Why do parachutes hurt so much?

[saskwach]

I just returned from LKO with a Mk 1-2 pod. The craft was just Mk 16-XL, pod, heat shield. I went from about 80km to about 20km, which used zero ablator. My question is really around when to pop the chutes. I've been waiting until the reentry heating effects stop, in the 2-5 km range, and I still see the G-meter spike up into the +15 zone. Do we just expect a brief burst of absurd acceleration when the chute pops into drogue mode?

Edited May 1, 2015 by saskwach

[Gaarst]

In 1.0 the new aerodynamics make chutes OP: you can open chutes at 20+ km high at 2.5 km/s, you will have a huge G-force spike but your craft should be fine.

I guess the acceleration spike will be there no matter at which altitude you deploy chutes, at least in 1.0.

[stupid_chris]

Basically the major complain about the chutes was that they would deploy too fast and cause huge G spikes. What appears to have been done was to make it so that when the parachute fully deploys the whole craft has already slowed down so much that there can't be a huge G spike. But in order to do that, the craft must slow down before. Now instead of having large G spikes on deployment, they're on predeployment.

tl;dr: they buffed predeployment to slow you down a lot, and cause huge spikes, then full deployment shifts you from 30 to 6m/s smoothly because it's hard to have 15Gs when you have such a small speed change.

[magnemoe]

Basically the major complain about the chutes was that they would deploy too fast and cause huge G spikes. What appears to have been done was to make it so that when the parachute fully deploys the whole craft has already slowed down so much that there can't be a huge G spike. But in order to do that, the craft must slow down before. Now instead of having large G spikes on deployment, they're on predeployment.

tl;dr: they buffed predeployment to slow you down a lot, and cause huge spikes, then full deployment shifts you from 30 to 6m/s smoothly because it's hard to have 15Gs when you have such a small speed change.

It also looks like the parachutes open fully more slowly. If you used drouge shutes in 0.9 you was at 60-90 m/s then the main opened, even if you just used two on an large stage to slow you down to 20 m/s it was still an shock.

However partial opening give more drag this has an drastic effect at high speed and you come in far faster in 1.0.

[Claw]

It's a recognized problem. Chutes deployment times were slowed down to help with opening shock, but chute drag is a bit on the high side. Hopefully it will be rebalanced soon.

Cheers,

-Claw

[adinfinitum]

I will say that it's definitely possible to deploy chutes without mush-inducing g-forces, but I'm not sure how rare of an occurrence it is. I sent a science mission to Minmus, and the only part that reentered Kerbin's atmosphere was, in order from top to bottom, a mk16 parachute, mk1 command pod, mk1 lander can, rockomax adapter 2, and 2.5m heatshield. I set my periapsis to about 29.5km, and opened the chutes just under 2km and at roughly 250m/s. I only ended up pulling about 8 or so g's, I know for sure it didn't go into the red.

[Alshain]

LOL I for one am glad this issue happened because right now it is the only way to deal with the "my pod flipped around into the heat" problem. Just deploy the chutes! They won't burn off.

[KSK]

LOL I for one am glad this issue happened because right now it is the only way to deal with the "my pod flipped around into the heat" problem. Just deploy the chutes! They won't burn off.

I can't speak to using anything larger than a Mk1 pod but I'm just not having this problem. I have two standard reentry vehicles: chute + pod + shield and chute + pod + equipment bay + shield. Using a shallow reentry trajectory and they both get through just fine. Granted, they both need a bit of flying now but that's just a case of making small adjustments to keep them lined up along the prograde vector. I'm not finding them wildly unstable.

Other folks mileage clearly is varying though. *puzzled*

[Alshain]

I can't speak to using anything larger than a Mk1 pod but I'm just not having this problem. I have two standard reentry vehicles: chute + pod + shield and chute + pod + equipment bay + shield. Using a shallow reentry trajectory and they both get through just fine. Granted, they both need a bit of flying now but that's just a case of making small adjustments to keep them lined up along the prograde vector. I'm not finding them wildly unstable.

