Re-entry-proof your return module

[Mast]

Since one of the last updates it's no longer possible to return unwieldy, fragile objects from space to Kerbin without disastrous damage.

To prevent a command module from completely evaporating (I'd say that's the bare minimum to speak of a successful return), a heat shield is a must have. But what else is out there to battle the heat? I've seen myself resort to quite unorthodox tactics (among others: use spare fuel tanks as a buffer to survive re-entry, instead of cutting them loose the moment they're empty) and I feel I'm doing it wrong.

I'm especially interested in how to fix this in early-career, but wall-of-text answers with the whole shebang would be appreciated as well.

[Snark]

A few strategies.

Wall-of-text answer is below, but here's a really simple strategy for early-career reentry from LKO without a heatshield:  use body lift.  That is, your reentry vehicle is a command pod, on top of a cylindrical fuel tank (like the 2-ton LFO one), on top of an engine.  Enter at a shallow angle, retrograde (so that the engine takes the brunt of the heat), but tipped about 20-30 degrees from retrograde so that the cylindrical fuel tank generates lots of body lift to keep your altitude high while you slow down.

 

Okay, longer answer:

First, you have to care about temperature tolerance now.  Not all parts can take the same temperature.  For example, if you're flying a spaceplane:  there are "spaceplane" parts and there are "airliner" parts.  The latter has a much lower temperature tolerance than the former.  So make sure that any parts that aren't protected by a heatshield or other part can handle at least 2000 degrees, if you care about them.

A heatshield's not mandatory for returning from LKO, at least not for reasonably lightweight craft.  I do it all the time.  Engines are fairly heat-resistant; entering retrograde with the engine taking the brunt of the heat often works.

You need to be aware of how heavy your craft is relative to the amount of drag it generates.  Craft that are very draggy relative to their mass (i.e. big and not so dense) fare better and can tolerate higher reentry speeds without a heat shield, because the drag slows them down more rapidly before they get too hot.

Use lift to mitigate reentry heat.  This is a big one.  If you can use lift to keep your altitude up where the air is thin while you bleed off lots of speed, then you don't get fried when you descend down into the thick stuff.  This is what a "spaceplane style" reentry is all about:  you keep the nose up, and the wings generate lots of lift.  However, you don't need wings to get advantage from lift.  Body lift is your friend.  Any long, cylindrical shape will generate plenty of lift at reentry speeds, if you keep it up-angled to the airflow at 20-30 degrees.  This works just fine even if you have no airfoil parts at all on your ship.

 

Edited February 1, 2016 by Snark

[Mast]

@Snark I can imagine plotting a landing course gets a lot trickier if you plan to use lift as long as possible to help with the re-entry?

 

[Temstar]

8 minutes ago, Mast said:

@Snark I can imagine plotting a landing course gets a lot trickier if you plan to use lift as long as possible to help with the re-entry?

No it's actually easier, because body lift can be used to fine tune reentry trajectory. Once you've passed peat heat load you can pitch and yaw your craft so that the lift generated by the body deflects your craft in a direction you want. So assuming you're facing prograde, pitch up to make you land long, pitch down to land short, and yaw to get cross range. Retrograde orientation means controls are reversed.

You can see this happening in real life if you observe how an Apollo capsule reenters. It flies with a high alpha reentry to both reduce the peak acceleration by creating lift, as well as give the craft some steering. It achieves this by having an offset CoM and two RCS thrusters than can roll the capsule.

Edited February 1, 2016 by Temstar

[Snark]

9 minutes ago, Mast said:

@Snark I can imagine plotting a landing course gets a lot trickier if you plan to use lift as long as possible to help with the re-entry?

Plotting a landing course is no problem for me at all.  I want to go down.  So I plot a landing course that goes down, and it works like a charm! 

I suppose it might be a little more complex if I actually cared about my course to a finer degree of granularity than "down."  For example, if I cared where I come down.  But why the dickens would I care about that?  Yes, it's worth a smidgeon more cash if I come down closer to KSC... but it's really chicken-feed, the amounts involved are so tiny relative to the cash that one gets from contracts or World Firsts that it's simply not bothering with, unless you have some sort of role-playing reason to want to do it, or enjoy the challenge just for the sake of challenge.

The only time I care at all about where I come down is, occasionally (not usually, but sometimes) I have a preference for land versus sea-- e.g. if I have a particularly unwieldy craft that I'm concerned might not handle a hard landing well, so I'll want to splash down.  But that's pretty easy.  Continents are big, oceans are big, that's a pretty big target to aim for.

And in any case, as @Temstar points out, using body lift actually gives you considerably more control over your entry than a traditional heat-shield entry does, because you actually have the ability to steer, somewhat.

[Mast]

1 hour ago, Snark said:

But why the dickens would I care about that?

To get science from the appropriate biomes, for example. Set-up satellite dishes, mining outposts, heck should I know what thousand reasons there are to land on target. Perhaps I'm just old-fashioned in trying to land somewhat accurately.

