1.2.1 reentry help!

[nascarlaser1]

Hi guys!

I've recently made the leap from 1.0 to 1.2.1, and with it comes new discoveries. Mostly being, g-forces...

I was doing a Kerbin reentry with a m1 cockpit and a generic Kerbal, when I discovered that my Kerbal can't survive the blunt force that comes with entering the atmosphere, and he was promptly knocked unconscious. Sadly, he did not wake up in time to deploy the parachutes, and we discovered what a Kerbal looks like when it goes splat against the north pole.

My question is, how can I fix my reentry so that my Kerbal can stay awake and/or if they do pass out wake up fast enough to survive??

[James Kerman]

It is now safe to stage parachutes before you hit the atmosphere - they will deploy when it's safe.

At what altitude did your kerbal pass out?

Edited November 21, 2016 by James Kerman

[nascarlaser1]

1 minute ago, James Kerman said:

It is now safe to stage parachutes before you hit the atmosphere - they will deploy when it's safe.

YAAAYY!! Thank you thank you thank you thank you!!!!!

This is a life saver!!!

[Ultimate Steve]

14 minutes ago, James Kerman said:

It is now safe to stage parachutes before you hit the atmosphere - they will deploy when it's safe.

Unfortunately, you can't change this in flight, so when you just did a huge mission, but your terminal velocity is just above the safe limit, and if you deployed it it would still be fine, it won't let you deploy the chute, resulting in Jeb dying.

Other than that, it's an excellent feature!

[nascarlaser1]

1 hour ago, Ultimate Steve said:

Unfortunately, you can't change this in flight, so when you just did a huge mission, but your terminal velocity is just above the safe limit, and if you deployed it it would still be fine, it won't let you deploy the chute, resulting in Jeb dying.

Other than that, it's an excellent feature!

what if I set it before I come into the atmosphere, to turn the symbol blue? Would that deploy it once its safe in the atmosphere?

[septemberWaves]

27 minutes ago, nascarlaser1 said:

what if I set it before I come into the atmosphere, to turn the symbol blue? Would that deploy it once its safe in the atmosphere?

Yes, that's what the feature does. The problem is that if you don't slow down to a velocity that it can safely deploy at, it simply will not deploy (because it needs to be travelling at a safe velocity in order to deploy). You can sometimes solve this by using drogue chutes as well (not on their own, you will crash), which have a higher safe deploy speed, but if you use a particularly steep re-entry trajectory then your only real option is to switch to a shallower trajectory - from experience, a 20km periapsis will slow any simple pod setup (just a pod and heat shield), as well as most other vehicle designs, enough to safely deploy standard parachutes regardless of your atmospheric entry velocity (obviously there is a limit to this but it should be fine even if you're returning on a high-energy transfer from Plock-Karen (which I think tends to be in excess of 6km/s) so long as your heat shield has enough ablator).

[MaxL_1023]

2 hours ago, nascarlaser1 said:

Hi guys!

I've recently made the leap from 1.0 to 1.2.1, and with it comes new discoveries. Mostly being, g-forces...

I was doing a Kerbin reentry with a m1 cockpit and a generic Kerbal, when I discovered that my Kerbal can't survive the blunt force that comes with entering the atmosphere, and he was promptly knocked unconscious. Sadly, he did not wake up in time to deploy the parachutes, and we discovered what a Kerbal looks like when it goes splat against the north pole.

My question is, how can I fix my reentry so that my Kerbal can stay awake and/or if they do pass out wake up fast enough to survive??

In that case, it would. I suspect your entry angle is too steep. Generally, there is an inverse relationship between G-load, total heat load and your entry angle. A steeper re-entry (think suborbital for the worse cases) will not burn a lot of ablator (you slow down too soon) but you will face extreme G-forces. On the other hand, a shallow re-entry may require multiple passes to finally fall out of orbit. Your deceleration is gentle (think 3 or 4 Gs tops for a Mk I pod at this angle) but you will need more ablator and may run out if you are re-entering from the Mun or Minmus (or any high orbit) and need several passes to decelerate. 

