How can i not burn up in my situation?

[modybird]

I cant seem to reenter without everything exploding, i face retrograde with a standard heasheidl but it does not help. 

 

Here is my situation and im really low on fuel. What can i do?

[Spricigo]

Raise your periapsis as much as needed to not burn, if that is not enough to capture just make more passes. The fuel left use for the eventual adjustments at apoapsis.

You can also send a kerbal in EVA to collect the science.

 

[Reactordrone]

It should be fine unless it's moving off the retrograde marker due to asymmetric mass. You do still have a fair amount of delta-v so try to reduce your speed just before atmosphere entry (angle up a little so you don't drop your periapsis too low) but a light probe with a full heatshield shouldn't have overheating issues coming back from the Mun if it's holding retrograde.

Edited June 26, 2017 by Reactordrone

[foamyesque]

Command pods generate lift; you can, by flying not quite pure retrograde, keep yourself in the upper atmosphere longer, which will lower your peak temperatures.

[bewing]

Don't jettison the engine and tank. They can absorb plenty of heat on reentry before they blow up. Extend the landing legs, they will provide a lot of drag before they blow. The decoupler will also provide a lot of drag and heat absorption before it blows. You will need the fuel during reentry, because the gimbal will help you stay retrograde while you burn fuel gently. If you start to fall off retrograde, go to full thrust.

 

[invision]

bring PE to 58k instead of 31k and go around a few times so it slows you down without hitting reentry too hard before finally coming down to land

[Zeiss Ikon]

First thing I thought on seeing that orbit plot is: your periapsis is too low.  Don't raise it too high, though -- as noted, if you go as high as 58 km, you'll need multiple passes and may burn up your ablator before you actually get a ground intersect.  In my experience, for Mun or Minmus returns, a periapsis of 40-42 km seems about right.  Low enough not to skip off or spend so long in a plasma that you use up the whole ablator, but high enough you don't get excessive G loads or heating and just explode.

Of course, the other issue is, what kind of pod is your heat shield mounted on?  The two-kerbal Lander Can actually protrudes beyond the standard heat shield far enough to cause the can to explode during reentry.  This isn't a problem with the Mk. 1 Command Pod, as long as you reenter shield first, and there's no need to keep SAS on or actively control for retrograde pointing after you get below about 60 km; aerodynamic forces will do that for you.

[Spricigo]

5 hours ago, Zeiss Ikon said:

Of course, the other issue is, what kind of pod is your heat shield mounted on? 

None. Parachite, probecore, antenna,  solar panel,  goo canister,  material bay,  heatshield,  decoupler,  fuel tank,  landing legs and terrier. I guess, given or taken,  400kg he want to recover and 700kg below it.  

The weak point seems to be the material bay. Keeping it shielded from heat may be tricky. If it had the same  heat resistance of a Mk1 Mk1 command pod it would be be easier because of higher drag and lower weight. 

 

[Zeiss Ikon]

Ah.  The shape of the Science Jr. is the problem.  Unlike a conical command pod, that science can will be exposed to reentry plasma that converges onto the side walls, even though it's the same diameter as the heat shield.  Combine that with its low temperature tolerance, and you might be unable to recover that unit even from LKO in a prograde equatorial orbit (your polar inclination adds 400+ m/s to the velocity you have to dump).  Leaving the Terrier and fuel tank attached will help, but not that much -- you'll still have plasma convergence heating the side walls of the Science Jr.

Best suggestion I can give is use very high aerobraking (above 55 km, at a minimum, 58 km is probably a better figure) to lower your apoapsis and save your remaining fuel to pull your periapsis up out of the atmosphere once apoapsis is low enough to suit, then build a claw-equipped, larger diameter vessel to "rescue" your science.  If you haven't unlocked the claw yet, you may have to leave it up there until you do, or send a Kerbal up to collect the science from the can.

[Spricigo]

16 minutes ago, Zeiss Ikon said:

Ah.  The shape of the Science Jr. is the problem....  Combine that with its low temperature tolerance, and you might be unable to recover that unit even from LKO in a prograde equatorial orbit ...

