

[xcorps]

Spinning on its axis or pitching/yawing?

[FloatingGrass]

Spinning on its axis or pitching/yawing?

Pitching and yawing.

[FloatingGrass]

A screenshot of your ship with the UI showing might help diagonose the problem. In the meantime, is it possible your joystick is sending unintentional attitude commands?

I can't take screenshots in career mode, either. I've tried F1 and F12, looked in the controls menu and still nothing. Screenshots work fine in sandbox mode.

As for the altitude commands, I doubt it, since the pitch/yaw were static.

[xcorps]

Yeah, it would really need a picture.

Do you have any radial fuel tanks that are empty? Do you have a goo canister? A monoprop tank?

Something has moved your COM away from your COT. If it's not thrust, it has to be mass.

[Pecan]

...Just today I was on a sub-orbital trajectory around Kerbin when I aimed at the Mün...

First get to orbit :-)

'Sub-orbital' covers a lot of ground (as it were) but from everything that then went wrong I'm assuming you were a) still in atmosphere and, probably past apoapsis (high point of flight). Basically, you'd got 'high' but not really into space - then rushed at Mun while you were more or less already falling out of the sky.

1. Get a stable orbit - apoapsis and periapsis (low point of orbit) both above 69km, preferably around 75km and roughly equal.

2. Change plane to match Mun (0 degrees equatorial orbit).

3. Perform a Hohmann transfer to intercept Mun.

[Vanamonde]

I haven't heard of that screenshot issue. You might want to write it up as a bug report, though if you do, please keep these requirements in mind.

[Nurph]

How much is 100% thrust for you? Accelerating to hard can make weak connections bend and compress.

[NoClass]

As to screenshots... that's weird. You might try copying your craft into a sandbox mode save, simply to get a screenshot.

The pitching and yawing... Does the craft move back and forth, or just one direction constantly? If you have SAS on, do your pitch, roll, and yaw indicators show that it is fighting the movement?

[FloatingGrass]

As to screenshots... that's weird. You might try copying your craft into a sandbox mode save, simply to get a screenshot.

The pitching and yawing... Does the craft move back and forth, or just one direction constantly? If you have SAS on, do your pitch, roll, and yaw indicators show that it is fighting the movement?

Yes, it is fighting the movement. I tried to turn SAS off but it still happened. It was just extremely violent. As I had said before the goo and stuff probably didn't cause much, because I think they were symmetrical.

I had already made it to the moon with the craft before (ran out of fuel, went on EVA and crashed Jeb into the surface). That time I made it there were no issues.

[FloatingGrass]

Wait, my bad! The screenshots WERE working all along. The thing is, in 0.24, Steam doesn't say "screenshot taken" as it used to. I checked in the screenshots folder (seeing that when I pressed the hotkey the frames dropped) and there they were

I'll upload a pic of the craft later.

[Xavven]

Alternatively you can post a .craft file, but we look forward to seeing your screenshot soon!

Also, do you have a long and skinny rocket? They tend to cause unwanted flexing. If your command pod is at the very top, it can cause SAS to think your whole rocket has changed direction instead of just bending, and it starts to overcompensate and worsen the oscillations (like an inexperienced driver who worsens a fishtail skid on the road)

[FloatingGrass]

Here we go!

[Pecan]

A picture makes many things clear - you have fuel lines running in both directions between the radial tanks. That's creating a loop straight away and throwing things out. You only want fuel lines in one direction.

[Zwer.ch]

I'd say leave the fuel lines completely away for now. I don't know if this is an attempt for asparagous staging, but in any case you might experience an uneven flame-out of the engines, causing spins.

On top: this craft looks either heavily over-engineered (if used to get from LKO to Mun), or under-engineered, if used to launch directly from KSC. The LV-909 makes a bad atmospheric launch engine due to the low thrust and low atmospheric ISP (compared to e.g. the T30/T45 engines).

[FloatingGrass]

I'd say leave the fuel lines completely away for now. I don't know if this is an attempt for asparagous staging, but in any case you might experience an uneven flame-out of the engines, causing spins.

On top: this craft looks either heavily over-engineered (if used to get from LKO to Mun), or under-engineered, if used to launch directly from KSC. The LV-909 makes a bad atmospheric launch engine due to the low thrust and low atmospheric ISP (compared to e.g. the T30/T45 engines).

I use it as my orbital vehicle/lander. The reason it has so much tanks is because I always run out of fuel on the way.

[vetrox]

those fuel lines are screwing you over. I just made a quick mock up and the tanks all drain in a peculiar way. Its propably flyable for a short period because of all the rcs you have keeping things in check but it can only do so much.

The center vehicle alone has enough dv to go from kerbin orbit, land on the mun, take off go land on minmus and come home

Edited July 23, 2014 by vetrox

[SDEngineer]

I use it as my orbital vehicle/lander. The reason it has so much tanks is because I always run out of fuel on the way.

