Philosophy and Ideology of Skin Temperature in KSP Universe (present and future), RE 1.0.5

[Violent Jeb]

[redacted, done]

Edited August 16, 2016 by Violent Jeb

[Starhawk]

I just finished my Jool-5 mission. Re-entry vehicle was just the Mk1-2 (3 kerbal) capsule with heat shield.

I burned a few hundred remaining m/s from my tanks and decoupled the return stage. I entered atmo at about 6 km/s with a periapsis of about 27 km. I burned off most of the ablator and had a completely nominal reentry.

Mass of the craft at atmospheric entry was about 5.7 tonnes.

Happy landings!

ETA: All settings were default, and no mods that alter physics were installed.

Edited October 21, 2015 by Starhawk

[arise257]

I've had reasonable success decelerating large craft into Kerbin's atmosphere by using aerobraking with multiple passes. If you have the control authority, pitching up (30 degrees or less) to expose more underbelly at about 45-50km up will bring your speed down a lot faster than going in prograde - I'm a patient man though, and I've waited as many as 10 passes to bring my speed down from about 5000m/s to 3500m/s. I feel like 3500 is about the fastest you can come down without most parts exploding during descent. Definitely use heat shields and radiators though, they will improve your craft's durability to a point.

[Violent Jeb]

^^ How did you make it to 45 km without exploding? Heat shield(s)? Usually, I can only bleed off around 50-100 m/s diving that deep. Assuming I don't burn up, it still requires 500-1000 m/s retroburn to pull me into an orbit. After that I can usually follow a similar profile and "de-orbit" after apx 10 passes. Having to reduce to just the command pod seems a little ridiculous to achieve a "prompt" maneuver.

Maybe i'm the odd man out, but I really don't see the point in arbitrarily raising the complexity for something that is less fun. At the rate the complexity is increasing, I probably won't be able to get manned teams on the other planets, due to the massively increased complexity of re-entry and return cost. It's comparable to orbit docking to reduce launch fuel or building ships in space, you can do it if you really want to but it's more hassle than its worth.

In the case of heat management you have all the hassle with literally no benefit. It's not like you can "limp" a craft around with a few melted parts, and redesign for the next mission. You're basically designing a monstrosity, with no way to know if you'll be able to compensate for the arbitrary heat, that much worse if it's a career game, because if you're running 15 parallel missions, then there's no revert.

Or i can play sandbox.. but I don't feel like i should have to..

I just finished my Jool-5 mission. Re-entry vehicle was just the Mk1-2 (3 kerbal) capsule with heat shield.

I burned a few hundred remaining m/s from my tanks and decoupled the return stage. I entered atmo at about 6 km/s with a periapsis of about 27 km. I burned off most of the ablator and had a completely nominal reentry.

Mass of the craft at atmospheric entry was about 5.7 tonnes.

Subsequent post indicates that 3500 m/s is above critical speed. How did you enter at 6 km/s periapsis 27km and only burn off "a few hundred" m/s and still survive? I burn up with half that velocity.

Not to question your flight but i'd love to see pics of a 6 km/s atmo entry survival. At that kind of speed i would expect to be destroyed by g forces even if i could survive the upper atmo. Oh, and how was that Jool atmosphere.

Edited October 21, 2015 by Violent Jeb

[A_name]

Subsequent post indicates that 3500 m/s is above critical speed. How did you enter at 6 km/s periapsis 27km and only burn off "a few hundred" m/s and still survive? I burn up with half that velocity.

Not to question your flight but i'd love to see pics of a 6 km/s atmo entry survival. At that kind of speed i would expect to be destroyed by g forces even if i could survive the upper atmo.

Well if he only had a capsule, those are very resilient to heat and have the ideal aerodynamic properties for reentry. What did your Duna return craft look like?

[Starhawk]

You haven't mentioned heat shields. Are you adding heat shields to your craft?

Happy landings!

- - - Updated - - -

Here are some pics.

I should mention that I actually ended up skipping back out of the atmo before the final reentry. The first three pics show the craft ascending after hitting periapsis. The last two show the final reentry.

Happy landings!

[Laie]

Reentry heating is pretty straightforward, possibly even realistic: the amount of heat you receive is directly proportional to how much kinetic energy you lose.

