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MoridinUK

RE-entry issue or am I simply hitting mountains?

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MoridinUK    10

Hi all,

 

I've returned to the game and so am a 1.2 newbie, most of my experience was back in 0.9 so I'm still very much struggling with an atmosphere! 

I just started a new career and I've just killed Jeb.. No option to revert!  This was my first orbital flight.  I burned for reentry to bring jeb down somewhere in the badlands to complete a science mission.  

It seemed to me that re-entry was hotter for a lot longer than my previous sub orbital flight.  I lost a mystery goo experiment to heat, but I was still flashing the red flames (not even the white ones) when Jebs pod smashed into the badlands at high velocity...

So far I've assumed this is because I was much too shallow?  That because of that I had heating for longer and less breaking?

Or is it because I actually accidentally landed him on a mountain and he needed that extra few thousands of meters? 

This means I WILL need to plan for a serious re-entry burn?  I can't simply let the atmosphere do that work for me?

I'm asking because having lost Jeb I don't want to risk losing Valentina too... :wink:

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Pand5461    92

Maybe a combination of steep reentry, high ground at landing and high mass of reentry vehicle?

From a 80km orbit, I have no problems landing a Mk1 capsule with periapsis at 20km. The capsule is light and heat-resistant, so it does not burn even without a heatshield and decelerates to terminal velocity well above the ground.

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bigcalm    91

Er.

> Jebs pod smashed into the badlands at high velocity...

You remembered parachutes, right?

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MoridinUK    10

It was never safe to use the parachutes (which I didn't forget!!), it never got cool enough... 

Mk1, with a service bay with a Kerbal engineer thing in it.

I'm really loathed to 'try again' to figure it out and risk another kerbal... :(

opps just landed on the SPH... which doesn't count for the science around ksc missions... gulp..

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Spricigo    437
24 minutes ago, MoridinUK said:

It was never safe to use the parachutes (which I didn't forget!!), it never got cool enough... 
 

You may now forget, since there is an option "deploy when safe" enabled by default.

 

Quote


Mk1, with a service bay with a Kerbal engineer thing in it.

 

it reentered point end first or blunt end first? You want blunt end first, which is draggier and reduce your velocity much more, opening the service bay to make it act like a improvised airbrake.

 

Quote

I'm really loathed to 'try again' to figure it out and risk another kerbal... :(

opps just landed on the SPH... which doesn't count for the science around ksc missions... gulp..

Just do a few flights in sandbox mode (or unkerbaled fligths)  to get used with the new aerodynamics (and some other thing you may need to relearn). It's like ride a bicycle: everyone fail while learning, it may hurt when you fail and when you learn to do it correct you think  "how clumsy I was". :cool:

 

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MoridinUK    10

I re-entered blunt end first, but got into a spin when the engine I didn't throw off blew up!  (I probably shouldn't have bothered to try to save the LT-30 sigh...) but I did regain control and point blunt end forwards.. :(

Maybe the mass was just too much but I'd have thought not, I'll retry in sandbox to see what will happens... :)

Also I can't get an efficient climb to orbit, I'm blowing like 4.1k dv... though I'm only a little way into the tech tree...

1 hour ago, Pand5461 said:

Maybe a combination of steep reentry, high ground at landing and high mass of reentry vehicle?

From a 80km orbit, I have no problems landing a Mk1 capsule with periapsis at 20km. The capsule is light and heat-resistant, so it does not burn even without a heatshield and decelerates to terminal velocity well above the ground.

Now I think about this more, it couldn't have been too shallow?  I didn't have a Periapsis!  But I did hold on to some fuel tanks and an lt-30 as it still had a little dv in it... could that have added way too much weight?

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Pand5461    92
3 minutes ago, MoridinUK said:

Now I think about this more, it couldn't have been too shallow?  I didn't have a Periapsis!  But I did hold on to some fuel tanks and an lt-30 as it still had a little dv in it... could that have added way too much weight?

Probably, yes, a heavy engine gave it too much weight to decelerate in time. You should've burned that dv somewhere around 20km and relieve poor kerbonaut of that burden ASAP.

