Docking Port Strength

[Securus]

Good Afternoon Everyone,

Hoping someone can help, but mostly cause I'm bored at work.

I messed up on my Mun lander and forgot enough fuel and parachutes to recover it and Jeb. I got a Rescue craft created that will provide it enough fuel and 4 parachutes attached via docking port, however... will that docking port hold?

Edited October 7, 2014 by Securus

[Alshain]

Picture?

Depends on where your trying to dock and with what. It will be easier if you have enough fuel to get it to orbit.

[capi3101]

Better question is whether or not you have a docking port on the lander already. If not, you won't be retrieving the lander...

[Securus]

You'll probably need to know how much the craft weighs, don't know exactly but it has the standard manned pod, 5 of the smallest 1m fuel tanks, Nuclear motor, some scaffolding, legs, Goo, and 4 sphere RCS tanks. So overall it shouldn't weigh too much. Plus it'll be out of gas on reentry.

[Securus]

Sorry I would post pics but its at home

Luckily I had SOME foresight and it does have a docking port, the lander, so that wont be an issue. I don't plan on keeping the Rescue craft attached, that will be jettisoned with only a small "Parachute Pod" still attached to the lander via docking port. I can see this ripping off as soon as one of the parachutes deploy.

[Alshain]

Sorry I would post pics but its at home

Luckily I had SOME foresight and it does have a docking port, the lander, so that wont be an issue. I don't plan on keeping the Rescue craft attached, that will be jettisoned with only a small "Parachute Pod" still attached to the lander via docking port. I can see this ripping off as soon as one of the parachutes deploy.

No, it won't rip off on re-entry, at least not in stock. But my concern is how are you going to dock it. Is it on the Mun surface or is it in orbit? Or can it get to orbit? They don't break real easy but they do bend and even if you manage to land directly on top of the craft on the Mun, the moment you decelerate it's going to fall over. It's best if you can at least get to an 8k orbit.

It's still possible from the surface but it takes some skill. You have to land the docking port an dock the craft together while one is flying and the moment you dock hit the gas to pull away from the surface. The rescue craft absolutely can not stop all acceleration. Basically a celestial claw game. Another way would be to build your rescue craft to "wrap around" the other but with it sitting on the moon, getting it the perfect height would be difficult.'

Finally, do you need the other craft at all? You could just land another craft near by with enough seating space for your kerbals and leave that one where it is. This is probably the easiest method if you can't get to orbit.

Edited October 2, 2014 by Alshain

[arne_brun]

Hello

I attached parachutes with docking ports to one of my Mun landers (4x radial chutes).

The lander weighs about 2 tons (~10% fuel left), landed with a vertical speed of 5 m/s. There was no space between the docking ports when the parachutes unfolded, so they are good for more weight.

Good luck

Edited October 2, 2014 by arne_brun

[tater]

Why bother returning the lander at all? Have Jeb take the science with him, EVA to the reduce ship, and head home. Or am I missing something?

[Progressm]

You can design a craft that sits under the failed lander on reentry to avoid tearing off.

Check 'Sibylla' for reference ( use a docking port, of course).

forum.kerbalspaceprogram.com/threads/60694-Mutiny-in-orbit%21?p=822408

Easiest way to save crew is to just get then with another lander, though.

[Securus]

Arne_brun: Thanks! That helps give me some confidence that it'll stay together!

Alshain: The craft is stuck on the surface, not enough fuel to get it into an orbit of any kind, so I'm really glad you mentioned the stuff about docking on a landed craft, I had no idea it was going to give me trouble. You're saying I should thrust vertical once I'm about to get the dock lock?

tater: You're totally right, I could do that. But for me, it wouldn't be as fun Although I will be setting up the rescue craft for return with science just in case.

[Alshain]

Alshain: The craft is stuck on the surface, not enough fuel to get it into an orbit of any kind, so I'm really glad you mentioned the stuff about docking on a landed craft, I had no idea it was going to give me trouble. You're saying I should thrust vertical once I'm about to get the dock lock?

It kind of depends on your craft and which size docking port. If your refueler is small and light enough it might could just land on it, but if it makes the ship top heavy the docking port won't be rigid enough, it will bend like a Slinky going down stairs. The idea is you keep enough accelleration to prevent a full landing but not so much you don't go down, so the moment you lock you then accelerate lifting the other craft with it. You will actually have a reaction time to play with, it's not going to fall that fast, just don't linger.

