The Mk16-XL parachute is disattaching my capsule from the lander stage at Duna

[Commissioner Tadpole]

After a lot of pain and suffering, I finally managed to set up an aerobrake manuever on Duna to land. However, each time I deploy the parachutes at 5km, the Mk1-2 capsule and the Rockomax decoupler get yanked off the lander stage, rendering Bill, Mitkin and Mallan Kerman stranded on Duna. What am I doing wrong? After so much pain getting to Duna now I can't land...sheesh. (My lander stage weights 27t, if it helps. Dem Rockomax parts.)

My rocket uses two radially-attachable parachutes and a Mk16-XL parachute(the large blue one, not the large orange one or the small white one), both stock. I tried only deploying the 16-XL and it still yanked off the capsule from the lander. What is going on? I doubt there's a way to add struts between the decoupler and the X200-32 fuel tank. It really sucks because I can't perform my first sucessful Duna landing. See, this is why I claim that there's a mysterious force impeding me from getting to & landing on other planets/moons.

Edited December 1, 2013 by Commissioner Tadpole
Question solved.

[Boris_T_Roach]

Its the weight of your lander vs the drag loading of the parachutes that causes the problem

In particular the speed at which the parachutes fully inflate, which in your case , sounds too high

The solution I adopted, after many kerbals got splattered and stranded , is to ignite the landing rockets before the 'chutes fully open, thus reducing the amount of shock to the lander, and of course then using the rockets to slow the lander before final touchdown.

Boris

[Murph]

The shock force when the chute opens is just too much for the link between the capsule and the rest of the ship. There's 2 major factors which cause this in 0.22: 1) Chute shock force is much too harsh. 2) Parts are held together with duct tape and used chewing gum, unless you go nuts with struts.

There are some things you can try, however. You need to reduce your speed as much as possible before the chute opens fully. You can do this either by trying for a much longer aerobrake (shallower angle into the atmosphere), some judicious retro burning during descent, or opening the chutes as early as possible (trigger them as soon as you begin your descent, then let them open automatically as atmospheric pressure rises). The partly deployed state provides some useful drag, before they go to fully deployed and give you the problematic shock load. You can also try using the orange/red drogue chute on future builds, in addition to normal chutes.

You certainly should be able to strut the connection between the decoupler and tank, but only in the VAB, not on the mission (without mods). 27t is reasonably heavy for a parachute lander, so plenty of struts, plenty of chutes, and some judicious retro burning are most likely the answers. If the radial chutes are attached lower down the stack, you could try triggering them before the capsule chute.

If you don't care about your exact landing spot, circularise your orbit just above the atmosphere, e.g. at 42x42, then drop just barely into the atmosphere, e.g. 40x42 (it starts at 41, if memory serves). Then just let it orbit, with all chutes triggered, and let the orbit drop slowly. Experts may have a better strategy, but I believe that should give you approx max aerobraking. Just before the chutes fully deploy, use retro thrust to reduce velocity to a manageable level (trial and error will be required to figure out just what that is).

You might also want to describe your flight profile more fully, as the starting orbit for your descent will make a huge difference. E.g. if you start at a 500x500 orbit and go straight for the lower atmosphere, you going to be carrying LOTS of velocity into the aerobrake then chutes. Start the descent from as low an orbit as possible to minimise the speed.

[Commissioner Tadpole]

Oh....

Well, I was going for a straight aerobrake, directly to the point... my Duna intercept ended up with an Apoapsis of around 53,000,000m if I'm right, and I set the Periapsis to 7,000m... no wonder it's going really fast. But problem is I'm trying to save fuel for returning to Kerbin. And yeah, I don't really care about where I'll land, as long as it's a relatively flat area...though I'd be a bit comfortable if it was a site facing Ike. Not required, though. (And from what I heard, Ike has a big sphere of influence, so that might interrupt me as I take off.)

[Geschosskopf]

Well, 1st off you've got WAY too few parachutes for a 27-ton lander. You'll need probably 6 or 8 of the bluetips and a dozen or so radials for the parachutes to do you much good, which add beaucoup weight, which means you'll have a harder time getting there and coming back. Check out the parachute calculator for the bad news. Also note that you need to enter your landing site's altitude. Unless you're aiming for one of the rare depressions, the vast bulk of Duna's surface is 2000-3000m.

Also, Duna's air is both thin and shallow. Thus, for even the right amount of chutes to do their thing, you have to give them the longest time possible in the air. This means you need to come in on a very long, flat trajectory, like start at 50km orbit and aim to land about 1/4 to 1/3 of the way around the planet. And even then you'll usually have to retroburn long and hard anyway. Pop the chutes at 20km so they streamer as soon as possible, slowing you down (with the retroburn) so you don't have such a severe shock when they fully open. Using 1 or 2 of the drogue chutes helps here, too.

And then of course everything needs to be structurally sound. You can easily add struts, to, from, and bypassing decouplers and just about everything else. And because you'll have so many chutes stuck everywhere on the lander, pretty much all parts need to be heavily strutted.

