1.0 Re-Entry - Help!

[Potterus]

Been playing a new 1.0 career since launch and run into a bit of a problem, namely trying to re-enter the atmosphere after a steep sub-orbital flight.

I was trying for the orbit Kerbin contract but came up with another mission of my own, namely getting plucky Val into high orbit and grabbing goo/bay/report science points to advance up the tech-tree. The craft is a mk1 command pod with one inline and two radial parachutes, an equipment bay with two goo cannisters, two science juniors and a heat shield.

That was fine but when I come into the atmosphere of Kerbin the craft, which is lined up with the trajectory, flips end over so the command pod is facing forward into the oncoming air. This then promptly explodes due to overheating. I've tried it with SAS off and on. The only difference is that the flip happens sooner with it turned off. It's not a question of electric charge either as I have had at least 10 units.

I do have the heating effect at 100% for a bit of a challenge but after several quick save reverts I am at a bit of a loss how to proceed.

Am I entering the atmosphere too steeply in the new atmospheric model? Is the SAS of the mk1 pod just not strong enough to overcome the turbulence of re-entry?

[Feradose]

Yes, try a shallower re-entry. For example, try to travel at least 1/4 of kerbin while in atmosphere.

[Potterus]

Thought as much. Guess I'm far too used to the old model, where you could chuck craft in at almost an angle and be okay (obviously heating was only cosmetic before unless modded).

[Taki117]

Your best option is to use one of your parachutes as a high altitude drogue. Pop it high in the atmosphere(semi-deployed) and it should keep you pointed in the right direction.

[NathanKell]

Aerodynamics actually matters now. That means if you put a light, draggy thing below a heavy thing, the craft will orient so the light draggy thing is behind the heavy pointed thing.

[Laie]

What NathanKell said. Even a plain pod+heatshield isn't inherently stable, so you actively have to turn it into the wind. A pod with light bits below it will require considerable torque to remain pointed the right way.

Maybe you should go head-on silly and mount the heatshield to the top of the pod? With radial chutes, that spot should be available.

[Mister Dilsby]

Same thing happening to me, even re-entering from a pretty shallow angle with Mk1 pod + science jr + heatshield there is just not enough torque to maintain heading. After killing Val a few times I tried popping the 'chute just as the craft was about to flip over. That seemed to work, it did not rip off at 1400 m/s and it deployed for a successful splashdown.

WOW re-entry just got a lot more exciting. Haven't decided if I love this or hate it, but it's certainly one or the other.

[MrCynical]

Having even one science junior under the capsule will always make it flip over because the heat shield doesn't have enough (any?) mass. Your options if you want to land one are:

A)Deploy the parachute as soon as possible, typically at 25000 km. It won't burn up on rip off, and it holds the craft the correct way round.

B)Put the heatshield on the TOP of the capsule (you'll probably need a nosecone for launch). Then when the craft flips over the heatshield is on the right end.

I'm attempting to find a non ridiculous looking way of doing this, but so far no luck.

[Kelderek]

Make sure your CoM is low enough (toward your heat shield) and your pod will not flip at all. Parachutes can be semi-deployed at very high altitude/high speed combos and not rip off. I'm pretty sure I've have them semi-deploy around 2km/s speed - this will slow you down drastically, but keep in mind you will drop almost straight down if you are targeting a certain landing spot. In fact you might be able to avoid the heat shield entirely and just use the semi-deployed chutes to slow you down (you'll pull mega Gs though if that matters to you) - I haven't tried this though. I don't think the heat shield comes into play at all before 15-20km as you descend (this is when I notice the ablator starting to decrease).

[lajoswinkler]

It is a bug. Here.

http://forum.kerbalspaceprogram.com/threads/116839-Heat-shield-seems-to-be-treated-as-having-0-mass

[Wintersdark]

Ok. I can confirm that you can deal with this via having a single Mk16 nose parachute open at very high altitude, before reentry effects start (or even just as they do) and the parachute will act as a drogue and keep the capsule+service bay+science jr in line. In fact, in this configuration the heat shield is probably superfluous.

I brought 2 Radial Mount chutes(just in case) and the Mk16, but didn't actually need the radials.

[Person012345]

B)Put the heatshield on the TOP of the capsule (you'll probably need a nosecone for launch). Then when the craft flips over the heatshield is on the right end.

I've done this and my heatshield just explodes. What's up with that?

[dervd123]

Use roll to keep your preferred orientation moving you towards the prograde marker. Also use it to steer your reentry to a net +pitch. Also stop your deorbit burn when you're 10-20km periapsis just past your preferred landing point. It's not a bug, it's lift and its how real astronauts don't get hit with 20 Gs during reenty.

[lajoswinkler]

Use roll to keep your preferred orientation moving you towards the prograde marker. Also use it to steer your reentry to a net +pitch. Also stop your deorbit burn when you're 10-20km periapsis just past your preferred landing point. It's not a bug, it's lift and its how real astronauts don't get hit with 20 Gs during reenty.

No, it is not normal. Capsules do not flip during reentry. Their shape and position of CoM puts them in a stable equilibrium during reentry. Thrusters can be used to tilt the capsule and cause some lift force, but that's it. You can't possibly flip it.

