Easily manage heat load without air brakes

[RocketBlam]

So for the umpteenth time I launched a spaceplane and forgot airbrakes. I tried to re-enter once, and actually managed to keep most of the craft intact (at least the lifting and surviving parts). Then, since I had forgotten to turn off overheat indicators, the game crashed.

On my next attempt, I decided to try something. Rather than just point prograde the whole way down, I turned on SAS and angled up about 10 degrees above prograde. The effect was, frankly, shocking. I managed to fully re-enter the atmosphere and enter flight mode with no damage, and the reduction in heat buildup was immediately obvious.

First, this is what it looks like while just flying prograde until the craft slows down enough. Notice how much of the heat effects there are. What you can't see in this image is parts of my craft exploding and filling me with angst.

Ah, here are the explosions... 20,000 altitude and 1500 m/s.

Now, this series shows the various altitudes on the second pass, when I angled up 10 degrees on re-entry. You can see what altitude I am at.

35,000 altitude, re-entry heat begins. 2086 m/s.

33,500, angled up at about 10 degrees. 1950 m/s.

I've come up about 1,000 feet, and heat effects stop altogether. 1730 m/s.

When you start to pick up heat, you angle up a little. If you've gotten rid of the heat, angle back down.

This actually works a lot better than airbrakes. Of course, this assumes your craft is moderately controllable at high speeds and can manage that kind of angle of attack, but if it's not, it's got other issues.

Anyway, I hadn't seen this mentioned. Hope it helps. The first time I forgot airbrakes, before I did this, I just jumped out of the remains of my spaceplane and jetpacked to the ground, since that plane was impossible to re-enter without destroying itself.

[viktor19]

I think this is a way any spaceplane should reenter atmosphere. Anyways, congratulations for figuring it out by yourself!

[Zzabur]

In my opinion, this is a matter of entry speed. I managed to build a few spaceplanes in 1.0.2 that can bring about 10 kerbins to orbit and refuel my space shuttles or stations around Kerbin.

Before re entering, i burn retrograde like any other ships, actually, i try to brake a lot using space engines (got no RAPIER atm) between 70km and 40km. Just before 40km, i turn the ship prograde and then i can adjust pitch.

The best way to brake is, as you said, a pitch a bit higher than prograde, i would say about 10-15° (big planes need a bit more pitch, aound 15° i found), you'll also move the landing spot a bit further. But i also could use some negative pitch ! You lose altitude and speed faster, generating more heat, but if you have braked enough before 40km, the plane can still survive re entry.

So, using this 70-40km retro burn, i can adjust my pitch to land exactly where i want, if i see that i will land before the KSC, i raise my pitch until +10°, if i am missing it and fall into the sea, then i lower my pitch to -10° (only if my speed is low enough, or i will burn the ship before ground).

In 1.0.2 career, i now only use SSTO to resupply because i don't lose much money as they can land at KSC in one piece.

[Mic_n]

Yup.

Think of it this way. Airbrakes work by creating drag - putting an aerodynamic surface against the oncoming flow of air. Your entire craft is an aerodynamic surface. You can create that same drag by just turning it a bit. Heck, in the upper atmosphere, point the damn thing straight up.

Actually, depending on how much control authority you have, that's a strategy you can run with the whole way through re-entry. Point it prograde, pull straight up, turn on SAS and just let it try to hold. As the atmosphere thickens up and the drag gets heavier, the craft will try to come nose first (assuming you've built it right, otherwise the tail end may try to come around.. still not necessarily a bad thing since you've generally got engines there and they can deal with that heat really nicely anyway).. But you're slowing down as much as possible as high as possible, which spreads that heat load out over a longer time rather than just having a giant burst it needs to dissipate all in a hurry.

That, and don't put your Pe down too low. Keep it up nice and high and just let it drop as you aerobrake in the upper atmosphere. If you're coming in from a high AP, it might take a couple of passes, but that gives you a chance to cool off in between.

I find around 40km is a nice height for a Pe.. good amount of braking and not too much heat buildup.. Once you've done it a few times you start to get the hang of predicting where you're going to land based on your craft, your starting AP, all that sort of thing.

Re the previous post: I don't mean to sound like an ass, but burning from 70-40km is astoundingly wasteful when you can just use all that atmosphere to aerobrake. Burning at that point means you're carrying fuel for it that you don't need, which means you're lugging that around the entire rest of your mission, which means you're increasing your fuel needs exponentially. Your craft should be basically dry when you come back in.. maybe a little there for emergencies, but that's about it. Instead of pointing your engines forward from 70-40km, try pointing your belly there, and use all those lifting surfaces as a whopping great airbrake in themselves. You might not notice it much, but there's still plenty of air up there to slow you down.