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MoridinUK    10

Ahh,, poor Jeb...  I was not happy I'd MIA'd him... but I have an explanation.  I'm not sure it hadn't blown off by 20k though...  lol

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Urses    537

To sgallow is mostly problematic for spaceplanes at ascend. They are to long in dense atmo and build up way to much on heat. On reentry and woth pod mk-1 feom LKO is a periapsis between 20-25km is mostly a sure way and like mentioned above you dont need a heat shield for this. For becoming a feeling for the landing procedure it is best to go first in near Circular orbit at 70-80 km do a reentry burn to drop peri at 20-25km stage all  things and let it plumb in. As i understand your description yoz was to heavy and to steep. If you do all right you habe mostly the safe hight for parachutes to deploy at around 12 to 10 km. And this is way safe to land at mountains too.

The pod is aerodibamicaly stable on its own to go blunt first if he is alone. And as mentoned above you can missuse the strorage doors as aerobreacks. But if you do so ise jeatshield too because the container had lower  heatabsorption. And if you a little too imconcentrated you get a dart through atmosphere.

As you described your ascend you has the same atmospheric strugles. You have to begin at start with graviturn and not ad before at around 10km. 

Hope some tipps help you.

Funny Kabooms 

Urses 

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Starman4308    701
Posted (edited)
1 hour ago, MoridinUK said:

Now I think about this more, it couldn't have been too shallow?  I didn't have a Periapsis!  But I did hold on to some fuel tanks and an lt-30 as it still had a little dv in it... could that have added way too much weight?

That isn't too shallow: it's way too steep. You want to come in with a periapsis of maybe 20-30 km. If you're coming in with a periapsis below the surface, that isn't reentry, that's a suicidal death plunge.

EDIT: Alshain suggests 10-20 km. Seeing as how he almost certainly has more recent experience with stock than I do, I'd do what he says.

Edited by Starman4308

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WanderingKid    199

Sounds like you came in waaay too steep, and then to boot you tagged a mountain on the way in losing another 2k worth of good atmo for final slowdown.

You pretty much HAVE to skim now in the 20-30km range.  Highly aggressive landing patterns are detrimental to your Kerbal's health if you're not running Drogue chutes.

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Alshain    4728
Posted (edited)

I usually set Pe between 10 and 20km.  20-30 seems a bit high to me (not overly though).  If you skim too high (45+ km) you will spend too much time in the heat and burn up.  Heat is cumulative so it's better to face fiery hell for short time than a campfire for a long time.  Basically, don't go too low, but also don't go too high.

Edited by Alshain

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bewing    1274

Reentries are indeed trickier now. Some parts have very low drag and will not slow you down. Some have very high drag and will slow you down easily. You can use aerodynamic surfaces that change how much drag they produce in flight. Add some mass to some vessels and you won't slow down enough to ever deploy a parachute. Retroburn until your surface speed is 1500 m/s and you can reenter anything with no heating problems at all, and you will have plenty of time to stop when you get low. And yes, it's often important to avoid the mountains. It's tricky now -- there are lots of variables. So yes, it would be very wise to get a feel for the new setup in sandbox mode.

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GoSlash27    3048

Going along with what @Pand5461 said. Plus a reentry vehicle that's not aerodynamically stable in a high- drag orientation.

Best,
-Slashy

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Streetwind    3817

@MoridinUK - this thread is full of good advice, but I still wonder how you managed to slam what's essentially a pod plus an empty service bay into the ground, blunt end first, while still showing red flames. You need to be approaching half orbital velocity if memory serves in order to get red flames. 400-500m/s I'd consider realistic with a super steep trajectory, but a thousand? That doesn't sound right. I could be wrong, of course, since I didn't see your descent, but it just doesn't sound right. The service bay isn't nearly heavy enough to ruin your ballistic coefficient that much, especially not with barely anything in it.

Perhaps you will be able to get a proper reentry with the advice you've gotten here. With that kind of craft, you should be able to safely open your chutes at at least 4 kilometers up, even without the silly "open service bay doors for drag" trick. Aerodynamic effects should be completely gone by that point too, even the white ones. If you can pull off something similar to that, then everything is fine and I'm just interpretating your words wrong.

But if your craft still goes way faster than that, something isn't right with the drag on the way down. Check the following:

1.) Make sure nothing you put into your service bay clips through the bottom floor too much. Parts have a tendency to attach partially clipped into the floor of service bays. You don't want the part to sink in so much that its collider (which you can't see) extends below that of the service bay, making that part become the primary drag inducer on your way down. And that part is definitely gonna induce less drag than the much larger service bay.