I just checked and actually they have the same Max temp *. Also the  lower mass helps to slowdown. A bad trajectory may be a problem, but pretty safe from LKOish.

 

Although the lower mass of the material bay may make it get hot quickly. I admit my understanding of KSP's heat is flawed at best.

Edited June 26, 2017 by Spricigo

[Virdin]

Not much really, just raise your periapsis to ~40-50km since you are going too steep into the atmo. Keep as much mass as possible to absorb energy and have higher drag forces. 

[felcas]

As others said, you need to raise periapsis.
Why? Because you are coming too fast.
Since you don't have fuel to slow you down the solution is to use high atmosphere as friction to slow down your ship, it should flame but not long enought to burn any parts (or at least not any important part).

You will overshot the atmosphere and orbit again. Each time the flyby on upper atmosphere will slow you down a bit and in consequence will diminish your Apoapsis (and your periapsis too). Soo be patience, you need to make several passes, I would say to start with something like 65km or 60km, if you get no friction, try with -1km increments (59, 58,57 etc...)

Once you get friction and you see your peri and apo diminish you are on the right track, if you burn and get something that should not be destroyed, reload game and try again with a higher periapsis. 

There is a point you just can't get back to orbit and you will fall, if you didn't get destroyed  by now, pray a little more.

Extend the gear, they will help you with drag, but do this only on the final reentry.

HINT: during endless re-entry tests I made I discovered that even a small ammount of fuel can save the day on retrograde. Keep an eye for any important parts (science parts?) that start to overheat, as soon as it reaches 1/3 or half the bar, apply full engine! This may just slow you down to the point where the part no longer overheat and save your valuable stuff. Actually in my last mission I just had to save a tiny bit of fuel on the 1st stage to retrograde enought to allow the airbrakes to open and do the rest.

Finnaly, sometimes the situation is soo F#$%%up that you really can't save your ship as much as you try, just give up and make it again.

TIP for your next mission, there is an imaginary "cylinder of coolness" that extend from the widest part in contact with atmosphere, soo lets say you use a 1,25 engine or ablative, thats the size of your cylinder of coolness, anything inside it will be protected from heat (considering you keep aligned with your flight path - pointing craft retrograde) soo, try to build your ship with that in mind, NEVER make a ship with protuding parts out of the cylinder of coolness because it WILL acumulate heat on re-entry.

 

Edited June 27, 2017 by felcas

[felcas]

Hooo, there is another hint that will call up for your piloting skills.

Read my previous message about the "cylinder of coolness". 

The interesting thing here is that if after all I said you still have parts destroyed you can try one last thing, your can try to tilt your ship nose up just a bit, a few degrees, what will happen is that you will partially expose one side of the ship but you will create an area of coolness on the other side. Lets say you have an experiment like a thermometer on just one side you can roll your ship before doing this maneuver in such way it will be located in the cool part.

OR another thing you should also try is to roll your ship as sides get heated. This should buy you some time while your ship deacelerate to cooler speeds and be able to parachute.

Good luck!

Another solution would be to stabilize a low orbit around Kerbin and get back to the darwing board to develop a rescue ship to go up there and  get it. I made this a few time and it is challanging, to fix up what I screw up in 1st place with resources from the game and not load and save. Maybe you can fit all this (except the engine and tank) in a 2.5 service bay?

Or just get a science kerbonaut up there and collect all data. 

Edited June 27, 2017 by felcas

[Snark]

By the way, @modybird:  All the above discussion is centered on "how do I get home, given the ship that I'm already in right now," which is fine.

Just so it's clear, though, for future reference:  Your trajectory is a perfectly reasonable one.  31 km or so is a great Pe altitude for reentering on Kerbin when coming home from Mun or Minmus.  It works great, doesn't require multiple aerobraking passes, doesn't need any fuel for slowing down, and a normal heat shield withstands it easily without even straining itself, and doesn't need a full ablator load, either.  Just plow straight into atmosphere at full speed and it's fine.