Edited June 7, 2015 by Mic_n

[rudi1291]

I have no airbrakes in career yet, so this is the only way to do it. Except i´m doing it at ~40 degrees until 20k because at 10 degrees it will still lose its front winglets... It helps to slow down the craft a lot

[Mic_n]

losing winglets? my spaceplane lifter doesn't even lose the solar panels on the nose during re-entry! You guys are coming in waaayyyy too hot.

[theend3r]

...I managed to build a few spaceplanes in 1.0.2 that can bring about 10 kerbins to orbit...

Those must be some huge spaceplanes

[problemecium]

Yes, I find that A: tilting the plane / rocket increases drag in the upper atmosphere, so when you hit the thick stuff you're going a lot slower and thus not heating as much, and B: it helps to distribute the heat "load" among several parts, i.e. a rocket flying sideways will have everything heated up a moderate amount, while on a rocket going forward or backward, one end gets all the heat and explodes.

[Levelord]

In b4 elitists start telling everyone that this method is 'unrealistic', overpowered and should be nerfed despite the fact that the space shuttle does this anyway.

[sal_vager]

In b4 elitists start telling everyone that this method is 'unrealistic', overpowered and should be nerfed despite the fact that the space shuttle does this anyway.

Heh yeah this is what the STS does, so it's very realistic, make as much drag as you can, come down as low as you safely can, get subsonic as soon as you can, and you'll not overheat anything like as much.

Most of the STS re-entry wasn't while on fire, it was after losing enough speed to stop settings fire to the air in front of the shuttle, but having to S-bend to avoid massively overshooting, as with no drive the shuttle came back with much more spare potential energy (altitude, speed) than it needed so as to ensure it would not fall short of the runway.

[Laie]

Yes, I find that A: tilting the plane / rocket increases drag in the upper atmosphere, so when you hit the thick stuff you're going a lot slower and thus not heating as much, and B: it helps to distribute the heat "load" among several parts

And don't forget that you're descending slower: I'm not doing planes that often and still struggle to come down near KSC; when I'm afraid of falling down on the wrong side of the mountains and pitch up even more, I sometimes begin to climb again. Losing speed all the time, of course.

Then again, I wonder how much of that heat is due to friction and how much is because the ambient temperature appears to be 1600K. Maybe it would be better to not idle around for too long.

[arq]

In b4 elitists start telling everyone that this method is 'unrealistic', overpowered and should be nerfed despite the fact that the space shuttle does this anyway.

Here I am! While 10deg sounds exceptionally reasonable to me (a little conservative, even), the OPness of 15G+ 'pancake' re-entries (entering at stall AoA, where you can drop from orbital speeds to maneuvering speed in 10 seconds) is a bit much. The reason that I call it OP is because it completely subverts any 'challenge' introduced by re-entry. Humans don't handle such stresses very well, airframes don't, and I can't imagine it's great for kerbals either.

Usually I play FAR which sorts this out (though I'm waiting to play stock 1.0.3 aerodynamics before I make the switch). It puts aerodynamic limits on wings (they'll shear off in this sort of re-entry) and implements hypersonic lift reduction and CoL changes that make holding a large AoA very difficult even if you wanted to. And DRE adds G-tolerances for kerbals.

That said, I'm not sure what I would want Squad to do about it. The hypersonic aerodynamic changes are difficult to understand as a beginner and greatly complicate design, so I don't much like that idea. Aerodynamic stresses are an option but are possibly sidestepped with moar struts, not to mention they could be annoying in other contexts. So it may just be that pancake re-entries are here to stay and for people to use if they so desire.

[regex]

Here I am! While 10deg sounds exceptionally reasonable to me (a little conservative, even), the OPness of 15G+ 'pancake' re-entries (entering at stall AoA, where you can drop from orbital speeds to maneuvering speed in 10 seconds) is a bit much.

The Space Shuttle eentered at a 40 degree angle and performed S-turns at a very high angle to increase drag as much as possible, reducing speed and heating at the same time. 10 degrees seems ... unreasonable to me.

Anyway, the key thing to remember is that we're talking 2.2km/s vs. @7km/s for reentry speed with atmospheric effects that are much more abrupt than on Earth. Unfortunately, you really can't compare the two or expect similar heating/drag/reentry profiles.

Edited June 8, 2015 by regex

[moogoob]

I love when KSP has realistic solutions to common problems.

[herbal space program]

On my most recent space plane, I did multiple aerobraking passes pitched up like this and ended up not even having any flames on re-entry. The trick is to hit the top of the atmosphere with maybe a 40km periapsis at a low angle (e.g. descending from a 150km apopapsis) and pitched up like 40 degrees above prograde. My periapsis kept increasing as I approached it from the lift I was generating. I was thus able to skim along the top of the atmosphere around 50 km until my speed was below 1400m/s, at which point I started to stall and had to pitch down more, but I never even reached the point where my ship was engulfed in flames, unlike it was going to orbit!