For example, check out this 18-ton Kethane lander. It had 2 bluetips, 8 radials, and 2 orangetip drogues. This was NOT enough chutes to land by themselves, just to help so it didn't need as much fuel to land. Observe the rat's nest of struts everywhere.

And here it is on landing approach using the long, flat descent outlined above. It's still at about 15km, retroburning full throttle, with all chutes streaming. It ended up landing about 2/3 of the way to the far horizon, bang on target .

Edited November 30, 2013 by Geschosskopf

[Commissioner Tadpole]

Oh.... So, mission failure, I guess?

What stinks is that I've spent several days on this mission... well, in-game, but I can feel the Kerbals at the Minmus colony being pretty annoyed for being over 108 days in there. Maybe except Jebediah, who doesn't cares and alterady spent several days crammed in a Mk1 Command Pod alone at the Mun. He's in a much more comfortable Hitchhikers with a total of 5 other Kerbals to keep him company.

Anyway... so I should just send the rocket back to Kerbin and perform changes, huh...that stinks. Is there any other workaround for me to land that rocket on Duna, even if it has to sacrifice a bit of fuel(but still keeping enough for a Kerbin return trip, prefferably an aerobrake one)?

[Geschosskopf]

Anyway... so I should just send the rocket back to Kerbin and perform changes, huh...that stinks. Is there any other workaround for me to land that rocket on Duna, even if it has to sacrifice a bit of fuel(but still keeping enough for a Kerbin return trip, prefferably an aerobrake one)?

Well, it sounds like any landing you try shouldn't use the chutes because they seem to kill you every time, but you CAN of course land with just engines, provided you have both the TWR and the fuel for it. First, of course, you need to aerocapture into a 50-ish-km orbit to lose your extra interplanetary speed. Then take a look at your fuel situation. It costs about 1400-1500m/s (using in-atmosphere ISP) to land on Duna with just engines, and about the same to take off again, starting and ending in a 50-ish-km orbit. Then it takes about 500m/s to get back to Kerbin, after which you're safe (assuming aerocapture there).

So, if after aerocapture, you have fuel > 3600, no worries. If you have 3000 < fuel < 3600, you're not getting home if you land. You can, however, land and get back into orbit to await rescue, which is much easier than having to rescue somebody off the surface. If you have 1500 < fuel < 3000, you can land but won't be able to take off again, which will make for a rather more difficult rescue. If you have 600 < fuel < 1500, you can't land but can return to Kerbin after a fly-by. If you have fuel < 600, you're not coming home at all and should spend what fuel you have left getting into an orbit that's easy to get rescued from.

[Commissioner Tadpole]

Well, I managed to land on Duna... thing is, I think my rocket has just around 860 fuel left. But it's likely not going to be a problem, I just need to send them a refueler. ^^

[Geschosskopf]

Well, I managed to land on Duna... thing is, I think my rocket has just around 860 fuel left. But it's likely not going to be a problem, I just need to send them a refueler. ^^

Hey, looks like your chutes deployed and didn't rip off the capsule. How'd you manage that? And note that you'll have to repack them to use them on return to Kerbin, which is another trap for the unwary. But before we can worry about that, we have to get your guys back to Kerbin.

So, you say "860 fuel". Is that fuel or delta-V? I'm afraid I might have misled you in my post above because I was saying things like "3000 < fuel". What I meant was "3000m/s < delta-V", which I thought was obvious from the context but might be confusing to somebody unfamiliar with the terms. It's a bad habit KSPers get into, using fuel and delta-V interchangeably when they're not the same thing. So I hope I haven't put you in the hurt locker here.

Anyway, I'd at least try to get back into Duna orbit. F5, give it a try and if it doesn't work, F9 and stay on the ground. If you can get into orbit but lack the delta-V to get home, that's an easier fix than not being able to take off. Even if you can't dock, you can probably do an orbital rendezvous within 1-2km. It's no problem to EVA across that distance to the rescue ship. If you're stuck on the ground, though, that means the rescue ship needs to land within easy walking distance of the stranded ship, and then of course take off again. I don't see a docking port on your ship here, so a tanker isn't going to help. Looks instead like you'd need a probe ship with empty seats. But if it doesn't have to land and take off, it doesn't have to be very big.

[Commissioner Tadpole]

Hey, looks like your chutes deployed and didn't rip off the capsule. How'd you manage that? And note that you'll have to repack them to use them on return to Kerbin, which is another trap for the unwary. But before we can worry about that, we have to get your guys back to Kerbin.

So, you say "860 fuel". Is that fuel or delta-V? I'm afraid I might have misled you in my post above because I was saying things like "3000 < fuel". What I meant was "3000m/s < delta-V", which I thought was obvious from the context but might be confusing to somebody unfamiliar with the terms. It's a bad habit KSPers get into, using fuel and delta-V interchangeably when they're not the same thing. So I hope I haven't put you in the hurt locker here.

