Hot atmosphere? LOLWUT?

[Laie]

I just tried to land on Eve for the first time since 1.0.

The moment I entered the atmosphere, the vessel lit up like a christmas tree. No noticable drag yet, no deceleration... from which I deduce that there was no friction, either. Yet from one moment to the other, every single part reported high temperatures.

Is that really how it's supposed to be?

[falloutaddict]

How fast were you going?

[SkyRender]

Eve's scale height is kind of absurd compared to Kerbin or Duna. Coupled with that is the fact that you hit it going so fast, and the fact that the atmosphere itself is actually pretty hot as well. Aerobraking at Eve is a dangerous prospect as a result. It's generally best to capture with a burn, and slow your orbit down over multiple passes.

[Laie]

How fast were you going?

Didn't check. I was on a 110km orbit before, and made a 40m/s deorbit burn. I don't think it gets much gentler than that.

EDIT, replayed it using hyperedit: dropping out of timewarp at 90km, 3220m/s. Accelerating to 3230m/s @85km over the course of 40 seconds. In the same time, a full orange tank goes from 290K to 1040K (skin) / 290 -> 320 (internal temp).

In my original attempt the vessel was almost empty: I assumed this would make for an easier entry. As it seems, you want every tank full to the brim to increase thermal mass.

Edited July 9, 2015 by Laie

[samstarman5]

Eve's scale height is kind of absurd compared to Kerbin or Duna. Coupled with that is the fact that you hit it going so fast, and the fact that the atmosphere itself is actually pretty hot as well. Aerobraking at Eve is a dangerous prospect as a result. It's generally best to capture with a burn, and slow your orbit down over multiple passes.

Would hardly call it absurd when Eve's gravity is higher than Kerbin's, which allows for a thicker and denser atmosphere.

[Hcube]

Would hardly call it absurd when Eve's gravity is higher than Kerbin's, which allows for a thicker and denser atmosphere.

But it's still disproportionally exagerated (1 or 2 "g"s ? no idea)

[Starwhip]

According to the (possibly outdated) wiki, Eve has a surface gravity of 1.7 g's, and a sea-level pressure of five atmospheres.

[falloutaddict]

Didn't check. I was on a 110km orbit before, and made a 40m/s deorbit burn. I don't think it gets much gentler than that.

IIRC when I landed a probe at Eve i was going 4km/s + and hit the atmo at 85k and my probe went poof. Try slowing down to around 3km/s or less and come in really shallow. I managed to land my probe without a heatshield

- - - Updated - - -

Edit: I should note that I had to burn the rest of my fuel to slow down sufficiently. This was sure a learning experience.

[SkyRender]

Would hardly call it absurd when Eve's gravity is higher than Kerbin's, which allows for a thicker and denser atmosphere.

That's not actually how atmospheric formation works. The primary determinants of atmospheric formation appear to be gravity, magnetic field, gas density, and systems (organic or otherwise) that continue to distribute and maintain the atmospheric elements as they bleed off into space and/or settle back down onto/into the surface. The distribution systems count for more than anything, as demonstrated by Venus in the real solar system: lower gravity than Earth, much thicker atmosphere. Even with the heavier elements comprising Venus' atmosphere, the whole mess of it would eventually settle back to the surface (and bleed off into space for the lighter elements) without the heavy vulcanism on the surface constantly stirring up the mix. The main reason why Mars' atmosphere is thinning so fast is because it lacks any sort of system to keep the atmosphere in place and replenished: no vulcanism, no magnetic field. Gravity not being "strong enough" to hold it in place is not the cause, or Titan wouldn't have any atmosphere to speak of.

[Geschosskopf]

Would hardly call it absurd when Eve's gravity is higher than Kerbin's, which allows for a thicker and denser atmosphere.

What is absurd is that the atmospheres of other planets don't fade out gradually like Kerbin's, but end rather abruptly (I'm told they really do taper down to zero but the slope is nearly vertical). Only Kerbin has a real "atmosphere" that behaves like a wad of gas bounded only by gravity. Observe how the upper 1/3 to 1/2 of Kerbin's atmosphere is so thin you don't get any flames at all until at or below 40km. The other planets, in contrast, effectively have oceans, not atmospheres, due to their lack of wide zones of low-density gas. The result of this is that you ship slams into much denser air than should be there even when just barely dipping into the top of the atmosphere. Another way to look at it is that the arbitrary heights of the atmospheres decapitate them.

