atmospheric decent

[Valiant]

first off, ive been playing for years. i started a new career just after 1.4 . one of the first missions you can accept is leave the atmo. ive always done that and recovered the craft with no deaths, no problems. all the sudden now, my craft is always going WAY too fast for chutes to deploy. The atmosphere doesn't seem to be slowing me hardly any. ive tried shallower angle, i just don't get it. never had trouble before. did something change in 1.4? i reinstalled the game with no mods. i haven't unlocked drogue yet but shouldn't have to sacrifice a pilot

[bewing]

Nothing has changed in the aero or drag model since 1.2.0 or something like that.

Drogue chutes only cost 20 science at this point, and the fact that they are so low in the tech tree is really an indication that you are actually supposed to be using them. Even if you don't spend the science on them, you are certain to get them on a part test contract.

If you refuse to use drogue chutes, you basically have 3 choices:

Bail out your pilot after the hot part of the reentry, and let him use his parachute. (However, your pilot probably does not have enough experience to use a personal parachute yet.)

Save some fuel and use that to slow yourself to a safe parachute speed once you are near the ground.

Utilize aerodynamics. Get rid of any heatshield -- they are deathtraps for any mission lower than the Mun, because they have very low drag so you don't slow down. You have the basic fins at least. If you put some near your empty CoM, you can use your reaction wheel to make your RV "fly". Or use some kind of control surface that has low drag on the way up, and high drag on the way down.

 

Edited March 24, 2018 by bewing

[DerekL1963]

13 minutes ago, bewing said:

Utilize aerodynamics. Get rid of any heatshield -- they are deathtraps for any mission lower than the Mun, because they have very low drag so you don't slow down.

Right.  That's why I've flown hundreds of missions lower than the Mun but with heatshields - and no deaths.

[Tokoshoran]

57 minutes ago, DerekL1963 said:

Right.  That's why I've flown hundreds of missions lower than the Mun but with heatshields - and no deaths.

Given how this game is with physics, I don't doubt that their roundness is slightly aerodynamic.

Edit: Actually, you can put them on upside-down. Wouldn't that increase drag?

Edited March 24, 2018 by Tokoshoran

[Starwaster]

@bewing Maybe you're thinking about its ballistic coefficient because of the extra mass it adds to the craft but it is not physically possible for it to have less drag unless there's something seriously wrong with the game's aerodynamics.

[bewing]

You guys know how ablative heatshields work? They can and do in fact have extra low drag IRL and in the game.

 

[DerekL1963]

16 minutes ago, bewing said:

You guys know how ablative heatshields work? They can and do in fact have extra low drag IRL and in the game.

Yes, I know how ablative heat shields work.  When heated during re-entry, they absorb the heat and are (by various mechanisms) converted to gas and that gas carries the heat away.  And yes, they can be low drag.  That's why the re-entry vehicles of modern ICBM's are cone shaped.  (The reasons they want low drag are beyond the scope of this discussion.)  But the heat shields in question IRL and in game are not pointy.  In both IRL and in game they are blunt - they work by increasing drag.  And they would increase drag whether they were made of ablative materials or not - it's the shape that matters.

No offense, but you're putting out some very bad information here.
 

4 hours ago, Valiant said:

did something change in 1.4?

No, nothing has changed with respect to aerodynamics.  I've only done a couple of re-entries since installing 1.4/1.4.1 and have had no problems.  I'd try drogue chutes.

[Valiant]

I've got like 1500 hrs in on this game. Ive never had this happen b4. imagine the simplest of rockets. command pod with  3 or 4 of the smallest tanks and the swivel engine. start the ascent and gradually turn to 45 degrees b4 running out of fuel. reach 50-70 km and come back down. I'm still going 750-1200m/s at splashdown. just under flaming speed. if i do it just right i can get drogue to deploy. but that still leaves having to sacrifice a couple pilots to get enough science to unlock that node.  Just to be sure, there is nothing in the difficulty settings that would change this?

Edited March 24, 2018 by Valiant

[Zeiss Ikon]

@Valiant If you're reentering with your engine and tank still attached, you won't slow down anything like as rapidly as you would with just the command pod, with or without a heat shield -- you have much more mass (the Swivel weighs almost as much as the Mk. 1 pod), lower drag (engine shape vs. blunt heat shield or pod base) -- the only viable reentry with the full vehicle at minimum tech is to keep enough fuel to slow down for parachute deployment, then make another burn just before splashdown if you want to avoid using the engine and tanks as explosive shock absorbers.

