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ilackoriginality

Parachuting back to Kerbin

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Just getting back from my first flight to the Mun. Quite proud.

Thankfully I quicksaved 20 minutes or so earlier, but what happened is I opened my 3 parachutes at 4000 meters or so when I was going at about 100 m/s and my rocket (everything except for the command pod) blew up. I had two side-parachute thingies and one on the top (excuse my amazing KSP vocabulary) on the lander. I obviously cannot redesign my rocket in-flight, but why does this occur and is there any way to get my lander safely down to Kerbin? I have roughly 8 fuel and 9 oxidizer for a lander. I don't know exactly how much it weighs, but based on some other landers I have seen I would call it medium/small.

Thanks for any help :)

Every small bit of help is appreciated.

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It's hard to say without pictures, but there are two suggestions I can give you. 1) Open the chutes sooner so that braking is more prolonged and gentle. 2) If you've got fuel left (which I think is what you're saying), burn the engines as the chutes are opening to take some of the deceleration load off of the chutes. Either way, burn off any remaining fuel to reduce weight.

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Post a picture. Otherwise people are just going to tell you to: use more parachutes, open the parachutes higher, and be careful about radially attached parts as they can sometimes get ripped off by parachutes (or lack of parachutes).

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What kills you is the big jerk when the chutes open fully. There are several ways to avoid this in the VAB, such as adding struts between the chutes and whatever they're attached to, and if they're attached to something other than the main core, strut that, too. You can also use tweakables to vary their opening properties. But of course this doesn't do you any good here.

So what I suggest is that you open your chutes at very high altitude. They fully open at 500m AGL but will streamer long before then. The longer they streamer, the more you slow down before they fully open.

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The default parachutes (except for the "drogue" parachute), if triggered while in orbit, will partially deploy at above 20 km sea-level altitude, and fully deploy 500 metres above the surface (whether it's the top of a mountain, or the top of the ocean). When my landers spontaneously disassemble at parachute deployment, it's because their joints can't survive the "jerk" that accompanies the parachutes fully opening.

As Vanamonde says, there are two things to try: 1) deploy the parachutes MUCH earlier, so their "partial" state can slow you down more, and 2) burn the last dregs of your fuel to slow your lander down just before you hit 500m AGL.

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I've never had a craft spontaneously explode like that.

It was, probably, a glitch in the game that may never appear again or you have Deadly Re-entry installed (you would know if you did).

At 4000m altitude and 100 m/s speed, it wasn't the parachutes fault. There is virtually no chance it opened all the way and if it did, the G forces would have been well under the upper threshold.

(edit, after re-reading your post, it sounds like something to do with your engines. If you were re-entering Kerbin after a successful trip to the Mun and lost none of your science modules, just chock it up to shoddy Kerbal engineering/manufacturing).

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A good rule of thumb if you're using expendable hardware for a Mun mission is to jettison everything but the capsule and chutes before re-entry, the way Apollo jettisoned the service module and only returned with the command module. This reduces the weight on the chutes. Two side mounted chutes will slow the large command pod just fine.

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look for structural weak points like a SAS module between the command pod and fuel tank. I've had chutes destroy craft because the part couldn't handle the G-force load of chutes opening many times before.

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I never open my main cutes (vanilla game) high up, on average i deploy them around 1500 to 1000 meters above the surface, when the speed bleeded off to around 100/150 m/s.

Kerbins atmosphere has enough density to slow even fast descents (3000 m/s at 100km Orbits to 150 m/s at 1500 mtrs) where its save enough to pull out the main chutes without a hard jerk.

It depends a bit on the weight of the return craft, but in the early stages of the career i can easely manage with 3 chutes at most for most crafts i build to touch down safely, and bleeding most speed of just by waiting while failing down to the surface, using the atmosphere as break.

https://www.dropbox.com/s/lvldijukdmhr7rc/screenshot0.png

Here is an example of the ships i bring back to kerbin, it only needs 3 chutes, and nothing special further needed, and you can clearly see the chutes placed.