Other folks mileage clearly is varying though. *puzzled*

If you maintain SAS and a constant vigil on them with just a command pod you can bring it in, I've done it. However, in stock and FAR for previous versions you could turn SAS off and the pod would hold retrograde.

Now, if you bring in a Mk1-2 Pod with a hitchhiker below it for those ferry contracts... even SAS can't over correct that, it will flip around making your heat shield pointless. Good news is, it's a confirmed bug by Squad and for now we have the OP parachutes to save us.

Edited May 1, 2015 by Alshain

[Venusgate]

Another part of it i think is that the sweetspot for aerobraking changed and narrowed by an order of magnitude. Also, since fins burn up quick, you can't lawndart your way down.

[KSK]

If you maintain SAS and a constant vigil on them with just a command pod you can bring it in, I've done it. However, in stock and FAR for previous versions you could turn SAS off and the pod would hold retrograde.

Now, if you bring in a Mk1-2 Pod with a hitchhiker below it for those ferry contracts... even SAS can't over correct that, it will flip around making your heat shield pointless. Good news is, it's a confirmed bug by Squad and for now we have the OP parachutes to save us.

Ahh - fair enough. Yes, I have been using SAS. Putting the caps lock on for fine adjustments and tapping the pitch controls occasionally is enough, so it's not too strenuous a vigil. I'm not fighting the pod all the way down but yes, I do need to pay attention.

Haven't encountered the ferry contracts yet, let alone unlocked the Mk1-2 pod but even once the heatshield bug is fixed, I'm thinking that slinging a hitchhiker module under the pod is going to do funky things to your centre of gravity. Intuitively, I wouldn't expect that to work well but intuition and spaceflight don't always mix well.

[Chaos_Klaus]

right now it is the only way to deal with the "my pod flipped around into the heat" problem

You can download a handy mod, called "Stock Bug Fix Modules". It fixes the heatshield (which are flagged physicsless at tht moment) and the service bays (which don't pass on heat like they should) ... and many more. It's a sticky in the add-on releases subforum. It makes for stable reentry without SAS.

As for the chutes: You can modify the time they take to deploy.

[saskwach]

LOL I for one am glad this issue happened because right now it is the only way to deal with the "my pod flipped around into the heat" problem. Just deploy the chutes! They won't burn off.

http://forum.kerbalspaceprogram.com/threads/117279-How-to-fix-those-heatshields%21-%28get-rid-of-command-pod-flipping-into-the-heat%21%29

[saskwach]

Hooray, 1.0.1 (and 1.0.2) fixed this!

[SRV Ron]

Hooray, 1.0.1 (and 1.0.2) fixed this!

Just be aware that chutes will now burn off if you fly the old 1.0 profile. So, watch your speed and angle of reentry.

G forces are now better. No sudden 15G jerk on deployment.

[MarvinKitFox]

It's a recognized problem. Chutes deployment times were slowed down to help with opening shock, but chute drag is a bit on the high side. Hopefully it will be rebalanced soon.

Cheers,

-Claw

The high drag of the chutes is ok, but why are the chutes made of UNBURNABLE UNBREAKEABLE material?

Deploying a parachute at hypersonic speeds while still in the plasma of reenty should result in crispy-fried parachute.

Parachute cords should have a yield strength. just HOW does my parachute manage to stay attached to a 50-ton lander, while decelerating it at 30+ g's? Those poor cords need to have a break strength in excess of 1500 tons!

Surely

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[SRV Ron]

The high drag of the chutes is ok, but why are the chutes made of UNBURNABLE UNBREAKEABLE material?

Deploying a parachute at hypersonic speeds while still in the plasma of reenty should result in crispy-fried parachute.

Parachute cords should have a yield strength. just HOW does my parachute manage to stay attached to a 50-ton lander, while decelerating it at 30+ g's? Those poor cords need to have a break strength in excess of 1500 tons!

That has been fixed under the two patches. Chutes now burn off from reentry heating if deployed too early.