So, really the issue here is the design of the ship.  As folks have suggested, having a low-temperature tolerance part right behind the heat shield is the problem.  And when you think of it... there's no reason for it to be there.  Put the Science Jr. below the decoupler, and put the heat shield on the bottom of the command pod instead.  There's no reason why you need to bring the Science Jr. home with you, other than recovering a paltry few extra funds.  What really matters is the science, and you can pull that out of the Science Jr. and bring it home with you in the pod.

[Spricigo]

4 hours ago, Snark said:

Command pod. 

Let's assume the next time is also an unmanned vessel (I'd say for the sake of consistency).  In that case we are talking about an Experiment Storage Unit + Probecore combination instead of command pod. 

Yet another option is to maintain the sensible parts shielded by fairing,  service bay or cargo bay. 

Quote

So, really the issue here is the design of the ship.  

I suspect that possible issue was spotted by some  people when the OP posted a picture of his vessel in a previous thread. No one though a warning was necessary and the OP didn't had the same experience to avoid the trouble by himself . Unfortunately in the hard way, but at least the lesson is given. 

The important now is find out some way to salvage the mission and,  to a lesser extent,  avoiding  to commit the same mistake again in the future. There is,  so far,  plenty of good advice for this but in case of doubt ask. 

 

[Loren Pechtel]

A slightly different approach:

Raise your periapsis to the high 50s, make multiple passes.  If your engine etc survive, fine, but if you lose the stuff below your heat shield turn around and go nose first to protect your ablator.  You don't get nearly as much drag nose first so it will take more passes to slow down, but likewise, because you're cutting the air much better you take less heating and that high in the atmosphere nose first is safe.  Keep an eye on your apoapsis, make sure to turn tail before your last pass or else you'll lawn dart.

[Kryxal]

I'd say pull the science out, go ahead and lose the materials bay, just land the pod.  It can survive just fine from a Mun return if you're not going too low, just point retrograde once the bay explodes.

[wumpus]

2 hours ago, Kryxal said:

I'd say pull the science out, go ahead and lose the materials bay, just land the pod.  It can survive just fine from a Mun return if you're not going too low, just point retrograde once the bay explodes.

[This might as well be a necro-post for the OP, but as basic principles for the forum I'll include it].

Looking at the actual craft makes this look like a non-option.  I think it's a probe, and it also looks like decoupler is on the wrong side of the science jr. (presumably an extremely new player, just sending a probe to Mun).

I'd expect two real options:

Raise your PE for the "several passes" system.  Try coming in both on your heatshield and on your engine (the engine might do better than a heatshield+science jr).
Raise your PE for the "several passes" system, then raise your PE to leave the thing in orbit (and send up a recovery ship [including Jeb or Bob if you want the science and don't have a kerbal on board]).  You *can* dock with the thing in Munar Transfer Orbit, but Low Kerbin Orbit is so much easier/cheaper.

[weissel]

On 26/06/2017 at 6:36 AM, foamyesque said:

Command pods generate lift; you can, by flying not quite pure retrograde, keep yourself in the upper atmosphere longer, which will lower your peak temperatures.

By flying 10-25° off retrograde (point the shield end more down towards Kerbin) you can generate lift, thus keeping you in the thinner atmosphere for longer, hitting the dense "we are going to cook you" atmosphere layers slower.  By the same token you have a limited steering ability (left and right) by tilting the pod left and right.

Unfortunately you are unlikely to have enough electrical energy or monoprop to manage holding that position.  There are other options, left as an exercise for the reader, alternatively investigate how the Apollo capsule did it.  I do not think you can fix this problem in flight without certain mods and parts you don't have.

You could raise your periapsis to above 70 km and launch a rescue mission when you pass Kerbin, collecting the stranded Kerbal --- assuming you can already do EVA in space.  If not, be happy that Kerbals need no life support while you go get that ability and rescue him/her, possibly years later.

[Spricigo]

46 minutes ago, weissel said:

 stranded Kerbal

The craft in question is this one:

 

Also the question is pretty old. Probably the OP got the issue sorted by now.