Thread of the Month: Be Kind to your Kerbonauts - Reentry Technique

[Northstar1989]

I use this as my guide: http://en.wikipedia.org/wiki/G_force#Human_tolerance_of_g-force

Sitting upright and sustaining g's along the vertical axis (spine), an untrained human can withstand 4 or 5 g's. Trained and equipped with flight suits, 9 g's can be sustained.

But astronauts get the benefit of sitting in a "laying on your back" position so that the g forces are sustained along the z-axis, or "eyeballs in". This gives an untrained human tolerance of 10 g's for a minute or 20 g's for 10 seconds. I'm sure a trained astronaut could sustain more. Apollo 16 reentry from the Moon peaked at 7 g's.

Assuming Kerbals have similar tolerance, I'm okay with a re-entry that peaks at 20 g for less than 10 seconds. Most of my interplanetary re-entries are direct with a periapsis of 20km, and are well within these g limits.

A 30km periapsis is more gentle, but unfortunately I did have a Jool return end with a skip out of the atmosphere and out of Kerbin's SOI. The resulting recovery mission was annoying, so now all my returns are at 20km periapsis.

Indeed. Deadly Re-Entry definitely makes Kerbals far too fragile (more so than their real-life counterparts). That's one reason I don't use it.

All you need to do is place your astro(Kerbo)nauts in an "eyeballs in" position, and they can realistically sustain short (10 second) peaks of 20 G's.

Pulling that many G's with DRE would kill your Kerbals. It's simply not a realistic mod- it's another one of those mods that overdoes "realism", and actually makes the game less forgiving than real-life. Every game has them- mods by cynics who don't actually understand real-life: and DRE is just KSP's version.

Regards,

Northstar

[Zeroignite]

But isn't that what config files are for?

[Northstar1989]

But isn't that what config files are for?

If a mod that's supposed to add "realism" makes it so the default state of things is more unrealistic than without the mod (unmodded, at least Kerbals won't die under a few seconds at 15 g's), then the mod doesn't really do what it thinks it's doing- regardless of whether configs allow you to set things straight.

Regards,

Northstar

[Seret]

I just rocked into Kerbin's atmosphere near-vertically on the way back from the Mun last night. Jeb was loving it. No problem there then.

[John FX]

I set my pe to about 35-38Km. You enter, get to your Pe and start to rise but don`t have enough speed to get out of the atmosphere so you do a sort of double dip entry. You enter, go down to just under 35km then rise to nearly 40km then drop lower again and finally land. This extends your slowdown time considerably and reduces forces by the same. Often I have well under 5G and can enter from pretty much anywhere.

[Javster]

I prefer a direct trajectory downwards in all situations/

[Dwight_js]

it's another one of those mods that overdoes "realism", and actually makes the game less forgiving than real-life. Every game has them- mods by cynics who don't actually understand real-life: and DRE is just KSP's version.

lol - just slightly overly harsh.

Sounds like you've also not really had a good look at DRE, because it has a configuration GUI where you can adjust everything from heating to g force tolerance on the fly. So if the mod is running unrealistic numbers for you, it's your own fault.

[Guest]

The main problem with DRE is that it doesn't seem to model the G-force duration well, and that it doesn't care about how the Kerbals are oriented. Especially the latter issue makes the realistic G-force damage problematic. DRE seems to assume the G-force acts "down", because about 15G is what you can do in this position (though you still blackout if you hold 10 or so for too long).

[undercoveryankee]

Indeed. Deadly Re-Entry definitely makes Kerbals far too fragile (more so than their real-life counterparts). That's one reason I don't use it.

All you need to do is place your astro(Kerbo)nauts in an "eyeballs in" position, and they can realistically sustain short (10 second) peaks of 20 G's.

Pulling that many G's with DRE would kill your Kerbals. It's simply not a realistic mod- it's another one of those mods that overdoes "realism", and actually makes the game less forgiving than real-life. Every game has them- mods by cynics who don't actually understand real-life: and DRE is just KSP's version.

