Keeping G-Forces low for re-entry?

[Pingonaut]

What's the best way to re-enter Kerbin, keeping your G-forces under 12Gs? Recently got into the re-entry mod and it causes you to explode at 11.6Gs <-Is that realistic or could I bump that up to 12-12.5 Gs before you explode?

As an addition, is there an auto-rendezvous on MechJeb? There's a rendezvous button but it just gives more information, not automatic. I'm learning how to rendezvous better but some automation would be helpful when I don't want to go through the tediousness myself.

Edited October 14, 2012 by Pingonaut

[UNSC]

re-enter as slow as you can rather than just diving in.

[Pingonaut]

Well yeah but I'm wanting a bit more than just go slowly. I'd like just a general max altitude to come in from and best angle.

[Cykyrios]

The ideal descent profile would go smoothly from a low slope to a high slope, but the main problem is that the closer you get to the planet, the faster you will go (until you are actually slowed down by the atmosphere).

If you place your Pe somewhere around 30-35 km, it generally ensures that you will not get over 5G, but it really depends on what altitude you start your deorbit burn.

[dikkjo]

Well it always depend where you were coming from, i.e if you are getting back from Jool you will probably go much faster than if you get back from the moon. anyway not getting your periapsis below 30'000 on reentry is a good starting point

[Pingonaut]

The ideal descent profile would go smoothly from a low slope to a high slope, but the main problem is that the closer you get to the planet, the faster you will go (until you are actually slowed down by the atmosphere).

If you place your Pe somewhere around 30-35 km, it generally ensures that you will not get over 5G, but it really depends on what altitude you start your deorbit burn.

That makes it hard for me, I like to land near KSC in the ocean next to it, so it makes it difficult to judge where I'm going to land when I'm not bringing my pe down low.

Well it always depend where you were coming from, i.e if you are getting back from Jool you will probably go much faster than if you get back from the moon. anyway not getting your periapsis below 30'000 on reentry is a good starting point

Usually when I re-enter Kerbin I bring my apo to 100 and peri to whatever, so that doesn't vary for me.

[Grizzlol]

For context, max g-force for a real world space shuttle during re-entry is around 3 g, and around 7 g for a pod, according to wikipedia. Around 5 g, is the limit for an untrained human being before loosing conciousness, though with special training and suits, one can handle a lot more, with a risk of dying being around 25 g. However, these limits also depend on the duration of the effect and the limit for a machine is very specific.

[The Destroyer]

I do 18KM PE, and thats fine on kerbin.

[Pingonaut]

Thanks for the info, I guess 11Gs is pretty bad, I guess I'll just have to get good at it!

[PakledHostage]

That makes it hard for me, I like to land near KSC in the ocean next to it, so it makes it difficult to judge where I'm going to land when I'm not bringing my pe down low.

Usually when I re-enter Kerbin I bring my apo to 100 and peri to whatever, so that doesn't vary for me.

I tried to work within the game's existing UI when I set the limit for max G's in the re-entry heat module. You won't have any trouble re-entering if you keep the g indicator needle out of the red arc on the navball. The longer the needle stays in the red arc, the more damage your spacecraft will sustain. And the higher the g's you experience, the quicker the spacecraft will reach its damage tolerance threshold.

In playing with the re-entry heat module myself, I have found that shallower trajectories result in increased shield temperatures (lower heat flux but high maximum temperatures due to longer term exposure), while steep trajectories result in higher g's and lower shield temperatures (i.e. high heat flux but lower maximum temperatures due to shorter term exposure).

I have also been working on the next release of the plugin already, in preparation for MrPwner's contribution to the project. His heat shield model will include a transparent bow shock effect that I will be able to display during re-entry as appropriate per the physics model. I have also added a "hard-core" mode that will allow users of the re-entry heat module to enable a lift force in the part's configuration file. Playing with the module with the lift enabled, I've found that it tends to reduce re-entry g's but increases heating due to longer term exposure to high temperatures. That result will probably require that slightly steeper trajectories be used when the "hardcore" mode is active.