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Loren Pechtel

How do you bring a long rocket through the fire in 1.4?

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Before my normal solution was grid fins (I forget what mod they come from).  Put them at the top of the rocket, deploy them at around 2000 m/s and it didn't matter how long (big passenger bus) the rocket was, it stayed retrograde.  Now with 1.4, though, they're delicate--I tried leaving them folded until I got in trouble--and they burned off anyway!  The only solution I see now is the utter kludge of building a rocket that doesn't care--keep the size constant, put a heat shield on the nose also, then a decoupler and a nose cone.  Blow the cone before re-entry and come in prograde.  Sometimes it flips but there's a shield there, also.

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Moving to Gameplay Questions.

@Loren Pechtel You're talking about "how to do reentry with a long/skinny craft", yes?

My usual approach for a craft like that is to put a pair of steerable fins on the back (the AV-R8 works great for this).  When I attach them, I make a point of using bilateral symmetry (i.e. like the SPH) rather than radial symmetry, so that when I set them to "deploy", they deflect in the same direction rather than opposite from each other.

Then I just reenter :prograde: on a somewhat-shallow entry path, make sure the control authority on the fins is cranked up to maximum, and set them to "deploy" so that they aerodynamically hold the craft in a nose-up position, similar to a spaceplane reentry.  The combination of drag and body lift from the fuselage does the trick:  the craft slows down nicely, without losing altitude down into the soup until it's slowed to a safe degree.

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9 hours ago, Snark said:

Moving to Gameplay Questions.

@Loren Pechtel You're talking about "how to do reentry with a long/skinny craft", yes?

My usual approach for a craft like that is to put a pair of steerable fins on the back (the AV-R8 works great for this).  When I attach them, I make a point of using bilateral symmetry (i.e. like the SPH) rather than radial symmetry, so that when I set them to "deploy", they deflect in the same direction rather than opposite from each other.

Then I just reenter :prograde: on a somewhat-shallow entry path, make sure the control authority on the fins is cranked up to maximum, and set them to "deploy" so that they aerodynamically hold the craft in a nose-up position, similar to a spaceplane reentry.  The combination of drag and body lift from the fuselage does the trick:  the craft slows down nicely, without losing altitude down into the soup until it's slowed to a safe degree.

Well, what I'm currently struggling with isn't exactly skinny but it's long compared to it's width.  So you're saying to deploy the fins and come in prograde?  I've done that high up before when returning from a moon--set the periapsis to 50km and come in prograde, it doesn't get too hot and it lowers the apoapsis.  Takes a few passes to get down to low orbit speed but it means a lot cooler dive when I finally do fall out of orbit.

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24 minutes ago, Loren Pechtel said:

So you're saying to deploy the fins and come in prograde?

Yep.  Body lift is your friend.

24 minutes ago, Loren Pechtel said:

set the periapsis to 50km and come in prograde, it doesn't get too hot and it lowers the apoapsis.

That works.  Though I'd suggest that you can be a lot bolder than that-- in my experience, I can just dive right in, i.e. set Pe to 30 km or something similar.  Depends on your ballistic coefficient (i.e. ratio of mass to drag) and just how fast you're coming in (e.g. from LKO, from Mun/Minmus, or from solar system).

Doing the "prograde nose-up body lift without heat shield" thing works absolutely fine from LKO for just about any craft.  I suspect it probably works reasonably well for a Mun/Minmus return, if the craft's not too dense (though it might need a higher Pe and maybe more than one pass?)  Interplanetary returns will probably be too hot to do this way.

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6 hours ago, Snark said:

Yep.  Body lift is your friend.

That works.  Though I'd suggest that you can be a lot bolder than that-- in my experience, I can just dive right in, i.e. set Pe to 30 km or something similar.  Depends on your ballistic coefficient (i.e. ratio of mass to drag) and just how fast you're coming in (e.g. from LKO, from Mun/Minmus, or from solar system).

Doing the "prograde nose-up body lift without heat shield" thing works absolutely fine from LKO for just about any craft.  I suspect it probably works reasonably well for a Mun/Minmus return, if the craft's not too dense (though it might need a higher Pe and maybe more than one pass?)  Interplanetary returns will probably be too hot to do this way.

Unfortunately, I didn't have the part you suggested unlocked.  I did find there are now two separate sets of grid fins, though--the second is heavier and more expensive, but has more heat tolerance.  I held onto the booster as long as possible as I've found it tends to help (why?!?!?!), when it was about to blow I triggered the fins and blew the booster--and despite a bunch of fins my craft insisted on going in prograde.  The fins did their job, though, my chutes were green while still above 10,000m.  My kerbals didn't even get mad at the wild tumble they took when the booster came off.

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My tricks is to use equipment bays, the 2.5 meter is obviously better but even the smalls works well. open them and they generate lots of drag, the docking port with shield also give drag then open.

unlike airbrakes they don't heat up. 

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8 hours ago, magnemoe said:

My tricks is to use equipment bays, the 2.5 meter is obviously better but even the smalls works well. open them and they generate lots of drag, the docking port with shield also give drag then open.

unlike airbrakes they don't heat up. 

Interesting.  It never occurred to me the doors would survive the fire.

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6 minutes ago, Loren Pechtel said:

Interesting.  It never occurred to me the doors would survive the fire.

For some reason they do, yes its kind of an exploit. but you could make aerobrakes covered in shuttle tiles in various sizes. 

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@Loren Pechtel Giving us a picture of the craft greatly improves your chances of receiving direct tips, tricks and methods to solve/remedy your problem.