Try setting your PE to about 40 KM. You will easily make it down using a normal heatshield (even half full you should be fine) and will not usually go above 5 or 6 Gs. You should slow down to subsonic (350m/s) before an altitude of 10Km. For most of my entries, I could deploy parachutes at about 12Km if I wanted to - I usually wait for 5-8KM to save time on descent. 

One final point - Pilots can withstand significantly higher G-forces than Engineers or Scientists, with higher level Kerbals of all classes being more tolerant. Valentina can also take very slightly higher G forces than Jeb, maybe due to size or mass differences. 

Edited November 22, 2016 by MaxL_1023

[Bungthebadger]

What I recommend is to do aerobrakes at 50Km and if you have any remaining fuel left, burn the fuel when in the atmosphere as that will slow you down, resulting not burning you up. (As well as not experiencing too much G-force when you finally start falling towards the ground.)

[foamyesque]

Fly a lifting re-entry. It will dramatically reduce your g-loading, and the standard Mk1 pod has a lift rating for exactly this purpose.  If you have two of them you can even glide like a plane and do a safe splashdown completely parachute-free :v

[nascarlaser1]

21 hours ago, eloquentJane said:

Yes, that's what the feature does. The problem is that if you don't slow down to a velocity that it can safely deploy at, it simply will not deploy (because it needs to be travelling at a safe velocity in order to deploy). You can sometimes solve this by using drogue chutes as well (not on their own, you will crash), which have a higher safe deploy speed, but if you use a particularly steep re-entry trajectory then your only real option is to switch to a shallower trajectory - from experience, a 20km periapsis will slow any simple pod setup (just a pod and heat shield), as well as most other vehicle designs, enough to safely deploy standard parachutes regardless of your atmospheric entry velocity (obviously there is a limit to this but it should be fine even if you're returning on a high-energy transfer from Plock-Karen (which I think tends to be in excess of 6km/s) so long as your heat shield has enough ablator).

 

21 hours ago, MaxL_1023 said:

In that case, it would. I suspect your entry angle is too steep. Generally, there is an inverse relationship between G-load, total heat load and your entry angle. A steeper re-entry (think suborbital for the worse cases) will not burn a lot of ablator (you slow down too soon) but you will face extreme G-forces. On the other hand, a shallow re-entry may require multiple passes to finally fall out of orbit. Your deceleration is gentle (think 3 or 4 Gs tops for a Mk I pod at this angle) but you will need more ablator and may run out if you are re-entering from the Mun or Minmus (or any high orbit) and need several passes to decelerate. 

Try setting your PE to about 40 KM. You will easily make it down using a normal heatshield (even half full you should be fine) and will not usually go above 5 or 6 Gs. You should slow down to subsonic (350m/s) before an altitude of 10Km. For most of my entries, I could deploy parachutes at about 12Km if I wanted to - I usually wait for 5-8KM to save time on descent. 

One final point - Pilots can withstand significantly higher G-forces than Engineers or Scientists, with higher level Kerbals of all classes being more tolerant. Valentina can also take very slightly higher G forces than Jeb, maybe due to size or mass differences. 

Thanks guys! I am using drogue chutes on all of my craft, so being able to do that won't be a problem especially now that I know about being able to prime them ahead of time. My trajectory most of the time is straight back down, since this is career and I am just collecting science before I begin orbiting and stuff. I shoot straight up, and fall straight down, and let gravity do the rest.

[Jonfliesgoats]

Try a shallower reentry.  Here's a document with some handy formulae if you want to anticipate max acceleration and the altitude you expect to reach it.

https://www.faa.gov/other_visit/aviation_industry/designees_delegations/designee_types/ame/media/Section III.4.1.7 Returning from Space.pdf

[Kryxal]

It's best to not go straight up ... do your gravity turn, hit 70 km with a fair bit of horizontal speed, it means you're coming down slower.