I won't pretend I now know exactly how to fix my rockets, but your pointers definitely helped getting into the right direction. Best I tried so far was going as narrow as possible down behind a heat shield, and if you go down fast enough you'll evaporate your Kerbals anyway. For ascending a sharp rocket works best, but for descending a blunt rocket works better. And I guess I need to hide my science equipment from the heat so I can actually use the lift to my advantage while steering instead of loosing an instrument with every manoeuvre.

[Snark]

7 minutes ago, Mast said:

To get science from the appropriate biomes, for example. Set-up satellite dishes, mining outposts, heck should I know what thousand reasons there are to land on target.

• Getting science from biomes:  I never bother much with trying to hit all the Kerbin biomes, because the science rewards are so paltry compared with going to Mun/Minmus.  I'll take opportunistic advantage and grab all the science I can if I happen to land in one I haven't done yet, but that's about it.  If I did want to go to a particular location, I'd be more likely to fly an airplane there than to do an orbital reentry.  In any case, if all you care about is "which biome" rather than a pinpoint landing in one spot, that's not so hard to aim for-- biome patches are fairly large.
• Setting up satellite dishes:  I assume you mean for building a ground-based RemoteTech relay network?  A valid point, though I never bother with this-- it's so easy to set up a relay network of LKO comsats.
• Mining outposts:  Great for other planets, but I never bother with 'em on Kerbin, it's about the worst possible place to mine:  low demand (it's too easy just to launch stuff from KSC), expensive to transport the results (Kerbin's big and has a thick atmosphere).

13 minutes ago, Mast said:

Perhaps I'm just old-fashioned in trying to land somewhat accurately.

Well, it's all a matter of what you want out of the game.  I tend to be very pragmatic, and there's essentially no practical benefit to doing pinpoint landings on Kerbin, so to me they're just a waste of time.  But everyone has their own play style.  If you like doing more "role playing," there are plenty of adventures on Kerbin to be had.    Or maybe you just like the challenge of pinpoint landings.

(I do plenty of pinpoint landings everywhere except Kerbin, e.g. when I need to land one ship right next to an already-landed ship.  But Kerbin is the one place where pinpoint landings matter the least, because I can always recover just by clicking a button.)

If you do care about controlling your landing location accurately:  consider putting some wings (even stubby ones) and control surfaces on your reentry vehicle; you'll be able to steer a lot better than you can with just body lift.

16 minutes ago, Mast said:

For ascending a sharp rocket works best, but for descending a blunt rocket works better.

Yup.  But if you come in at an angle and use body lift, you can have your cake and eat it, too-- pointy during ascent, controllably blunt while reentering.

17 minutes ago, Mast said:

And I guess I need to hide my science equipment from the heat so I can actually use the lift to my advantage while steering instead of loosing an instrument with every manoeuvre.

Yup, they're fairly delicate.  Sticking them in a service bay is one way to do this.  Another way, if you're going to be coming in angled to take advantage of body lift, is to put them all on the same side of the rocket, and make sure that that side is the top side during reentry, so that the body of the rocket is shielding them from the worst of the heat.  Or if you have a conical command pod like the Mk1 and are entering retrograde, you can put them on the narrow sloping sides of the capsule, and the wide blunt end will shield them pretty well.

[numerobis]

Me, I'm a fan of the broadside: I just point my spacecraft normal and hold the attitude. I set periapsis high -- no less than 40km from LKO, 50 km from Mun.

That works fine with airliner parts, solar panels, and so on. The solar panels, thermometers, and goo containers get hot but just barely don't pop.

With a materials bay, they tend to be structural elements of my rocket, so I tend to be more jittery as the bar starts to accumulate heat. But what works well in that case is to turn off SAS and set up a strong spin along the normal-radial axis, so you are spin-stabilized in the direction of travel, then add on a rolling momentum so that no face of the materials bay spends much time facing the hottest part of the shock wave.

And then there's radiators. 20kg of radiator will suck a lot of heat out as you sink through the atmosphere.

[RizzoTheRat]

In the early game I don't bother trying to land anything except capsules,  the crew can collect the science data before rentry and I drop the science modules as soon as any instability means the extra drag isn't worth it any more. 

Later in the game reusable launchers come down engine first with airbrakes to drop them to parachute speeds. 

[Warzouz]

8 hours ago, Snark said:

Well, it's all a matter of what you want out of the game.  I tend to be very pragmatic, and there's essentially no practical benefit to doing pinpoint landings on Kerbin, so to me they're just a waste of time.  But everyone has their own play style.  If you like doing more "role playing," there are plenty of adventures on Kerbin to be had.    Or maybe you just like the challenge of pinpoint landings.

Well, there is 2 (nearly identical) cases where you want to do precise landing in Kerbin

• Space planes and Shuttles, but they are designed to have much control autority and even power to fly to their target (usually KSC landstrip)
• Recoverable rockets (SSTO or not), because you want high recover value of this expensive vehicle to soft your launch price. You need to lande them near KSC. Those vehicles usually have little control authority (especially since airbrakes were nerfed)

Other than that, I agree there is not much use of precise landing of a few cheap price parts return vehicle.

As for Kerbin exploration, the best is to do it by plane, if you like that stuff.