kerbin reentry help

[brontok28]

i was on mission after recover part in orbit around gilly, and i set the orbit to aerobraking mode (30-ish km Pe) at kerbin hopefully can reentry (my dv left 600m/s). but as soon as i approach the atmosphere around 60km (speed is around 4200 m/s), heat is ragingly destroyed my vessel. i've tried change the Pe a bit higher (40-ish km) but my Ap couldnt make circular orbit even after retroburn (and empty fuel). any suggestion how can i reentry? attaching bigger shield can overcome this? thanks

[maj.solo]

You are coming in hot. There is just so much aerobreaking can do in a single pass. You need more fuel. And you already know this I am sure.

Well you know more about KSP then I do if you been out there. But I am catching up to you guys. I came back to kerbin with an asteroid doing 3800m/s or more dont remember and with very little fuel left. My brain just like yours reasoned I need aerobreaking and I need to dip low into atmosphere. I when down to 32K even if I knew it be suicide. Sure things exploded and fell off but I came out with the center of ship intact and it had an engine on it and was flyable.

The ship managed to slow down enough to avoid kerbin escape. And I knew that if I aerobreaked higher up I would end up with the problem you are having that one does not slow down enough and will escape kerbin again.

How to overcome that? Well if you are at KSC and have not started yet you rebuild the ship for the mission. The challenge is if you already is in space.

1) Rebuild ship add fuel to aid in the breaking around kerbin.
2) Oversized heat shield sure will help
3) Ultra tricky is try use Mun .... no it is impossible to time it .... use a moon for gravity assist slowdown and then magically continue and hit kerbin atmosphere. I would not bother witht his one ... need to keep it simple.

Someone should make a table of typical lethal speeds at various altitudes for a typical ship. I was googling but didn't find any. One just have to wing it using memory of hundreds of earlier landings.

[AoD_lexandro]

As solo said, 4k m/s is just far far too fast for safe entry. For the actualy entry you want to be at 2200 ms or slower. If you faster than that, use aerobraking at 55Km (ish) altitude and skim the atmosphere in multiple passes till you lose enough V to come in properly.

[brontok28]

it turns out......

at frist, my ejection burn from eve is around 1200m/s so it added to my kerbin encounter speed. thats why im so fkn fast while reentry. after my second try, i managed to make ejection burn around 560 m/s, then my reentry speed is much much slower. phew... safe from burning my ass off. thanks 4 the responses anyway

[George Kerman]

Originally posted by maj.solo:

Someone should make a table of typical lethal speeds at various altitudes for a typical ship. I was googling but didn't find any. One just have to wing it using memory of hundreds of earlier landings.

Well it's probably too complex a topic for just a table. A simple example is, how 'bout the inclination. 3000m/s orbital speed east is quite different than 3000m/s west. Another thing is your ships profile, what part takes the heat? Is the heat shield covering everything (I remember in 1.1 even LKO re-entries became difficult for my models because the Science Jr. would be ever so slightly exposed and would explode (I mean the first LKOs when I didn't have the retro hold ability) )? Another thing, is the ship 100% stable to have a retro hold with zero deviations? In case of debris recovery, that's probably not the case (I mean, it's possible but you have a lot of claw alignment work to do). And it's very likely that the recovered part will take part of the heating depending on design.So now we go into the recovered part's tolerance which we don't know before we see it. So I'd still go with experience (with that specific design) over a general table.

[UFO]

Just tried something ugly that turned out to be feasible. 10 ton Munar lander, engine and landing gears hanging off the heat shield (2.5m just to cover up the lander can and assorted science gear on top of it) survived a 3100m/s atmospheric re-entry on Kerbin without losing any components at all. Even had two drop tanks hanging off the sides without exploding. Plenty of retro burn involved, I might add. Chalking this one up in the "Stupid things attempted while low on ablator" column...

[maj.solo]

Well just a rough table, I know there are a lot of angles and variables BUT since this is aerobraking table the trajectory must not hit the surface and that eliminates a lot of angles. And you can eliminate a lot of silly altitudes at low level in the atmosphere. Eliminates even more angles. And you can eliminate some very high PE values high in the atmosphere where aerobraking would be useless.
And you can eliminate slow speeds like 1500 and below which would not be called anything then a normal landing. And you can eliminated speeds above 6000 - 8000 m/s that might be suicidal whatever altitude you try.
You then get like a limited set of angles you can enter the atmosphere in. Like a window / box the craft can go through when trying aerobreaking.
And then one should be able to create a rough table as a guide for someone coming in and just winging it and help select the right PE value while still in space based on his speed. And the speed will change ofcourse and bla bla bla. And the effectiveness of the aero breaking is different depending on surface area and weight and so on ofcourse .... but a rough table for typical ships. Should be possible. Gravity of the body ofcourse change everything. But a rough table with basic numbers to start from and then the guy doing the aerobreaking can just check gravity of the planet and thickness of atmosphere and then check his speed and then guestimate how many percent deep into the atmosphere he should go. I just think it is doable. Maybe I do a table one day.

[George Kerman]

So I was testing Kerbin re-entries limit at altitudes of 35-40 km, which, as any experienced player knows, are the safest ( 70-35 entry works, as well as 80 000 - 35 km). Check out this endurance test:

https://www.twitch.tv/george_ardeleanu86/v/103534479

Disclaimer: Obviously, most designs are not just a heat shield with chutes like mine is.

Long story short, an entry with about 8500m /s orbital speed eastward is OK for this design and it will land in 2 tries. At almost 9000m / s the 1.25m shield gets destroyed. 100% re-entry heating settings (gave myself unlimited fuel because reasons). Obviously, I don't think this is a "safe" reentry speed but I was surprised that the shield doesn't get destroyed so I kept pushing it higher and higher. I'd be very interested in what such a table says.

Later edit: Now that I consider that, in real life, a real heat shield withstands more than the usual 7.7 km/s that is the usual velocity in LEO, it does make sense. Maybe in real life they have a procedure equivalent to a 70-60 orbit above Kerbin which is a very gentle entry after some orbits, idk.

[brontok28]

apart from the table, maybe this one sound useful?
https://alterbaron.github.io/ksp_aerocalc/

[maj.solo]

yeah I pinned those on my web browser I need to investigate.