Regards,

Northstar

I assume that DRE doesn't try to calculate G tolerance based on orientation because nothing else requires part authors to define which direction the kerbals are facing inside a part. You can use the same part facing different directions on the rocket and imagine that the seats are internally set up differently, but the code would have no way to know what you were thinking.

So the g-tolerance code has to be a compromise: better than you would be able to do in a bad orientation, but not necessarily what you could take in the optimal orientation. I can think of a couple of considerations that I would take into account if I were designing DRE:

• Gameplay-relevant: Both success and failure should be possible at Kerbin-scale speeds and altitudes.
  
• Consistent with the stock interface: Squad put a red arc on the acceleration scale on the navball, and the actual behavior should be consistent with the instrument.
  

I think stock DRE is fairly good at meeting those goals. I definitely wouldn't call NathanKell a cynic.

[joethebeast22]

on returns to Kerbin, i always put my PE at 20,000 meters, the gradual decent heats up the pod alot, but it never gets to the red, it stays between the green and red, smack dab in the middle of the gray. then as soon as the fires go out from the speed, then i hit my chutes at about 600 m/s, thats usually more than enough time for my crafts to safely slow down and descend with no damage

[Avanti]

Hey guys, in my many missions to the Mun, i have learned that a periapis of 31.5 Km results in an all in one reentry that never exceeds 2 G's. going from interplanitary missions i tent to use 25Km which results in 4

G's.

- - - Updated - - -

Hey guys, in my many missions to the Mun, i have learned that a periapis of 31.5 Km results in an all in one reentry that never exceeds 2 G's. going from interplanitary missions i tent to use 25Km which results in 4 G's.

[Tex]

During my experiments, I find that a periapse of about 20-25km will result in G levels below 4 in most cases. With the 25km periapse, I've successfully returned from Minmus at ridiculous speeds and never even went halfway to the red on the G-meter. That's usually the return to Kerbin I follow nowadays.

[JethroReading]

According to my studies, kerbals are much more able than humans to withstand excessive G-forces.

Haha, just strap some Sepratrons to a capsule and test how high you can get! (p.s. What's the highest G force you've reached? I've had a probe returning from Minmus reach 45gs when the parachutes deployed)

[davidpsummers]

<blockquote>

You mean I shouldn't enter Kerbin's atmosphere near-vertically on the way back from Eeloo?

</blockquote>

I wonder if you could build something big enough, and enter it fast enough, that it punches right down to the ground without decelerating to terminal velocity?

[HellboundBait]

You mean I shouldn't enter Kerbin's atmosphere near-vertically on the way back from Eeloo?

I used to do that too but this was back in .15 when i still knew nothing so I would fire my engines straight down... I'd end up near escape velocity on a sub-orbital flight in an attempt to land near the KSC. Other than that I kept a small engine to burn constantly from re-entry to touch down to help parachutes if I want to be really careful with the ship... but this is KSP so I end up seeing if I can break speed records.

[Whackjob]

How do I handle reentry?

Embrace the flames

[Starwhip]

What is this thing you call "Re-Entry"? I don't need no Mun to get me up to those speeds!

Whackjob, that needs to be a T-Shirt.

[Whackjob]

If we're gonna do a T-Shirt, we might as well go with your re-entry on the way up theme.

[WinkAllKerb'']

moooooooorrrreeee strut in adequation with the boosters that been left away

[J4CKAL2014]

I've had no problems with straight returns from Minmus with a Kerbin periapsis of about 25km (and I'm using Deadly Reentry Continued, so exceeding about 12G isn't even viable!)

[IllicitMedic]

I always come in with my Periapsis at 25km and the capsules never see more then 2-4 G's. Super heating occurs around 36km and is finished and cooling at around 20km, chutes out at 10-15km.