Mk2 Cockpit Heating

[Suedocode]

I think this is a well-known problem throughout many versions of ksp, but (I believe) because the Mk2 cockpit is a single all-in-one nosecone, it generates a monstrous amount of re-entry heat. I have trouble not exploding the thing on relatively gentle reentry angles (40km periapsis) just returning from 450k orbits (still true in 1.2 despite pointy-object aerodynamic changes). The inline Mk2 and Mk3 cockpits have separate parts as noses (like a shielded docking port) which seems to disperse the heat better and solve the issue. Just about any re-entry is quite harrowing with the Mk2.

Is this the intended (rather than simply emergent) behavior of the Mk2 cockpit? I wish there was a way to add more ablative coating at the cost of increased weight, but that is perhaps getting into modding territory. It does look pretty damn good imo though, so I'd hate to have to switch to the inline Mk2.

[fourfa]

Prolly want to read this thread

[EpicSpaceTroll139]

What kind of re-entry profile are you using? To bleed off speed and reduce the peak heating on the nose (and in this case cockpit) of any spaceplane you'll want to be coming in with a significant angle if attack (just like the space shuttle did). I generally find 40° works great. You have to be careful to account for the lift this generates. Might wanna swerve from side to side to dissipate speed that way if you're coming in fast enough.

[Jarin]

There does seem to be something wrong in that blunt noses like the docking port take heat better than the aerodynamic Mk2. There's a reason I use Mk3s for almost everything now...

[Guest]

@Suedocode 40k is steep for a spaceplane re-entry corridor. I use 55-60 in 1.2, 50-55 in 1.1. No problems with the Mk 2 cockpit in either version.

[Magzimum]

I keep my spaceplane with Mk2 cockpit at "Radial out" for as long as possible. I even mounted 4 Place-Anywhere 7 Linear RCS Ports on the bottom of the cockpit to keep it up for longer. because I have large wings at the back, at some point during the descent the drag becomes too much, and the nose comes down despite me keeping the SAS at Radial Out and the RCS on. But I can usually still keep the plane at 30-60 degrees up, which still slows it down significantly, all the way down to 1300 m/s at which point I finally point the nose prograde and set the SAS to the regular "Stability assist".

I can do my re-entry with a periapsis anywhere between 40k and 20k.

I'd post a picture of a re-entry, but I don't have any.

[DunaRocketeer]

High angles of attack are a great way of sparing parts excess re-entry heat - in the upper atmosphere I will sometimes go fully 90 degrees AoA. My spaceplane de-orbit burns always have periapses of 0 altitude as well.

Good for managing heat and landing point accuracy.

Very bad for fuel efficiency...

[EpicSpaceTroll139]

6 hours ago, Jarin said:

There does seem to be something wrong in that blunt noses like the docking port take heat better than the aerodynamic Mk2. There's a reason I use Mk3s for almost everything now...

Actually this is realistic once your craft is going past a certain speed. Blunt objects get to benefit from something called shockwave detachment (creating a bow shock). This is effectively caused by the air immediately in front of the nose not being able to get out of the way fast enough, and thus creating a sort of barrier between the nose and the supersonic/hypersonic airflow. This results in the shockwave (which is what we hear as a sonic boom) being moved forward, away from the nose. This greatly reduces the amount of heat which thee nose must endure. That being said, it does produce a rather significant amount of drag

[Vaporized Steel]

Theres a reason why high speed aircraft or spacecraft (spaceshuttle) have blunt noses.
Sharp edges tend to soften or even melt faster then a more blunt end on a fuselage.

Less of a volumetric area means it absorbs and dissipates heat more quikly. Which is why radiator ribbons are small and not big. That's why it takes in upwards of an hour for your icecube to melt and decades for the polar caps to melt. The polar caps have more volume and can absorb that energy alot longer.

Those properties of a nosecone (i.e. a metal) however are based on the ambient temperature. And the ambient temperature during re-entry is to high to make sharp metal edges. The material becomes to weak because it has to little volume to dissipate that heat and basically gets heatblasted and your fuselage starts to crack and deform and at some moment you'll get a boom and the result is a funeral with some new headstones.

OT

KSP doesn't simulate that and as far as I know not a single game does. (hit me if I'm wrong)
It would explain why blunt shielded docking ports don't overheat as quikly but that can also be the bowshock effect as is pointed out.