[dervd123]

From Wikipedia. http://en.m.wikipedia.org/wiki/Apollo_Command_Module#Command_Module_.28CM.29

"The Command Module's center of mass was offset a foot or so from the center of pressure (along the symmetry axis). This provided a rotational moment during reentry, angling the capsule and providing some lift (a lift to drag ratio of about 0.368[4]). The capsule was then steered by rotating the capsule using thrusters; when no steering was required, the capsule was spun slowly, and the lift effects cancelled out. This system greatly reduced the g-force experienced by the astronauts, permitted a reasonable amount of directional control and allowed the capsule's splashdown point to be targeted within a few miles."

You spin it if you want to go straight

[lajoswinkler]

I didn't say the capsule was not capable of lift or that it was just a rock falling down.

Yes, CoM with a small offset and thrusters enabled them to gain some lift, but the shape of the body has stable mechanical equilibrium. It can not flip in a stream of atmosphere. It will try to go retrograde whatever you do, just like those dolls that tilt themselves upright.

[panzer1b]

Sofar im finding reentry a joke, at least in kerbin.

Javascript is disabled. View full album

Bigger issue is getting to orbit, thats bloody painful with stock heat, especially when you try to exceed like 1.5km/s below 15km. Anyways, my 1st 1.0 SSTO works, even if it abuses the crap out of battery spam (it has effectively 250 massless batteries clipped inside, which to save part count ive edited into the cockpit, increasing its Echarge, yes this is kinda cheating, but its no worse then abusing massless batteries so who cares).

Btw, this thing has 6K dV after attaining orbit

[Claw]

Anyways, my 1st 1.0 SSTO works, even if it abuses the crap out of battery spam (it has effectively 250 massless batteries clipped inside, which to save part count ive edited into the cockpit, increasing its Echarge, yes this is kinda cheating, but its no worse then abusing massless batteries so who cares).

They should be contributing mass, but aren't. However, the batteries would actually count against you in terms of drag

On topic, yes, parachutes are a bit draggy and also have high heat tolerance. So they can help out slowing down craft even on steep reentries.

Cheers,

~Claw

[Khazar]

I had same problem and tried many things like keeping empty fuel tanks and dropping them at around 12-13k alt in hope they would absorb some heat. Deploying chute at 25-20k does the trick. Would it also work in real world ? I mean, wouldn't that chute got burned or torn apart ?

[TokiTech]

You should try the new air-braking part in the aerodynamics section. It helps quite alot and starts its effectiveness at around 69km i believe. I use only one for my spaceplane but it helps plenty already.

[Mars Mullo]

From Wikipedia. http://en.m.wikipedia.org/wiki/Apollo_Command_Module#Command_Module_.28CM.29

"The Command Module's center of mass was offset a foot or so from the center of pressure (along the symmetry axis). This provided a rotational moment during reentry, angling the capsule and providing some lift (a lift to drag ratio of about 0.368[4]). The capsule was then steered by rotating the capsule using thrusters; when no steering was required, the capsule was spun slowly, and the lift effects cancelled out. This system greatly reduced the g-force experienced by the astronauts, permitted a reasonable amount of directional control and allowed the capsule's splashdown point to be targeted within a few miles."

You spin it if you want to go straight

Hey this is great! Not what I expected in 1.0.

Can you confirm if you spin slowly that the pod will centre (or near to centre) on the retrograde marker?

Do I need to spin excessivly if i have other mass attached to the pod?

[dervd123]

It is still a little twitchy, but I noticed if you have it spinning at a slow speed (1 or 2 rpm) with reaction wheels you'll go a lot straighter. A better practice is to stay deflected from prograde and spin clockwise or counterclockwise depending on which way you're drifting. Some pics and yaw is still needed, but not nearly as much.

Edit: pointing radial+ early in the decent (until you start seeing reentry effects) can also bleed off some speed if you have a big service bay on the bottom of your capsule. Good if you're likely to overshoot your landing point.

Edited April 28, 2015 by dervd123

[Ape_Descendant]

Aerodynamics actually matters now. That means if you put a light, draggy thing below a heavy thing, the craft will orient so the light draggy thing is behind the heavy pointed thing.

LOL. I love your careful use of scientific language here :-)

[SpacePsilo]

For me, maintaining the ship a little above orbit retrograde does the job, your ship has to be a little aerodynamic, I don't know if it should be considered an issue, but doesn' the standard one man capsule with one chute and the heatshield should have the center of mass a little down to avoid this flipping problem?

Also you can add a unused full small fuel tank above the heatshield to lower the center of mass and help your ship stabilize the right way.

Remeber, pointing your ship toward space is always the good way .

[Space Peanut]

never had an issue in my short experience - 2 sub-orbital returns, 2 orbital returns, 2 returns from the Mun [sOI / Orbit] - so far.

capsule with 2x radial chutes + service module [loaded with batteries and goo canisters] + heat-shield - my parachutes deployed while still in orbit [in same stage as stage-separator]. turned my capsule retrograde so heat-shield facing the right direction = happy landings.

not sure what other people are doing differently? sure will happen to me too eventually (in another way!) but seems like a lot of us are following old habits that don't necessarily work in 1.0 instead of taking into account the [moderately] increased realism.