Edited March 24, 2018 by Zeiss Ikon

[Zeiss Ikon]

I just tested this exact situation in my 1.4.1/MH sandbox -- Mk. 1 command pod, Mk. 16 parachute, 4 FL-T100 tanks, and a Swivel.  No decoupler, no heat shield, monopropellant drained from the pod.  If I burned all my fuel and finished with a 45 degree climb, the rocket would in fact slow enough to deploy the parachute before hitting the water, but only just; first deployment was below 10 km, and final deployment was still at 250+ m/s, finishing deceleration barely 200 m above the water.  This rocket, however, wouldn't leave the atmosphere.

If I built the rocket with six tanks, it would leave the atmosphere with a 45 degree final climb, but wouldn't slow enough to fully deploy the parachute before impact.  If I saved approximately 20% of the fuel (100-120 units), I still cleared the atmosphere for close to two minutes, and was able to make a burn at 10 km to permit parachute deployment, and another just above 2 km prevented shredding the parachute from excessive speed.  Alternately, if the parachute was "destroyed by heat and aerodynamic forces", I had just about enough fuel left to slow the rocket before splashdown and let the engine and one or two tanks act as crush zones to keep the pod (and Jeb) intact.

I don't recall this as being different from 1.3.0 or 1.2.2 (first version I played).  These rockets are barely recoverable before you get decouplers, at least.  OTOH, it's not too hard to get the science you need to unlock decouplers without even launching a rocket -- "pad science" and a short hike into another microbiome or two (crawler track, KSP lawns) with surface samples can get you enough science to unlock decouplers; you won't need a heat shield until you go beyond LKO.

[magnemoe]

13 hours ago, Zeiss Ikon said:

@Valiant If you're reentering with your engine and tank still attached, you won't slow down anything like as rapidly as you would with just the command pod, with or without a heat shield -- you have much more mass (the Swivel weighs almost as much as the Mk. 1 pod), lower drag (engine shape vs. blunt heat shield or pod base) -- the only viable reentry with the full vehicle at minimum tech is to keep enough fuel to slow down for parachute deployment, then make another burn just before splashdown if you want to avoid using the engine and tanks as explosive shock absorbers.

Add the problem that you can easy go down nose first you will get an very high reentry speed, 
Pointy end first, fins in back will keep you nose first. 

Not had any issues with heat shields on the other hand, even on early tourist runs with MK1 pod and two MK1 passenger cabins, granted that ship also had an 1.25 m equipment bay who helped high speed braking. Was more than slow enough for normal parachutes. 

[Zeiss Ikon]

Coming back from orbit is actually better than suborbital for this situation.  When deorbiting, you have a lot of velocity high up, which gets you useful amounts of drag at 40-55 km.  When coming back from a barely suborbital jaunt, you won't get useful drag until you're below 30 km (in my tests yesterday, I wasn't getting plasma -- which is based on both air density and speed -- until  just above 25 km).  This is why you get much higher G forces during reentry from a near-vertical suborbital launch than you do coming back from the Mun or Minmus, unless you set your Pe much too low.  Valiant didn't mention fins (with a Swivel, using just heading hold would easily allow flying to orbit without them) -- if you try to reenter with fins (i.e. nose-first stable), there's no way you'll be able to hold retrograde after you hit air, and then there's no chance you'll be subsonic before impact.

BTW, I was incorrect in one of the quoted points above.  I went back and looked, and the Swivel doesn't weigh almost as much as the Mk. 1 Command Pod -- it weighs more than twice as much.  The combination of lower drag than the blunt base of a pod, with roughly four times the mass (including empty tanks, along with the pod and engine -- any science attached will make this still worse) and you get a craft that is extremely trajectory critical in terms of being able to slow down enough to deploy parachutes without a retro burn.  BTW, @magnemoe two Mk. 1 Passenger cabins and the 1.25 equipment bay, plus four more Kerbals, still weigh less than a Swivel, I think.

[Valiant]

thanks for all ya'lls input. my problem was pretty much pointy end first.

 

[Tokoshoran]

On 3/25/2018 at 2:11 AM, magnemoe said:

Add the problem that you can easy go down nose first you will get an very high reentry speed, 
Pointy end first, fins in back will keep you nose first. 

Not had any issues with heat shields on the other hand, even on early tourist runs with MK1 pod and two MK1 passenger cabins, granted that ship also had an 1.25 m equipment bay who helped high speed braking. Was more than slow enough for normal parachutes. 

I've had that happen a few times, then upon decoupling, it immediately turns around and goes retrograde. is the pod just shaped in a way that it does that when it's alone?

[HeliosPh0enix]

On 3/26/2018 at 9:29 AM, Tokoshoran said:

I've had that happen a few times, then upon decoupling, it immediately turns around and goes retrograde. is the pod just shaped in a way that it does that when it's alone?

Yes.  The center of mass of the pod is in the bottom, by the flat end, so it naturally wants to have that end pointed retrograde.