AFAIK length of a craft shouldn't make things more difficult.
Flight characteristics of a long craft with one stack means it is more aerodynamic so aerobraking through body drag will be less effective. As long as you use other methods of aerobraking besides the use of the body it doens't matter how thing it is.
I also never use any heatshielding to protect my nose or anything when retrieving upper stages. The most simplistic working design is a stage that does no flipping at all. It just stays retrograde with the engines facing the fire.

On another note...

@Snark Gave a brilliant solution that I use myself, very often. Control surfaces have very high 2400k heat tolerances so they can be extended during aerobraking. Using them to slow down high in the atmosphere will keep critical temperatures of bottom engines below overheat threshold. And consequently it will keep your rocket oriented the way you want.

 

Personally I don't see the use of grid fins in stock KSP unless your using KoS and you want to land at a specific spot. In ksp it doesn't matter whether you land on the grass, runway or a small hill. Grid fins can be used to show off VAB, Helipad or barge landings but that is proof of concept, gameplay wise it's not really gamey. I do use a lot of vernors myself to orient the craft before touchdown to help with rotation near touchdown.
 
Then there is the fairing staging trick. You can cover elevons inside a interstage fairing to make the top of your rocket very draggy when staging off the fairings. This creates drag to aerobrake and makes the engines pointing downward.
I used both methods on a test craft, which took me a few minutes to build.
The first set of pictures on the album below show off the stage fairing trick.
The second set of pictures on the album below show off the control surface method advised by Snark. I took it another step forward by rotating them and "change deploy direction" in flight for a even greater deflection angle by the elevons.
 
 
 

   

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This game hates me!

While my rocket insists on turning prograde the instant the booster comes off the fins will slow it fine.  If it comes down on land, fine, but if it goes into the water it pops up to turn turtle and blows up (and where did that fireball come from?  There was no fuel on board!) when it hits the water coming back down.  I'm going to have to rearrange the recovered portion to lower the center of mass.

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If you have a lot of reaction wheel, you can turn on SAS and then recover the vessel really fast. ;)

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4 hours ago, bewing said:

If you have a lot of reaction wheel, you can turn on SAS and then recover the vessel really fast. ;)

This thing is driving me nuts!  I rebuilt it lowering mass in the part that's recovered--and now it won't fly even with some big steerable fins on it.  Oh, well, I guess I have to make it fatter and shorter.

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7 hours ago, Loren Pechtel said:

This thing is driving me nuts!  I rebuilt it lowering mass in the part that's recovered--and now it won't fly even with some big steerable fins on it.  Oh, well, I guess I have to make it fatter and shorter.

Without seeing pictures it's hard to be sure, but I get the impression you're having a CoM problem, or just possibly a stubby nose problem. These are the most common causes of rockets being unstable.

On the way up, your rocket has to be nose-heavy and have a pointy nose. That way aero forces will keep it pointed the right way.

On the way back, assuming you're re-entering tail first, you have to have a heavy tail. Normally this sorts itself out by itself because your engines are heavy and your body will be light, since you will have burned all your fuel.

If you want to re-enter nose first, you'll have to do a quite a bit of somewhat intricate balancing -- you'll have to design your craft so that it has a pointy and heavy nose even with empty tanks. (This is in fact one of the harder challenges in designing reusable SSTO aircraft.)

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8 hours ago, Brikoleur said:

Without seeing pictures it's hard to be sure, but I get the impression you're having a CoM problem, or just possibly a stubby nose problem. These are the most common causes of rockets being unstable.

On the way up, your rocket has to be nose-heavy and have a pointy nose. That way aero forces will keep it pointed the right way.

On the way back, assuming you're re-entering tail first, you have to have a heavy tail. Normally this sorts itself out by itself because your engines are heavy and your body will be light, since you will have burned all your fuel.

If you want to re-enter nose first, you'll have to do a quite a bit of somewhat intricate balancing -- you'll have to design your craft so that it has a pointy and heavy nose even with empty tanks. (This is in fact one of the harder challenges in designing reusable SSTO aircraft.)

Yeah, but long, nose-heavy craft that land in water are in trouble.  It's a balancing act for which I haven't yet found the right balance.

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3 hours ago, Loren Pechtel said:

Yeah, but long, nose-heavy craft that land in water are in trouble.  It's a balancing act for which I haven't yet found the right balance.

Getting to space is easy.
Getting to orbit is quite easy.
Docking is hard, interplanetary is hard, re-entry is hard, landing is hard.  \o/  Fun, isn't it?

(Be of good cheer.  All the other things you've already done show that it's not you and it probably isn't even KSP - it's just spacecraft)

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On 11/12/2018 at 2:36 PM, Pecan said:

re-entry is hard, landing is hard

Re-entry and landing are easy...living through it, that's a bit more problematic

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On 11/12/2018 at 2:36 PM, Pecan said:

Getting to space is easy.
Getting to orbit is quite easy.
Docking is hard, interplanetary is hard, re-entry is hard, landing is hard.  \o/  Fun, isn't it?

(Be of good cheer.  All the other things you've already done show that it's not you and it probably isn't even KSP - it's just spacecraft)

Going to space is easy??

I came up with a design that I think could have both flown and landed.  Unfortunately, it was unflyable due to control oscillations--MechJeb's usual 90 degree turn ended up being more than 180--and the return even more--each twist getting farther off and it tumbled before reaching 20km.

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9 hours ago, Loren Pechtel said:

Going to space is easy??

Stayputnik, Hammer, Basic Fins.  It goes up, it comes down (and blows up).  It goes to space.

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