[LABHOUSE]

If it's in orbit get out and push via jetpack.

[tomf]

I recently tried docking one craft on top of another on the Mun. Both crafts were specifically designed for it, the docking one being extra light and maneuverable, I consider myself a fairly good pilot and I spent one of the most fustrating 2 hours of my life. I recomend saving yourself a lot of bother and landing a new craft as near as possible to the old one and getting Jeb to jetpack/walk across

[Dust]

Landing a docking port on top of another docking port is pretty demanding. I did it once, but it took an hour, several crashes & reloads, half a bucket of sweat, and probably shortened my life expectancy by a day.

If you're using mods MechJeb has some tools to help, specifically one which can hover at a set altitude for you while you position yourself over the target, then you can set the descent rate to lower your rescue craft onto the port. Kerbal Attachment can also be used to add struts between the two crafts if you're worried about rigidity across the docking ports.

You could give it a go, it's always good to try something yourself for the experience. We're just forewarning you so you know what you're getting yourself into.

[Kryxal]

Would the claw on a rover be reasonable to connect ships together for fuel? If so, do a two-parter ... landed rover for refuel, parachute pod in a 20k orbit or something for return.

[Crown]

As Alshain already said, the Docking Port will hold. According to Wiki about the Docking Port it will withstand a force of 1100kN because it functions kind of as a spring. I am sure that applies to the other docking ports too. More concerning would be if all the other parts below will hold. Here are my pennys on that:

My personal approach would be to try to detach unneeded weight before re-entry (just like in Space Cowboys) if that's possible (and not loose much stability). That will loose you some money (if in career) but will more likely save the Kerbal.

Secondly to reduce the load on parachute deploy, you could try to deploy each single parachute separately.

You can adjust the half-deployment pressure and full-deployment altitude (above ground) in the VAB for symmetrically placed parachutes. So if you placed them in a 4-symmetry and edit one parachute, the other three parachutes are set to those values too. But after launch, those numbers are adjusted individually for each parachute and changing one will not affect the other three (and I like it that way).

Make sure that you full-deploy the parachutes one after one on descent. Maybe starting at 300 meters and going up 100 meters each parachute. The half-deployment pressure can stay unchanged. The first parachute that is to open will shake the vessel heavily to the side but will reduce the load that tries to rip it apart. On further descent all the other parachutes deploy and slow it down step by step - versus the shock of going from 96m/s to 8m/s in one single second.

Docking that refuelling vessel to your landed ship will be a big challenge, agree (quicksaving at a certain point will help a lot), but I am sure you will find a way to master that.

[Progressm]

While refuelling with the claw could make sense, how about carrying a couple of SRB's with claws and probe bodies next to the stranded craft with a rover, attach them to each side with claws and fire up both...voila, your craft is on a high Munar suborbital trajectory and you can do a Scott manley scoop rescue to get the craft to a safe orbit and home.

Clearly this is the simplest way to go about it all.

[Padishar]

Yes, docking a skycrane to the top of a landed vessel is awkward but it is possible. You'll probably need to quickload a few times. It is much easier if you land next to your target first so you don't have to keep repeating the descent and have plenty of time to set the target port and prepare things...

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[eataTREE]

At one point I was trying to build a stock-only reusable SSTO rocket that could deliver payloads to orbit. Since there were no stock cargo bays yet, the best solution I came up with was to carry the payload in the center of the ship "inline". When the target orbit was reached, the ship would separate into three parts. The payload would move out of the way, then the top and bottom ship sections would dock back together.

Well, this all worked great except that when it came time to land, all the parachutes were on the top half of the rocket. When the 'chutes deployed, the bottom simply fell off.

It worked fine after I relocated most of the parachutes to be connected to the bottom ection.

[Securus]

Thanks all for the suggestions. I did try landing my rescue structure overtop of my lander but as some of you pointed out that processes is crazy and beyond my skill! Made a new lander that actually has enough fuel to get to the Mun and back and Jeb is home safe. Good to know that the docking ports can take some stress as someone pointed out here!