So, that's broken. Until the other planets get fixed, you have several choices:

* Leave reentry heat at 100% and have dangerous reentry from LKO, accepting that interplanetary aerocaptures (and even aerobraking) are well-nigh impossible. Then either do the well-nigh impossible to make them happen or just bring enough fuel to do without.

* Lower reentry heat to about 20%, which makes "traditional" aerocapture at Jool and Eve possible but still rather challenging, but also makes any less-energetic contact with atmospheres a walk in the park.

* Turn off reentry heating entirely and play like it was still 0.9.

Eve is probably the worst-case scenario because at Jool, you can (with some effort and forethought) gravity brake off one of the big moons to capture without touching Jool's atmosphere and will little extra fuel burned. But no big moon at Eve so if you choose to leave heat set high, you either have to brake with engines or build some monstrous heat shield.

[Laie]

Orbital velocity at 100km is 3200m/s, just for scale.

On my last test, I extended radiators. They're totally useless, of course, but they remained firmly attached to the vessel when full orange tanks went BOOM from the heat. I'm pretty certain that the vessel doesn't heat up from friction, but just because.

@Sal_Vager, ere you ask: my thermal settings data read 1, 20, 6, 0.25, 1 -- just as they should be.

[Wjolcz]

Woah, I better not visit my probe I landed there in 1.0.2. Probably will boil and explode as soon as it loads.

[Finndibaenn]

I never landed on Eve yet, but maybe you could have kept your periapsis higher ? like 60 or even 70 km to allow deceleration to occcur ?

[Violent Jeb]

What is absurd is that the atmospheres of other planets don't fade out gradually like Kerbin's, but end rather abruptly (I'm told they really do taper down to zero but the slope is nearly vertical). Only Kerbin has a real "atmosphere" that behaves like a wad of gas bounded only by gravity. Observe how the upper 1/3 to 1/2 of Kerbin's atmosphere is so thin you don't get any flames at all until at or below 40km.

Well this is simply wrong.

I get flames at 55km orbit from a simple mun return, so if you're comparing an ultra slow controlled flight where you don't see kerbin flames until 40km, then it is no wonder you think Eve or jool is extreme.

With that in mind, the real life equivalent (since the game tends to stay with current-ish tech) is a simple atmosphere skip, or double dip re-entry. Ships IRL don't handle the increase in the total absorbed heat well. A legitimate manned aerocapture has never been done, nor is it standard procedure. Therefore even Mun landings should "realistically" call for a braking burn, to withstand the atmosphere. I would expect to bring "slow down staging" to enter Jool or Eve atmosphere.

As I understand it, the total amount of heat absorbed is higher when performing aerocapture, vs. higher maxiumum temperatures incurred with steeper re-entry.

This means that the Kerbol system atmosphere is probably more forgiving than our atmosphere (capped atmospheric height non withstanding), given that our ships can handle aerocapture within reliable parameters (that or they have stronger building materials). If they're able handle aerobrake maneuvers than it should be at the cost of multiple passes/time, as it is now.

If these atmospheric bodies with the strongest forces (Jool and Eve) had their atmospheres extended by around 100km, and their curves adjusted to be slightly more forgiving, this could fix the problem, no? I don't think that the atmosphere of Kerbin needs much tweaking, i find it to offer a fantastic challenge. Coming in with a 51 - 53km PE is the magic number IMO.

Edited July 10, 2015 by Violent Jeb

[juanml82]

Ok, I've yet to try interplanetary aerocapture in 1.04, but could the complaining about ships without heatshields being unable to aerocapture stop?

Want to aerocapture? Use heat shields. If that doesn't work, then complain.

[Skylid]

I never landed on Eve yet, but maybe you could have kept your periapsis higher ? like 60 or even 70 km to allow deceleration to occcur ?

Actually, on Eve, that periapsis would probably kill you instantly. if I remember correctly, Eve atmosphere extends well above 115Km, so an periapsis of around 90 or so should put you in the hotseat. Just hopefully not to hot...

[falloutaddict]

Ok, I've yet to try interplanetary aerocapture in 1.04, but could the complaining about ships without heatshields being unable to aerocapture stop?

Want to aerocapture? Use heat shields. If that doesn't work, then complain.

Agreed, but at the same time, if you hit that atmo at 4km/s or more, heatshield or not, you are pretty much toast. One of the reasons aerocapturing at jool is not a good idea.

[Laie]

if I remember correctly, Eve atmosphere extends well above 115Km,

You're mistaken. It used to be 100km, currently it's 90. I had put my periapsis to 80. As you can see from the stats in the picture, the atmosphere has quite an impact even that high up.

