getting things back through the atmosphere.

[GungaDin]

My capabilities have reached a point where I can orbit and return with no problems.  However, when I bring along an SC-9001 Science Jr.  or an Mk1 Crew Cabin it overheats and blows up on re-entry even when I slap a heat shield on it.  Am I coming in at the wrong angle or is there another trick?  Thanks.

[Cavscout74]

Both of those - especially the Science Jr - are much less heat resistant that the space capsules like the Mk 1 Pod or Mk 1-3 pod.  Even though the heat shield protects against the worst of the reentry heating, it gets very hot & that heat gets conducted to the next part touching the heat shield.  The best trick is to put something more heat resistant between the heat shield and science jr or crew cabin.  Service bays are excellent for this, but even batteries, reaction wheel modules and monoprop fuel tanks all have higher temp tolerance than the science jr.

Another option that I've used for high speed Eve entries has been to put a second heatshield with little or no ablator underneath the "main" heatshield to prevent the temperature from transferring to more delicate stuff.

Edit:  One other option for the science jr - put an experiment storage unit somewhere safe (like in a service bay), transfer the experiment from the science jr to the storage unit, and have the science jr on part that gets staged away for reentry so you don't have to worry about it.

Edited October 18, 2019 by Cavscout74

[paul23]

Yes those two "labs" are basically "not meant for reentry". Sure you can but thematically they are meant to do science, send science using antenna or a recovery vehicle, stay in orbit.

[Streetwind]

I safely reenter with the Mk1 Crew Cabin all the time. The trick is making sure the heat shield actually faces forward.

My typical reentry vessel of a pod with chutes, the crew cabin, and a heat shield, will not be aerodynamically stable. That is, it will tend to skew off retrograde if you let it. At that point, the oncoming airstream hits the side of the crew cabin and will quickly dismantle it.

However, if you have at least a level 1 pilot (effortlessly achieved by doing one oribtal flight around Kerbin and returning), then you can set SAS to "hold retrograde". The Mk1 pod has enough torque to keep the craft straight during reentry, so only the heat shield is facing the airstream. That way, the crew cabin survives just fine.

The same likely applies to the Science Jr. materials bay. It weighs much less than the capsule, and therefore, the center of mass is moved away from the heatshield, which causes aerodynamic instability and makes the craft want to skew (or perhaps even flip). Be sure to tell your pilot to always hold retrograde during reentry. If that isn't enough to keep the craft stable, either rebuild it in a more aerodynamically stable fashion (heavy bits at the front, draggy bits at the back), or just add more reaction wheels.

 

Edited October 18, 2019 by Streetwind

[Vanamonde]

One thing that helps to retrieve the materials bay intact is to right-click on it after use and close the door. 

[Guest]

Try adjusting the angle of how you come in. A shallow angle will take longer but give you more time to slow down, and a steep one will be shorter but give you less time to slow down.

[bewing]

Using aerodynamic control surfaces to increase reentry drag works about 100 times better than any method of heat shielding, to allow reentry of delicate parts.

 

[Waxing_Kibbous]

Having a command pod + L1 pilot + heat shield is the best way to re-enter, you can grab the science from your experiments and ditch them before re-entry. If you want 2 kerbals, eg a pilot and scientist, a command pod-lander can-heat shield works.  The pilot holding retrograde is the key, trying to do it manually can get a bit hairy when it matters most. Make sure you have enough EC when doubling up! A command pod by itself will orient itself aerodynamically.

Edited October 18, 2019 by Waxing_Kibbous

[paul23]

57 minutes ago, Waxing_Kibbous said:

Having a command pod + L1 pilot + heat shield is the best way to re-enter, you can grab the science from your experiments and ditch them before re-entry. If you want 2 kerbals, eg a pilot and scientist, a command pod-lander can-heat shield works.  The pilot holding retrograde is the key, trying to do it manually can get a bit hairy when it matters most. Make sure you have enough EC when doubling up! A command pod by itself will orient itself aerodynamically.

Actually you do not wish to go fully retrograde, you wish to create slight amount of lift so that you're not in a ballistic trajectory but rather a more smooth trajectory. (And hence more distance through atmosphere). Typically it means that you try to push the front of the thing you're flying 'up'. (so the top further down).

 

Also if you design decent you'll be able to land hands free easily. As always aerodynamic forces will put the aerodynamic center (center of lift) "behind" the center of gravity with respect to the direction of flight. So if you check the last stage (landing stage) make sure the aerodynamic center is *above* the center of gravity, then you'll fall down retrograde without doing anything. (This is opposed to going up, there you wish to have the center of lift below the center of gravity).

 

You can easily see those by using the buttons in the lower left (just bottom right of the part selection), select "center of lift" and "center of gravity". Gravity is a big yellow thing, lift a small blue thing sphere. (if you don't notice lift, it might be because it's fully encapsulated by the cog).

[Streetwind]

6 hours ago, paul23 said:

Actually you do not wish to go fully retrograde, you wish to create slight amount of lift so that you're not in a ballistic trajectory but rather a more smooth trajectory. (And hence more distance through atmosphere). Typically it means that you try to push the front of the thing you're flying 'up'. (so the top further down).

Stock settings and speeds are so benign that this isn't really required, IMHO. I do direct, fully ballistic reentries from Minmus with just a service bay, no heat shield, that don't even reach 3G peak deceleration. And if I was pulling 5G, it would still be perfectly safe unless there were paying tourists on board. So why bother making it more complicated and time consuming than it needs to be?

Granted, with mods and tweaked settings, that kind of thing may very well be the difference between life and death.

[SirGouki]

I achieve this without heat shields.  Mainly with the Crew Cabin as I usually forget about the Science Jrs until I start trying to make space stations.

I do this by having enough fuel in my last stage to slow down in the upper atmosphere.  Sometimes, when I can't do that, I just enter way more shallow than you would normally.  I.E. Instead of aiming for around 30k periapsis on reentry, I aim for 65k.  I also circularize before reentry around 120k (or larger, but try to get it under 300k, as you can reenter space at those speeds even as low as 50k) so that I don't bounce in and out of space too much.  This lets me bleed off speed before the atmosphere thickens, often *just* enough to prevent an explosion.

Edited October 19, 2019 by SirGouki