[zarakon]

The same idea can be applied to upper stages of rockets. You can bring back a capsule without a heat shield as long as you keep the upper stage engine+tank attached for the first part of re-entry. Just put your rocket sideways to get the most surface area facing forward at high altitude. When it starts being unable to hold that heading, put it into a tumble to keep the drag up and also spread the heat around to different ends of the rocket.

[KerikBalm]

In b4 elitists start telling everyone that this method is 'unrealistic', overpowered and should be nerfed despite the fact that the space shuttle does this anyway.

Reentering with a positive AoA to produce lift and more deceleration to higher in the atmosphere and decelerate more before reaching the lower atmosphere?

How non-obvious and unrealistic....

Seriously? this solution wasn't already obvious?

You think its unrealistic?

(10 degrees is a bit low.... but reentry heating is pretty low too, and thats due to the 1/10th scale... and a whole slew of changes would be needed to get it similar to realistic levels)

[Warzouz]

You could also induce a flat spin high as possible by transfering all fuel backwards. Then transfert the fuel forward (the hardest part is to click on those spining menu buttons) to regain control. You might not even see any heat effect.

My experience is that diving into atmo is better because the drag increases faster than the heat builds up. So you slow down faster than your ship could blow up.

Once, I did a reentry from Minmus (well just outside SOI, truthfully). I had a streamlined MK3 (non plane) return vehicle with heatshield and air brakes. I feared the heat effect. So I tried to skim the atmo to reduce speed before diving. I did 3 aerobraking lower and lower. The ship totally burnt up and exploded at 25km...

What I've learnt is it's not good to stay in upper atmosphere too long because your ship might not radiate heat faster than i built up as you don't slow enough. You must slow down faster so heat stops building up. Staying prograde/retrograde is quite dangerous, especially on streamlined ships.

That's why I prefer to pitch to the ground instead of pitching upward when trying to induce excessive drag to slow down.

Edited June 10, 2015 by Warzouz

[Chaos_Klaus]

Reentering with a positive AoA to produce lift and more deceleration to higher in the atmosphere and decelerate more before reaching the lower atmosphere?

How non-obvious and unrealistic....

Seriously? this solution wasn't already obvious?

You think its unrealistic?

(10 degrees is a bit low.... but reentry heating is pretty low too, and thats due to the 1/10th scale... and a whole slew of changes would be needed to get it similar to realistic levels)

While 10deg sounds exceptionally reasonable to me (a little conservative, even), the OPness of 15G+ 'pancake' re-entries (entering at stall AoA, where you can drop from orbital speeds to maneuvering speed in 10 seconds) is a bit much.

People ... do you even read the thread before you answer?

Of course it is not realistic to enter in a way that would rip apart your plane and kill your crew due to the g forces.

I was used to FAR in beta and when I went pancake on a reentry in 1.0.2 I went "Oh crap, I lost the plane". But then it took like 5 seconds of my plane wildly spinning around and suddenly I was subsonic. You can under no circumstances call that a realistic reentry.

But, yes. Just go ahead and call some random person stupid. All hail the internet.

[DaMichel]

In 1.0 you could come to almost full stop at 30km altitude if you pitched up 30 deg. Not sure if it still works though.

[Warzouz]

Yes, I event put my plane to a radial orientation, but air flow force is prograde. Still I can oscillate to create intermitent high drag. I prefer pitching downward, it's faster (denser atmo)

PS : nice plane though

[Captain Sierra]

So the OP has found the technical correct way to reenter a plane. Yes guys, this is how we're supposed to do it instead of leveraging those overpowered airbrakes . . . but hey, give us a tool and we will abuse.

[xtoro]

I stopped putting brakes on my space planes for Kerbin a while back, might be better for other planets though, like Duna. I also stopped landing just a capsule with heat shield and instead I land the entire last stage with no explosions. Set PE to 35km, point retro and land with chutes. I think reentry heat is a little weak to be honest.

[Rufledt]

I'm going to try that. So far i've been losing parts re-entering space planes but I haven't really spent time trying to figure out a solution, the planes have always just been a thing to mess with for me.

[KerikBalm]

People ... do you even read the thread before you answer?

Of course it is not realistic to enter in a way that would rip apart your plane and kill your crew due to the g forces.

I was used to FAR in beta and when I went pancake on a reentry in 1.0.2 I went "Oh crap, I lost the plane". But then it took like 5 seconds of my plane wildly spinning around and suddenly I was subsonic. You can under no circumstances call that a realistic reentry.

But, yes. Just go ahead and call some random person stupid. All hail the internet.

Do you even read the posts you quote?

Is there anywhere in my post where I talk about a reentry "that would rip apart your plane and kill your crew due to the g forces."

-No

I talk about keeping a positive AoA on re-entry rather than simply following prograde.

The other guy you quote talks about 10 degrees being reasonable, and how ridiculous "pancake" reentries are.

Nor did either of us call anyone stupid.