Now, actual orbital velocity didn't change by much and going from 100/80km to 80/50km would be about ~60m/s, but I also went in at an angle, creating more drag and some lift. So the actual delta-V I received must have been more. Certainly 100m/s, maybe (maybe!) even 200. Which was enough to deep-fry my vessel.

On the one hand, 200m/s for a 400t vessel are quite a lot. On the other, compare that to how much braking you can do at Kerbin before you even see the first hint of heat.

But what really bugs me is that the part heat data suggests that the atmosphere itself is quite hot: I received most of the heat through convection.

[Anglave]

If these atmospheric bodies with the strongest forces (Jool and Eve) had their atmospheres extended by around 100km, and their curves adjusted to be slightly more forgiving, this could fix the problem, no? I don't think that the atmosphere of Kerbin needs much tweaking, i find it to offer a fantastic challenge.

Yes, that's what needs to happen. I don't think anyone is suggesting changing Kerbin's atmo.

The problem with the current system is that there is no way to aerobrake at Jool from typical interplanetary transfer speeds. If your periapsis is 200,010m you get no braking whatsoever because you're outside the artificially decapitated atmosphere. If it's 199,990m you burn up instantly. Not only is this not realistic, it essentially eliminates a mainstay of Joolian missions in KSP.

Much the same is true at Eve. With shields and airbrakes and a very high periapsis, you might survive, but you probably won't capture. A lower PE at interplanetary speeds is death. There is no practical option for slowing down at Eve except to pack along the extra fuel and burn your engines to make orbit. Even thereafter, aeorbraking to shrink your orbit and eventually slow to a landing requires many many passes through upper atmosphere.

The "many passes" problem is relatively realistic, but it's tedious as hell to perform in the game. I'm not keen to spend hours watching my ship travel in a circle with no need for control input, and I can't time warp effectively because I keep dipping through atmo.

I'm not bothered if it requires a heat shield, but for game play reasons I feel it should be practical for typical craft to aerocapture from a Hohmann transfer at bodies with dense atmospheres. Currently in stock at 100% heating, it is not.

1) The atmospheres don't continue to get thinner and thinner out into space, they terminate at an arbitrary altitude, which means you can't aim "high enough" to not burn up almost instantly. I've heard it claimed that there is actually a curve to the density as it approaches the decapitation altitude, but if that's the case the curve is ridiculously sharp.

2) The heating math doesn't seem to be scaling correctly at non-Kerbin planets. Something about the way it scales off velocity or density or altitude is broken. Example: once you've slowed down enough at Eve that you can make a braking pass through the very highest part of the atmosphere, you make as deep a pass as you dare and nearly fry everything to a crisp, only to find that your velocity is almost unchanged.

If the atmosphere isn't dense enough to slow you down meaningfully, it really shouldn't be cooking your craft in seconds. Something about the "turbulent flow" heating wasn't balanced for non-Kerbin atmospheres or interplanetary transfer speeds.

- - - Updated - - -

But what really bugs me is that the part heat data suggests that the atmosphere itself is quite hot: I received most of the heat through convection.

I suspect that this is the new "turbulent flow" feature, which kicks in if you're going "too fast, too low". I'd bet that speeds above SoI escape speeds are "too fast" as soon as you touch the upper bound of Eve or Jool's atmosphere (meaning the highest possible atmospheric contact is "too low" and turns on the new Turbulent Flow heating feature.

Because obviously my rover is fine sitting on the surface not melting or anything. So the atmo can't be THAT hot, especially not at 80km.

Edited July 10, 2015 by Anglave

[Laie]

If the atmosphere isn't dense enough to slow you down meaningfully, it really shouldn't be cooking your craft in seconds. Something about the "turbulent flow" heating wasn't balanced for non-Kerbin atmospheres or interplanetary transfer speeds.

This. That's what I'm talking about, or trying to.

So the atmo can't be THAT hot, especially not at 80km.

IIRC earth's atmosphere gets cold and colder up to ~50km and then becomes warmer and eventually quite hot. However, the truly "hot" parts are usually considered space (a few hundred km) and the atmosphere is extremely thin. So yeah, the atmosphere that matters for our purposes is indeed quite cold.

Edited July 10, 2015 by Laie

[jkool702]

are there any mods which re-tool atmospheres such that they actually taper off into nothingness instead of (in the case of Jool and to a lesser extent Eve) having substantial atmosphere just below the limit of space?

[Anglave]

IIRC earth's atmosphere gets cold and colder up to ~50km and then becomes warmer and eventually quite hot. However, the truly "hot" parts are usually considered space (a few hundred km) and the atmosphere is extremely thin. The occasional particle you encounter will be going quite fast however.