2.) Did you do a straight reinstall, or did you upgrade KSP from an older version? Sometimes, especially in older days, KSP just doesn't like upgrading, and something with the physics might get screwy. If you updated, try backing up your save (if it's even worth it if you are so early in the playthrough) and installing the game from scratch. If it's already a fresh installation, nevertheless delete physics.cfg and partdatabase.cfg in your KSP root directory. They will be recreated the next time you start the game.

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MoridinUK    10

@Streetwind  Me?  me?? But I wasn't piloting! Jeb was! :wink:

I really think I messed up because I held on to the lt-45 and fuel tanks for too long, in fact it all messed up, because I came in bottom  first but I never detached the engine till way too late, I was worried that it wouldn't actually go anywhere!  So I turned and then separated and then tried to get back bottom first, but I think this was one of several reasons why I can in way too fast!  That and the way too steep entry.

The PE at 10 to 20 km, how much further will my craft carry on east ward in that last 20 k?  I'm trying to hit a particular destination for a contract!  I can't use trajectories until I have patched conics right IIRC?

I had/have no idea about clipping, I'm actually clueless on how to equip my rockets.  I can build them, but adding instruments, well, I notice that even a temp sensor on the back of a command module on top of a 400 fuel tank an lv-909, and 2 400 fuel tanks an lt-45 and then 4 thumpers is still unbalanced enough to make it tip northwards (or is it southwards lol) during my gravity turn...

I have no idea how I'm to get any kind of comms sat into orbit without fairings... and they seem to want so much research and then unlock tiny ones! 

It was a straight install I think!  I could back up the mods and the saves and re do it, later today to try but it may be the clipping issue.  I should really put a heatshield on it!

As for retroburning, until I can master an efficient assent, I have so little left this sounds like dreaming...

9 hours ago, bewing said:

Reentries are indeed trickier now. Some parts have very low drag and will not slow you down. Some have very high drag and will slow you down easily. You can use aerodynamic surfaces that change how much drag they produce in flight. Add some mass to some vessels and you won't slow down enough to ever deploy a parachute. Retroburn until your surface speed is 1500 m/s and you can reenter anything with no heating problems at all, and you will have plenty of time to stop when you get low. And yes, it's often important to avoid the mountains. It's tricky now -- there are lots of variables. So yes, it would be very wise to get a feel for the new setup in sandbox mode.

Retroburn to this speed in orbit or once partway back into the atmosphere?

If in orbit wont that bring my PE down along way?

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bewing    1274
11 minutes ago, MoridinUK said:

Retroburn to this speed in orbit or once partway back into the atmosphere?

If in orbit wont that bring my PE down along way?

If you really need to avoid heat during a particular reentry, then generally a massive retroburn of this type works best when partially into the atmosphere (above 50km). Otherwise you end up picking up a lot of speed while you fall, afterward. And if you are going to slow down this much by burning fuel, then you really don't need to worry about what your Pe is anymore. You are only going to make it another 100km before you are on the ground, if you slow down this fast.

 

However, in general, contracts that ask you to take readings when you are low or on the ground are designed to be filled by airplanes. They exist to encourage you to build airplanes. I know there are players who attempt to fill them with this sort of ICBM ballistic technique, but that's really hard to get right.

 

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MoridinUK    10
2 minutes ago, bewing said:

However, in general, contracts that ask you to take readings when you are low or on the ground are designed to be filled by airplanes. They exist to encourage you to build airplanes. I know there are players who attempt to fill them with this sort of ICBM ballistic technique, but that's really hard to get right.

 

The target spot is halfway round the world which is why I thought an icbm approach 'may' work.  I have never managed to build a single working plane!  So I haven't even looked at unlocking the tech for it as I'm science poor at the moment...

hmmm

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Pand5461    92

Hitting a particular area from orbit is quite tricky, and even more so with unpowered landing and barely any control surface. I'd suggest building proper planes for "below something" and surface contracts and suborbital hops for "above something" contracts in the early career.

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MoridinUK    10

In this case it only has to be a particular biome!  lol

 

 

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Das_Sheep    7
2 hours ago, Pand5461 said:

Hitting a particular area from orbit is quite tricky, and even more so with unpowered landing and barely any control surface. I'd suggest building proper planes for "below something" and surface contracts and suborbital hops for "above something" contracts in the early career.

I'm a fan of having the active contract (I upgrade to get a lot of contacts early as it's cheap) and eventually I'll probably drop a pod through it due to half attempt / half luck.

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