The problem around Jool, Eve or even Laythe is that you have a quite dense atmosphere even at high altitudes, making it hard to hit a sweet spot where you can slow down without blowing up, even at reasonable speeds.

The problem when returning from far away is that kinetic energy is 1/2mV² -- that is, at 6km/2 you have four times as much energy to bleed off compared to 3km/s. In a system that's tuned so that returning from LKO is already dangerous, returning from Jool will be very dangerous indeed.

Still, entering at insane speeds is possible:

The vessel came in with 6+km/s and survived. That's because heatshields are magic and will soak up any amount of energy/time. They can only take a limited amount of heat, but they can absorb that whole amount in an instant without trouble. And as of 1.04, g-forces are no problem (though I presume this will change). So it's just a question of a) having your entire vessel protected by heatshield(s), and having enough ablator to soak up the energy.

[Gaarst]

It is the Kerbin system that is biaised, not the thermal heat on reentry.

While being far from perfect, it is not that bad (only talking about reentry here) in terms of equilibrium: try reentring the Earth on RSS or Kerbin x64 at >7 km/s, you'll need that heatshield, but you'll be fine with it.

It doesn't make any sense that a craft should overheat at 2500 m/s, in terms of realism. 2500 m/s is just in the hypersonic regime, there is barely any shock heating at this speed, at least not enough to justify a heatshield.

I agree that atmospheric maps should be readjusted: that is the problem with Jool (as Eve and Laythe to a lesser extent), and the reason why your craft will explode as soon as it touches Jool's atmosphere. Jool's atmosphere is simply too dense at higher altitudes: even at reasonable speeds, you'll heat way too much than expected. Your ship will almost always blow up if you're not prepared.

And by the way, in RSS, for a pressure of 1 atm asl, the Earth's atmospheric height is 130km, almost twice as high as Kerbin. This is why you explode when reentring at 3.5 km/s at Kerbin, while you survive Earth reentry at 7.5 km/s, 11 km/s from the Moon or further.

Having a too steep reentry is equivalent to hitting denser layers of the atmosphere too fast: this increases the heat flux maximum. During reentry, most of the energy goes into skin temperature, and as soon as you hit the maximum skin temperature of a part, it will blow up, end of story.

As it turns out, real life doesn't happen this way: your heatshield will not magically explode as soon as you reach the temperature is was made for. Actually, the peak reentry temperatures experienced by heatshields are often significantly higher than the ablator's boiloff point (often around 3000°C) and that is what makes it actually ablate, and protect the craft by creating a boundary layer and insulating the craft better than any solid material could. In KSP, ablators start to ablate whenever they want to (800K IIRC) and blow up when actual heatshields only start to ablate. This is another reason why, past a certain speed in KSP, your heatshield won't help you anymore: the heat flux is stronger than what the heatshield can withstand, it heats and explodes, even if the boundary layer would insulate your ship otherwise.

Squad could always add a multiplier to the reentry heat factor to make it hazardous at Kerbin but that won't solve the problem at all.

While I don't have the magic answer, I think that reworking the atmospheres and heatshield mechanics is a good start. And drag is high enough as it is.

[Violent Jeb]

My duna craft was more "re-usable", it had additional weight. I'm going to try a retroburn stage, and decoupling everything, with a heat shield under it.

Back when I thought you could perform reasonable re-entry in this game I was relying on my engines for shielding which is perfectly sufficient within the soi. Things behave as normal, and your ship doesn't vaporise in atmosphere.

Never bothered with the ablator because then it's really not re-usable in any sense of the word anyway!

I wanted to eventually build spaceplanes and shuttle back and forth from layth, but once again this is something that will never happen for a post .90 player, like myself. I just find the constraints to be too much. not fun anymore to sit and try to guess where the 5% sweet spot might be. Its just my opinion on how jacked they made the heat system.

They need to do SOMETHING. SOI heat is fun and intuitive, and interplanetary is a complete nightmare.

Edited October 21, 2015 by Violent Jeb

[Starhawk]

Inside Kerbin's SOI, you don't need a heat shield to handle reentry. Interplanetary, you do.

As far as spaceplanes to Laythe and back, there was a whole challenge thread about it and many successful craft and techniques are on display there.

Happy landings!

