Mk1 Capsule Re-entry Experiment

[Torquemadus]

I've been starting from scratch, trying to re-learn how to play KSP. I was curious about how to make the mk1 capsule re-enter correctly and whether it is indeed bugged.

I'm using the parts I have to hand in the early game, so I did what I could to shift the centre of mass of the capsule upwards to keep it stable. I sent the capsule on a sub-orbital flight to complete the escape from atmosphere contract. I turned off SAS after final stage burnout, and allowed the capsule to enter a slow tumble.

The tumble corrected itself after the capsule started to encounter significant drag.

It remained stable thereafter.

It looks like I need something to ballast the capsule to keep it stable. I'm going to experiment with other parts as I unlock them.

[Eric S]

A few more data points I've learned (all purely stock, without the "physicsless heatshield" fix:

A capsule and parachute, no other parts yield inherently stable results and will orient itself retrograde. Because of the high heat tolerance of capsule parts, it will also survive if you use the right reentry angle and such (30km periapsis, tested from LKO and a bit higher, have not tested from Munar return yet).

A capsule and heat shield, no other parts, yield similar results, though the impact will kill it.

A capsule, parachute, and heat shield yeild a less stable result. In fact, as near as I can tell, it wants to fly backwards, and stops only because that would mean turning far enough that the parachute is no longer occluded, which pushes the parachute back towards the center, resulting in an entry just far enough off of retrograde to burn up the parachute.

[juanml82]

That's because the heatshield is massless which, IMHO, requires a hotfix. There is a mod that fixes it already

[Highlad]

I think what is happening here is not because you have moved the COM higher, it's because the part you added causes enough drag to correctly orientate the craft by moving the centre of air pressure further up, much like a parachute would.

I think any low mass, high drag part would have the same effect.

[Frybert]

That's because the heatshield is massless which, IMHO, requires a hotfix. There is a mod that fixes it already

Quick correction.

Massless parts aren't anymore. Their mass gets added to their parent part in flight; the mapview mass display is wrong.

[r_rolo1]

I think what is happening here is not because you have moved the COM higher, it's because the part you added causes enough drag to correctly orientate the craft by moving the centre of air pressure further up, much like a parachute would.

I think any low mass, high drag part would have the same effect.

In better words, the chute + MK1 capsule + 1,25 m ablative shield has the center of drag in front of the center of mass if you try to put it with the ablative shield in the right direction ( due to the confirmed bug about the ablative shield being massless ). That is a highly unstable proposition and the ship will flip backwards as soon as you get too far of the velocity vector.

What the OP made was to put the center of drag further behind by putting the extra part in between the chute and the capsule, making it stable again ...

[Drillgorg]

I believe their drag gets added to the parent part too?

[Depth]

You need a low centre of mass, not a high.

[sal_vager]

Did you know pods aren't aerodynamically stable when they are the sole part? They aren't in .90 or .25 either, I had to go check.

[Renegrade]

Did you know pods aren't aerodynamically stable when they are the sole part? They aren't in .90 or .25 either, I had to go check.

Actually they are stable in FAR in previous versions of KSP thanks to Ferram and co~

[sal_vager]

FAR is a mod I believe, if you modify the game to make them stable then of course they are going to be stable

[tater]

I suppose that might be my problem as well. Of course in other versions pod orientation doesn't matter even a little (without mods like FAR or DRE).

[LordFerret]

That's because the heatshield is massless which, IMHO, requires a hotfix. There is a mod that fixes it already

There's a mod made for that already? By whom? The only thing I've seen thusfar, and used, is a manual edit of the configuration files - see this post.

[Torquemadus]

In a follow-up test, I flew the same capsule arrangement down from orbit. It doesn't fly completely straight, but it's stable enough to survive re-entry.

The re-entry graphical effects made me start to worry about the parachute.

The heatshield seems to have adequately occluded the rest of the spacecraft.

I've been setting the parachute to deploy at 0.5 pressure, as this gives the spacecraft a chance to slow down to a reasonably sane speed!

[jwenting]

yes. Just the capsule will survive. Add a science bay under it however and it will tumble and burn up.

I've managed to get it to come down by adding an additional small tank of fuel as a counterweight under that. Not pretty but it works (now if only I'd remembered to add additional parachutes so it wouldn't disintegrate on hitting the ground...).

In all, it's got a lot harder to get things down safely without engines.

[Renegrade]

yes. Just the capsule will survive. Add a science bay under it however and it will tumble and burn up.

True, but as soon as you unlock EVA, you can steal the data from the science jr and then decouple it. Not as much cash recovery without the jr, but let's be honest, the game is like 95% building cost, 5% rocket cost. Recovery for a disposable design is already tiny, making it a bit tinier won't affect much

[juanml82]

There's a mod made for that already? By whom? The only thing I've seen thusfar, and used, is a manual edit of the configuration files - see this post.

The mod uses module manager to make that change in the configuration file

It's this

http://forum.kerbalspaceprogram.com/threads/97285-KSP-v1-0-Stock-Bug-Fix-Modules-%28Release-v1-0-0-27-Apr-15%29-Misc-Utilities-%2818-Jan-15%29

It includes several other fixes

[problemecium]

I've just been leaving out the heatshields. It turns out the Mk1 Pod can handle a surprising amount of heat on its own.

[togfox]

Are the heat bars removed from 1.0? You know - in the bottom left corner - they don't seem to show no matter how hot I get things.

[monophonic]

Are the heat bars removed from 1.0? You know - in the bottom left corner - they don't seem to show no matter how hot I get things.

They only appear for engines, and possibly other parts that generate heat themselves.