Anyway, I'd at least try to get back into Duna orbit. F5, give it a try and if it doesn't work, F9 and stay on the ground. If you can get into orbit but lack the delta-V to get home, that's an easier fix than not being able to take off. Even if you can't dock, you can probably do an orbital rendezvous within 1-2km. It's no problem to EVA across that distance to the rescue ship. If you're stuck on the ground, though, that means the rescue ship needs to land within easy walking distance of the stranded ship, and then of course take off again. I don't see a docking port on your ship here, so a tanker isn't going to help. Looks instead like you'd need a probe ship with empty seats. But if it doesn't have to land and take off, it doesn't have to be very big.

I had to sacrifice some of the fuel to reduce my rocket's speed to ~150m/s. It was a close call, I was around 650m away from the surface. And yes, I repacked the 'chutes, I just took the picture before I repacked them.

Yes, it's fuel. Liquid Fuel, even. And it's alright.

But I'm not planning to send them back to Kerbin(yet). In fact, after I landed the trio in there I think I'm going to set an operational base on Duna. And I use the Kerbal Attachment System, so it's a simple matter of sending a tanker with a pipe end and a storager module containing another pipe end, have a Kerbal grab it, carry it to the main rocket, attach it, connect the pipes, and transfer fuel. ^^

[Liowen]

One thing I found is to mount chutes to the piece that is ripping off along with drag chutes. Since drag chutes open higher up it will greatly decrease the m/s before fully deploying along with the radials. While I do not have a picture of all the chutes on this on this craft you can kind of get an idea on how many chutes this one had. It also weighed in at just a hair over 27T and fuel is nearly full for takeoff.

700NitroXpress helped me tweek an earlier design I was trying to use and made this one work like a gem. The discussion can be seen here: http://forum.kerbalspaceprogram.com/threads/59747-My-single-crew-Duna-Lander-in-need-of-help. Hopefully it helps in seeing what was done to make it work.

Edit: This is all stock parts, but I would believe that you could use mod stuff in place of certain items and make a craft even better.

Edited December 1, 2013 by Liowen

[Commissioner Tadpole]

Hm, I thought the Drogue parachutes were supposed to do that - deploy high up and not enough to slow your craft enough to prevent it from exploding by itself, but enough for you to safely deploy the main 'chutes. That's how I've been doing after I landed that rocket. I even sent them some rovers using that strategy.

[rpayne88]

You can download Kerbal Joint reinforcement. That may increase the structural strength between your lander and your decoupler.

[FenrirWolf]

Send it to Ike instead! There, mission salvaged.

[Liowen]

Hm, I thought the Drogue parachutes were supposed to do that - deploy high up and not enough to slow your craft enough to prevent it from exploding by itself, but enough for you to safely deploy the main 'chutes. That's how I've been doing after I landed that rocket. I even sent them some rovers using that strategy.

Yes and no...yes they will slow your craft down, however if your main chutes are too high up or near a part line it could shear them off. At least this has been my experience with them and why on my ship I have main chutes on the engines as well as the capsule. When they all open the force is spread out and the stress is not in one area of the ship, also the more m/s negated before landing the less I have to use the engines. I am not 100% sure if how I am doing it is right, but so far my ships have not broken on landings so that has to account for something.

[Geschosskopf]

I had to sacrifice some of the fuel to reduce my rocket's speed to ~150m/s. It was a close call, I was around 650m away from the surface. And yes, I repacked the 'chutes, I just took the picture before I repacked them.

Well, I still feel guilty here.

Anyway, in case you didn't know, repacked chutes are a major problem. They will NOT work in the spacebar-activated staging ever again after the 1st time, so if you plan on reusing repacked chutes, you need to assign "deploy chutes" to an action group, which sadly has to be done back in the VAB before you launch unless you have whatever that mod is that allows action groups on the fly. And sometimes your ship explodes for no reason when you deploy repacked chutes with an action group, which leads to using right-click on each chute instead of an action group. Problem with that is when you have off-center chutes, because you can only do 1 at a time and after the 1st one, the ship starts spinning so fast it's next to impossible to ever right-click on another. But it IS doable, with luck, so if you don't mind a bunch of F5/F9 "simulated" landings before the "real" one, there's always that option.

Which is all to say that if you intend to bring folks home from Duna in the same ship they landed there in, it's probably best not to use the chutes at Duna. Or, If you have to use the chutes at Duna, to leave the ship in LKO when it returns and send up a new ship with unused chutes to bring the crew back down.

But I'm not planning to send them back to Kerbin(yet). In fact, after I landed the trio in there I think I'm going to set an operational base on Duna. And I use the Kerbal Attachment System, so it's a simple matter of sending a tanker with a pipe end and a storager module containing another pipe end, have a Kerbal grab it, carry it to the main rocket, attach it, connect the pipes, and transfer fuel. ^^

Well, connecting them isn't the problem. Landing them close enough together for the pipe to reach is . That's why it's easier to do rescues in orbit than on the surface. So unless you can do such a landing, it's probably better to send a probe ship with empty seats than it is to worry about refueling the original ship.