As others noted, the problem is in your fuel lines - it looks to me like what you are trying to do (based on the staging) is have the external 4 tank/engine combos be a orbital insertion/landing stage, then have the central vehicle be the return stage. If this is the case, here is how you want to lay the fuel lines out: You'll want just a single set of fuel lines from the side mounted tanks running to the central vehicle:

.....T.....

.....|......

.....v.....

T->O<-T

.....^....

.....|......

.....T.....

Make sure the arrows on the fuel lines are pointed the correct way - fuel lines only conduct fuel in one direction. When you connect them, you attach them from the tank they are transferring fuel FROM first, then connect to the tank they are transferring fuel TO. The above arrangement will ensure that the central tank is completely full when the outside tanks are empty, since it will draw from the outside tanks first.

However, I agree with the others on this thread - your vehicle is seriously over-engineered for a simple Mun lander - and it will get you into trouble as-is. The problem with it is that since it has been so over-engineered, it masses a ton (or rather many, many tons) - and will be difficult to land on the Mun intact for an inexperienced pilot.

My suggestion is to take the core (only) and practice landing on Minmus a dozen times - it is a little more difficult to get to orbit around Minmus (you need to match planes, and costs more dV) but it is ten times easier to learn to do a powered landing on Minmus as opposed to the Mun. Once you can land anywhere you want on Minmus surely and quickly with no mistakes, you are ready for the Mun (until I started practicing on Minmus I was hopeless at Munlanding)

Advantages of Minmus vs. the Mun:

1) the "Flats" are ideal locations to learn the basics of landing. Perfectly flat and at 0m elevation. All you have to worry about is learning to kill horizontal velocity properly and manage your descent speed. You will be very hard pressed to find anywhere on the Mun that is flat or at 0 elevation, and none at all that are both and easy to target to land at from orbit. This makes it easy to practice the basics of landing before getting into more complex stuff like trying to aim for a "nice" spot while doing a powered descent, and dealing with trying to eyeball (or check in the cockpit) your "real altitude" while still managing your descent speed and horizontal velocity.

2) Much lower surface gravity. The practical effect of which is that everything happens at about one fifth the speed it happens on the Mun - giving you much more time to think about what you are doing, and much more leeway for error. A misstep that would be absolutely fatal on the Mun is much more likely to be recoverable on Minmus.

3) Because of 2 - much lower dV requirements for landing, and once landed, taking off again - making Minmus much more fuel economical even though it takes more fuel just to get there - while it may take 15% more fuel to get there and achieve orbit, it requires about one quarter the fuel to land and take off again.

Edited July 23, 2014 by SDEngineer

[Idrryl]

Advantages of Minmus vs. the Mun:

1) the "Flats" are ideal locations to learn the basics of landing. Perfectly flat and at 0m elevation. All you have to worry about is learning to kill horizontal velocity properly and manage your descent speed. You will be very hard pressed to find anywhere on the Mun that is flat or at 0 elevation, and none at all that are both and easy to target to land at from orbit. This makes it easy to practice the basics of landing before getting into more complex stuff like trying to aim for a "nice" spot while doing a powered descent, and dealing with trying to eyeball (or check in the cockpit) your "real altitude" while still managing your descent speed and horizontal velocity.

2) Much lower surface gravity. The practical effect of which is that everything happens at about one fifth the speed it happens on the Mun - giving you much more time to think about what you are doing, and much more leeway for error. A misstep that would be absolutely fatal on the Mun is much more likely to be recoverable on Minmus.

3) Because of 2 - much lower dV requirements for landing, and once landed, taking off again - making Minmus much more fuel economical even though it takes more fuel just to get there - while it may take 15% more fuel to get there and achieve orbit, it requires about one quarter the fuel to land and take off again.

It's kind of funny to think about it, really. The Mun was intended to be a tutorial on how to land on other bodies before they changed it's terrain, I imagine it's pure hell for new players now. And because of it, people forget about Minmus, which is, as you pointed out, a better choice for learning how to land.

[SRV Ron]

This is my Mun lander modified from the original demo. It has more then enough delta v to add two goo canisters and a materials bay. Note, only a single set of fuel lines to the core. Also, no RCS. You don't need it for landing. All you need to do is use the Nav Ball retro marker and line up on it. When you can get it centered to up at under 10m/sec, you have successfully cancelled out the drifting.

A much smaller lander is possible.

Example of getting the drift to near zero. At 1.5m/second, what drift is still left can be ignored.

Edited July 23, 2014 by SRV Ron

[Pecan]

It's kind of funny to think about it, really. The Mun was intended to be a tutorial on how to land on other bodies before they changed it's terrain, I imagine it's pure hell for new players now. And because of it, people forget about Minmus, which is, as you pointed out, a better choice for learning how to land.

There's no hell for new players, there's Mun for the 'foolishly daring' ;-0

In other words - if people won't look at even the simplest planning information they've only got themselves to blame.

Huh? Why was it Apollo Eleven that landed on the moon? I can do it right now!

[Anizer]

I also have Mun troubles, my kerbal got stuck on the surface of the Mun lol.. he can't move or board anything