Capsule w/ SAS stuck offcenter on reentry?

[dvp]

Sorry for the lack of screenshots: I'm not home a/t/m, but this has been bugging me.

With sufficiently advanced tech and a bit of trial-and-error, I've been happy to find that landing capsules is pretty "easy button.":

• Enter a low (<100km) orbit
• Drop periapsis  to 40km
• Turn on SAS
• Set SAS to keep the nose pointed retrograde
• Watch the lightshow
• pop the 'chutes.

This is pretty much the same regardless of what other stuff I have hanging off the back of the capsule - cargo bays, empty fuel tanks, science containers, etc. With a heat shield, enough radial-mount parachutes, and a reentry speed <2600m/s, it's pretty safe.

The problem is specifically when I have a "tourist box" consisting of a Mk1-2 command module on top of a hitchhiker container and a heat shield. Very simple, right? Except it wants to tumble - even with SAS on, it'll spend a good chunk of the reentry stuck about 20 degrees off-axis. I've got plenty of electricity.

They're surviving reentry, and I know that any landing you can walk away from is a good landing, but I won't lie - it makes me nervous.

Is there something inherently off-balance about the hitchhiker container? Is there a way to balance it better? Or maybe change the aerodynamics of it so it's more stable? (I could put on some reversed tail fins... or would that interfere with takeoff?)

TIA

[Geonovast]

Ideally you want the COM as close to the heat shield as possible.  It's pretty good with just the command pod:

Not so with the hitchhiker in the mix:

Some fins on top would help, but as you said, would mess up launch.  You could use airbrakes instead if you have them researched:

Or attach your fins and put the whole shebang in a fairing for launch.

[Spricigo]

not exactly the most elegant solutions but it actually works.

1.use 2 Hitchhikers and a probecore

2.Put the Command Pod the below the hitchhicker.

For the ascent use fairings/nosecones to deal with the drag and try to not think much about the looks of your ships.

 

[bewing]

Just so long as you use steerable fins around the top, they can actually make you more stable during ascent.

And the fact that your RV flips around nose first can sometimes mean that you can just throw away the heatshield and reenter nose first. You will need to add a couple little drogue chutes to make a nice landing though.

The heatshields are often unnecessary. They can even do more harm than good on many occasions.

 

[linuxgurugamer]

You could do what I do, which is put two heat shields on the bottom in order to move the center of mass down.

Edited September 13, 2017 by linuxgurugamer

[dvp]

2 hours ago, linuxgurugamer said:

You could do what I do, which is put two heat shields on the bottom in order to move the center of mass down.

Hmmm... when I tried that in the construction area, I saw some weird graphical glitching between the heat shields, so I kind of assumed I wasn't supposed to do that.

Thanks for the advice above, all. :-)

[steuben]

Go with the airbrakes. They look cool when you couple them with SAS.

[mk1980]

the cone shaped capsules don't really need SAS for reentry - they will automatically keep that retrograde alignment even if you turn the SAS off. they also don't really need a heatshield to reenter from low orbit on their own.

the problem with an mk1-2 on top of a hitchhiker is that the mk1-2 is much heavier than the hitchhiker, so their combined CoM tends to be fairly high up. you would be better off using two hitchhikers and control the vessel with a probecore. the CoM for two hitchhikers sitting on top of each other will be right in the middle between them, so once you add a heatshield below them, the CoM will shift towards the shield.

or you could use the mk1 or mk2 passenger cabins instead of hitchhikers - they have better heat resistance and crash tolerance and lower mass per seat. the hitchhiker isn't really designed to survive re-entry - i think the flavor text of the part also mentions this.

you probably won't need a heatshield to bring the spaceplane cabins down safely from low orbit. i've also landed unshielded mk2 passenger cabins returning from mun or minmus - those spaceplane parts have pretty decent heat tolerance.

[Spricigo]

11 hours ago, dvp said:

Hmmm... when I tried that in the construction area, I saw some weird graphical glitching between the heat shields, so I kind of assumed I wasn't supposed to do that.

Graphical glitches in the editor are somewhat common (unfortunately) but by no means an indication you are doing something wrong.

Actually part clipping will more often make little to no difference other than aesthetic.  (Part clipping through fairings are a notable exception, be warned)