Help with re-entry in V1.1.2

[Stryks]

So ... I stopped playing for a while, but decided to pick it back up again with a new career.  Fresh start and all that.

First up, trying to get around the starting part and mass limit was a new twist for me.  And I found getting an orbit more challenging than I remember.

But ... I can't for the life of me figure out this whole re-entry heat and drag situation.  I realise the old way was probably too easy.  There was a time you could just throw a craft at the ground and as long as you had enough chutes, you were golden.  I stopped playing around the time when heat became more of an issue, but you could just quicksave before retro and try again if you had issues.  No biggie.

Now though, I cant seem to get anything down.  I start out shallow, but the extended time in the heat eventually melts my craft.  I gradually make it steeper until I can make it to the cooler air, but then I am going way to fast, and the chutes cant be deployed before hitting the ground.  I even went so far as to stage the craft to only bring the capsule down (with chutes of course) but again, no go.  I can't deploy chutes (drogue or normal) inside the atmosphere ... I just seem to be going too fast.  The result is the same ... the chutes just never become available.

The only way I can seem to do it is to bring in a heavily fuelled craft and do a massive retro burn to try and slow down enough to deploy chutes.  But maybe I'm just playing the way I used to.  So I'd like to know how you would do this.

From a stable 100km orbit, and with a basic craft (Mk1 capsule, FL-T200 tank and an LV-T45 engine, with am Mk16 and two Mk2-R chutes), how would you approach bringing it down, assuming that you only have the fuel to set your entry path?  As I said, in the old days, I would have just retro burned until my Pe was like 5k and just ridden it in.

Thanks

[egoego]

With the current physics you need a shallow reentry path (PE above 30km or something like that) so you slow down enough while in the thin upper atmosphere before you fall down into the thick lower atmosphere. Where your PE should be for your craft and orbit depends on so many things that I don't want to start a discussion about the perfect PE here, just try to come in shallower until your craft survives.

[Warzouz]

The target PE is largely dependant of your vehicle shape. It it's too streamlined you many not slow down enough to be able to open chutes.

As stated, by @egoego, 30km is a quite nice target. Beware the 35km may not slow you down enough.

Try to make your reentry vehicle lighter as possible. Drop all engines, tanks, science parts (get them with EVA). If you come farther from Kerbin SOI, add a heatshield. Don't forget that you can drop the heatshield too (embedded feature)

Is your vehicle is bigger, you may need to use drogue chute. You never nee many of them (one or 2 is largely enough, even for a heavy vehicle). Airbrakes were nice to use in 1.0.4 but will blow quickly since 1.0.5 (they've been nerfed)

A a last resort you can orient your ship sideway (radial or normal) to increase drag. But beware of heating. Further more, in lower atmosphere you may not have enough torque to do it.

For pods, you can always use body lifting to "fly" a little so you'll get more time to slowdown.

For out of SOI reentry, heatshield is needed (maybe not from Duna or Eve, though) but you d'ont need to fill the "ablator" at 100%.

If you come very fast (> 4500m/s), even heatshield might not save you. 2 options :

• Keep some fuel to do a pre-entry slowdown
• Do a gravity assist to lose speed and retry later at next orbit.

In any case, don't forget to save before the attempt.

 

 

[Streetwind]

1 hour ago, egoego said:

With the current physics you need a shallow reentry path (PE above 30km or something like that) so you slow down enough while in the thin upper atmosphere before you fall down into the thick lower atmosphere.

BZZZT. Wrong!  

You don't slow down in the upper atmosphere at all, you only collect heat. The place where you want to be is the middle. That is indeed the reason why you set your PE to about 30 km, as you correctly stated. But making your descent too shallow is not a good idea, because your vertical speed will be low right after leaving your apoapsis, and thus you will soak heat in the upper atmosphere for a long time before getting anywhere useful. Basically, there's an optimal corrdidor where you are not too shallow, but not too steep either.

In the OP's case, reentering from a 100 km apoapsis is just fine. Lowering the apoapsis to 70 km first and then trying to reenter would be strictly worse in every sense.

 

@Stryks - do I read that right that even your drogue chutes are still red when your capsule alone plows into the ground? That should never happen. Drogue chutes can safely deploy at over 500 m/s to my knowledge, and with a little risk at over 600 m/s. Even dropping straight down like a rock with no sideways motion at all should not result in your capsule being that fast at sea level.