Fair enough, I should have said the atmosphere won't transfer much heat, rather than saying it's not hot. :-P

Edited July 10, 2015 by Anglave

[Signo]

Do not dive nose first, nose cones are not as resistant as Mammoth engines. Mammoths are a lot better than heatshields: they do not ablate and they do not overheat as fast as the heatshields. If you experiment a little bit with that you will notice that in a comparable re entry situation a 3.75m heatshield will show a skin temperature in the range of the 2000° and counting while the mammoth will stay close to 750°/1000° all the way down.

Extendable radiators will break up while descending at an average altitude between 45000 and 35000m if not extremely carefully shielded. They are however useless due to the fact that, as you already noticed, you'll be dead long before experiencing a normal overheating.

A polar insertion will save you a few drag due to the less dense atmosphere.

The best available transfer window will get you to the Eve rendez-vous at the "affordable" speed of around 4000m/s.

I can not see any airbrake on your ship, they are extremely useful there.

The plasma flux is not just a cosmetic effect anymore (not saying it works as intended, just that it works somehow): fairings might help in this case to shape an aerodynamic deflector.

With this few "tricks" I usually manage to dig deep to 70000m for my aerocapture followed by a few adjustment aerobrakings.

A free fall descent is almost impossible now: usually I constantly burn to control my descent speed - we could say that a "Eve rocks" lvl1 it is now less feasible than a Jeb level: better to go for a completely powered descent, no legs and no chutes or just a few of them to save some fuel.

For a safe landing I usually try to pass the atmospheric 90k border at less than 2800m/s, less than 2100m/s @45k, from here till 11k you need to slow down 1100m/s at least - chutes opening altitudes by default are around 13000m for drogues and around 11000m for commons.

So, yes, I agree that the game need some tweaking but it is feasible even if not particularly fun.

[Anglave]

Signo, I appreciate your feedback, but I have some questions

Do not dive nose first, nose cones are not as resistant as Mammoth engines. Mammoths are a lot better than heatshields: they do not ablate and they do not overheat as fast as the heatshields. If you experiment a little bit with that you will notice that in a comparable re entry situation a 3.75m heatshield will show a skin temperature in the range of the 2000° and counting while the mammoth will stay close to 750°/1000° all the way down.

In my experience at Eve I was not diving nose first, but my attitude generally didn't matter much. Either I burned up completely or not. However, I have to ask, what reasonable interplanetary mission is bringing Mammoths? That's one massive heat shield! Maybe if you're planning an Eve ascent, I guess?

A polar insertion will save you a few drag due to the less dense atmosphere.

And cost you a boatload of ÃŽâ€v in plane change, unless your orbit is polar already.

I can not see any airbrake on your ship, they are extremely useful there.

I'm surprised. Since the problem is overheating, how do the airbrakes help? Or are you saying they generate more drag for you when you've already slowed enough to make an (otherwise frustratingly ineffectual) braking pass in the uppermost atmosphere? That may be, but what's your overall mission ÃŽâ€v cost for bringing otherwise useless airbrakes? Does it outweigh just bringing the fuel to slow down on engines?

A free fall descent is almost impossible now: usually I constantly burn to control my descent speed - better to go for a completely powered descent, no legs and no chutes or just a few of them to save some fuel.

That's odd. The last thing I did land at Eve (in 1.0.4), I slowed down to orbital capture on engines, aerobraked through about 15 passes in order to slow enough to eventually dive into atmosphere for a landing, lost a lot of speed and almost died from heat coming in, but after that the atmosphere slowed me down dramatically, and my whole landing was unpowered. Losing the speed was the hard part, once you've done that, falling through the atmosphere to the ground is trivial.

I popped chutes and floated down nice and gentle.

For a safe landing I usually try to pass the atmospheric 90k border at less than 2800m/s, less than 2100m/s @45k, from here till 11k you need to slow down 1100m/s at least - chutes opening altitudes by default are around 13000m for drogues and around 11000m for commons.

Wait, if you're doing 2800m/s at 90k altitude, you are not talking about entering the atmo at interplanetary transfer speed (which you point out is ~4km/s). Which is it? Is this braking to land after several previous braking passes? If so, talking about your speed at 90km doesn't make much sense?

[Laie]

I'm surprised. Since the problem is overheating, how do the airbrakes help?

I've not tried it myself, but read a lot about how airbrakes make reentry easy. This only makes sense if the amount of heat you receive is not related to the acceleration you experience... which can be entirely true in the KSP universe.