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A good rule of thumb if you're using expendable hardware for a Mun mission is to jettison everything but the capsule and chutes before re-entry, the way Apollo jettisoned the service module and only returned with the command module. This reduces the weight on the chutes. Two side mounted chutes will slow the large command pod just fine.

Yes indeed. I put a pair of separatrons on my command pod and set the abort button to blow the final decoupler and fire the separatrons. Removes the excess baggage and kicks me clear of everything so I don't take a fuel tank to the face on the way down.

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When partially deployed, they do almost nothing to slow you down. I think the partially deployed drag should be increased by a lot. 4 is way too little, it should be at least 20.

This won't help you now, but for future missions when using multiple parachutes, you might consider choosing drogues for a small percentage of them. A three-parachute craft does well with 2 regular XLs and a drogue.

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Burn your rockets retrograde (so the rocket pointing down, in this situation) to keep the speed below 70m/s (rhoughly). That should prevent the chutes ripping off the rest of the rocket.

For the future: Spread out your parachutes on everything you want to keep alive, and put a decoupler below that point. Ditch the heavy engine and fuel during decent. Less weight means safer decent. And you don't need them anyway

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When partially deployed, they do almost nothing to slow you down.

Sure, they don't do a lot, but if you partially deploy early enough to get maximum benefit from them (and I'm not sure just how early that is, tbh, but earlier is better), they do give some extra braking. Sometimes all you need is just a little bit more, sometimes early partial deployment can provide just enough. Sometimes you need everything, max partial deployment, burning the engines at max just before full deployment, etc. Of course, if the design is so marginal that it needs everything to avoid failure, the real problem is the design itself, which can be fixed for the next mission.

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Pressing F3 will show you a log of events, including things like parts blowing up or colliding.

My guess is that a connector snapped or a part decoupled and then immediately collided with the slower moving parachute part causing them to both explode. Physical timewarp (2x-4x) can increase the likelyhood of this for even minor bumps.

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Small chute:

Weight: 0.1 t

Semi-Deployed Drag 1.0

Fully-Deployed Drag: 500

Radial chute:

Weight: 0.15 t

Semi-Deployed Drag 1.0

Fully-Deployed Drag: 500

XL chute:

Weight: 0.3 t

Semi-Deployed Drag 1.0

Fully-Deployed Drag: 500

Drogue:

Weight: 0.2 t

Semi-Deployed Drag 4.0

Fully-Deployed Drag: 170

One semi-deployed drogue provides as much drag as 3 semi-deployed XL chutes, 5 radial chutes, or 8 small chutes

One fully deployed drogue provides as much drag as 113 semi-deployed XL chutes

When landing anything bigger than just the pod, mount at least one drogue. Anywhere. It's totally worth it.

Open chutes early enough. Do NOT use time warp around the limit where chutes fully open.

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Since we've got tweakables now, you could right click on one of the parachutes and bring the opening altitude up by fifty. Staggering the deployment should reduce that vessel-killing jerk.

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Get as low to the ground as you possibly can, using the atmosphere to slow you down. When you thinks it's a good time to activate the chutes (Eg. 150 metres above ground or sea level) then do it. By then your craft should be going at around 60 metres per second. What ever type of parachute you have, struts or not, will not rip your craft apart.

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Besides what has already been suggested, make sure you aren't using time/physics warp when you deploy them or when they reach their full opening altitude.

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To answer what you were asking in regards to completing your current flight, after 4000m, you aren't going to decelerate any more. Also, it is like has been suggested, the sudden drag will shockload your lander and blow it. Especially if not using one of the conic style lander pods. The squarish ones are light but weak.

Here is what I recommend trying. First, split your parachutes into different stages. Possibly have top one open at a very high altitude if possible with tweakables. Then deploy each one after the other slows up. I like manual better than tweaked so you can be sure it is after each shock G-force lowers. If you have any leftover fuel or engine, try holding onto them until you get close to parachute deployment altitude then FULL BURN that puppy to kill a bit more speed before you deploy parachutes.

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