If that still happens to you, perhaps your physics settings, or the drag settings for some of your parts, have become borked. I recommend deleting Physics.cfg and PartDatabase.cfg in your KSP root directory. KSP will recreate them with default values the next time you launch the game. Then, try again.

Nominally, a simple mk1 capsule on a standard reentry profile like the one you've chosen should be able to slow down enough to be able to open its main chute before hitting the ground, no drogues necessary (but they help alot with heavier things).

[Plusck]

If I can, to save grief, I've tended to save just a little fuel, set Pe very low, then burn halfway between radial out and retrograde as soon as I feel the atmosphere trying to push the craft off its bearing (or if I'm chicken, as soon as heating effects show - so generally this ends up being somewhere around 50km). Basically I try to turn a suborbital trajectory into a wholly in-atmosphere one. That plus a drogue chute works quite well, and often lets me recover the engine too.

[Greythorn032]

1.1 update has also added the new stock inflatable heat shield which is big enough to protect and slow down most of the crafts so you may want to consider using them as well. Strong reaction wheels should keep your craft stable while the atmosphere gets thicker.

[Stryks]

Thanks for the feedback guys.  Appreciate it.  I'm just about to head off to have another crack at it.

@Streetwind - I think I'll give removing those files a try.  It seems insanely difficult to land even the simplest of craft.  As I said, even the detached pod hits the ground with all chutes in the red.  I sometimes try and throw them ... just in case, but generally they just rip off seconds before I hit the deck.

 

[Warzouz]

1 hour ago, Greythorn032 said:

1.1 update has also added the new stock inflatable heat shield which is big enough to protect and slow down most of the crafts so you may want to consider using them as well. Strong reaction wheels should keep your craft stable while the atmosphere gets thicker.

Well, you shouldn't rely on any SAS device to keep your ship retrograde. Your ship should naturally stay retrograde. Electricty can be scarce on final reentry and SAS may consume a lot (mostly do to overcompensation).

[Greythorn032]

1 minute ago, Warzouz said:

Well, you shouldn't rely on any SAS device to keep your ship retrograde. Your ship should naturally stay retrograde. Electricty can be scarce on final reentry and SAS may consume a lot (mostly do to overcompensation).

You might be right on that one. Most of the ships I built were aerodynamically unstable, so what I said there kinda applies to me.

[bewing]

If you get down to 10km and are still going fast (but not too fast), then a radial drogue chute can help a lot. Otherwise one of the best answers is aerodynamics. Movable fins that have low drag during launch, but can be set into a high-drag configuration for reentry.

[mrclucks]

I have also found reentry to be a pain in 1.1.x.  Coming in how I used to in 1.0.5 just has Me heating up uncontrollablly even though a PE of 30-40km should be good enough.  The way I got around heating too much is to use active radiators so it can disapate heat and not blow me up

[Stryks]

Well ... I reset the files and it does seem to make a difference.  It's actually most noticeable during launch.  I kept the old ones and did a comparison on them, and they were definitely different.  Not much, from what I saw, but different anyhow. 

I've landed my craft a few times now, but I think the shallower approach helps a lot as well.  Tilting nose down (where nose is facing retrograde) when you get out of the heat zone seems to bleed off a fair amount of speed as well, so that's definitely one to remember.  Bleeds off a lot of electricity as well, but I'll settle for dead batteries over dead crew.

I'm kinda moving towards a drogue stage on all my craft now as well.  I'm often still well under 5k before I can throw them out, but they still help to slow me enough to pop the proper chutes.  Still ... throwing chutes at around 1k feels a little wrong.

[Lucky Spacer]

I found in early career before you get air brakes that reentry is the hardest part. I had to completely relearn how to reenter. I fly shallow and make my capsule light.  Also, I used my FL-T200 tank and an LV-T45 engine  to slow down my craft while I was in the 30k altitude.  I had a really hard time first couple of flights getting the craft below 2000m/s.  It's been a couple of weeks since I was at this point in my restarted career mode but I think if I could get the craft down to 1500m/s I was safe.  I just kept flying shallower and shallower until I could get the craft that speed.  But my best solution is get the science to get air brakes as soon as possible.  Here is the link to the wiki on A.I.R.B.R.A.K.E.S

[moogoob]

I find it odd that so many aim for a 30km periapsis. I don't do that for anything but a Mun return, in fact I aim at 35 or so and take two passes.  LKO gets a 15km periapsis, whether it's my Koyuz, the Nastybird shuttle or just a plain old Mk 1 capsule with heat shield. *shrugs*. Works fine - maybe you all are aiming too high?