[FancyMouse]

I don't understand. Completely reusable is just unrealistic. Even space shuttle uses ablators. And you are asking for "fixing" things because your craft doesn't work without ablators?

That's simply not right. Not squad, but your craft.

[tseitsei]

My duna craft was more "re-usable", it had additional weight. I'm going to try a retroburn stage, and decoupling everything, with a heat shield under it.

Back when I thought you could perform reasonable re-entry in this game I was relying on my engines for shielding which is perfectly sufficient within the soi. Things behave as normal, and your ship doesn't vaporise in atmosphere.

Never bothered with the ablator because then it's really not re-usable in any sense of the word anyway!

I wanted to eventually build spaceplanes and shuttle back and forth from layth, but once again this is something that will never happen for a post .90 player, like myself. I just find the constraints to be too much. not fun anymore to sit and try to guess where the 5% sweet spot might be. Its just my opinion on how jacked they made the heat system.

They need to do SOMETHING. SOI heat is fun and intuitive, and interplanetary is a complete nightmare.

Why should you be able to re enter atmosphere straight from interplanetary transfer AND WITHOUT A HEATSHIELD? That's literally what heatshields are made for.

How many of the real life spacecrafts have tried to use their engines as a heatshield instead of an actual heatshield?

The fact that you can do it from inside kerbins SOI means that reentry heat is actually still quite forgiving...

Also SSTO spaceplanes to laythe are completely doable in 1.04 stock ksp. Just go to challenges subforum and look for "SSTO to laythe and beyond".

If you cant do it, it's not the games fault. You just need to learn more to be able to do it.

The bigger problem IMO is that heatshields act quite differently than they should (as already stated in this thread).

And that we cant coat the underside of our spaceplanes with heatshielding material (like the spaceshuttle did). Still even without that I have succesfully reentered spaceplanes to Eve so reentry is possible still to anywhere but aerobraking often isnt because using heatshield/ablator isnt reaöly possible for spaceplanes currently...

[Streetwind]

*snip*

At 50% thermal effect, it is hard to create overheat within the Kerbin SOI, and yet, based on the information i've seen this will still make for an un-penetrable joolian atmosphere.

*snip*

For one, I believe the atmosphere height maps for some of the larger planets will have to be adjusted (see doubled) for kerbin, aerodynamic drag could start higher or have more effect than heat for the higher parts of atmosphere.

If people are going to talk about realism, i'm interested to know how this aerodynamic model compares with real life. If the ksp system is 1/7 scaled down, I am going to speculate that the heating effects are only scaled down 1/2 vs real life, if at all.

You seem to be operating under some false presumptions and/or lack of information regarding some topics, so I'll attempt to infodump you a little:

- Jool's atmosphere is borked regarding heat. This is a known issue with KSP 1.0.3/4, and said to be fixed in 1.0.5.

- Atmospheric height for Kerbin is already much greater than realistic, for Kerbin's size. Our Earth has a far thinner sheath of air around it than you realize; if Kerbin's atmosphere was sized to scale to Earth's atmosphere for its diameter, then we'd be looking at roughly 20-30 kilometers worth of air, not 70 as we currently have.

- The KSP solar system is not scaled down to 1/7th. In fact it doesn't have an overall scaling factor at all; each planet does it differently. They are meant to be only vague analogues to real bodies, not scaled representations. For the main bodies, the size comparison to their realworld analogues yields: Sun 1/3, Moho 1/10, Eve 1/8.5, Kerbin 1/11, Duna 1/10.5, Dres 1/3.5, Jool 1/11.5, Eeloo 1/12.

- Heating effects are not scaled down compared to real life. The opposite is true - heating effects are scaled up, and quite a lot, too! Orbital velocity in low Earth orbit is ~8 km/s, compared to Kerbin's 2.2 km/s; returning from the Moon is ~11.5 km/s, compared to 3 km/s for a Mun return. As such, with a realistic heat simulation, you wouldn't even get any noticable heat or beautiful reentry effects at all, because you are traveling so much slower! So in order to force these things to appear anyway, at the speeds appropriate for KSP, the devs had to fudge various physical constants to completely unrealistic values.

- As a side effect of this, you can also configure these values yourself if you like, but it's complicated.

Edited October 22, 2015 by Streetwind