Apollo style FAIL, how do I un-fail

[wdsmith3]

the mission goal was a maned landing on Duna and Ike for some science. It was a 2 launch mission, csm first, then launched the duner lander and docked them nose to nose apollo style. When I went to escape the Kerbin SOI, I throttled up and this happened. I was able to successfully abort the mission, landed my 4 crew safely on the ground.

how do i prevent this? I was using the small docking port (the size of the top of the 1 man command pod)

[Epthelyn]

Either there's something wrong with the image you've posted or Firefox is messing up, but I can't see what you're referring to; the image isn't visible.

Anyway, the url works if used manually, so:

Did the lander detach entirely, or remain attached but bend around a lot?

Edited April 30, 2014 by Epthelyn

[blizzy78]

OP tried to post this image (click for larger version):

[Red Iron Crown]

You could use a 1-kerbal lander can with a medium docking port instead of the smaller one, should be stiffer and your lander will be a bit lighter, too.

[BudgetHedgehog]

Did you... is that a Mainsail on the back with a Jr docking port at the bend? No wonder it won't work, you're pushing a wet noodle!

I presume that's the remnants of your lifter stage (I see an LV-N tucked in the middle there) so just limit thrust, don't go full throttle and make sure your ship isn't moving at all during thrusting or you'll end up with this again. I also don't see any SAS units in there so any unwanted turning will take ages to correct.

As an aside, with that weight, you're going to be burning for ages on one nuke. Better to have two or more radially attached (ideally, somewhere near the middle of the whole craft). Also, you could safely halve that number of struts and also also, I hope there are other RCS ports on your lander that I just can't see or you're going to have a bad time tying to translate because they don't look terribly balanced.

Edited April 30, 2014 by ObsessedWithKSP

[ripvanlemon]

I just wanted to add -- although I think this is probably a VERY minor part of your problem -- you may want to toggle torque on the lander's capsule. If it's enabled, that can make wiggle problems a lot worse.

[MarkyJ279]

Short answer: if you want to try and salvage what you've already got, right click on your mainsail and set the thrust limiter to something low (between 10% and 20% maybe?). Or you can just use less throttle but be advised mechjeb will always whack the throttle up to full so don't use the autopilot until you switch to the nuke (very little thrust there you should be fine) or set the thrust limiter.

Next time you might want to use a bigger docking node. Jrs just don't have the strength to hold under heavy acceleration.

[wdsmith3]

Did you... is that a Mainsail on the back with a Jr docking port at the bend? No wonder it won't work, you're pushing a wet noodle!

I presume that's the remnants of your lifter stage (I see an LV-N tucked in the middle there) so just limit thrust, don't go full throttle and make sure your ship isn't moving at all during thrusting or you'll end up with this again. I also don't see any SAS units in there so any unwanted turning will take ages to correct.

As an aside, with that weight, you're going to be burning for ages on one nuke. Better to have two or more radially attached (ideally, somewhere near the middle of the whole craft). Also, you could safely halve that number of struts and also also, I hope there are other RCS ports on your lander that I just can't see or you're going to have a bad time tying to translate because they don't look terribly balanced.

ya, the mainsail is part of the original lifting stage (I had 9 mainsails in total asparagus staged) and i had a bit of fuel left over. I had a poodle staged in between the mainsail and the LV-N to use as a mid stage booster, but i didn't end up using it. I ended up aborting the entire mission and i only now realize i didn't have any RCS on the lander.

[G'th]

Another option, if you're not opposed to mods, is to get Kerbal Attachment System and put some KAS struts between the CSM and the lander. That'll help stop the bending.

You could also get Kerbal Joint Reinforcement. That might help with this issue as well.

Beyond that though, whats already been suggested will be your best bet. Short of redesigning pretty much your whole setup there (so that your transfer rockets are pulling the payload rather than pushing, which will solve your issue mods or not) there isn't much else to do.

[cantab]

Yet another possibility is to place a stack separator (the blue ones, not the normal decouplers!) between the two docking ports, then strut across. That will steady things for the high thrust burns, and you can then trigger the separator which will break the struts when you want to undock. You can't replace the struts when you redock this way though.

[Baythan]

It looks like a total lack of SAS apart from what's in command modules, having RCS on(I see RCS nozzles on the lander firing) and a rather over-done lift stage are all part of the issue.

Were you controlling the vessel from the lander command module or the big command module? If the lifter or one of the docking ports was the current control center, it can also cause SAS and RCS to go wonky.

If you use something that can calculate Delta-V for you you'll be able to design a lifter that drops its last lift stages just before circularizing and that nuke engine could finish the circularization burn and still have plenty of fuel to reach Duna.

I just see too many engines in the middle of that rocket, which makes it really long and flexible.

Yet another possibility is to place a stack separator (the blue ones, not the normal decouplers!) between the two docking ports, then strut across. That will steady things for the high thrust burns, and you can then trigger the separator which will break the struts when you want to undock. You can't replace the struts when you redock this way though.

The problem with this idea is that he lifted the Duna lander separately, it wasn't built into that ship.

Edited May 1, 2014 by Baythan

[NoMrBond]

For Apollo Style unfail, I would suggest putting the Landing Module (LM) behind the Command Service Module (CSM) in the stack because (a) this is Apollo, and ( a landing module is a really heavy thing to have in front early on. Have the CSM do the classic flip-pickup after the TMI maneuver to pick up the LM.

There's a whole thread of Apollo style missions which might give you some inspiration

Otherwise get KAS and put some struts on there after you pick up your lander.

[MarvinKitFox]

Now don't get your nose all bent out of shape, but I think your shaft could use some stiffening!

Ahem.

Let's rephrase that.

Your rocket is wobbly. You are putting a comparatively heavy weight at the end of a long pole, so it will already be resistant to following any turn of your main rocket.

To compound the problem, you are connecting the two elements using a small docking post, which is not a very stiff item.

Even worse, you have the docking port mounted on an RCS tank, and those are about as stiff as a bowl of jello.

Advice, to retain the design "look", but make it all a bit more stabile:

1) Lose the inline RCS, use a couple of radials rather.

2) Bigger docking port. In a vertical stack like this, the large dock is not only twice as strong, but its larger diameter also reduces the leverage of torque forces. In effect, it is 6-8 times as strong for this role.

3) LESS THRUST!! At this point in your trip, you are already on orbit, and with your orange tank virtually empty and a hefty engine pushing at 100%, you must be pulling quite a few g's.

4) Are you sure you have SAS switched off on the lander? If it was on when docking, it might very well still be on, even though your combo vehicle's sas is switched off.

[Skorpychan]

Well, you fail because of some pretty poor design decisions.

What you did wrong:

Docking ports too narrow - I use Sr docking ports for major craft, nowadays. Heavier, but much more stable.

Pushing - Pulling is far more stable.

Stack Separator - Use docking ports for this sort of mission. You can strut past them for the initial boost stage.

Only one nuke - You'll be burning for AGES like that. Plus, using two lets you pull better.

RCS on the main craft - Should turn the thrusters off, and only use it to stabilise the pulled components.

[TerLoki]

Protip: Stock struts between parts that are "docked" at launch with clamp-o-trons will disappear when the two craft undock. That would be the simplest and least invasive fix I can think up.