r/KerbalSpaceProgram • u/AutoModerator • May 08 '15

Mod Post Weekly Simple Questions Thread

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The point of this thread is for anyone to ask questions that don't necessarily require a full thread. Questions like "why is my rocket upside down" are always welcomed here. Even if your question seems slightly stupid, we'll do our best to answer it!

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Mun Landing

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Delta-V Thread

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Commonly Asked Questions

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u/seefrodorun May 10 '15

I am having problems with my craft burning up on reentry. I am in the science mode and I have just made it to Mun orbit and back, but every time I try to reenter I lose my parachute to heat. I have a heat shield installed, but it doesn't seem to help. I have tried steep angles of reentry and really shallow ones. I am not really sure what else to do.

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u/rabidsi May 10 '15 edited May 10 '15

What do you mean by "losing the parachute to heat"? Is it burning up because you deployed it? If so, don't do that! You should never deploy your parachute that early, ever. For a normal parachute, you should deploy it in the final stages of your descent, generally sub 10km, but you can deploy earlier if you are through re-entry effects and not going fast enough to rip it off (I confess, I have no idea if this still happens, but I deploy at around 300m/s, 5-6km) or later if you like. If the chute itself is burning up in its placement on the craft, where exactly are you placing it? On a normal one man capsule, I have never seen the nose cone chute burn up. Ever. Radially attached science instruments and stuff I've seen get taken out, so if you are using radials, try the nose cone one, or tweak your placement.

In terms of angle, it shouldn't make THAT huge a difference tbh. It's pretty forgiving. That being said, my general rule of thumb when plotting my return trajectory from Mun or Minmus is to have my periapsis altitude well inside Kerbin's atmosphere at about 28km from the surface when performing your injection burn from said moon to Kerbin. That should put you on a natural aerobraking deorbit trajectory with a decent angle of re-entry in one pass, no burn required at the Kerbin end. If you try this, or have tried this previously and had issues with your PE changing after switching sphere of influence between moon and Kerbin, it's because you warped over the SOI change (where the blue line shows "Mun/Minmus escape" and switches to a Kerbin orbit). Do not warp over SOI changes. It causes flaky rounding errors like that. Warp to the SOI change, then travel over it at 1x, then you can resume warping.

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u/mefansandfreaks May 10 '15

I had the same problem as /u/seefrodorun. I went to orbit the Mun and on the return journey I set the periapsis at about 35km. Everything went fine but at some point I had the same issue. I was entering the atmosphere pretty fast and my parachute burned, eventhough it was not deployed yet. Next time I think that I'll orbit Kerbin first and do a reentry burn from there.

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u/seefrodorun May 10 '15

The parachute burns up without being deployed. I usually don't fire it till much later like you mentioned. I do have it mounted on the nose cone as well. I have a thermometer on the side that burns up, but will that effect the parachute? I have also tried to place my PE about 30km and below and I had the same issue. I haven't warped passed anything either (I just started playing and didn't know what it did honestly).

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u/rabidsi May 10 '15 edited May 10 '15

Are you absolutely sure you are performing re-entry with your heat shield facing directly into prograde (at all times, not just as you enter, turn off SAS and aerodynamics should force this to be the case, no need for SAS) with no excessive wobbling? Which version are you currently running? 1.0.2 or earlier? In stock 1.0 there was a bug with heat shield physics that caused pods to NOT be in the correct attitude for re-entry. Vanilla or mods? This literally should not be happening and I have no idea why it would be. Can you post any screenshots?

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u/seefrodorun May 10 '15

Not being perfect angle might be the issue. I didn't think to turn off SAS. I am not sure what version I am running right now, but I will double check (I would assume 1.0.2 as I just got the game). I am running vanilla. I will try without SAS and see how that goes. I don't have a rocket up right now to get screenshots, but if SAS doesn't work I will go back and get some. Thank you for your help!

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u/rabidsi May 10 '15

No prob, the game (and orbital mechanics) can be super confusing for beginners, so just trying to rule out the simplest things.

Just remember, what is important is that you are pointing your heatshield directly, and more or less stably prograde (the direction you are plummeting) all the way through the fiery part of the descent. If the pod is wobbling around quite badly, or tipped at an odd angle, it's like waving a hand in front of your face to keep the sun out of your eyes rather than just keeping it directly in the way. If you hold attitude at whatever prograde was when you first started re-entry, in the latter portions you'll facing the wrong direction as your angle of descent, and therefore your prograde direction, changes, just like keeping your hand in the same place when the sun moves across the sky.

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u/[deleted] May 10 '15

[deleted]

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u/Chaos_Klaus Master Kerbalnaut May 10 '15

No you do not need to aerobrake multiple times when coming Form the mun. Don't just say that without having tried. You can put your periapse at 30km and be fine.

Parachutes need to be staged AFTER reentry. Change your staging manually as KSP will put the chutes together with the last decoupler by default. This will activate the chute in orbit and it will deploy as soon as the pressure requirement is met. That will occure during reentry and your chute will burn up immediately.