It's the fact you decelerate on a high AoA alone that explains the results your getting as you say that you used a gentle re-entry aproach at first. This is basically the worst to do anyway from any Orbit or atmospheric encounter.
If your nose cannot hold a high AoA in your current plane design then try to move fuel from one tank to another to move the CoM to your CoL.
The lower heat on a Mk2 nosecone on a high AoA seems more a result of aerobraking as you'll decelerate more opposed to going in the atmosphere nose first (hypothesizing that in both scenarios they'd have the same re-entry aproach, speed, except for the attitude that is)

While I haven't tested this out recently I can remember my own first attempt at building SSTOs since v1.x and I had a few instances where I went nose first during re-entry due to bad designing of my craft. The difference between nose first and a high 40-60 degree AoA on the same spaceplane or aircraft for that matter is game changing. With a nose first aproach and a few airbrakes you'll need almost half a orbit from the KSC to land due to poor deceleration. But with a high AoA aproach without any airbrakes I'll need about a quarter orbit from my de-orbit burn to get to land.

Keeping that AoA during descent is all about balance. You can do it without any control surfaces and thus with the cockpits onboard reactions wheels only. Although you'll need very good balance. So make sure you'll have a fuel tank in front of your Col and behind your Col so you can transfer mass from one end to another to center it over your CoM. If you balance it well enough the plane will almost reenter by itself.


 

Edited October 6, 2016 by Vaporized Steel

[Jarin]

2 hours ago, Vaporized Steel said:

So make sure you'll have a fuel tank in front of your Col and behind your Col so you can transfer mass from one end to another to center it over your CoM. If you balance it well enough the plane will almost reenter by itself.

The biggest problem is doing this entirely by "feel", since you can't see CoM and CoL indicators in flight.

[Suedocode]

10 hours ago, Brikoleur said:

@Suedocode 40k is steep for a spaceplane re-entry corridor. I use 55-60 in 1.2, 50-55 in 1.1. No problems with the Mk 2 cockpit in either version.

 

7 hours ago, DunaRocketeer said:

My spaceplane de-orbit burns always have periapses of 0 altitude as well.

Interesting how you guys have exact opposite methodologies. I can't use a 55-60km re-entry because I'll end up skipping off the atmosphere. I can't target a landing destination very well like that, and spending more time is expensive because I play with life support. I'll try the 0 altitude periapsis when I get home. My spaceplane usually enters at about 45 degrees from prograde and keeps it that way for as long as possible until the atmosphere forces it into prograde flight. Despite all that, the cockpit really heats up even as soon as I hit 50km. I've had a ton of landings with the cockpit still at nearly critical temperature, where all other parts are fine. I'll try to post images to give an example (although I don't know how to embed images on this website).

[Vaporized Steel]

@Jarin

You are right. But you know how to change your Com by draining fuel from your tanks in the vab/sph as much as you would have during re-entry.

You then now where to change the com to and by how much. A little offcenter is also not necessarily catastrophic. 

[Guest]

9 minutes ago, Suedocode said:

Interesting how you guys have exact opposite methodologies. I can't use a 55-60km re-entry because I'll end up skipping off the atmosphere. I can't target a landing destination very well like that, and spending more time is expensive because I play with life support. I'll try the 0 altitude periapsis when I get home. My spaceplane usually enters at about 45 degrees from prograde and keeps it that way for as long as possible until the atmosphere forces it into prograde flight. Despite all that, the cockpit really heats up even as soon as I hit 50km. I've had a ton of landings with the cockpit still at nearly critical temperature, where all other parts are fine. I'll try to post images to give an example (although I don't know how to embed images on this website).

To be fair I've only used spaceplanes to haul stuff to and from LKO. It's not hard to hit KSC on the nose with that; setting Pe 58 (1.2-pre) or 50 (1.1) right over it will get it into the ballpark, and then you have to tune a bit depending on the individual model. I have no idea how I'd hit anything on, say, Duna or Laythe, without several trials. 

[EpicSpaceTroll139]

@Vaporized Steel A while back NathanKell made a post dealing with reentry heating in KSP.  If you don't want to read that (and I wouldn't blame you haha), then this is the important bit

On ‎2‎/‎11‎/‎2016 at 1:06 PM, NathanKell said:

One other wrinkle: the blunter the bit that's facing the wind, the more likely you are to get a detached shockwave, rather than one attached to your forward-most part. That will greatly lower the shockwave temperature that you feel. For this reason, if you're flying a spaceplane, always come in bottom-first, not nose-first.

I'm guessing that "bottom-first" = belly-first, because it would be a bit... unstable and weird to fly a spaceplane backwards through reentry (but definitely Kerbal! )

Edited October 6, 2016 by EpicSpaceTroll139